WO2019145911A2

WO2019145911A2 - Stepped radar cross-section target and marking tape

Info

Publication number: WO2019145911A2
Application number: PCT/IB2019/050640
Authority: WO
Inventors: Mohsen Salehi; Marcel DOERING; Christian Weinmann; Joern Buettner; Susannah C. Clear; Edmund J. Ring; Robert A. Sainati; Thomas P. Hedblom
Original assignee: 3M Innovative Properties Company
Priority date: 2018-01-26
Filing date: 2019-01-25
Publication date: 2019-08-01
Also published as: WO2019145911A3

Abstract

A pathway article that includes a radar reflective structure with a large radar cross section (RCS) in a compact planar structure. The radar reflective structure may include a plurality of elements that act as antennae and may be spaced appropriately on a planar surface creating a radar reflecting surface. The antenna may be a reflecting surface of a stepped triangular slot. Selecting the spacing between the antennae may cause constructive interference and reflection substantially opposite the direction of the incident radar radiation. Pathway articles may also include at least one additional feature that may be detected by other sensors. Examples of other features include retroreflective features detectable by the human eye, visible camera and similar sensors. This redundancy in the detectable features of the pathway article may enable use of sensor fusion to provide greater confidence of detection of the pathway article under a wide range of conditions.

Description

STEPPED RADAR CROSS-SECTION TARGET AND MARKING TAPE

TECHNICAU FIEUD

The disclosure relates to roadway marking.

BACKGROUND

Automotive radars in a narrowband range are widely implemented for applications such as adaptive cruise control and blind spot monitoring. There has been global activity toward automotive radar systems that may distinguish objects on a roadway with greater accuracy than narrowband systems. A larger bandwidth radar system may enable higher spatial resolution, compared to a narrow bandwidth system, which may limit resolution. Some vehicle radar system manufacturers have begun to develop and implement higher frequency and wider bandwidth radar systems.

SUMMARY

In general, this disclosure is directed to a pathway article that includes a radar reflective structure with a large radar cross section (RCS) in a compact planar structure. A pathway article may include a pathway marking tape, traffic cone or barrel, stop sign, and similar articles. The radar reflective structure may include a plurality of elements that act as antennae and may be spaced appropriately on a planar surface creating a radar reflecting surface. Selecting the spacing between the antennae may cause constructive interference leading to reflection in the backscatter direction, substantially opposite the direction of the incident radar radiation. The radar reflecting structures may provide cues for radar equipped vehicles traveling along a pathway that includes a pathway article of this disclosure.

Pathway articles of this disclosure may also include at least one additional feature along with these radar reflective structures that may be detected by other sensors on a vehicle. Examples of other features include retroreflective features detectable by the human eye, visible camera, infrared camera, and similar sensors. This redundancy in the detectable features of the pathway article may enable use of sensor fusion to provide greater confidence of detection of the pathway article under a wider range of conditions and to enable distinction between marking and other radar-reflective objects, such as other vehicles, in the field of view of the radar system.

In one example, the disclosure is directed to a radar reflecting structure device, the device comprising: a first angled sawtooth notch comprising a first reflecting surface and a first angled surface substantially perpendicular to the first reflecting surface; and a second angled sawtooth notch, comprising a second reflecting surface and a second angled surface substantially perpendicular to the second reflecting surface wherein: the second slot is positioned such that the second reflective surface is a grating distance from the first reflective surface; the second reflective surface is substantially parallel to the first reflective surface; a radar signal that reflects off the first reflecting surface results in a first reflected signal; the radar signal that reflects off the second reflecting surface results in a second reflected signal; the second reflected signal causes a phase interference in the first reflected signal; the phase interference causes the first reflected signal and the second reflected signal to form a reflected beam, wherein the reflected beam comprises a direction of travel substantially opposite to a direction of travel of the radar signal.

In another example, the disclosure is directed to an article comprising: a sheet material comprising: a continuous base sheet including an upper surface and a lower surface; a sensable layer applied to the upper surface of the continuous base sheet, wherein the sensable layer comprises a traffic bearing protective layer, wherein the sheet material comprises a long axis and a short axis; a radar reflecting structure comprising: wherein the radar reflecting structure is disposed between the sensable layer and the continuous base sheet, in the plane of the continuous base sheet, the radar reflecting structure comprising: a first angled sawtooth notch comprising a first reflecting surface and a first angled surface substantially perpendicular to the first reflecting surface; and a second angled sawtooth notch, comprising a second reflecting surface and a second angled surface substantially perpendicular to the second reflecting surface wherein: the second slot is positioned such that the second reflective surface is a grating distance from the first reflective surface; the second reflective surface is substantially parallel to the first reflective surface; a radar signal that reflects off the first reflecting surface results in a first reflected signal; the radar signal that reflects off the second reflecting surface results in a second reflected signal; the second reflected signal causes a phase interference in the first reflected signal; the phase interference causes the first reflected signal and the second reflected signal to form a reflected beam, wherein the reflected beam comprises a direction of travel substantially opposite to a direction of travel of the radar signal.

In another example, the disclosure is directed to a system for vehicles on a traffic -bearing surface, the system comprising : a pathway configured to support vehicle traffic; a pathway-article assisted vehicle (PAAV) comprising: one or more radar transceiver devices; one or more sensor devices; one or more processor circuits configured to interpret a first signal from the one or more radar transceiver devices and a second signal from the one or more sensor devices; a pathway article comprising a radar reflecting structure, wherein the pathway article is arranged on the pathway within a field of regard (FOR) of the one or more radar transceiver devices.

In another example, the disclosure is directed to a method for making a marking tape material comprising: providing a continuous base sheet including an upper surface and a lower surface; applying a sensable layer to the upper surface of the continuous base sheet; applying a continuous conformance layer to the lower surface of the continuous base sheet; adding a radar reflective structure disposed between the sensable layer and the continuous base sheet, in the plane of the continuous base sheet, wherein the radar reflecting structure comprises a conductive material.

The details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example system 100 including pathway marking tape with radar reflecting structures, according to one or more techniques of this disclosure.

FIGS. 2A-2D are conceptual diagrams illustrating top views of example arrangements of radar reflecting structures within pathway articles, according to one or more techniques of this disclosure.

FIG. 3A is a conceptual diagram illustrating a top view of example arrangements of radar reflecting structures within a within pathway article, according to one or more techniques of this disclosure.

FIG. 3B is a conceptual diagram illustrating a top view of example of radar reflecting structures within a within pathway article, with curved angled sawtooth notches according to one or more techniques of this disclosure.

FIG. 4 is a conceptual diagram illustrating an example system including a vehicle equipped with radar devices and a marking tape, according to one or more techniques of this disclosure.

FIGS. 5 A - 5C are conceptual diagrams illustrating an example angled sawtooth notch radar reflecting structures according to one or more techniques of this disclosure.

FIGS. 6A - 6C are conceptual diagrams illustrating an example angled sawtooth notch radar reflecting structures with a radius according to one or more techniques of this disclosure.

FIG. 7A is a conceptual diagram illustrating an example radar reflecting structure configured to redirect incident radar radiation with refraction and reflection, according to one or more techniques of this disclosure.

FIGS. 7B - 7D are plots illustrating the simulated performance of the example radar reflecting structure configured to redirect incident radar radiation refraction and reflection.

FIGS. 8 A - 8D are conceptual diagrams illustrating periodic arrays of antenna elements that include transmission lines according to one or more techniques of this disclosure.

FIGS. 9A - 9C illustrate example techniques to increase the RCS of a vehicle depending on the angle of incidence of the incident radar radiation.

FIG. 10 is a diagram illustrating a side view of an example reflection and scattering of a radar beam with a radar reflecting array of this disclosure.

FIG. 11 is a diagram illustrating a top view of an example reflection and scattering of a radar beam with a radar reflecting array of this disclosure.

FIG. 12A is a block diagram illustrating an example compact planar structure that includes a radar reflecting array according to one or more techniques of this disclosure.

FIGS. 12B and 12C are conceptual diagrams illustrating example marking tape with a retroreflective sensable layer and a radar reflecting array layer according to one or more techniques of this disclosure.

FIG. 13 is a flow chart illustrating an example technique for making a marking tape according to one or more techniques of this disclosure. DETAILED DESCRIPTION

This disclosure is directed to a pathway article that includes a radar reflective structure with a large radar cross section (RCS) in a compact planar structure. A pathway article may include a pathway marking tape, traffic cone or barrel, stop sign, and similar articles. The radar reflective structure may include a plurality of elements that act as antennae and may be spaced appropriately on a planar surface creating a radar reflecting surface. There may be one or more rows of these antennae that form a periodic structure which can interact with the radar’s electromagnetic wave. The dimensions and spacing between the rows of antennae is a function of expected angle of incidence and the expected frequency of the radar. Selecting the spacing between the antennae causes constructive interference leading to a reflection of energy in the backscatter direction.

A vehicle with radar systems or other sensors that takes cues from a vehicle pathway may be called a pathway-article assisted vehicle (PAAV). Some examples of PAAVs may include the fully autonomous vehicles, a vehicle with advanced Automated Driver Assist Systems (ADAS), as well as unmanned aerial vehicles (UAVs) (aka drones), human flight transport devices, underground pit mining ore carrying vehicles, forklifts, factory part or tool transport vehicles, ships and other watercraft and similar vehicles. A vehicle pathway may be a road, highway, a warehouse aisle, factory floor or a pathway not connected to the earth’s surface. The vehicle pathway may include portions not limited to the pathway itself. In the example of a road, the pathway may include the road shoulder, physical structures near the pathway such as toll booths, railroad crossing equipment, traffic lights, the sides of a mountain, guardrails, and generally encompassing any other properties or characteristics of the pathway or objects/structures in proximity to the pathway.

This disclosure also describes pathway articles that include these radar reflective structures and at least one additional feature that may be detected by other sensor systems mounted on the PAAV, such as an automobile. Examples of other features include retroreflective features detectable by the human eye, visible camera, infrared camera, and similar sensors. Other features may be detectable for example by LIDAR, or a magnetic detector. The radar reflective structures and the additional feature(s) may be located in the same region of the pathway article, such as marking tape, or adjacent to each other. This redundancy in the detectable features of the pathway article may enable use of sensor fusion to provide greater confidence of detection of the pathway article under a wider range of conditions and to enable distinction between marking and other radar-reflective objects, such as other vehicles, in the field of view of the radar system. In some examples, a magnetically detectable component may be applied in a spatially separated and distinct location from the radar reflecting structure.

One embodiment of this invention is a pavement marking tape where the radar reflective structures are spaced along the axial direction of the pavement marking tape, and where they are positioned at an angle relative to the axial direction of vehicle travel. For pavement marking tapes that delineate lane boundaries, in some examples this angle may be between zero to ninety degrees relative to the axial direction of vehicle travel. A vehicle equipped with a radar traveling along the roadway, this configuration would generate a periodic response of backscattered power. When illuminated with a frequency modulated continuous wave (FMCW) signal, such as in some automotive radars, the radar system may observe a shift in frequency at which the relative signal peak at the design frequency of the array of the reflected signal occurs for a given array as the vehicle moves relative to the array. The time delay associated with this peak may assist the PAAV to determine the distance of the tape from the radar transceiver unit.

FIG. 1 is a conceptual diagram illustrating an example system 100 including pathway marking tape with radar reflecting structures, according to one or more techniques of this disclosure. System 100 includes PAAV 110, vehicle pathway 130, and one or more pathway articles 132A-132C (collectively, “pathway articles 132”).

In some examples, pathway article 132 include a pavement marking tape, a traffic sign (e.g., a stop sign, yield sign, mile marker, etc.), license plate, a decal or similar article attached to a vehicle, a temporary traffic sign (e.g., a traffic cone or barrel), or other infrastructure articles. In some examples, a pathway article may also include any item along a pathway, such as an article of clothing, for example on a construction worker, a bicycle, and similar articles. For example, as illustrated in FIG. 1, pathway article 132A includes a pavement marking tape indicating an outer edge of vehicle pathway 130 (e.g., for traffic traveling left to right), pathway article 132B includes a pavement marking indicating a center line of vehicle pathway 130 (e.g., dividing traffic that travels left to right from traffic traveling right to left), and pathway article 132C indicates another outer edge of vehicle pathway 130 (e.g., for traffic traveling left to right).

In accordance with techniques of this disclosure, each pathway article of pathway articles 132 includes one or more radar reflecting structures. For example, as illustrated in FIG. 1, pathway article 132A includes radar reflecting structures 134AI-134A_N, pathway article 132B includes radar reflecting structures 134BI-134B_N, and pathway article 132C includes radar reflecting structures 134Ci- 134C_N (collectively,“radar reflecting structures 134”). In some examples, each of radar reflecting structures 134 is configured to receive radar radiation and reflect the radar radiation in the direction from which the radar radiation was received. For example, radar reflecting structures 134 may be configured to reflect radar radiation of a particular wavelength, such as radiation with a frequency between approximately 24 GHz and approximately 28 GHz or a frequency between approximately 76GHz and approximately 8 lGHz. It is to be understood that the wavelengths are example wavelengths only and that other ranges of wavelengths are possible. In some examples, radar reflecting structures 134 may include a plurality of antennas, which may be linear slot antennas, u-shaped antennas, or other shapes of antennas. In some examples, a plurality of radar reflective structures may also be referred to as a radar reflective array.

In some examples, each of pathway articles 132 may include additional human or machine detectable features. For example, pathway articles 132 may include a colored (e.g., yellow, white, etc.) surface detectable by a human operating or located within PAAV 110. In other words, at least a portion of pathway articles 132 may be colored in the human-visible light spectrum, such that pathway articles 132 are perceptible by humans. As another example, at least a portion of pathway articles 132 may include text, images, or other visual information. Similarly, pathway articles 132 may include a machine- perceptible surface. For example, at least a portion of pathway articles 132 may detectable via an infrared camera (e.g., an infrared camera onboard PAAV 110).

System 100 includes PAAV 110 that may operate on vehicle pathway 130. As described herein, PAAV generally refers to a vehicle that may interpret the vehicle pathway and the vehicle’s environment, such as other vehicles or objects. A PAAV may interpret information from one or more sensors (e.g., cameras, radar devices, etc.), make decisions based on the information from the one or more sensors, and take actions to navigate the vehicle pathway.

PAAV 110 of system 100 may be an autonomous or semi -autonomous vehicle, such as an ADAS. In some examples PAAV 110 may include occupants that may take full or partial control of PAAV 110. PAAV 110 may be any type of vehicle designed to carry passengers or freight including small electric powered vehicles, large trucks or lorries with trailers, vehicles designed to carry crushed ore within an underground mine, or similar types of vehicles. PAAV 110 may include lighting, such as headlights in the visible light spectrum as well as light sources in other spectrums, such as infrared. PAAV 110 may include other sensors such as radar, sonar, LIDAR, GPS, and communication links for the purpose of sensing the vehicle pathway, other vehicles in the vicinity, environmental conditions around the vehicle, and for communicating with infrastructure.

As shown in FIG. 1, PAAV 110 of system 100 may include one or more image capture devices 150, one or more radar devices 152, and computing device 140. PAAV 110 may include additional components not shown in FIG. 1 such as engine temperature sensor, speed sensor, tire pressure sensor, air temperature sensors, an inclinometer, accelerometers, light sensor, and similar sensing components.

Image capture devices 150 may convert light or electromagnetic radiation sensed by one or more image capture sensors into information, such as digital image or bitmap comprising a set of pixels. Each pixel may have chrominance and/or luminance components that represent the intensity and/or color of light or electromagnetic radiation. Image capture devices 150 may include one or more image capture sensors and one or more light sources. In some examples, image capture devices 150 may include image capture sensors and light sources in a single integrated device. In other examples, image capture sensors or light sources may be separate from or otherwise not integrated in image capture devices 150.

Examples of image capture sensors within image capture devices 150 may include semiconductor charge- coupled devices (CCD) or active pixel sensors in complementary metal-oxide-semiconductor (CMOS) or N-type metal-oxide-semiconductor (NMOS, Live MOS) technologies. Digital sensors include flat panel detectors. In one example, image capture devices 150 includes at least two different sensors for detecting light in two different wavelength spectrums.

In general, image capture devices 150 may be used to gather information about a pathway. Image capture devices 150 may have a fixed field of view or may have an adjustable field of view. An image capture device with an adjustable field of view may be configured to pan left and right, up and down relative to PAAV 110 as well as be able to widen or narrow focus. Image capture devices 150 may capture images of vehicle pathway 130, which may include images of lane markings, centerline markings, edge of roadway or shoulder markings, as well as the general shape of the vehicle pathway 130. Responsive to capturing images of vehicle pathway 130, image capture devices 150 may generate information indicative of the images and send the image information to computing device 140.

PAAV 110 includes one or more radar devices 152. Each radar device of radar devices 152 include a radar transmitter configured to emit radar radiation (e.g., radio waves) and one or more radar receivers configured to detect radar radiation. In some examples, one or more radar receivers may be placed to measure off-angle shift in power and/or frequency. In some examples, radar devices 152 emit radar radiation with a frequency between approximately 24 GHz with approximately a 200 MHz bandwidth, or a frequency between approximately 76GHz and approximately 81 GHz. It is to be understood that the frequencies listed are merely example frequencies and that other radar frequencies may be used.

Radar devices 152 may be include stationary radar devices 152, such that the radar transmitter emits radar radiation in a single direction and the radar receiver receives or detects radar radiation from a single direction. In some examples, one or more of radar devices 152 are pivotable or rotatable, such that the radar transmitter emits radiation in a range of directions (e.g., 45 degrees in a horizontal direction and 45 degrees in a vertical direction) and the radar receiver receives radar radiation from a range of directions. In some examples, the radar device may be physically stationary, but the beam may be steered (e.g. via a phased array.) In some examples, radar devices 152 detect radar radiation and output radar information about the detected radar radiation to computing device 140. The region illuminated by the transmitted radar radiation and in which the radar receiver receives radar radiation may be referred to as a radar devices field of regard (FOR).

In the example of FIG. 1, computing device 140 includes an interpretation component 142 and a vehicle control component 144. Components 142 and 144 may perform operations described herein using hardware, hardware and software, hardware and firmware, or a mixture therein. Computing device 140 may execute components 142 and 144 with one or more processors. Computing device 140 may execute any of components 142 and 144 as or within a virtual machine executing on underlying hardware.

In some examples, interpretation component 142 may information from image capture devices 150, radar devices 152, or both, and determine one or more characteristics of vehicle pathway 130. For example, computing device 140 may receive image information from image capture devices 150.

Responsive to receiving the image information, interpretation component 142 of computing device 140 may perform image processing (e.g., filtering, amplification, and the like) and image recognition on the received image information. For example, interpretation component 15 may determine (e.g., using image recognition techniques) that the image information includes information indicative of pathway articles 132 and that pathway articles 132 correspond to pavement lane markings. Responsive to determining that pathway articles 132 correspond to pavement lane markings, interpretation component 142 may determine a position of vehicle 110 within a lane of pathway 130.

Similarly, interpretation component 142 may determine a position of vehicle 110 based at least in part on radar information received from radar devices 152. For example, radar devices 152 may output radar information that indicates an object was detected, a distance to the object, a direction of the object relative to vehicle 110, or any combination therein. In some examples, interpretation component 142 determines the direction and distance to the object (e.g., pathway article 132) based on the received radar information. Interpretation component 142 may determine that the radar information indicates the radar radiation was received from (e.g., reflected off) a pathway article, such as a pavement marking tape. Responsive to determining the radar information indicates that the radar radiation was received from a pavement marking tape, interpretation component 142 may determine a position of vehicle 110 with a lane of pathway 130. For example, interpretation component 142 may determine a distance to the pavement marking tape based on the received radar information. Responsive to determining the position of vehicle 110 within vehicle pathway 130, interpretation component 142 may output information about the vehicle position to vehicle control component 144. To simplify the description of the figures, this disclosure may focus on pathway articles that are pavement marking tapes. However, as described above, a pathway article may include other objects, including objects in which a marking tape according the techniques of this disclosure is affixed. Some examples may include guard rails, such as concrete barriers, traffic barrels, curbs, impact attenuator or sand attenuator, energy absorption device highway crash absorption systems and similar articles.

Vehicle control component 144 may control or adjust operation of PAAV 110 based on the information received from interpretation component. For example, vehicle control component 144 may receive, from interpretation component 142, information indicating that vehicle 110 is approaching a pavement marking tape and may output a command to an electronic control unit (ECU) of vehicle 110 to apply a force to the steering to keep vehicle 110 within its current lane.

In some examples, computing device 140 may use information from interpretation component 142 to generate notifications for a user of PAAV 110, e.g., notifications that indicate a characteristic or condition of vehicle pathway 130. For example, responsive to receiving information indicating that vehicle 110 is approaching a pavement marking tape, vehicle control component 144 may output a notification (e.g., audible, graphical, or tactile) to warn an occupant of vehicle 110 that vehicle 110 is approaching the pavement marking.

Pathway articles that include radar reflective structure of this disclosure may have advantages over other types of pathway articles. Including radar reflective structures in the pathway article may increase the ability of a PAAV to detect a pathway in various conditions (e.g., inclement weather conditions), reduce the cost and complexity of components utilized by the PAAV to detect the pathway (e.g., by eliminating the need for other more costly components such as LIDAR), provide redundant techniques for the PAAV to detect the pathway, or a combination therein. For example, computing device 140 of PAAV 110 may combined the input from visual, radar and other sensors to provide a more complete interpretation of the vehicle pathway. For example, a lane assistant system based on optical camera systems may detect and analyze the course of the lane mainly by detection of the contrast between road surface and pavement marking. In hazardous or extreme weather condition like fog, snow, or other precipitation e.g. the detection rate may decrease significantly. A pavement marking tape that includes radar reflective structures according to this disclosure may provide a redundant and more precise lane detection method. A PAAV may more accurately detect the vehicle pathway based on a radar return signal received from the pathway article, which may increase vehicle and passenger safety.

Examples in which the radar reflective structures of this disclosure are combined with other sensable elements may provide additional advantages over other types of pathway articles. For example, pavement marking tapes comprising these radar reflective structures and at least one additional sensable feature that may be detected by other sensor systems mounted on the automobile, such as magnetic detectors, to provide additional redundancy in a compact planar structure. In some examples, the radar reflective structures and the additional sensable feature may be located in the same region of the marking tape or adjacent to each other. In other words, the redundancy in the detectable features of the marking tape may enable use of sensor fusion to provide greater confidence of detection of the pavement marking under a wider range of conditions and to enable distinction between pavement marking and other radar- reflective objects in the field of view.

To simplify the explanation, the description in this disclosure may focus on the example of a pathway article on a pathway with the radar transceiver on the vehicle. However, the radar reflecting structures of this disclosure may equally apply in examples in which the radar reflecting structure are in a compact planar structure affixed to a vehicle, such as a license plate, a decal, or similar article. In some examples a radar transceiver may be stationary along the vehicle pathway and transmit incident radar radiation toward a vehicle and receive reflected radar radiation from the radar reflecting structure on the vehicle. In other examples, a first vehicle may transmit radar radiation toward a second vehicle and receive reflected radar radiation from the radar reflecting structure on the second vehicle. In some examples, a decal that includes radar reflecting structures may be placed on a non-metallic portion of a vehicle to increase the RCS.

The radar reflective structures in a compact planar structure according to the techniques of this disclosure differ from other types of radar-reflective pavement markers. For example, the radar reflective structures of this disclosure and the compact planar structure may have advantages over cat’s eye pavement markers, because of lower cost, ease of maintenance and pavement marking tape may be more applicable in areas subject to snowfall and the use of snowplows than cat’s eye type pavement markers.

The radar reflective structures of this disclosure may also have advantages over frequency selective surfaces. For example, the radar reflecting structures of this disclosure have may broader range of detection distance, when compared to other structures. Also, periodic placement and angular directionality may enable the radar signal transmitter to be at least one pulsed signal transmitter on one or both sides of a PAAV. By placing a marking tape of this disclosure on either side of a vehicle pathway may protect marking tape from abrasion, wear, fouling, plasticization from oil and grease on roadway that may deleteriously affect the modulus of marking tape. In examples of a marking tape with a low RCS compared to the marking tape of this disclosure, the low RCS marking tape may have to be placed on a pathway somewhere under the vehicle. Therefore, the wear, soiling and damage of a low RCS marking tape may limit the durability of other sensible features than would otherwise enable redundancy via sensor fusion. FIGS. 2A-2D are conceptual diagrams illustrating top views of example arrangements of radar reflecting structures within pathway articles, according to one or more techniques of this disclosure.

FIGS. 2A-2D illustrate example respective pathway articles 232A-232D (collectively, pathway articles 232”), which may correspond to any of pathway articles 132 of FIG. 1. Pathway articles 232 illustrated in FIGS. 2A-2D are only examples and other pathway articles 232 may exist.

Each pathway article of pathway articles 232 include a plurality of edges 240, 242, 244, and 246. In some examples, edges 240, 242 may be referred to as long edges or long axis and edges 244, 246 may be referred to as short edges or short axis. For example, pathway articles 232 may be relatively longer than they are wide. For instance, pathway articles 232 may be pavement marking tapes that indicate a boundary of one or more lanes of traffic and may be defined by a width on the order of several inches (e.g., approximately 4 inches, or approximately 10 centimeters) and a length on the order of yards (or meters), tens or hundreds of yards (or meters), miles (or kilometers), or longer.

As illustrated in FIG. 2A, pathway article 232A includes a plurality of radar reflecting structures 234A_I-234A_N (collectively,“radar reflecting structures 234A”). Each of radar reflecting structures 234A include a plurality of antennas. For example, radar reflecting structure 234Ai includes antennas 236A_l; 236A₂, 236A₃ and 236A₄ (collectively,“antennas 236A”).

In some examples, each radar reflecting structure of radar reflecting structures 234A may be orientated in the same or similar direction. For examples, as illustrated in FIG. 2A, each of radar reflecting structures 234A are orientated such that the lateral members 238, 239 of antennas 236 are substantially parallel to edges 244, 246 of pathway article 232. Similarly, each of radar reflecting structures 234A may be orientated such that each antenna 236 is substantially parallel to edges 240, 242 of pathway article 232. For instance, radar reflecting structures 234A may be squared with pathway article 232A. In some examples, orientating radar reflecting structures 234A square with pathway article 232A may enable a radar equipped vehicle (e.g., PAAV 110 of FIG. 1) to detect pathway articles adjacent (e.g., directly adjacent) to vehicle 110 using radar devices that are orthogonal to the direction of travel of vehicle 110.

As illustrated in FIG. 2B, pathway article 232B includes a plurality of radar reflecting structures 234B_I-234B_N (collectively,“radar reflecting structures 234B”). Each of radar reflecting structures 234B include a plurality of antennas similar to antennas 236A of FIG. 2A. As illustrated in FIG. 2B, each of radar reflecting structures 234B are orientated in a same or similar direction (e.g., within a threshold number of degrees, which may be defined by a manufacturing tolerance) as one another. As further illustrated in FIG. 2B, each radar reflecting structure of radar reflecting structures 234B is angled relative to pathway article 232B. In other words, of radar reflecting structures 234B are not squared to pathway article 232B. Orientating radar reflecting structures 234B as shown in FIG. 2B may enable radar reflecting structures 234B to receive incident radar radiation from, and redirect the radar radiation back to, directions that are not orthogonal to edges 240, 242 of pathway article 232B. In this way, radar reflecting structures 234B may enable a radar equipped vehicle (e.g., PAAV 110 of FIG. 1) to detect pathway articles ahead of or behind vehicle 110 using radar devices that directed within a threshold number of degrees (e.g., between approximately 30 and approximately 60 degrees) relative to the direction of travel of vehicle 110.

As illustrated in FIG. 2C, pathway article 232C includes a plurality of radar reflecting structures 234C_I-234C_N (collectively,“radar reflecting structures 234C”). Each of radar reflecting structures 234C include a plurality of antennas similar to antennas 236A of FIG. 2A.

Radar reflecting structures 234C may be orientated in different directions. For example, as illustrated in FIG. 2C, radar reflecting structure 234Ci is orientated in a first direction and radar reflecting structure 234C₂ is orientated in a different direction. In some examples, radar reflecting structures 234C may be orientated in alternating directions. For example, radar reflecting structure 234Ci may be orientated in a first direction and radar reflecting structure 234C₂ may be orientated 180 degrees opposite the orientation of radar reflecting structure 234Ci. In some examples, orientating radar reflecting structures 234C as shown in FIG. 2C may enable radar reflecting structures 234C to receive incident radar radiation from different directions, and redirect the radar radiation back to the respective direction from which the radiation was received. For instance, pathway article 232C may include a pavement marking tape dividing traffic traveling in opposite directions (e.g., such as pathway article 132B of FIG. 1) and may enable a single pathway article to reflect radar radiation to vehicles on opposite sides of a road. In this way, radar reflecting structures 234C may enable different radar equipped vehicles (e.g., PAAV 110 of FIG. 1) that are traveling in opposite directions to detect the same pathway article 232C.

As illustrated in FIG. 2D, pathway article 232D includes a plurality of radar reflecting structures 234D_I-234D_N (collectively,“radar reflecting structures 234D”). Each of radar reflecting structures 234D include a plurality of antennas similar to antennas 236A of FIG. 2A.

Radar reflecting structures 234D may be orientated in different directions. In some examples, radar reflecting structures 234D are orientated in a pattern. For example, as illustrated in FIG. 2D, radar reflecting structure 234Di is orientated in a first direction, radar reflecting structure 234D₂ is rotated approximately 45 degrees from radar reflecting structure 234Di, radar reflecting structure 234D₃ is rotated approximately 45 degrees from radar reflecting structure 234D₂, and so on. In some examples, orientating radar reflecting structures 234D as shown in FIG. 2D may enable radar reflecting structures 234D to receive incident radar radiation from different directions, and redirect the radar radiation back to the respective direction from which the radiation was received.

In this way, radar reflecting structures 234B may enable radar equipped vehicles to detect a given pathway article at various locations from various distances and detect the pathway article when traveling in different directions.

FIG. 3A is a conceptual diagram illustrating a top view of example arrangements of radar reflecting structures within a within pathway article, according to one or more techniques of this disclosure. As illustrated in FIG. 3 A, pathway article 252A includes a plurality of groupings of radar reflecting structures 254A_I-254A₄. Pathway article 252A is similar to pathway articles 232A - 232D depicted in FIGS. 2A - 2D. Each of radar reflecting structures in pathway article 252A includes a plurality of antennas similar to antennas 236A of FIG. 2A. The groupings of radar reflecting structures may be called a radar reflective array. In some examples there may be a predetermined distance or spacing 258 between groupings of radar reflective structures in a pathway article, such as pathway article 252A. The number of radar structures and spacing may convey additional information to a PAAV. As one example, pathway article 252A may be a pavement marking tape for a lane indicator on a vehicle pathway. A PAAV traveling along a vehicle pathway may detect a pattern of an array of three radar reflective structures followed by an array of two radar reflective structure, similar to the pattern depicted by radar reflective arrays 254A1 and 254A2. However, a PAAV going in the opposite direction may only detect a pattern of two radar reflective structures, such as depicted by radar reflective array 254A3. In some examples, the PAAV may be configured to determine that the first pattern indicates the correct direction and the second pattern indicates that the PAAV is traveling in the wrong direction on the vehicle pathway. In other examples, groupings or patterns of radar reflective structures may convey other information to a PAAV.

This separation between periodic arrays is also useful to counteract CTE effects. CTE is be a percentage of expansion over a baseline distance. If a feature is quite small, an expansion of 2% of the dimension of that feature is a relatively infinitesimal amount. If the feature is quite large, the overall expansion from edge to edge can be quite a substantial distance. Large elements, such as long antennas, i.e. long prism features, embedded in a length of the tape may buckle with expansion. Instead, using smaller elements in multiple radar reflecting structure in separated arrays of radar reflecting structure may help maintain dimensional integrity. In some examples, additional stress-relieving separation between the “radar reflective structure” may help to maintain dimensional integrity of the radar reflecting structures.

FIG. 3B is a conceptual diagram illustrating a top view of example of radar reflecting structures within a within pathway article, with curved angled sawtooth notches according to one or more techniques of this disclosure. As illustrated in FIG. 3A, pathway article 252A includes a plurality of radar reflecting structures 254B_I-254B_N. Pathway article 252B is similar to pathway articles 232A - 232D depicted in FIGS. 2A - 2D. Each of radar reflecting structures in pathway article 252A includes a plurality of antennas similar to antennas 236A of FIG. 2A. For example, radar reflecting structure 254Bi includes antennas 256Bi, 256B₂, 256B₃ and 256B₄ (collectively,“antennas 256B”).

Antennas 256B of radar reflective structure may be configured with a radius. The radius may change the shape or direction of the reflected radar radiation from radar reflective structure 254B1, when compared to a radar reflective structure comprising antennas without a radius. In the example of FIG. 3B, PAAV 250 with a direction of travel 260 may output radar radiation from a radar transceiver installed in PAAV 250. The incident radar radiation may reflect from any of the radar reflective structures 254Bi- 254B_N in pathway article 252B and the reflected radar radiation may return to PAAV 250. In other words, radar reflective structures 254B_I-254B_N may be arranged such that the radius 262 is configured to be in substantially the same direction as the direction of travel of the reflected radar signal. The reflected radar signal may be configured to be substantially opposite to the incident radar signal.

In some examples, such as FIG. 3B with regularly spaced intervals between radar reflective structures 254B_I-254B_N, a signal strength 264 of a reflected radar signal 268 may be received by PAAV 250 as a regular series of peaks 266. In other examples, such as the groupings depicted in FIG. 3 A, signal strength 264 of reflected radar signal 268 may have an irregular series of peaks 266. For pathway articles that include radar reflective structures at a plurality of angles, signal strength 264 may vary depending on the position of PAAV 250 relative to the radar reflective structure. In some examples, the spacing, grouping, different angles and other features of radar reflecting structures within a pathway article may be considered to convey information in a code that may be interpreted by a PAAV.

FIG. 4 is a conceptual diagram illustrating an example marking tape and an example vehicle equipped with radar devices according to one or more techniques of this disclosure. Even with advances in autonomous driving technology, infrastructure, including vehicle roadways, may have a long transition period during which fully autonomous vehicles, vehicles equipped with ADAS, as well as traditional fully human operated vehicles share the road. Some practical constraints may make this transition period decades long, such as the service life of vehicles currently on the road, the capital invested in current infrastructure and the cost of replacement, and the time to manufacture, distribute, and install fully autonomous vehicles and infrastructure.

Autonomous vehicles and ADAS, which may be referred to as semi-autonomous vehicles, may use various sensors to perceive the environment, infrastructure, and other objects around the vehicle. These various sensors combined with onboard computer processing may allow the automated system to perceive complex information and respond to it more quickly than a human driver. As mentioned above, some examples of PAAVs may include the fully autonomous vehicles, as well UAVs, human flight transport devices, underground pit mining ore carrying vehicles, forklifts, factory part or tool transport vehicles, ships and other watercraft and similar vehicles. A vehicle pathway may be a road, highway, a warehouse aisle, factory floor or a pathway not connected to the earth’s surface.

FIG. 4 depicts pathway article 210 and PAAV 200, which is equipped with one or more sensors including longer range radars (LRR) 202A and 202B, medium range radars (MRR) 204A and 204B and short range radars (SRR) 206A and 206B. PAAV 200 may also include other sensors, such as cameras, as described above in relation to FIG. 1. The radar system configuration of PAAV 200 depicted in FIG. 4 is just one example for illustration. In other examples, PAAV 200 may be equipped with additional, or fewer, radar systems and arranged in other configurations. To simplify the description of FIG. 4, PAAV 200 will be described as a roadway vehicle, such as an automobile, traveling along a roadway. However, in other examples, PAAV 200 may be other types of vehicles traveling on other types of pathways, as described above in relation to FIG. 1.

LRR 202A and LRR202B may be radar systems with a field of regard (FOR) in the direction of travel of PAAV 200 and used to detect and/or track objects ahead of and behind PAAV 200. In the example of FIG. 4, the FOR of LRR 202A is the region facing forward of PAAV 200 and LRR 202B is the region facing behind PAAV 200. In some examples, LRR 202A and LRR 202B are narrowband systems in the 24 GHz or 76 GHz bands. In other examples, LRR 202A and LRR 202B may be broadband systems in the 77 GHz band. Narrowband systems in the 24 GHz and 76 GHz bands may be used for applications such as adaptive cruise control and blind spot monitoring. A broadband radar system, for example with a bandwidth of 4 GHz, may be also used for adaptive cruise control, blind spot monitoring and obstacle or pathway detection. A broader bandwidth may enable higher spatial resolution of the radar system, relative to a unit based on 77 GHz, for example, with a 200 MHz bandwidth, which limits resolution to one meter (1 m). Higher frequency devices, such as in the 79 GHz range, may enable miniaturization of the radar unit due to physical requirements on antenna size, and also produce a lower emission power, which has the added benefit of mitigating the risk of mutual interference from units on the same roadway. Examples of units in the range of 79 GHz may be useful for short-range and medium-range applications where distinguishing potential obstacles on a vehicle pathway may be valuable.

MRR 204A and MRR 204B may have a wider azimuth FOR toward the front and rear of PAAV 200, when compared to LRR 202A and LRR 202B. In some examples, the only overlap between the MRR and LRR systems is facing forward between 76-77 GHz. To account for that overlap, in some examples may be to have the LRR 202A - 202B at 77 GHz unit have two polarizations, so that it could be distinguished from a signal generated by a MRR unit at 79 GHz. To account for that overlap, in some examples LRR 202A - 202B may have a different polarization, so that the LRR may be distinguished from a signal generated by a MRR unit. For example, a radar transmitter may transmit radar signals with transverse magnetic (TM) polarization or with transverse electric (TE) polarization. TE modes have the electric field (E-field) transverse to the direction of propagation. TM modes have the magnetic field transverse to the direction of propagation. For example, the RCS for a radar reflecting structure of this disclosure may be larger for a signal at low incident angles from a TM mode radar transmitter where the E-field is vertical in relation to the radar reflecting structure.

SRR 206A and 206B may include an FOR to the right and left of the vehicle. Some applications for SRR 206A and SRR 206B may include imminent collision warning, for example to trigger air bags, as well as blind spot monitoring.

Pathway article 210, in the example of FIG. 4 may be a pavement marking tape or a tape attached to a barrier, such as a guardrail. Pathway article 210 includes radar reflective structure 212, radar reflective structure 214 and radar reflective structure 216. Each radar reflective structure 212 - 216 is at a different angle relative to the long axis 211 of pathway article 210. In contrast to radar-reflective pavement markers based on cat’s eye pavement markers and frequency selective surfaces, the radar reflective structures according to the techniques of this disclosure are in a compact planar structure. The compact planar structure may provide advantages over other types of roadway, for example that radar reflective structures of this disclosure may be included in marking tape that may be applied to pavement or other pathway structures.

As described above in relation to FIGS. 1 - 3B, the reflected radar radiation from the radar reflective structure 212 - 216 may be at a maximum when the lateral member or lateral portion of the radar reflective structure is substantially orthogonal to the incident radar radiation. For example, radar reflective structure 220 is at an angle 212 that is parallel to long axis 211 of pathway article 210. In this orientation, radar reflective structure 220 is approximately orthogonal to the incident radar radiation from SRR 206B when PAAV 200 is approximately adjacent to radar reflective structure 220.

In another example, when PAAV 200 moves to be adjacent to radar reflective structure 224, which is at angle 216 relative to long axis 204, radar reflective structure 224 would not be orthogonal to the incident radar radiation from SRR 206B. Therefore, SRR 206B may receive less reflected radiation from radar reflective structure 224 when PAAV 200 is adjacent to radar reflective structure 224.

Similarly, SRR 206B may receive less reflected radar radiation when adjacent to radar reflective structure 222 at angle 214 relative to long axis 211. In contrast, the incident radar radiation from MRR 204A and LRR 202A may be orthogonal to radar reflective structure 222 or radar reflective structure 224 when PAAV 200 is at some distance from radar reflective structure 222 or radar reflective structure 224.

Therefore, MRR 204A and LRR 202A may receive a more reflected radiation from radar reflective structure 222 or radar reflective structure 224 when PAAV 200 is at some distance from radar reflective structure 222 or radar reflective structure 224.

In this manner, by selecting the angle of a radar reflective structure relative to the long axis of pathway article 210, and therefore relative to the position of PAAV 200, the radar reflective structure of this disclosure may be adapted to a variety of functions. As one example, radar reflective structure 220 at angle 212 may be used in a lane guidance function, in addition to any lane guidance function from a visual or other type of camera. The lane guidance function from multiple sources may be used as a cross check by computing device 40 depicted in FIG. 1. In other examples, such as if the lane markings are obscured by low visibility radar reflective structure 220 may provide a more accurate lane guidance function than can be provided by a visual camera under these conditions. Similarly, radar reflective structure 224 may be used to provide forewarning of an upcoming curve or lane shift based on the reflected radiation from MRR 204A and LRR 202A.

FIGS. 5 A - 5C are conceptual diagrams illustrating an example stepped angled sawtooth notch radar reflecting structure according to one or more techniques of this disclosure. FIG. 5 A illustrates an example marking tape 300 that includes a plurality of angled sawtooth notch radar reflecting structures, such as radar reflecting structure 302. Pathway article 300 is similar to pathway articles 232A - 232D depicted in FIGS. 2A- 2D, as well as pathway article 252A depicted in FIG. 3 A. Each of radar reflecting structures in pathway article 300 includes a plurality of antennas similar to antennas 236A of FIG. 2A.

The antennas of radar reflecting structure 302 take the form of stepped angled sawtooth notches.

FIG. 5B is a conceptual diagram illustrating atop view of an example stepped angled sawtooth notch radar reflecting structure. The radar reflecting structure of FIGS. 5 A - 5C is configured as a non resonant structure. The slot dimensions of the radar reflecting structure according to this disclosure reflect a radar signal incident on the structure for radar systems in which the receive antenna is in close proximity to the transmit antenna. Though many types of structures maybe used to back-scatter the incident radar signal toward the receive antenna, scattering efficiency depends on the material of the radar reflecting structure, number of scattering elements, dimensions and other factors. In some examples, the angled sawtooth notch structure may be coated with a continuous conductive surface, such as vapor- coated metal, electroplated metal, electroless plated metal, molded graphene sheet, composite coating comprising enough conductive carbon black to have substantial surface conductivity. In some examples, the angled sawtooth notch structure may be coated with a coating that presents a large difference in dielectric constant relative to air. In some examples, the entire angled sawtooth notch structure may be constructed of composites comprising materials that are known to be high permeability (e.g. strontium ferrite) or high permittivity (e.g. barium titanate), as described above.

One example of a radar reflecting structure is a resonant structure, such as an array of antennas with dimensions that are a function of the expected frequency. For example, an array of antennas with a length that is one-half the wavelength of the expected frequency. A resonant structure type of radar reflecting structure may have the advantage of increasing the directivity of the backscattered radar signal because the elements of a resonant type of radar reflecting structure may be designed to eliminate unwanted scattering directions. However, the bandwidth for a resonant type radar reflecting structure may be limited to the bandwidth of the resonating element. The length of the resonating element may be tuned to a desired frequency band, such as a length of one-half wavelength. In the example of a half wavelength dipole, the RCS may be maximized at resonance. Therefore, wider bandwidth radar systems may get less efficient backscatter, i.e. a smaller RCS, as the frequency of the radar signal differs from the bandwidth of the resonating element. Also, the resonance frequency of a resonant structure type may be influenced by material surrounding the structure, which may be difficult to control.

In contrast, non-resonant structures may be very small size compared to the radar signal wavelength such that each element exhibits an omni-directional diffraction pattern. Therefore, non resonant RCS structures may not suffer from“out-tuning” issues. Some examples of non-resonating elements may include strips or slots with extremely small height (sub-millimeter). However, the techniques of this disclosure include stepped angled sawtooth notches 306 with dimensions configured to reflect incident radar radiation back to the radar transceiver. The angled surfaces oriented such that they are orthogonal relative to the axis of the incident electromagnetic wave. Other advantages of non resonant structures may also include that RCS is less sensitive to manufacturing tolerance and electromagnetic loading by nearby objects which may results in change of electrical length of the elements. This is because the non-resonant structure may be less dependent on the dimensions of the elements. Also, the RCS of a radar reflecting structure of this disclosure may be larger due to the fact that the radiating elements are not limited to the resonant length. Because spacing is tied to frequency, a radar reflecting structure may exhibit larger RCS over a wider range of frequencies by using“non-uniform” spacing. In other words, if a large array of radar reflecting structures includes smaller sub-arrays, each with different spacing to cover adjacent frequency bands, overall bandwidth may be widened without having to change the dimensions of each element.

Material of the radar reflecting structure of this disclosure may be metallic, conductive, ferro magnetic or a material with high dielectric properties. One example of this radar reflecting structure is a flexible construction with this geometry buried beneath a layer of material with low dielectric properties in the marking tape, such as pavement marking tape described above. In some examples, the radar reflecting structure is number of parallel angled sawtooth notches, such as depicted in FIGS. 5B and 5C.

In other examples, the radar reflecting structure includes a number of parallel angled sawtooth notches with shaped in an arc or radius, such as depicted in FIG. 3B. In examples in which the sawtooth structure is embedded beneath one or more layers of a marking tape, the sawtooth portions may be covered with a top layer to ensure the integrity of the three-dimensional sawtooth structure. In some examples the sawtooth structure may be constructed of a molded or embossed material and coated with a metallic or other radar reflective coating. In other examples, the elements may be etched from a plate. In other examples, the sawtooth structure may include high permeability material that may be detectable by magnetic detectors. In some examples, magnetic material, detectable by magnetic detectors, may be included in a marking tape in layers beneath the sawtooth structure. In other words, the magnetic material may be placed so it does not interfere with the radar reflective properties of the radar reflecting structures.

The spacing between the parallel notches 306 are set to cause a phase interference between the reflected radiation signal from each slot such that the phase interference results in constructive interference in the opposite direction of incidence from the transmitter. The constructive phase interference causes a focused beam at a predefined angle toward the radar transmitter/receiver. In the example of pavement marking tape, the angle of incidence of the radar signal from the vehicle may be small, and more elements, i.e. more parallel notches, may result in improved phase interference and therefore improved backscattering toward the receiver. The spacing and other dimensions of the triangular notches is a function of angle of incidence and frequency of the incident radar radiation within a small angular range.

Depending on the configuration and operation of the radar, this reflected signal, comprising reflected radar radiation, may be used to determine factors such as the presence, the angular location and distance of the radar reflecting structures relative to the PAAV. As one example, discussed above in relation to FIG. 1, the reflection of illuminating power from the incident radar radiation that is generated from and detected by a vehicle-mounted radar from the marking tape may be used by the PAAV to determine the position of the PAAV within a lane.

FIG. 5C is a conceptual diagram illustrating the geometry of the radar reflecting structure according to one or more techniques of this disclosure, which comprises triangular notches in a flat surface, i.e. compact planar structure. The electromagnetic energy, i.e. reflected radar radiation, from an object when illuminated by a radar beam is its RCS value, as described above. An object’s RCS can be configured to reflect incident energy in a specific direction, thereby making the object appear mirror-like to the incident electromagnetic radiation.

Each triangular slot, such as slot 314, includes a slant length 316, a depth 318, a width 310 and an angle 312. Slant length 316 may be referred to as the floor 322 of the slot. Depth 318 may define the reflective surface 320 of the slot. Angle 312 is configured to conform to the expected angle of incidence of the incident radar radiation, i.e. transmitted radar signal. The example of FIG. 5C will be described for an expected incident angle of 25 degrees and a frequency of 65 GHz. In other examples, other frequencies, such as 77GHz or 79 GHz, and different expected incident angles may change the dimensions of the triangular notches.

Slant length 316 for floor 322 of each slot is half the wavelength, or an integer multiple of half the expected wavelength, of the incident beam, i.e. the incident radar radiation. For example, for 65 GHz, the wavelength, l = 182 mils or 4.6 mm. Therefore, slant length 316 is approximately l/2 = 91 mils or 2.3 mm. Slant length 316 may also be an integer multiple of the half-wavelength, i.e. N*l/2. Floor 322 of each slot is angled parallel to the incident beam, so that the angle between floor 322 of each slot and a flat plane across the top of the radar reflective structure is equal to the angle of incidence of the radar illumination. In other words, floor 322 intersects the top plane, and slants downward from the top plane of the device at angle 312. In the example of FIG. 5C angle 312 is 25° (25 degrees). In some examples, floor 322 may be referred to as an angled surface and slant length 316 referred to as an angled surface length.

The back wall, or reflective surface 320, of each slot is orthogonal to floor 322. Therefore, determining the expected wavelength and angle of incidence of the incident radar radiation defines depth 318 of the back wall of the slot as well as the width 310 of opening 321 at the top surface of the slot. In other words, reflective surface 320 intersects the top plane and floor 322. In the example of FIG. 5C, depth 318 is approximately 42 mils or 1.1 mm. Width 310, in this example, is approximately 100.2 mils or 2.5 mm. Selecting slant length 316 as an integer multiple of the half-wavelength will change the dimensions of the reflecting surface 320, or back wall, as well as width 310 of the top opening 321 of slot 314. Width 310 of opening 321 may be referred to as the grating length. Also, reflecting surface 320 of slot 314 is substantially parallel to the reflecting surfaces for the other angled sawtooth notches.

The grating length, in the example of FIG. 5C may be considered the spacing between the stepped notches, and the spacing between the reflecting surfaces. In some examples the spacing may be affected by the coefficient of thermal expansion (CTE) of the material of the pathway article. In some examples, the PAAV may be configured to detect changes in the reflected radar radiation caused by changes in spacing between notches. In some examples, the PAAV may be able to determine a temperature of the pathway article based on determining changes in the spacing between the notches.

With a slant length 316 of floor 322 of each slot equal to N*l/2, when an electromagnetic wave strikes notches that are arranged as in FIGS. 5B and 5C, the reflected waves, i.e. reflected radar radiation, will add constructively and appear as if the radar reflecting structure is a single surface. The constructive interference may be referred to as phase interference. The effective surface, or RCS, will be

approximately the reflecting surface 320 depth 318 times the number of notches 306 and 314.

In the example of FIG. 5C, the incident angle of the incident radar radiation is referred to as theta (Q). The actual incident angle Q may be greater or less than the expected incident angle 312. The expected incident angle will be referred to as 0d. For the parallel notches 306 and 314 of FIGS. 5B and 5C, when Q is less than 0d ( 0 < 0d ), the stepped angled sawtooth notches operate as a single reflector off the reflecting surface. In this case the electromagnetic wave reflection angle, in other words, the angle of the reflected radar radiation is 0 r = 0d + | 0d - 0|. In other examples, when the incident angle 0 is greater than 0d, the notches operate as a double reflector off reflective surface 320 and floor 322.

Therefore, case the reflection angle of the reflected radar radiation is 0r = 0.

The radar reflecting structure of FIGS. 5A - 5C may also operate as a grating array, a.k.a a grating structure. The radar reflective structure will backscatter the incident electromagnetic wave according to the following equation:

where n is an integer ( n = 0, ±1, ... ), Q is the angle of incidence, l is the wavelength of the incident radar radiation, Qh is the scatter angle and d is the grating length, which corresponds to width 310 of opening 321. The angle of incidence is measured for a direction normal or perpendicular to the surface of the radar reflecting structure. Constructive interference and therefore reflection in the backscatter direction occurs according to the equation

The above equation provides the dimensions for the spacing of the periodic array of reflecting surfaces 320 created by stepped triangular notches. As described above, the spacing is a function of angle of incidence and frequency. A pathway article with stepped angled sawtooth notches according to one or more techniques of this disclosure may help overcome the challenge for vehicle based radar systems to detect pavement markings because of the shallow angle of incidence formed by the incident radar radiation from the radar transmitter. The location and orientation of the pavement marking with respect to a vehicle radar may result in most of the radar energy to be reflected away from the radar transceiver. The techniques of this disclosure may enable radar-reflectivity by including radar reflective structures that cause the reflected radar radiation to send the energy back toward the radar transceiver. In other words, the techniques of this disclosure may increase the RCS of planar resonating structures that are in a compact planar structure.

In other words, in the example of a pavement marking tape, the angle of incidence, or entrance angle, of the incident radar radiation may be low, compared to the surface of the pavement marking tape. The antennas may be configured to create a large RCS for radar reflecting structure 302 based on a low entrance angle. In other examples, such as on a pathway article, such as a barrier, or a license plate on a vehicle, the expected angle of incidence for the incident radar radiation may be high, i.e. have a high entrance angle. The dimensions and spacing for the periodic array of reflecting surfaces 320304A - 304N, may be configured to create a large RCS for radar reflecting structure 301 based on a high entrance angle.

In the example of FIGS. 5B and 5C, all the dimensions of the stepped triangular notches are the substantially the same. In other examples, a radar reflecting structure 302 may include notches of different dimensions, for example, to account for a broader bandwidth of expected frequencies of the incident radar radiation, or a wider variation in expected angle of incidence. The stepped triangular notches are example of a reflecting object that may be considered a metallic or otherwise conductive sawtooth structure where the wave is diffracted off sawtooth facets. In other examples, the angled sawtooth notches may include other types of electromagnetic wave diffracting objects. In other words, the radar reflecting structure may also be considered an uneven surface with at least one dimension that is modulated in a periodic manner such that reflections from the periodic dimension cause constructive interference. The periodic array of reflecting surfaces, therefore may include at least one facet of the surfaces facing substantially in the direction of the incident radar radiation such that the reflections induced by the periodicity create a signal back towards the radar transmitter.

FIGS. 6A - 6C are conceptual diagrams illustrating an example angled sawtooth notch radar reflecting structure with a radius according to one or more techniques of this disclosure. FIG. 6A illustrates an example marking tape 330 that includes a plurality of angled sawtooth notch radar reflecting structures that include a radius, such as radar reflecting structure 331. Pathway article 330 is similar to pathway article 252B depicted in FIG.3B. Each of radar reflecting structures in pathway article 330 includes a plurality of antennas similar to antennas 256B of FIG. 3B. As with the radar reflective structure antennas of radar reflecting structure 302 take the form of stepped angled sawtooth notches.

FIG. 6B is a conceptual diagram illustrating a top view of an example stepped angled sawtooth notch radar reflecting structure with a curvature or radius. Similar to the radar reflecting structure of FIGS. 5 A - 5C, the radar reflecting structure of FIGS. 6A - 6C is configured as a non-resonant structure. Each slot 336 has a slight curvature or radius 338, with an arc length 334 which may create a focal point. In one example, for notches 336 with an arc of 10 degrees and a radius of 5 feet (1.5 m) results in a focal point of 5 feet (1.5 m). In some examples, the curvature may cause a more focused beam of reflected radar radiation in the focal direction, when compared to a straight element.

FIG. 6C is a conceptual diagram illustrating the geometry of the radar reflecting structure according to one or more techniques of this disclosure, which comprises triangular notches in a flat surface, i.e. compact planar structure. The electromagnetic energy, i.e. reflected radar radiation, from an object when illuminated by a radar beam is its RCS value, as described above. The example of FIG. 6C will be described for an expected incident angle of 15 degrees and a frequency of 65 GHz. In other examples, other frequencies, such as 77GHz or 79 GHz, and different expected incident angles may change the dimensions of the triangular notches.

Each triangular slot, such as slot 324, includes a slant length 348, a depth 318, a width 340 and an angle 342. Slant length 348 may be referred to as the floor 325 of the slot. Depth 350 may define the reflective surface 323 of the slot. Angle 342 is configured to conform to the expected angle of incidence of the incident radar radiation, i.e. transmitted radar signal, similar to the triangular slot 314, described above in relation to FIG. 5C.

As described above for FIG. 5C, slant length 348 for floor 325 of each slot is half the wavelength, or an integer multiple of half the wavelength, of the incident beam, i.e. the incident radar radiation. For example, for 65 GHz, the wavelength, l = 182 mils or 4.6 mm. Therefore, slant length 348 is approximately l/2 = 91 mils or 2.3 mm. Slant length 348 may also be an integer multiple of the half wavelength, i.e. N*l/2. Floor 325 of each slot is angled parallel to the expected incident beam, so that the angle between floor 325 of each slot and a flat plane across the top of the radar reflective structure is equal to the angle of incidence of the radar illumination. Angle 342 in the example of FIG. 5C is 15° (15 degrees). The flat plane, also referred to as the top plane, of the radar reflecting structure may be configured to have the radar signal pass through the top plane before striking the reflecting surfaces of the triangular notches, e.g. reflecting surface 89.

The back wall, or reflective surface 323, of each slot is orthogonal to floor 322. Therefore, determining the expected wavelength and angle of incidence of the incident radar radiation defines depth 350 of the back wall of the slot as well as the width 340 of opening 324 at the top surface of the slot. In the example of FIG. 6C, depth 350 is approximately 24.4 mils or 0.6 mm. Width 340, in this example, is approximately 94.2 mils or 2.4 mm. Selecting slant length 348 as an integer multiple of the half wavelength will change the dimensions of the reflecting surface 350, or back wall, as well as width 340 of the top opening 324 of slot 344. Width 340 of opening 324 may be referred to as the grating length. The reflected radar radiation angles and RCS function as described above for FIG. 5C.

The radar reflecting structures of this disclosure, such as those depicted in the examples of FIGS. 5A - 6C, employ appropriately spaced elements to create a diffracted beam of reflected radar radiation.

In some examples the beam may be reflected back in the direction of the incident radar beam. Each element, or antenna, scatters some of the incident electromagnetic wave. By appropriately spacing the elements, the scattered energy can be made to add up in a specific direction, as described above in relation to FIG. 5C., such back towards the radar transmitter. In other examples, the elements of a radar reflecting structure may cause the radar radiation to scatter by various mechanisms. In some examples, elements may be made of conducting materials, in which case, currents induced on the element by the incident radar radiation may re-radiate to create the scattered signal. In other examples, elements may also be physical structures which have material electrical properties, i.e., permittivity and/or permeability, that are different from those of other the materials in the vicinity of the elements. In this case, it is the abrupt change in electrical properties that creates scattering of the incident signal. For example, the material may have a high dielectric constant when compared to the surrounding air. In this disclosure, the term permeability refers to a quantity measuring the influence of a substance on the magnetic flux in the region it occupies. Permittivity refers to the ability of a substance to store electrical energy in an electric field. Dielectric strength refers to the ability of an insulating material of a specified thickness to withstand high voltages, i.e. an electric field, without breaking down. In other words, a high dielectric material can withstand a relatively higher voltage without breaking down, i.e. without experiencing failure of its insulating properties compared to a lower dielectric material.

FIG. 7A is a conceptual diagram illustrating an example radar reflecting structure configured to redirect incident radar radiation with refraction and reflection, according to one or more techniques of this disclosure. FIG. 7A is another example of a radar reflecting structure in a compact planar structure, similar to FIGS. 5 A - 6C described above, that may be included in a pathway article such as a marking tape. The radar reflecting structures in the periodic array 800 may be configured to increase the RCS of the pathway article based on the expected incident angle and frequency of the incident radar radiation. Periodic array 800 may include a plurality of radar reflecting structures. The example of FIG. 7A depicts three radar reflecting structures, however, in other examples, periodic array 800 may include more or fewer radar reflecting structures. Each radar reflecting structure includes a reflecting element 812A - 812C, covered by a refracting dielectric material 810A - 810C. Reflecting elements 812A - 812C include a reflecting surface, similar to reflecting surface 320 depicted above in FIG. 5C. As with reflecting surface 320, the reflecting surfaces of reflecting elements 812A - 812C may be covered with any radar reflective material, such as a metal. In other examples, the entire reflecting element 812A - 812C may comprise the same radar reflective material.

Incident radar radiation 802A - 802C strikes the surface of dielectric material 810A - 810C at an incident angle (0i) 816A - 816C from the vertical. Some of incident radar radiation 802A - 802C is transmitted into the dielectric layer by refraction as refracted radiation 818A - 818C at refracted angle (0a) 820A - 820C. Some of incident radar radiation 802A - 802C is reflected off of the dielectric surface as depicted by reflected radiation 804.

Refracted radiation (0a) 818A - 818C travels through dielectric material 810A - 810C and strikes the reflecting surfaces of reflecting elements 812A - 812C. The reflected radiation 822A - 822C travels back through dielectric material 810A - 810C and a portion of the radiation exits the dielectric material as reflected radar radiation 806A - 806C.

The dielectric constant e_G and the incident angle (0i) 816A - 816C determine the refracted angle (0a) 820A - 820C the radiation 8l8A - 8l8C is transmitted through dielectric material 810A - 810C, as well as how much of the radiation 8l8A - 8l8C is transmitted into the dielectric material (transmission coefficient, Tt) and how much of the wave is reflected 804 from the dielectric materials surface (reflection coefficient, Tr). In the example of FIG. 7A, the incident angles (0i) 816A - 816C are approximately equal.

The angle of the reflecting element 814A- 814C and choice of dielectric material 810A - 810C, with associated dielectric constant e_G may determine the properties of periodic array 800. For example, with an expected low entrance of incident radar radiation 802A - 802C, such as for pavement marking tape, the radar reflecting structures of periodic array 800 may be configured such the reflected radar radiation 806A - 806C returns to the radar transceiver at a low angle. In other examples, such as for a barricade, or a decal or license plate on a vehicle, periodic array 800 may be configured to reflect radiation based on an expected higher entrance angle than that expected for pavement marking tape.

In some examples of periodic array 800, the angles 814A - 814C of the reflecting surfaces for the radar reflecting structures may all be substantially the same. In other examples, such as the example of FIG. 7A, multiple reflecting elements 812 with multiple different angles 814 may be incorporated together providing a wide range return waves for a range of incident angles. For example, periodic array 800, may be configured to focus reflected radar radiation 806A into a tighter beam than the beamwidth of incident radar radiation 802A. Therefore, each of angles 808A- 808C will be different from each other. Similarly, periodic array 800 may be configured to spread reflected radar radiation 806A over a broader beamwidth, which may reduce the reflected power, but may improve detectability. The configuration of periodic array 800 follows the below equations. For the below:

Qί = incident angle for the incident radar radiation 802A - 802C

0a = refracted angle for the refracted radar radiation 818A - 818C

Tr = reflection coefficient, and

ft = transmission coefficient,

FIGS. 7B - 7C are plots illustrating the simulated performance of the example radar reflecting structure configured to redirect incident radar radiation refraction and reflection. The radar reflecting structures for the simulation of FIGS. 7B - 7C are similar to the radar reflecting structure of periodic array 800 depicted in FIG. 7A. For the examples of FIGS. 7B - 7C, the grazing angle is 90° - incidence angle.

FIG. 7B is a plot illustrating the RCS of a periodic array, similar to periodic array 800, over an angle in the x-z plane for an incident radar radiation of 66 GHz and 5° grazing angle incidence.

Therefore, a five degrees grazing equals 85 degrees incidence angle. FIG. 7C is a plot illustrating the RCS of a periodic array over an angle in the x-z plane for an incident radar radiation of 66 GHz and 15° grazing angle incidence. Therefore, a fifteen degrees grazing equals 75 degrees incidence angle. FIG. 7C is a plot illustrating the RCS of a periodic array, over an angle in the x-z plane for an incident radar radiation of 66 GHz and 25° grazing angle incidence. Therefore, a twenty-five degrees grazing equals 65 degrees incidence angle. FIG. 7D is a plot illustrating the RCS of a periodic array, over an angle in the x-z plane for an incident radar radiation of 66 GHz and 35° grazing angle incidence. The four plots show that the periodic array, such as periodic array 800, may produce a strong radar return, i.e. a high RCS, by selecting materials and configuration of the radar reflecting structures.

FIGS. 8 A - 8C are conceptual diagrams illustrating periodic arrays of antenna elements that include transmission lines according to one or more techniques of this disclosure. The periodic arrays are arranged to backscatter incident electromagnetic radiation back in the direction in which it was incident upon the array.

FIG. 8A is a schematic diagram illustrating a periodic array of antenna elements with pairs of antenna elements connected by transmission lines. Periodic array 830 includes antenna elements 832A - 832D, connected by transmission lines 834A and 834B. Transmission line 834A connects antenna elements 832A and 832D. Transmission line 834B connects antenna elements 832B and 832C. Incident radar radiation 836 strikes antenna elements 832A - 832D at angle of incidence 838.

By adjusting the electrical length of transmission lines 834A and 834B, and spacing (D) 835, periodic array 830 may form a retrodirective array whereby an electromagnetic wave of incident radar radiation 836 is backscattered in the direction of its incidence. In an example in which transmission lines 834A and 834B are not interconnected, periodic array 830 may forms a retroreflective array. The example of FIG. 8A includes a single row of antenna elements 832A - 832D, however other examples may include one or more rows of antenna elements. A radar reflecting structure similar to that depicted in the example of FIG. 8 A may provide a significant RCS in the direction of an incident radar signal.

Antenna elements 832 may be made from conductive materials such as metallic or conductive organic (e.g. carbon black) traces. Other examples of materials may include an inverse geometry configured with slots or apertures in a metallic foil or metallic or conductive organic coating on a substrate. As described above, in relation to FIGS. 5A - 7A, in some examples, periodic array 830 may be included as a protected layer in pathway articles, such as pavement marking tape for guidance of radar- augmented vehicles. The RCS of periodic array 830 may be detected by radar transceivers mounted on vehicles, or along a vehicle pathway, that are aimed to detect the array. A PAAV, for example may determine certain factors such as distance between the transceiver and periodic array 830 and presence or absence of signal at certain angles of incidence can be determined to interpret information about the surroundings of the PAAV. Directionality and spacing of periodic arrays 800 within a pathway article can be adjusted to encode information in the detected radar signal, as described above in relation to FIG. 3B.

As described above in relation to FIGS. 5A - 7A, in some examples periodic array 830 may be included in a pavement marking tape where retroreflective or retrodirective antenna arrays may be spaced along the axial direction of the pavement marking tape, and where they are positioned at an angle relative to the axial direction of travel, as depicted above in FIGS. 3B and 4. As the PAAV equipped with a radar travels along the roadway, a pavement marking tape that included a plurality of periodic arrays, such as periodic array 830, may generate a periodic response of backscattered power. This separation between periodic arrays of antenna elements may also useful to counteract CTE effects.

FIGS. 8B and 8C are conceptual diagrams illustrating a two-dimensional periodic array of antenna elements connected by transmission lines, similar to periodic array 830 depicted in FIG. 8A. Periodic array 840 includes antenna elements 842A - 842D, connected by transmission lines 844A and 844B. Transmission line 844A connects antenna elements 842A and 842D. Transmission line 844B connects antenna elements 842B and 842C. As described above in relation to FIG. 7A, by adjusting the electrical length of transmission lines 844A and 844B, and the antenna spacing, periodic array 840 may form a retrodirective array whereby an electromagnetic wave of incident radar radiation is backscattered in the direction of its incidence.

Antenna elements 842A - 842D are rectangular conducting patches in a microstrip patch antenna and function as a retroreflective radar array. The rectangular conducting patch elements are arranged in a periodic row. The individual elements are then connected to each other by transmission lines. The length (and, to a lesser degree, the width) of the rectangular conductive patch may be selected to create a radar reflecting structure operating at the radar frequency of the incident radiation. In the example of FIGS. 8A and 8B, the radar reflecting structure takes the form of a microstrip antenna, which is formed on dielectric substrate 843. The opposite surface of the dielectric substrate is selected to be a continuous conductive layer to form an electrical ground plane 848. Transmission lines 844A - 844B may utilize ground plane 848. Patch antennas 846A - 846D correspond to antennas 842A - 842D.

FIG. 8B depicts line of symmetry 845 at the center of the array of patches. The antennas are interconnected such that an antenna on one side of the line is connected, via a transmission line, to an antenna that is symmetrically displaced about line of symmetry 845. An incident electromagnetic wave, similar to incident radar radiation 836 depicted in FIG. 8 A, may induce signals on each patch antenna 842. In one example, as shown in FIG. 8A, in which incident radar radiation 836 is from the right at an angle 838 with respect the surface of the structure, incident radar radiation 836 will strike antenna number 842D first then antenna 842C and so on. In antenna array analysis, this time delay may be expressed as a phase shift. So, the signal received by antenna 842D may experience no phase shift while the signal received by antenna 842C includes a phase shift with respect to the signal received by antenna 842D, and so on.

The length of the transmission lines 844A and 844B, as with transmission lines 834A and 834B depicted in FIG. 8 A, may be selected to manage this phase shift to achieve a backscattered signal. If the electrical length of the transmission line connecting antennas 842D and 842A is an integral number of wavelengths at the signal frequency, antenna 842A will radiate the signal received by antenna 842D and vice versa. The signal applied to and transmitted from antenna 842A would have no phase shift, just as the signal from antenna 842D did not, when receiving signal from the direction as depicted in FIG. 8A. If the electrical length of the transmission line connecting antennas 842B and 842C is selected to be a different number of integral number of wavelengths, then the signal applied to and received from antenna 842B would have the phase shift experienced by antenna 842C and vice versa when it received a wave from depicted in FIG. 8A. Tailoring the transmission line lengths may create the phase shifts for periodic array 840 to reradiate the incident signal back in the direction of incidence.

In other examples, radar reflecting structures, such as periodic array 840 and 830 include additional pairs of elements that function in a similar manner. For example, to increase the backscattered signal level, several parallel rows of rectangular elements may be employed. The center-to-center spacing between rows in some examples may be less than a wavelength and may be approximately three quarters of the wavelength. The row spacing (not shown in FIG. 8B) may be less important than the transmission line length.

In other examples (not shown in FIGS. 8 A - 8C), a radar reflecting structure similar to periodic arrays 830 and 840 may be constructed of rectangular slots in a conductive layer, rather than conductive patches on a dielectric layer. The configuration of a slot type two-dimensional radar reflecting structure may appear similar to periodic array 840. In some examples a slot may be referred to as an aperture. The top surface of the slot-type retroreflective structure may include a conductive layer.

Apertures such as rectangular slots may be created in the conducting layer. These can form antennas. The slot length (long dimension of the slot), may be one half the wavelength of the operating frequency of the radar though other dimensions can be used. In some examples, the width of the slot may be approximately a tenth of the slot length though other widths may be used. The slot dimensions are variables that can be used to optimize the backscatter performance of the tape. The slots may be connected with transmission lines in the same manner as periodic arrays 840 and 830. In some examples, microstrip lines may be used as transmission lines 844A and 844B (with the conducting layer containing the slots used as a ground plane). In the example of microstrip lines used as transmission lines, one or more additional layers either above the conducting layer or below may be desirable. The layer below may be would be useful to isolate the microstrip from the road surface, in the example of a pavement marking tape, or from a guardrail or vehicle, in other examples.

In some examples, with aperture type antennas, the transmission line may be slotline, coplanar waveguide or other suitable structures embedded in the conducting layer. The rectangular slots may be arranged in a row. Columns may then be formed by multiple rows that are parallel to each other, similar to that described above in relation to multiple rows of patch antennas 842A - 842D. Similarly, center-to- center spacing between columns may be less important than the transmission line length, and in some examples, may be three quarters of the wavelength.

FIG. 8D depicts a radar reflecting structure that is a retrodirective array of conductive patches or apertures, similar to the patch antenna depicted in FIG. 8B. As described above in relation to FIGS. 8B - 8C, the elements or antenna 852A - 852D may be conductive patches on a dielectric layer or may be apertures, (also referred to as slots), in conductive layer.

Periodic array 850, may be a linear or planar array of antennas that may also be used to backscatter a radar signal. Periodic array 850 includes antenna elements 852A - 852D. Each patch or aperture may have its own transmission line with lengths 854A - 854D that are not connected to another antenna element. In other words, the transmission lines do not interconnect the antennas, but rather are terminated with either an open or short circuit.

In operation, a signal received by any one of antennas 852A - 852D is sent down the respective transmission line. When the signal reaches the terminated end 856A - 856D, the signal is essentially completely reflected back towards the antenna. Upon reaching the antenna, the signal is re-radiated. In the process of traveling both ways down the transmission line and being reflected by the termination 856A - 856D, the signal experiences a phase shift. By adjusting the length 854A - 854D of the transmission line, in conjunction with the type of termination 856A - 856D, periodic array 850 may produce the phase shift such that the radiation from each antenna is focused in the direction of the incoming signal. The phase shift of the reflected radar radiation from each antenna 852A - 852D may combine with constructive interference, as described above in relation to FIGS. 5A - 6C. As described above in relation to FIGS. 8B and 8C, several parallel rows may also be implemented to increase the backscatter magnitude. Any of the examples described above in relation to FIGS. 8 A - 8D, may be implemented in a compact coplanar structure, such as a marking tape. The retroreflective or retrodirective array, such as any of periodic arrays 830, 840 or 850, may include a layer that contains appropriately shaped metallic or conductive antenna elements, e.g., rectangles, circles on the“top” (side facing upward from the pavement) or apertures of similar geometry. Conductive transmission lines are attached to each antenna and may or may not connect one antenna to another. These conductive patches, or non-conductive apertures in a conductive layer, may prepared on the top surface of a dielectric layer (e.g. PET or aliphatic polyurethane film). This layer may have an additional conductive layer on the opposite face as an electrical ground plane. Both the top surface and bottom surface of the compact coplanar structure may be encapsulated with a low dielectric, reactive layer to prevent ingress of contaminants that might cause corrosion of the conductive structures. In some examples, the compact coplanar structure, such as a marking tape, may include an adhesive for attachment a surface.

This layer that carries the retroreflective or retrodirective array and optional adhesive may further have a non-conductive protective overlaminate. In the example of a radar-reflective pavement marking tape, the overlaminate may be a rubber composite or a polyolefin, with optional additional optics or abrasion-resistant particles adhered to the top surface with a polyurethane or other reactive binder.

In a representative application of a pavement marking tape, the row of patches may lie along the width dimension of the tape to enable detection from side-facing radar(s) mounted on a vehicle. The rows may alternatively be angled relative to the axis of the tape to accommodate a vehicle radar that is “looking” ahead at the tape, such as to ascertain future lane position. In some examples, groupings for radar reflecting structure that include patch antennas may be arrayed in a periodic fashion. In other examples radar reflecting structures may be deployed continuously along the length of the tape. In other examples, these radar reflecting structures may be deployed at different periodicities and at different angles of tilt to be detected with different radars in different locations on the vehicle to transmit additional information to the vehicle.

FIGS. 9A - 9C illustrate example techniques to increase the RCS of a vehicle depending on the angle of incidence of the incident radar radiation. FIG. 9A illustrates a vehicle to vehicle radar interaction. A radar transceiver on PAAV 862 transmits incident radar radiation 864 toward a second PAAV 860 and receives a reflected radar radiation 866. Note that vehicles in the example of FIG. 9A are automobiles, but the description applies to any type of PAAV, as described above in relation to FIG. 1.

In the example of FIG. 9A, PAAV 862 is at an angle of approximately 145° from the second PAAV 860. In some examples, the RCS from a vehicle may be different depending on from which angle the incident radar radiation strikes the vehicle.

FIG. 9B is a graph illustrating how the RCS for a variety of vehicle types changes depending on the angle of incidence of the incident radar radiation. As illustrated by regions 870 and 872, depending of the azimuth aspect angle, the RCS level may degrade at approximately 50° and/or 120°. The angles with low RCS may be referred to as‘low level angles.’ Therefore, a PAAV that includes a reflector tuned to increase the RCS at the low level angles may increase the visibility of the vehicle to a radar transceiver. The radar transceiver may be in a PAAV, such as for a driver assisted vehicle, or may be a fixed radar transceiver along a vehicle pathway.

Any of the radar reflecting structure described above in relation to FIGS. 5 A - 8D may be applicable to increasing the RCS of a pathway object, such as a vehicle. In some examples, the radar reflecting structure may be integrated into the license plate, a decal or some other compact coplanar structure on the pathway object. In the example of an automobile, a radar reflecting structure that is configured to increase the RCS for low level angles, such as approximately 50° and/or 120 may have advantages over other types of radar reflecting structures.

FIG. 9C illustrates an example of a radar reflecting structure that may have advantages in increasing the RCS of a vehicle, or other pathway article. The example of FIG. 9C illustrates a van Atta type array of antenna elements connected by transmission lines. The array of FIG. 9C operates similar to periodic arrays 830 and 840 described above in relation to FIGS. 8A and 8B. In other examples, a radar reflecting structure may include a Yagi antenna constructed similar to the radar reflecting structures described above in relation to FIGS. 8B - 8D. For example, a Yagi antenna as conductive elements on or embedded in a non-conductive layer. In other examples, the Yagi antenna may be constructed as a slot or aperture in a conductive layer.

FIG. 10 is a diagram illustrating a side view of an example reflection and scattering of a radar beam with a radar reflective structure of this disclosure. FIG. 10 illustrates a cross sectional view of a radar reflective structure 700A with 0 = 0 (theta = 0) indicating the angle orthogonal to antenna of the radar reflective structure. To simplify the description, the radar reflective structure will be described in terms of a radar reflective structure that is part of a pavement marking tape. Therefore, 0 = 0 indicates a direction straight up and + 90 and - 90 indicating directions along the pavement surface.

Incident radar radiation 701 strikes radar reflective structure 700A resulting in a reflected radar radiation 704 with 3 dB vertical beamwidth 706 as well as backscatter 702. Radar reflective structure 700A may include any one or more radar reflective structures, such as described above in relation to FIGS. 5A - 6C.

As described above, the type of radar reflective structure, as well as the length, number of structures, material, spacing and other properties of radar reflective structure 700A may determine the beamwidth of reflected radar radiation 704, the amount of energy that is reflected and in the backscatter 702 and the direction of reflected radar radiation 704. Also, in the example of notches, as described above in relation to FIG. 5C, the“sharpness” of the slot edges may also impact the amount of reflected radar radiation. For example, increasing the lateral length of each antennas of radar reflective structure 700A may have little impact on 3dB vertical beamwidth 706, i.e. the angular position of the 3dB boundary of reflected radar radiation 704 as well as little impact on the energy lost to backscatter 702 and sidelobes. However, increasing the lateral length may increase the energy in reflected radar radiation 704. Increasing the number of radar reflective structures in radar reflective structure 700A may increase the magnitude of the main lobe of reflected radar radiation 704 as well as decrease the 3dB vertical beamwidth 706. For example, a radar reflective structure with 100 reflective elements, or antennas, may have an increased magnitude of a main lobe when compared to a radar reflective structure with twenty- five elements. The number of radar reflective structures in an array may be limited by the angle of the radar reflective structure relative to the long axis of the pathway article, as well as the dimensions of the pathway article and spacing between radar reflective structures as needed for the expected frequency of the incident radar radiation.

In some examples, radar reflecting structure 700A may include a conducting groundplane below the reflective elements. The groundplane may be separated from the reflective elements by a dielectric substrate. The addition of a groundplane at a predetermined distance below the reflective elements of radar reflecting structure 700A may increase reflected energy in reflected radar radiation 704 by hindering incident radar radiation from passing through the notches into the ground. The added groundplane may also de-couples radar reflecting structure 700A electromagnetically from the ground materials. In some examples, the surfaces of the periodic sawtooth structure, such as the floor, and reflecting surface, depicted in FIGS. 5B - 6C may act as the ground plane.

FIG. 11 is a diagram illustrating a top view of an example reflection and scattering of a radar beam with a radar reflective structure of this disclosure. FIG. 11 is the top view example of similar radar reflective structure 700B that is similar to radar reflective structure 700A and may receive incident radar radiation similar to incident radar radiation 701 described above in relation to FIG. 10.

Radar reflective structure 700B includes a plurality of radar reflective structures with lateral length 720. The principles in the description of FIG. 11 apply also to radar reflective structures with radar reflective structures described above in relation to FIGS. 5A- 6C. Radar reflective structure 700B may reflect energy in the form of a main lobe of reflected radar radiation 714 with 3dB horizontal beamwidth indicated by 716A and 716B, as well as backscatter 712.

Similar to described above, increasing lateral length 720 of each antenna of radar reflective structure 700B may increase the magnitude of the main lobe of reflected radar radiation 714 and decrease the amount of energy lost to backscatter 712 and sidelobes. Increasing lateral length 720 may also decrease the 3dB horizonal beam width of reflected radar radiation 714. Increasing the number of radar reflective structures in radar reflective structure 700B may increase the magnitude of the main lobe of reflected radar radiation 714 but have less impact on the 3dB horizontal beamwidth or the energy lost to backscatter 712 and sidelobes. For example, doubling the number of radar reflective structures may increase the main lobe energy by four times, but have little effect on the horizontal beamwidth.

Increasing the number of radar reflective structures by five times can cause a significant increase in the main lobe magnitude of reflected radar radiation 714 as well as reduce the 3dB horizontal beam width.

As mentioned above in relation to FIG. 10 above, the number of radar reflective structures may be limited by the dimensions of the pathway article.

FIG. 12A is a block diagram illustrating an example compact planar structure that includes a radar reflective structure according to one or more techniques of this disclosure. Compact planar structure 900 will be described in terms of a marking tape, or pavement marking tape, but other examples, such as signs, license plates, decals and similar structures may equally apply. In some examples, such as examples including the stepped angled sawtooth notch radar reflecting structure depicted in FIGS. 5A - 6C, compact planar structure 900 will have a three-dimensional cross section from the sawtooth notch structures.

Compact planar structure 900 may include a backing layer 910, a radar reflective layer 908, a sensable layer 902 and one or more other layers, which may not be shown in FIG. 12A. In the example of a pavement marking tape, or a marking tape to be applied to a guard rail, traffic barrel and similar pathway articles, compact planar structure 900 may include an adhesive layer 914. In some examples, one or more layers included in backing layer 910 may be referred to as a carrier film, or a continuous base sheet. Some examples of materials that may be included in one or more layers may include polyethylene terephthalate (abbreviated as PET or PETE), polyesters, acrylics, rubbers, thermoplastics, polyolefins and similar materials.

In some examples, a marking tape comprising compact planar structure 900 may be used as a pavement marking for marking lanes, centerlines, edges or other features of a vehicle pathway. The dimensions of the marking tape may conform to a standard as prescribed by the region of use. In the example of a pavement marking for marking lanes, the material may be between about 7.5 and 30 centimeters (3 and 12 inches) wide and 30 centimeters (12 inches) long or longer. In the United States, pavement marking tapes are about 4, about 6, or about 8 inches wide (10 cm - 20 cm). In Europe, pavement marking tapes are typically about 15 or 30 centimeters wide.

In other examples, a marking tape comprising compact planar structure 900 may be used as a decal, or similar structure for use indoors, such as a warehouse or factory vehicle pathway. For an indoor application, compact planar structure 900 may not include for example, a protective layer or a conformance layer. In other examples, such as a decal or license plate used on a vehicle, compact planar structure 900 may include a protective layer to prevent moisture, oil, dirt or other contaminants from affecting the sensible layer and/or radar reflective layer but may not include protection from tires nor anti skid features, for example. Similarly, marking tape for application to a rough surface, such as a concrete barrier may include a conformance layer, while a marking tape for application to a smooth surface may not include a conforming layer. In other words, the construction of compact planar structure 900 may be specific for the particular application to which a pathway article that includes compact planar structure 900 may be used.

Sensable layer 902, in the example of FIG. 12A may include a retroreflective layer 906, with reflective elements and one or more protective layers 904. As discussed above, sensable layer 902 may also include any combination of LIDAR reflective elements, UV and IR reflective elements, magnetic elements, and other similar elements that may be detectable by one or more sensors on a PAAV (not shown in FIG. 12A). Examples of retroreflective layer 906 may include an exposed-lens system, an enclosed lens retroreflective sheet, encapsulated-lens, embedded lens, cube-comer type, microsphere- based retroreflective sheeting that comprise a monolayer of transparent microspheres partially embedded in a binder layer, and other types of retroreflective sheeting as well as combinations of any of the above. Retroreflective layer 906 may also include a texture to provide high retroreflectivity at both high and low light entrance angles. Sensable layer 902 is configured to allow radar signals to pass through sensable layer 902, where sensable layer 902 is placed over radar reflecting structures in radar reflective layer 908. In examples in which sensable layer 902 includes magnetic or metallic elements, the magnetic or metallic elements may be in a separate location from the radar reflecting structures of radar reflective layer 908.

Sensable layer 902 may also be colored in the visible spectrum to provide additional cues to vehicle operators or a computing device, such as computing device 40 described above in relation to FIG. 1. Some example colors may include red, yellow, white or blue. An example of an enclosed-lens retroreflective sheet that is gray colored initially, because of the aluminum reflective layer, can be changed to a desired color, for example, by adding an opaque colorant. In some examples, a combination of opaque and light transmissive colorants may be used. In this way, a pathway article that included compact planar structure 900 would have effective day and night time colors. Materials used in sensable layer 902, such as colorants, may be selected to avoid interference with the functions of the radar reflective structures in radar reflective layer 908. In some examples, an enclosed-lens retroreflective layer may not be used, and other types of non-metallic visible light retroreflective layers may be used to ensure that incident radar radiation may pass through sensable layer 902 to strike radar reflective layer 908. In other examples, visible light retroreflective portions that may include metallic elements may be placed in a separate location from the radar reflecting structures.

Backing layer 910 may include a conformance layer 912 and/or a scrim layer (not shown in FIG. 12A) and adhesive layer 914. In some examples, backing layer 910 may also a scrim material to impart increased tear resistance, which allows a temporary pavement marking to be removable. Conformance layer 912 may include material such as aluminum. Conformance layer 912 may allow a marking tape applied to a rough surface to conform and adhere to the surface, while ensuring that the rough surface does not substantially distort radar reflective layer 908 such that radar reflective layer 908 retains radar reflective properties.

Protective layer 904 may comprise a thin, high abrasion resistance and/or dirt resistant coating applied to the top surface of sensable layer 902 to protect it from traffic wear and dirt accumulation. Properties of protective layer 904 may include radar and light transmissive. In some examples, skid control particles may be partially embedded in protective layer 904, or in a layer on top of protective layer 904 (not shown in FIG. 12A). Skid control particles, may be referred to as anti -skid particles, and may be included in the upper surface of a pavement marking tape to improve the traction of vehicles. In some examples, protective layer 904 may include a release liner or apply a release treatment, e.g., silicone, to the top surface. Marking tape may be wound into a roll form and the release material may make it easier to dispense the marking tape.

Protective layer 904 may be single layer or multilayer, e.g., further comprising a top film overlying underlying layers. In some examples, aliphatic polyurethanes may be used for top films because aliphatic polyurethanes properties may include clear, resistant to dirt build-up, flexible enough to conform to the road surface, bond to inorganic anti-skid particles, and resist discoloration with exposure to ultraviolet radiation. Some other examples of protective layer 904 may include, but are not limited to, ceramer coatings or crosslinked water-based polyurethane coatings. As used herein, "ceramer" refers to a fluid comprising surface-modified colloidal silica particles dispersed in a free -radically polymerizable organic liquid. Advantages of a ceramer coating may include the ability to withstand outdoor conditions with resistance to moisture, light and heat, resistance to abrasion, chemical attack and coloration by automobile engine oil. In some examples, a ceramer precursor coating composition may be applied to the surface of retroreflective layer 906, preferably including the top surface of any refracting elements and portions of base layer 910 and radar reflective layer 908 not covered by refracting elements. The ceramer precursor composition may be cured to form sensable layer 902 with an abrasion resistant, light transmissive ceramer coating. Base layer 910, and other layers in compact planar structure 900, may protect the structure from deformation, such as from traffic, expansion and contraction of the surface on which it is placed and other causes.

Radar reflective layer 908 may include plurality of radar reflective structures as described above in relation to FIGS. 1 - 9C. The plurality of radar reflective structures may be arranged on radar reflective layer 908 with any combination of angles with respect to a long axis of compact planar structure 900, as well as combinations of groupings, and spacing. The combinations may also include combinations of straight and/or curved radar reflective restructures described above.

In some examples, radar reflecting layer 908 may include a conducting groundplane below the reflective elements (not shown in FIG. 12A). The groundplane may be separated from the reflective elements by a dielectric substrate. The addition of a groundplane at a predetermined distance below the reflective elements of radar reflecting layer 908 may increase reflected energy in reflected radar radiation by hindering incident radar radiation from passing through the radar reflecting structure into the ground. The added groundplane may also de-couples the radar reflecting structures in radar reflective layer 908 electromagnetically from the ground materials.

Radar reflective layer 908 may include high reflectivity at both high and low entrance angles. In some examples of compact planar structure 900, the spacing, or other dimensions of radar reflective structures of radar reflective structures in radar reflective layer 908 may be adjusted to account for the expected entrance angle, i.e. the radar signal angle of incidence. As described above, for example in relation to FIGS. 5A - 5C, the spacing and other dimensions of radar reflective structures is a function of the expected radar frequency and incident radar radiation. In examples of a pathway article that includes compact planar structure 900 in some applications, the dimensions of the radar reflective structure may be adjusted depending on the application. As one example, a marking tape in an application such as a stripe on a guard rail, Jersey barrier, or wall that is parallel a first vehicle pathway and perpendicular to a second pathway that intersects the first pathway on the opposite side of the first pathway from the second pathway. In this parallel/perpendicular application, a marking tape may include radar reflective structures configured for a low entrance angle and other radar reflective structures configured for a high entrance angle. In some examples, marking tape with radar reflective structures according to this disclosure will be resistant to corrosion in installed environments, and to retain dimensional stability. In examples that include a metal layer on the surface of the radar reflective structure, such as stamped foil, vapor deposited layer, or conductive ink, may be corrosion-protected by fully encapsulating with a protective layer comprising a weatherable, abrasion-resistant, low dielectric material to prevent the ingress of chlorides and water. Some examples may include an anti-corrosion surface treatment. Both metallic and non- metallic examples may be encapsulated with a weatherable, abrasion-resistant, low dielectric layer to prevent collection of debris that may interfere with the reflectivity. Some examples of pavement marking tapes with dimensionally stable arrays may be formed on filled rubber premix compositions that are not substantially deformed in operation.

Compact planar structure 900 may be assembled by providing a sensable layer 902, which may comprise retroreflective layer 906 and protective layer 904, and applying, such as by laminating, conformance layer 912 to the bottom surface of sensable layer 906. In some examples, a layer of adhesive or primer may be applied to the surface of one or more layers prior to laminating. The criteria for suitable adhesive materials and primers will be dependent in part upon the nature of the sheeting and the intended application. In some examples, either conformance layer 912 or a configuration member (not shown in FIG. 12A) could be first applied to retroreflective layer 906. For instance, in one example, a

retroreflective sheet may be applied to an aluminum conformance layer 912 followed by lamination of a configuration member, e.g., a mesh (not shown in FIG. 12A). However, any metallic structures may not be between the radar reflecting structures and the incident radar radiation. Optional adhesive layer 914 may be applied to the compact planar structure 900 before application to a desired substrate, such as a roadway. In some examples, adhesive layer 914 may be a pressure sensitive adhesive. A marking tape comprising compact planar structure 900 may be configured to withstand repeated traffic impact and shear stresses in combination with other effects of sunlight, rain, road oil, road sand, road salt, and vehicle emissions.

FIGS. 12B and 12C are conceptual diagrams illustrating example marking tape with a retroreflective sensable layer and a radar reflective layer according to one or more techniques of this disclosure. Compact planar structures 920 and 950 of FIGS. 12B and 12C are examples of compact planar structure 900 with a sensable layer comprising a retroreflective layer.

FIG. 12B includes sensable layer 921, radar reflective layer 940 and backing layer 934. Backing layer 934 comprises conformance layer 936, configuration member 932, and adhesive layer 938. As described above backing layer 934 may also include a scrim material (not shown in FIG. 12B). In some examples, radar reflective layer 940 may be included in backing layer 934, in examples in which the marking tape is configured to ensure metallic or other structures of the marking tape do not interfere with the radar reflective properties of the radar reflective layer.

Sensable layer 921 includes a protective layer 929 and retroreflective sheet 922. Protective sheet 929 is similar to protective layer 904 described above in relation to FIG. 12A. Enclosed-lens retroreflective sheet 922 may comprise a monolayer of retroreflective elements 924 formed into first portions of the monolayer arranged in an upwardly contoured profile 926A and second portions 928 of the monolayer are arranged a lower, sometimes substantially planar profile. First portions 926A are elevated above second portions 928 by configuration member 932. These upwardly contoured portions 926A, with their relatively vertical profiles may provide enhanced retroreflective performance. First, when the pathway article is oriented as a pavement marking or guard rail marking, the incidence angle or entrance angle of light to the upwardly contoured portions 926A may be lower than the incidence angle to the second lower portions 928. This may achieve and effective retroreflective result. Second, the higher elevation of upwardly contoured portions 926A may facilitate the run off of water that might degrade retroreflective performance. Third, in the example of pavement markings, upwardly contoured portions 926A have been observed to result in improved adhesion to the road surface.

Upwardly contoured portions 926A may be implemented in any way that will elevate portions of the retroreflective sheet. In the example of FIGS. 12B and 12C, such means is use of a configuration member. Configuration members may be of any shape so long as they elevate some portions of the retroreflective sheet. In some examples, the configuration member is a mesh or netting of strands or even simply an assembled array of unconnected strands. When the article is assembled the strands define the first upwardly contoured portions 926A and the openings between the strands define the second lower portions 928. Some examples of shapes may include rectangles, diamonds, hexagons, curves, circles, sinusoidal ridges (e.g., nested in parallel or intersecting), etc. Each second lower portion 928 may be essentially separated from neighboring lower portions or they may intersect, depending upon the shape of the first upwardly contoured portions 926A.

In the example of FIG. 12B, configuration member 932 is directly attached to retroreflective sheet 922. In some examples, compact planar structure 920 may include a tie layer (not shown in FIG. 12B) between one or more layers. The tie layer may be a layer that adheres well to the surfaces of mating layers. For example, ethylene methacrylic acid will adhere to both aluminum and nitrile rubber layers. In other examples, conformance layer 936 may be directly attached to the bottom of the radar reflective layer 940, followed by a configuration member and adhesive layer 938. In some examples, the retroreflective sheet and configuration members may be substantially coextensive, while in other examples may be not co-extensive. In the example of FIG. 12B, backing layer 934 comprises configuration member 932 bonded to optional conformance layer 936.

FIG. 12C is another example of a compact planar structure including radar reflective structures, according to one or more techniques of this disclosure. Compact planar structure 950 is similar to compact planar structures 900 and 920 of FIGS. 12A and 12B, with a different example of conformance members 952. Features among the figures with the same reference numbers have the same function and description.

FIG. 12C includes sensable layer 951, radar reflective layer 940 and backing layer 954. Backing layer 934 comprises optional conformance layer 936, and adhesive layer 938. As described above backing layer 934 may also include a scrim material (not shown in FIG. 12C). In some examples, radar reflective layer 940 may be included in backing layer 934 or may be considered a separate layer.

Sensable layer 951 includes a protective layer 929 and retroreflective sheet 922. Protective sheet 929 is similar to protective layer 904 described above in relation to FIG. 12A. In the example of FIG.

12C configuration member 952 is applied to retroreflective sheet 922 followed by lamination of radar reflective layer 940, conformance layer 936 and adhesive layer 938.

As with configuration member 932 of FIG. 12B, configuration members 952 may be polymeric. Some examples of polymeric materials may include polyurethanes and polyolefin copolymers such as polyethylene acid copolymer consisting of ethylene methacrylic acid 35 (EMAA), ethylene acrylic acid (EAA), ionically crosslinked EMAA or EAA.

Upward contoured portions 926B may be achieved by laminating configuration members 952 to any region beneath the retroreflective sheet 922. In other words, configuration members 952 may be placed between retroreflective sheet 922 and adhesive layer 938, which bonds the marking tape to a desired substrate, e.g., a roadway. Optional adhesive layer 938 may be applied before application to the desired substrate, Thus, the configuration member can be placed in any layer beneath the retroreflective sheet insofar as it results in the desired configuration. Because the purpose of the configuration member is to impart an upward profile to the retroreflective sheet, its placement can vary for processing

convenience.

In other examples, compact planar structures 900, 920 and 950 may be assembled by providing a sensable layer and backfilling upwardly contoured profiles with a filling material. The upwardly contoured profiles may be formed by variety of techniques. In one example, retroreflective sheet 922 may be gathered together in portions and any voids backfilled. In other examples, retroreflective sheet 922 may be fed into an embossing roll to form the upwardly contoured profiles of a variety of shapes, as described above. An embossing roll may have an advantage in causing less disruption of the sensable layer, when compared to laminating the sensable layer to a preformed configuration layer, such as in the example of Fig 12B. Disruption may lead to reduction of retroreflective brightness or reduce physical integrity of the sheeting. Some examples of material that may be used as an embossed layer may include rubber or structured elastomer.

Forming the profiles may create voids or depressions in the back of the retroreflective sheet (i.e., the non-reflective side). It may be desirable to fill the voids with some material that provides sufficient dimensional stability to retain the described profiles. Backfill material may be conformable, so the resultant marking tape is flexible and conformable while retaining the contoured profile described herein. For example, a polymeric film may be used as backfill material. The polymeric film may be heated to flow into the voids in the structured regions. Radar reflective layer 940 may be laminated or otherwise assembled to the sensable layer after the formation and backfill of the upwardly contoured profiles. As described above, a tie layer may be included between any of the layers.

Components of a marking tape that includes compact planar structures 900, 920 and 952 may be configured to be sufficiently conformable so that the desired upwardly contoured profiles 926A and 926B of retroreflective sheet 922 can be achieved. In some examples, configuration member, such as configuration members 932 and 952 may self-adhere to conformance layer 936, if present, which may have an advantage of improved durability when compared to other configurations. In addition to providing the functions disclosed herein, the configuration layer may impart improved mechanical properties to a pavement marking material in similar manner as the scrim layer described above in relation to FIG. 12B.

As described above, a variety of techniques may be used to add colorants to some portion the compact planar structures of this disclosures. Some examples may include a light and radar transmissive colored top film. In other examples, a colorless top film could be applied to a colored retroreflective sheet.

FIG. 13 is a flow chart illustrating an example technique for making a marking tape according to one or more techniques of this disclosure. The steps of FIG. 13 will be described in terms of FIGS. 12A - 12C, unless otherwise noted. The techniques in the description of FIG. 13 is just one example. In other examples, steps may be performed in a different order, and may include more steps or few steps then described in FIG. 13.

One technique for making a marking tape material according to one or more techniques of this disclosure may include providing a continuous base sheet including an upper surface and a lower surface (90). The base sheet may include any one or more of the layers included in backing layer 934, such as configuration member 932 and conformance layer 936. The base sheet may be one continuous length along the long axis, such as long axis 211 depicted in FIG. 4. In other examples, the base sheet may be a shorter length such as 15 cm, 1 meter or other lengths. The base sheet may be any width, as appropriate for the intended application, such as approximately 10 cm wide.

The techniques of this disclosure may include applying a sensable layer to the upper surface of the continuous base sheet, such as by laminating a surface of the sensable layer to the base sheet upper surface (92). The sensable layer may include features that are visible to the human eye or visual camera, such as retroreflective layer 922. The sensable may also include features such as magnetic elements that may be detectable by other sensors on a PAAV. In some examples, retroreflective layer 922 includes an embedded-lens retroreflective sheet, which may include a layer of transparent microspheres having front and back surfaces, a cover layer in which the front surfaces of the microspheres are embedded, and an associated reflective means behind the back surface of the microspheres. In other examples, retroreflective layer 922 may include a retroreflective sheet comprising a monolayer of cube-comer elements or non-metallic microspheres. In other examples, retroreflective layer 922 may include one or more first upwardly contoured profile 926A and 926B, which may be arranged in an interconnected network. As described above, examples of metallic retroreflective materials may be physically separated from the radar reflecting structures.

In some examples, a marking tape, including a compact planar structure, such as compact planar structure 950, may be further assembled by applying a continuous conformance layer, such as conformance layer 936 to the lower surface of the continuous base sheet (94). Conformance layer 936 may comprise a variety of materials, including aluminum, and may be applied along with a tie layer and a scrim layer. Some examples of marking tape may also include adhesive layer 938.

The marking tape may further be assembled by adding a radar reflective structure disposed between sensable layer 902 and the continuous base sheet, in the plane of the continuous base sheet (96). The radar reflective structure may be one of a plurality of radar reflective structures, such as radar reflective structures 220 - 224 depicted in FIG. 4. The radar reflective structures may be arranged at a variety of angles and spacings to perform various functions as described above in relation to FIGS. 1 - 3B. Radar reflective structures may comprise a conductive material and have dimensions and spacing configured to reflect incident radar radiation from one or more radar transceivers in a PAAV.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over, as one or more instructions or code, a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media, which is non-transitory or (2) a

communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer- readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but are instead directed to non-transient, tangible storage media. Disk and disc, as used, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term“processor”, as used may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described. In addition, in some aspects, the functionality described may be provided within dedicated hardware and/or software modules. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

It is to be recognized that depending on the example, certain acts or events of any of the methods described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the method). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially.

In some examples, a computer-readable storage medium includes a non-transitory medium. The term“non-transitory” indicates, in some examples, that the storage medium is not embodied in a carrier wave or a propagated signal. In certain examples, a non-transitory storage medium stores data that can, over time, change (e.g., in RAM or cache).

Various examples of the disclosure have been described. These and other examples are within the scope of the following claims.

The following are exemplary embodiments according to the present disclosure:

Embodiment 1. A radar reflecting structure device, the device comprising:

a first angled sawtooth notch comprising a first reflecting surface and a first angled surface substantially perpendicular to the first reflecting surface; and

a second angled sawtooth notch, comprising a second reflecting surface and a second angled surface substantially perpendicular to the second reflecting surface wherein:

the second slot is positioned such that the second reflective surface is a grating distance from the first reflective surface;

the second reflective surface is substantially parallel to the first reflective surface;

a radar signal that reflects off the first reflecting surface results in a first reflected signal;

the radar signal that reflects off the second reflecting surface results in a second reflected signal; the second reflected signal causes a phase interference in the first reflected signal;

the phase interference causes the first reflected signal and the second reflected signal to form a reflected beam, wherein the reflected beam comprises a direction of travel substantially opposite to a direction of travel of the radar signal. Embodiment 2. The device of embodiment 1, wherein the first angled sawtooth notch is the first angled sawtooth notch of a plurality of angled sawtooth notches and the second angled sawtooth notch is the second angled sawtooth notch of the plurality of angled sawtooth notches, wherein:

a respective reflecting surface of a respective angled sawtooth notch of the plurality of angled sawtooth notches is substantially parallel to the first reflecting surface,

each respective reflecting surface of each respective angled sawtooth notch is a grating distance from the respective reflecting surface of a respective adjacent angled sawtooth notch.

Embodiment 3. The device of any combination of embodiments 1 - 2, wherein a plane of first reflecting surface comprises a length L and the plane of the second reflecting surface comprises the length L, wherein the plane of the first reflecting surface, the second reflecting surface and length L are configured to be substantially orthogonal to the direction of travel of the radar signal.

Embodiment 4. The device of any combination of embodiments 1 - 3, wherein the plane of first reflecting surface comprises a first arc length L and radius R, and the plane of the second reflecting surface comprises second arc of length L and radius R, wherein:

the plane of the first reflecting surface and the second reflecting surface are configured to be substantially orthogonal to the direction of travel of the radar signal, and

the radius R is configured to be in substantially the same direction as the direction of travel of the radar signal.

Embodiment 5. The device of any combination of embodiments 1 - 4, further comprising a top plane of the device:

wherein the top plane is configured to have the radar signal pass through the top plane before striking the first reflecting surface and the second reflecting surface;

wherein the first angled surface slants downward from the top plane of the device at a first angle, wherein the first reflecting surface intersects the top plane and the first angled surface and wherein the first reflecting surface is substantially perpendicular to the angled surface,

wherein the second angled surface slants downward from the top plane of the device at the first angle, and

wherein the second reflecting surface intersects the top plane and the second angled surface and wherein the second reflecting surface is substantially perpendicular to the angled surface.

Embodiment 6. The device of any combination of embodiments 1 - 5, further comprising a first angled surface length and a second angled surface length,

wherein an intersection of the first angled surface with the top plane, and the intersection of the first angled surface with the first reflecting surface, in a direction substantially perpendicular to the first reflecting surface defines the first angled surface length, wherein an intersection of the second angled surface with the top plane, and the intersection of the second angled surface with the second reflecting surface, in a direction substantially perpendicular to the second reflecting surface defines the second angled surface length, and

the first angled surface length and the second angled surface length are configured to substantially equal one-half an expected wavelength of the radar signal.

Embodiment 7. The device of any combination of embodiments 1 - 6, wherein the intersection of the reflecting surface with the top plane defines a grating structure.

Embodiment 8. The device of any combination of embodiments 1 - 7, wherein the top plane of the grating structure includes a refracting layer.

Embodiment 9. An article comprising:

a sheet material comprising:

a continuous base sheet including an upper surface and a lower surface;

a sensable layer applied to the upper surface of the continuous base sheet, wherein the sensable layer comprises a traffic bearing protective layer,

wherein the sheet material comprises a long axis and a short axis;

a radar reflecting structure comprising:

wherein the radar reflecting structure is disposed between the sensable layer and the continuous base sheet, in the plane of the continuous base sheet,

the radar reflecting structure comprising:

the phase interference causes the first reflected signal and the second reflected signal to form a reflected beam, wherein the reflected beam comprises a direction of travel substantially opposite to a direction of travel of the radar signal. Embodiment 10. The article of embodiment 9, wherein the sensable layer comprises at least one feature selected from a group comprising: a retroreflective feature, an infrared feature, a magnetically detectable feature.

Embodiment 11. The article of any combination of embodiments 9 - 10, further comprising one or more conformance members disposed between the sensable layer and the continuous base sheet, wherein the one or more conformance members are configured to form one or more upwardly contoured profile portions in the sensable layer.

Embodiment 12. The article of any combination of embodiments 9 - 11, further comprising a continuous conformance layer applied to the lower surface of the continuous base sheet.

Embodiment 13. The article of any combination of embodiments 9 - 12, wherein the radar reflecting structure comprises a conductive material.

Embodiment 14. The article of any combination of embodiments 9 - 13, wherein the radar reflecting structure comprises a high dielectric material.

Embodiment 15. The article of any combination of embodiments 9 - 14, wherein the radar reflecting structure comprises a conductive material.

Embodiment 16. The article of any combination of embodiments 9 - 15, wherein the one or more conformance members comprise an embossed surface.

Embodiment 17. The article of any combination of embodiments 9 - 16, wherein the radar reflecting structure is a first radar reflecting structure, the article further comprising a second radar reflecting structure, wherein,

the first radar reflecting structure is positioned one the continuous base sheet at a first angle relative to the long axis of the sheet material, and

the second radar reflecting structure is positioned one the continuous base sheet at a second angle relative to the long axis of the sheet material.

Embodiment 18. The article of any combination of embodiments 9 - 17, wherein the first angle is different from the second angle.

Embodiment 19. The article of any combination of embodiments 9 - 18, wherein the sheet material protects the radar reflecting structure from deformation. Embodiment 20. The article of any combination of embodiments 9 - 19, further comprising a pressure sensitive adhesive layer applied to a lower surface of the continuous conformance layer.

Embodiment 21. The article of any combination of embodiments 9 - 20, wherein the first angle of the first radar reflecting structure and the second angle of the second radar reflecting structure are configured to form a code, wherein the code is configured to convey information based on a reflection of a radar signal from the first radar reflecting structure and the second radar reflecting structure.

Embodiment 22. The article of any combination of embodiments 9 - 21, further comprising a spacing length between the first radar reflecting structure and the second radar reflecting structure, wherein the spacing length is configured to form a code, wherein the code is configured to convey information based on a reflection of a radar signal from the first radar reflecting structure and the second radar reflecting structure.

Embodiment 23. The article of any combination of embodiments 9 - 22, wherein the information conveyed comprises one or more characteristics of the pathway.

Embodiment 24. The article of any combination of embodiments 9 - 23, wherein the one or more characteristics comprise a potential hazard on the vehicle pathway, and wherein the one or more characteristics comprise one or more of: a nature of the potential hazard, the location of the potential hazard relative to the vehicle pathway, and the portion of the vehicle pathway affected by the potential hazard

Embodiment 25. The article of any combination of embodiments 9 - 24, wherein the one or more characteristics is selected from a group comprising: a slope of the pathway, a curvature of the pathway, a change in recommended speed of a vehicle on the pathway.

Embodiment 26. The article of any combination of embodiments 9 - 25, further comprising a second radar reflecting structure, wherein the second radar reflecting structure comprises two or more conductive patches connected by one or more transmission lines.

Embodiment 27. The article of any combination of embodiments 9 - 26, further comprising a second radar reflecting structure, wherein the second radar reflecting structure comprises a conductive layer that includes two or more apertures connected by one or more transmission lines.

Embodiment 28. The article of any combination of embodiments 9 - 27, further comprising a second radar reflecting structure, wherein the second radar reflecting structure comprises two or more conductive patches, wherein each conductive patch includes a terminated transmission line. Embodiment 29. The article of any combination of embodiments 9 - 28, further comprising a second radar reflecting structure, wherein the second radar reflecting structure comprises a conductive layer that includes two or more apertures wherein each aperture includes a terminated transmission line.

Embodiment 30. A system for vehicles on a traffic-bearing surface, the system comprising:

a pathway configured to support vehicle traffic;

a pathway-article assisted vehicle (PAAV) comprising:

one or more radar transceiver devices;

one or more sensor devices;

one or more processor circuits configured to interpret a first signal from the one or more radar transceiver devices and a second signal from the one or more sensor devices;

a pathway article comprising a radar reflecting structure, wherein the pathway article is arranged on the pathway within a field of regard (FOR) of the one or more radar transceiver devices.

Embodiment 31. The system of embodiment 30, wherein the PAAV comprises one or more sensor devices selected from a group comprising: an image processing device, a magnetic sensing device, a LIDAR device, and a global positioning system (GPS) device.

Embodiment 32. The system of any combination of embodiments 30 - 31, wherein the image processing device comprises one or more devices selected from a group comprising: an optical camera, an infrared (IR) camera, an ultraviolet camera (UV).

Embodiment 33. The system of any combination of embodiments 30 - 32, wherein the pathway article is a marking tape.

Embodiment 34. The system of any combination of embodiments 30 - 33, wherein the marking tape is applied to a protective barrier along an edge of the pathway.

Embodiment 35. The system of any combination of embodiments 30 - 34, wherein the marking tape is applied to a temporary warning device positioned on the pathway within the FOR of the one or more radar transceiver devices.

Embodiment 36. The system of any combination of embodiments 30 - 35, wherein the temporary warning device is a vehicle impact reducing barrel.

Embodiment 37. The system of any combination of embodiments 30 - 36, wherein the pathway comprises pavement to support vehicle traffic and pathway article is a pavement marking tape. Embodiment 38. The system of any combination of embodiments 30 - 37,

wherein the pathway is a two-way pathway,

wherein the pathway article is disposed along a centerline of the two-way pathway, and wherein the one or more processing circuits is configured to determine a location of the centerline of the two-way pathway based on a radar signal reflected from the radar reflecting structure.

Embodiment 39. The system of any combination of embodiments 30 - 38, wherein the pathway article is disposed along an edge of a pathway and wherein the one or more processing circuits is configured to determine the location of the edge of the two-way pathway based on a radar signal reflected from the radar reflecting structure.

Embodiment 40. The system of any combination of embodiments 30 - 39, wherein the pathway article is disposed at a lane location of a pathway and wherein the one or more processing circuits is configured to determine the lane location based on a radar signal reflected from the radar reflecting structure.

Embodiment 41. The system of any combination of embodiments 30 - 40, wherein the radar reflecting structure comprises:

a material with a coefficient of thermal expansion (CTE);

one or more angled sawtooth notches disposed within the material,

wherein the angled sawtooth notches are arranged with a first spacing at a first temperature and the angled sawtooth notches are arranged at a second spacing at a second temperature, based on the CTE, wherein the angled sawtooth notches are configured to reflect a radar signal with a first return signal at the first spacing and to reflect the radar signal with a second return signal at the second spacing, wherein the one or more processors is configured to determine a temperature of the radar reflecting structure based on whether the one or more radar transceiver devices receives the first return signal or receives the second return signal.

Embodiment 42. The system of any combination of embodiments 30 - 41, wherein the radar reflecting structures is a first radar reflecting structure of a plurality of radar reflecting structures arranges within the FOR of the radar transceiver device.

Embodiment 43. The system of any combination of embodiments 30 - 42,

wherein the plurality of radar reflecting structures is arranged on the pathway article to form a code,

wherein the code is configured to convey information based on a reflection of a radar signal from the plurality of RCS devices, and wherein the one or more processor circuits is configured to interpret the information based on the code.

Embodiment 44. The system of any combination of embodiments 30 - 43,

wherein the information based on the code comprises one or more characteristics of the pathway; wherein the one or more processors is configured to:

determine the one or more characteristics of the vehicle pathway, based in part on interpretation of the information;

determine an adjustment for one or more functions of the PAAV based at least in part on the one or more characteristics; and

control the determined adjustment.

Embodiment 45. The system of any combination of embodiments 30 - 44, wherein the one or more processing circuits controls the determined adjustment for one or more functions of the PAAV based on the information in conjunction with a human operator.

Embodiment 46. The system of any combination of embodiments 30 - 45, wherein the one or more processors are further

configured to output a notification to an occupant of the PAAV based on the information.

Embodiment 47. The system of any combination of embodiments 30 - 46,

wherein the one or more processors are further configured to determine environmental conditions in a vicinity of the PAAV based on the second signal from the one or more sensor devices,

wherein the environmental conditions in the vicinity of the PAAV comprise one or more of: air temperature, precipitation level, precipitation type, incline of the vehicle pathway, presence of other vehicles and estimated friction level between PAAV tires and the vehicle pathway, and

wherein the determined adjustment for one or more functions of the PAAV is based at least in part on the environmental conditions in a vicinity of the PAAV.

Embodiment 48. The system of any combination of embodiments 30 - 47, wherein the one or more processors are configured to control the determined adjustment by one or more of: a change a speed of the PAAV, change a status of a headlight, change a damping coefficient of a suspension system of the PAAV, apply a force to a steering system of the PAAV and change an interpretation of one or more inputs from sensors.

Embodiment 49. A method for making a marking tape material comprising:

providing a continuous base sheet including an upper surface and a lower surface;

applying a sensable layer to the upper surface of the continuous base sheet; applying a continuous conformance layer to the lower surface of the continuous base sheet;

adding a radar reflective structure disposed between the sensable layer and the continuous base sheet, in the plane of the continuous base sheet, wherein the radar reflecting structure comprises a conductive material.

Embodiment 50. The method of embodiment 49, wherein the sensable layer is a retroreflective layer, the method further comprising:

(a) providing an enclosed-lens retroreflective sheet having a top surface and a bottom surface and comprising a cover layer and a monolayer of retroreflective elements;

(b) applying a conformance layer to the bottom surface of the retroreflective sheet; and

(c) laminating a configuration member to the conformance layer thereby creating first portions and second portions in the retroreflective sheet, wherein the first portions are arranged in an upwardly contoured profile and the second portions being arranged in a lower, substantially planar position.

Embodiment 51. The method of any combination of embodiments 49 - 50, wherein the configuration member is a polyolefin copolymer selected from a group comprising: ethylene methacrylic acid (EMAA), ethylene acrylic acid (EAA), ionically crosslinked EMAA, and ionically crosslinked EAA.

Embodiment 52. The method of any combination of embodiments 49 - 51 further comprising applying a layer of adhesive to the bottom surface of the configuration member or to the conformance layer.

Embodiment 53. The method of any combination of embodiments 49 - 52, wherein the configuration member is a mesh.

Embodiment 54. The method of any combination of embodiments 49 - 53, wherein the retroreflective sheet is selected from a group comprising: embedded-lens retroreflective sheet and encapsulated-lens retroreflective sheet.

Embodiment 55. The method of any combination of embodiments 49 - 54, wherein the embedded- lens retroreflective sheet comprises a layer of transparent microspheres having front and back surfaces, a cover layer in which the front surfaces of the microspheres are embedded, and an associated reflective means behind the back surface of the microspheres.

Embodiment 56. The method of any combination of embodiments 49 - 55, wherein the retroreflective sheet comprises a monolayer of cube-comer elements.

Embodiment 57. The method of any combination of embodiments 49 - 56, wherein the first portions are arranged in an interconnected network. Embodiment 58. The method of any combination of embodiments 49 - 57 further comprising applying a protective coating on a cover layer of the sensable layer. Embodiment 59. The method of any combination of embodiments 49 - 58 further comprising applying antiskid particles on the protective coating.

Embodiment 60. The method of any combination of embodiments 49 - 59, wherein the sensable layer comprises a conformable magnetic layer comprising a binder and a sufficient amount of magnetic particles within the binder to provide a magnetic signal.

Embodiment 61. The method of any combination of embodiments 49 - 60, wherein the magnetic layer comprises sections of alternating polarity along the length of the continuous base sheet.

Claims

CLAIMS:

1. An article comprising:

a sheet material comprising:

a continuous base sheet including an upper surface and a lower surface;

wherein the sheet material comprises a long axis and a short axis;

a radar reflecting structure comprising:

the radar reflecting structure comprising:

the phase interference causes the first reflected signal and the second reflected signal to form a reflected beam, wherein the reflected beam comprises a direction of travel substantially opposite to a direction of travel of the radar signal.

2. The article of claim 1, wherein the sensable layer comprises at least one feature selected from a group comprising: a retroreflective feature, an infrared feature, a magnetically detectable feature.

3. The article of any combination of any of the preceding claims, further comprising one or more conformance members disposed between the sensable layer and the continuous base sheet, wherein the one or more conformance members are configured to form one or more upwardly contoured profile portions in the sensable layer.

4. The article of any combination of any of the preceding claims, wherein the radar reflecting structure is a first radar reflecting structure, the article further comprising a second radar reflecting structure, wherein, the first radar reflecting structure is positioned one the continuous base sheet at a first angle relative to the long axis of the sheet material, and

5. The article of any combination of any of the preceding claims, further comprising a pressure sensitive adhesive layer applied to a lower surface of the continuous conformance layer.

6. The article of any combination of any of the preceding claims, wherein the first angle of the first radar reflecting structure and the second angle of the second radar reflecting structure are configured to form a code, wherein the code is configured to convey information based on a reflection of a radar signal from the first radar reflecting structure and the second radar reflecting structure.

7. The article of any combination of any of the preceding claims, further comprising a spacing length between the first radar reflecting structure and the second radar reflecting structure, wherein the spacing length is configured to form a code, wherein the code is configured to convey information based on a reflection of a radar signal from the first radar reflecting structure and the second radar reflecting structure.

8. The article of any combination of any of the preceding claims, wherein the information conveyed comprises one or more characteristics of the pathway.

9. The article of any combination of any of the preceding claims, wherein the one or more characteristics comprise a potential hazard on the vehicle pathway, and wherein the one or more characteristics comprise one or more of: a nature of the potential hazard, the location of the potential hazard relative to the vehicle pathway, and the portion of the vehicle pathway affected by the potential hazard

10. The article of any combination of any of the preceding claims, wherein the one or more characteristics is selected from a group comprising: a slope of the pathway, a curvature of the pathway, a change in recommended speed of a vehicle on the pathway.

11. The article of any combination of any of the preceding claims, further comprising a second radar reflecting structure, wherein the second radar reflecting structure comprises two or more conductive patches connected by one or more transmission lines.

12. The article of any combination of any of the preceding claims, further comprising a second radar reflecting structure, wherein the second radar reflecting structure comprises a conductive layer that includes two or more apertures connected by one or more transmission lines.

13. The article of any combination of any of the preceding claims, further comprising a second radar reflecting structure, wherein the second radar reflecting structure comprises two or more conductive patches, wherein each conductive patch includes a terminated transmission line.

14. A system for vehicles on a traffic-bearing surface, the system comprising:

a pathway configured to support vehicle traffic;

a pathway-article assisted vehicle (PAAV) comprising:

one or more radar transceiver devices;

one or more sensor devices;

15. The system of claim 14, wherein the PAAV comprises one or more sensor devices selected from a group comprising: an image processing device, a magnetic sensing device, a LIDAR device, and a global positioning system (GPS) device,

wherein the image processing device comprises one or more devices selected from a group comprising: an optical camera, an infrared (IR) camera, an ultraviolet camera (UV), and

wherein the pathway article is a marking tape.