SE545306C2

SE545306C2 - A circuit board-to-waveguide transition with an h-plane-fed patch antenna

Info

Publication number: SE545306C2
Application number: SE2130275A
Authority: SE
Inventors: Abolfazl Haddadi; Carlo Bencivenni; Hanna Karlsson; Julius Petersson
Original assignee: Gapwaves Ab
Priority date: 2021-10-13
Filing date: 2021-10-13
Publication date: 2023-06-27
Also published as: SE2130275A1

Abstract

A transition arrangement (100) for a patch antenna-to-waveguide transition. The transition arrangement comprises a waveguide module (130), a printed circuit board, PCB, (110), an antenna ground plane (180), and a metamaterial arrangement (156). The PCB comprises a patch antenna (120) fed by a feed line (121). The antenna ground plane (180) is arranged facing the patch antenna (120). The waveguide module (130) is arranged to interface with the PCB (110). The waveguide module comprises a waveguide aperture (140) arranged facing the patch antenna (120) such that an electric field direction of the patch antenna (120) is aligned with an electric field direction of the waveguide aperture (140). The metamaterial arrangement (156) is arranged intermediate the waveguide module (130) and the PCB (110) and is arranged to at least partly surround the waveguide aperture (140) and/or and the patch antenna (120) to define a passage (145) from the patch antenna into the waveguide aperture (140). The metamaterial arrangement (156) is arranged to attenuate electromagnetic signal propagation in a frequency band intermediate the waveguide module (130) and PCB (110) in any other direction than via the passage (145) and along the feed line (121). The feed line (121) connects to the patch antenna (120) from a direction perpendicular to the electrical field direction of the patch antenna (140).

Description

TECHNICAL FIELD The present disclosure relates to wireless communication systems in general, and to waveguide transmission mediums in particular. There are disclosed arrangements to transit a signal from a printed circuit board to a waveguide.

BACKGROUND Wireless communication networks comprise radio frequency transceivers, such as radio base stations used in cellular access networks, microwave radio link transceivers used for, e.g., backhaul into a core network, and satellite transceivers which communicate with satellites in orbit. Radar transceivers also comprise radio frequency transceivers for transmitting and receiving radio frequency signals.

A transmission medium is used to transport radio frequency signals to and from the radio frequency transceiver. A common type of transmission medium are waveguide structures. Waveguides are often implemented as hollow metal pipes or metallized tubular structures, and are commonly used at microwave and millimeter-wave, for such purposes as connecting microwave transmitters and receivers to their antennas. Another type of transmission medium is a planar transmission line. Planar transmission lines are often implemented on a printed circuit board (PCB). A planar transmission line, such as a microstrip, arranged on a PCB commonly comprises one or more conductive strips separated from a ground plane by a dielectric layer. lt is often desired to transition to and from a tubular waveguide, e.g., between a transmission line on a PCB and a rectangularwaveguide. Such transition is commonly using in array antennas, where integrated circuits (lCs) on a PCB are connected to various antenna waveguide feeds from transmission lines on the same PCB.

WO2020078652A1 discloses a transition from a patch antenna to a waveguide aperture surrounded by a repetitive structure.

There is a need for high-performance transition arrangements.

SUMMARY lt is an object of the present disclosure to provide improved transition arrangements for transitioning between a printed circuit board (PCB) and a waveguide, which, i.a., are compact, are easy to manufacture, and provide low losses.

This object is at least in part obtained a transition arrangement for a patch antenna- to-waveguide transition. The transition arrangement comprises a waveguide module, a PCB, an antenna ground plane, and a metamaterial arrangement. The PCB comprises a patch antenna fed by a feed line. The antenna ground plane is arranged facing the patch antenna. The waveguide module is arranged to interface with the PCB. The waveguide module comprises a waveguide aperture arranged facing the patch antenna such that an electric field direction of the patch antenna is aligned with an electric field direction of the waveguide aperture. The metamaterial arrangement is arranged intermediate the waveguide module and the PCB and is arranged to at least partly surround the waveguide aperture and/or and the patch antenna to define a passage from the patch antenna into the waveguide aperture. The metamaterial arrangement is arranged to attenuate electromagnetic signal propagation in a frequency band intermediate the waveguide module and PCB in any other direction than via the passage and along the feed line. The feed line connects to the patch antenna from a direction perpendicular to the electrical field direction of the patch antenna.

The waveguide aperture acts as an interface to a waveguide structure, such as in a distribution layer in an array antenna or a tubular waveguide attached to the external side of the module, while the passage allows for the patch antenna arranged on the PCB to couple electromagnetic waves into the waveguide structure and also to pick up radio signals exiting the waveguide structure.

The metamaterial arrangement (e.g., comprising a metamaterial structure, such as a plurality of protruding pins, facing a first ground plane) efficiently seals the passage such that electromagnetic energy can pass more or less unhindered between the patch antenna and the waveguide aperture (and therefore into the waveguide structure). The transition between the PCB and the waveguide module can be contactless in that no electrical contact is required between the waveguide module and the PCB. This is an advantage since high precision assembly is not necessary. The PCB can simply be attached to the waveguide module with fastening means such as bolts or the like, where electrical contact need not be verified.

The transition arrangement comprises a feed line arranged to connect to the patch antenna from a direction perpendicular to the electrical field direction of the patch antenna. ln other words, the feed line to connects to the patch antenna from a direction parallel to the magnetic field direction of the patch antenna. This type of feeding can be called H-plane feeding, where "H" refers to the magnetic field. This feeding arrangement provides a new flexibility in the arrangement of the feed line relative to the waveguide aperture. This flexibility is especially relevant for array antennas comprising a plurality of waveguides facing respective patch antennas since such array antenna can be made more compact with the disclosed transition arrangement.

According to aspects, the feed line comprises a planar transmission line such as a microstrip or differential microstrip. ln general, the feed line can be any single-ended or differential planar transmission line. Another example is coplanar. Normally, patch antennas are connected to single-ended feed lines. However, using differential planar transmission lines allows for directly interfacing the waveguide aperture (via the patch antenna) with differential components (such as an integrated circuit with differential ports) without first converting the differential line to a single line. Single-ended feed lines require a balun or equivalent converting network when connecting to differential components, which increases the required spaces and losses. Single-ended and differential microstrips are common planar transmission lines that are easy to implement. Coplanar lines may advantageously be used for impedance matching purposes and isolation purposes.

According to aspects, the patch antenna is fed from a center of an edge of the patch antenna. This is particularly suitable for differential planar transmission lines, such as differential microstrip, since two opposite sides of the patch antenna are excited with opposite phases. This provides a good transition between the feed line (via the patch antenna) and waveguide aperture.

According to aspects, the patch antenna is fed from a corner of the patch antenna. ln other words, the feed line connects to the patch antenna on a corner of the patch antenna. This is particularly suitable for single-ended planar transmission lines, such as microstrip, since two opposite sides of the patch antenna are excited with opposite phases. This provides a good transition between the feed line (via the patch antenna) and waveguide aperture.

According to aspects, the metamaterial arrangement comprises a first metamaterial structure and a first ground plane, wherein the first metamaterial structure is arranged on the Waveguide module. This way, the first metamaterial structure can be integrally formed on the waveguide module, which is easy to manufacture and provides good performance. The first ground plane may be arranged on the PCB, i.e., be a conductive layer of the PCB.

According to aspects, the metamaterial arrangement comprises a first metamaterial structure and a first ground plane, wherein the first metamaterial structure is arranged on the PCB. This way, the first metamaterial structure can be formed using various |ayers on the PCB, which can be cost-effective. The first ground plane may be arranged on waveguide module, i.e., be an integra| part of the waveguide module, such as the surface around the waveguide aperture.

According to aspects, the first metamaterial structure is arranged in contact with or at a distance from the first ground plane, where the distance is smaller than a quarter of an operation wavelength. This enables high attenuation of electromagnetic signal propagation in a frequency band intermediate the waveguide module and PCB in any other direction than via the passage and along the feed line.

According to aspects, the first metamaterial structure is arranged on the waveguide module and the antenna ground plane constitutes the first ground plane. This way, the transition arrangement can be more compact.

According to aspects, the metamaterial arrangement comprises a first metamaterial structure and a second metamaterial structure arranged facing each other. This is a Way of obtaining attenuation of electromagnetic signal propagation in a frequency band intermediate the waveguide module and PCB in any other direction than via the passage and along the feed line.

According to aspects, the first and/or the second metamaterial structure comprises a plurality of protruding conductive elements. This type of metamaterial structure is easy to manufacture and provides good performance (such as high attenuation).

According to aspects, the first metamaterial structure comprises at least one side pin arranged to intersect with a direction along the electrical field direction of the patch antenna. This arrangement can improve the coupling from the patch antenna into the waveguide aperture.

According to aspects, at least one of the protruding conductive elements is arranged such that a side wall of that protruding conductive element is aligned with a sidewall of the waveguide aperture. This arrangement can improve the coupling from the patch antenna into the waveguide aperture.

According to aspects, the PCB comprises a parasitic patch arranged to couple with the patch antenna. The parasitic patch can significantly improve matching between the feed line and the patch antenna and/or the coupling from the patch antenna into the waveguide aperture.

According to aspects, the waveguide module comprises a plurality of waveguide apertures and the PCB comprises a plurality of patch antennas, wherein each waveguide aperture is arranged to interface a respective patch antenna. According to further aspects, at least two waveguide apertures are arranged such that their respective electrical field directions are arranged extending in the same direction. ln other words, the electrical field directions may extend along the same line. lf the waveguide apertures are rectangular, this means that the waveguide apertures are arranged with their respective wide sides facing each other. According to additional aspects, at least two waveguide apertures are arranged less than a wavelength apart. Such compact arrangement is highly desirable in a distribution layer in an array antenna. This compact arrangement is enabled by the disclosed feeding arrangement.

There is also disclosed herein an antenna arrangement comprising the transition arrangement according to the discussions above. Furthermore, there is disclosed herein a radio or radar transceiver comprising the transition arrangement and/or the antenna arrangement. ln addition, there is disclosed herein a vehicle comprising the transition arrangement, the antenna arrangement, and/or the radio or radar transceiver.

There are also disclosed herein methods associated with the same advantages as discussed above in connection to the different apparatuses. There are also disclosed herein computer programs, computer program products, and control units associated with the above-mentioned advantages.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure will now be described in more detail with reference to the appended drawings, where: Figure 1 schematically illustrates an example transition arrangement; Figure 2A illustrates an example waveguide module; Figure 2B illustrates an example waveguide module and an example patch antenna; Figure 3 illustrates an example patch antenna; Figures 4A-4C illustrate different perspectives of an example transition arrangement; Figures 5A-5C schematically illustrate example patch antennas; Figures 6A-6H schematically illustrate example patch antennas; Figure 7 is a flow chart illustrating methods; and Figure 8A-8B show aspects of an example transition arrangement.

DETAILED DESCRIPTION Aspects of the present disclosure will now be described more fully with reference to the accompanying drawings. The different devices and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates othenNise.

As communication frequency bands go higher and higher, transmission components become smaller and smaller. This is because the size of many components, such as waveguides and filters are determined in proportion to a wavelength of the carrier frequency. This complicates manufacturing of transmission components since higher and higher mechanical precision is required in order to obtain satisfactory performance.

A radio or radar transceiver is generally comprised in one or more integrated circuits arranged on a section of printed circuit board (PCB). The transceiver transmits and receives signals via ports in the integrated circuits. The ports are often connected to one or more antenna feeds via planar transmission lines on the PCB. The antenna feeds often comprise waveguide apertures. lt is often desired to transition the signal along the planar transmission lines to and from the waveguide apertures. Such transitions are critical for performance of the overall system.

One way of transitioning from a PCB to a waveguide is to use a cavity-backed probe facing the waveguide aperture, where the probe can be a continuation of a microstrip. However, such cavity is undesired from a space perspective and reduces the flexibility of the arrangement of the PCB, especially multilayer PCBs.

Another way to transitioning from a PCB to a waveguide is by using a patch antenna. Preferably, the electrical field direction of the patch antenna is aligned with the electrical field direction ofthe waveguide to provide a good transition. These electrical field directions are present When a signal is propagating along the transition. The alignment may be perfect, i.e., parallel, but can also be slightly angled, e.g., within 20 degrees. One way of feeding the patch antenna is to arrange a feed line to connect to the patch antenna from a direction parallel to the electrical field direction of the patch antenna. This way is normally preferred since it is easy to match the feed line to the patch antenna, i.e., minimize the reflection in the transition from the feed line to the patch antenna. This is a well-established and robust solution used both for transition and patch antenna design. lt also gives a large freedom to optimize the performance adopting various matching solutions, such as stubs, indents, patch shape and others.

As an example, a patch antenna coupling to a rectangular waveguide aperture can be fed from a direction perpendicular to the extension direction of the rectangular waveguide aperture. However, if two or more of such transitions are arranged aligned and adjacent to each other, they must be arranged relatively far apart since the rectangular waveguides are arranged extending with their longer sides on the same line.

The present disclosure therefore arranges a feed line to connect to the patch antenna from a direction perpendicular to the electrical field direction of the patch antenna. ln other words, the feed line to connects to the patch antenna from a direction parallel to the magnetic field direction of the patch antenna. This type of feeding can be called H-plane feeding, where "H" refers to the magnetic field. With this feeding, when two or more transitions are arranged aligned and adjacent to each other, the rectangular waveguide apertures face each other with respective long sides, instead of facing each other with respective short side. The disclosed feeding arrangement therefore enables a compact array of transitions from a PCB to a plurality of waveguide apertures.

A rectangular waveguide aperture normally has a rectangular shape with two long sides and two short sides. A rectangular waveguide with corresponding rectangular waveguide aperture has width (longest direction) about half a wavelength of the cutoff frequency. The electrical field direction of a propagating wave of modes of interest is parallel with the short sides. ln the disclosed transition arrangement, the waveguide aperture is preferably rectangular. This includes a rectangular shape with rounded corners. However, the waveguide aperture may have other shapes, such as circular. No matter the shape of the aperture, a transition where the feed line connects to the patch antenna from a direction perpendicular to the electrical field direction of the patch antenna, and where the electric field direction of the patch antenna is aligned with the electric field direction of the waveguide aperture, provides flexibility, which is highly relevant in, e.g., array antennas. Furthermore, the waveguide aperture may comprise one or more ridges.

To summarize, there is herein disclosed a transition arrangement 100 for a patch antenna-to-waveguide transition. Figures 1, 4A-4C, and 8A-8B show different example embodiments of the disclosed a transition arrangement 100. Figures 2-3 and 5A-6H show different aspects of example transition arrangements 100. The transition arrangement comprises a waveguide module 130, a printed circuit board (PCB) 110, an antenna ground plane 180, and a metamaterial arrangement 156. The PCB comprises a patch antenna 120 fed by a feed line 121. The antenna ground plane 180 is arranged facing the patch antenna 120. The waveguide module 130 is arranged to interface with the PCB 110. The waveguide module comprises a waveguide aperture 140 arranged facing the patch antenna 120 such that an electric field direction of the patch antenna 120 is aligned with an electric field direction of the waveguide aperture 140. The metamaterial arrangement 156 is arranged intermediate the waveguide module 130 and the PCB 110 and is arranged to at least partly surround the waveguide aperture 140 and/or and the patch antenna 120 to define a passage 145 from the patch antenna into the waveguide aperture 140. The metamaterial arrangement 156 is arranged to attenuate electromagnetic signal propagation in a frequency band intermediate the waveguide module 130 and PCB 110 in any other direction than via the passage 145 and along the feed line 121. The feed line 121 connects to the patch antenna 120 from a direction perpendicularto the electrical field direction of the patch antenna The antenna ground plane 180 may be part of the PCB. For example, the PCB may be a single substrate layer 111 PCB where the patch antenna is formed on the top conductor and the bottom conductor constitutes the antenna ground plane. The PCB may alternatively be a multilayer PCB Where any conducive layer facing the patch antenna may constitute the antenna ground plane. However, the antenna ground plane 180 may be separate from the PCB, such as a conducive (e.g., metal) plate or layen The feature of the feed line 121 connecting to the patch antenna 120 from a direction perpendicular to the electrical field direction of the patch antenna 140 is to be given a broad interpretation also encompassing implementations where the direction is not perfectly perpendicular. A general idea of the arrangement is to provide flexibility in the orientations of the respective parts of the arrangement, which is highly relevant in, e.g., array antennas. Therefore, perpendicular here means, according to aspects, that the feed line 121 connects to the patch antenna 120 from a direction within 70- 110 degrees relative to the electrical field direction.

As mentioned, the electric field direction of the patch antenna 120 may be parallel to the electric field direction of the waveguide aperture 140, but can also be slightly angled, e.g., angled within 20 degrees.

The feed line 121 preferably feeds the patch antenna 120 in connection to an edge 123 of the patch antenna. More preferably, this edge is aligned with the electrical field direction of the patch antenna. This can, e.g., be one of the edges in a rectangular patch. Here aligned may be parallel, but can also be slightly angled, e.g., angled within degrees. The edge may be a tangent on a point, if, e.g., the patch is circular or oval.

The feed line 121 may extend in a direction perpendicular to the electrical field direction of the patch antenna 140. Perpendicular here is interpreted broadly and can include a direction within 70-110 degrees relative to the electrical field direction. According to aspects, the feed line extends at least a length corresponding to width of the feed line. Preferably, this length corresponds to at least three widths. lfthe feed line is differential, the width here can mean the width of one of the two lines.

The feed line 121 may comprise a planar transmission line such as a microstrip 126 or differential microstrip 127. ln general, the feed line can be any single-ended or differential planar transmission line. Another example is coplanar. Normally, patch antennas are connected to single-ended feed lines. However, using differential planar transmission lines allows for directly interfacing the waveguide aperture (via the patch antenna) with differential components (such as an integrated circuit with differential ports) without first converting the differential line to a single line. Single-ended feed lines require a balun or equivalent converting network when connecting to differential components, which increases the required spaces and losses. Single-ended and differential microstrips are common planar transmission lines that are easy to implement. Coplanar lines may advantageously be used for impedance matching purposes and isolation purposes. Furthermore, any of the feed line and patch antenna may be surrounded by one or more ground planes for isolation purposes. Such ground planes may be arranged closely to closely couple with the lines and/or antenna, such as a coplanar line. However, these ground planes may be arranged further away to have weak or no influence on the feed line and/or patch antenna.

The patch antenna 120 may be fed from a center 122 of an edge 123 of the patch antenna 120. For example, if the patch antenna is rectangular, it may be fed from a point equally distant to two adjacent corners of the patch. According to aspects, fed from the center 122 means within a distance corresponding to three widths of the feed line. This is particularly suitable for differential planar transmission lines, such as differential microstrip, since two opposite sides of the patch antenna are excited with opposite phases. This provides a good transition between the feed line and waveguide aperture. A differential planar transmission line may be connected in different ways, such as at the corner of the patch. ln such cases, however, thecoupling of electromagnetic energy of the feed line (via the patch antenna) into the waveguide aperture may be less compared to feeding from the center.

The patch antenna 120 may be fed from a corner 124 of the patch antenna 120. ln other words, the feed line 121 connects to the patch antenna 120 on a corner 124 of the patch antenna 120. This includes being fed from an area in connection to the corner, such as within a distance corresponding to three widths of the feed line. This is particularly suitable for single-ended planar transmission lines, such as microstrip, since two opposite sides of the patch antenna are excited with opposite phases. This provides a good transition between the feed line and waveguide aperture. A single- ended planar transmission line may be connected in different ways, such as at the center of the patch. ln such cases, however, the coupling of electromagnetic energy of the feed line (via the patch antenna) into the waveguide aperture may be less compared to feeding from the corner. Two examples are shown in Figures 6C and 6H, where a single-ended microstrip feeds a rectangular patch antenna from a corner of the patch antenna. ln Figure 6C, the microstrip line is arranged such that an edge of the microstrip extends in a direction that overlaps with an edge of the patch antenna. This arrangement is easy to manufacture. ln Figure 6H, the microstrip is arranged offset such that the extension direction of an edge of the microstrip is offset from the extension direction of an edge of the patch antenna. This arrangement can be used to improve matching between the feed line and patch antenna. ln general, when the patch antenna 120 is fed from a corner 124 of the patch antenna 120, the feed line can be arranged such that an extension direction of an edge of the feed line is offset from an extension direction of an edge of the patch antenna, where this edge is in proximity to the corner and is parallel to the feed line.

A patch antenna normally comprises a rectangular conducive patch which interacts with a ground plane, where the electrical field direction, during operation, is perpendicular to the extension direction (the extension direction is along the longer/wide side), and the magnetic field direction is parallel to the extension direction. The length of the conducive patch in the electrical field direction is typically around half a guided wavelength at a center frequency in a band of operation. However, this length is typically adjusted somewhat due to the height of the PCB. The length may also be adjusted by other factors affecting the electric field, such as adjacent protruding pins part of a metamaterial structure. The length in the other dimension, i.e., in the magnetic field direction, is typically adapted for impedance matching to the feed line. However, this length is often within 150% of half a guided wavelength.An example of the alignment of the electrical field directions 811 of the patch antenna 120 and waveguide aperture 140 is shown in Figure 8A. This figure also shows the electrical field 812 adjacent to the ground plane 180 and pins 150 of a metamaterial structure Figures 5A-5C show various examples example of patch antennas. Figure 5A shows a rectangular patch; Figure 5B shows a rectangular patch with rounded corners; and Figure 5C shows a circular patch. ln all three examples, a differential microstrip connects to the patch antenna from a direction perpendicular to the electrical field direction of the patch antenna, where the patch antenna 120 is fed from a centerof an edge 123 of the patch antenna.

The patch antenna is preferably comprised in an outermost conductive layer on the PCB. This way, a signal can propagate from the patch antenna into the waveguide aperture in the transition arrangement without passing through lossy substrates intermediate the patch antenna and the waveguide aperture. However, the patch antenna may be arranged on any conductive layer in a PCB. ln that case, the path between the patch antenna and the waveguide aperture should preferably not be obstructed by any conductive layers. The feed line 121 is preferably arranged on the same conductive layer as the patch antenna Figure 2B shows a top view of a transition arrangement where the antenna ground plane is transparent and where only the patch antenna of the PCB is showing. The patch antenna 120 is facing the waveguide aperture 140. The position of the patch relative to the waveguide aperture is arranged to maximize the coupling from the patch antenna to the waveguide aperture, i.e., signal propagation from the patch antenna to the waveguide aperture. ln Figure 2B, the patch antenna is centered with respect to the waveguide aperture in a direction perpendicular to the extension direction of the waveguide aperture (left-right in the figure). However, the patch is arranged slightly offset in the other direction. The patch antenna can be arranged more offset in any direction. ln general, the patch antenna is arranged relative to the waveguide aperture to couple electromagnetic waves between the patch antenna and the waveguide aperture.

The patch antenna 120 and/or feed line 121 may comprise a matching section 125. For example, one or more edges of the patch antenna may comprise notch, such as in Figures 2B, 3, 4B, 6B, and 6F. According to aspects, the notch extends into the patch at a length corresponding to the width of the feed line and/or the distancebetween the two lines in a differential feed line. Matching may also comprise varying the width of the feed line, such as in Figure 6D. Other matching strategies are also possible. The purpose of such matching is to reduce reflections in the interface between the feed line and the patch antenna.

The PCB 110 may comprise a parasitic patch 128 arranged to couple with the patch antenna 120. An example is shown in Figure 6G. The parasitic patch can significantly improve matching between the feed line 121 and the patch antenna and/or the coupling from the patch antenna into the waveguide aperture 140. The parasitic patch may be arranged on the same conductive layer on the PCB as the patch antenna. The parasitic patch is preferably grounded (e.g., through vias) for and improved effect. The parasitic patch is arranged separate from patch antenna at a distance to affect the electrical field of the patch antenna. According to aspects, this distance is less than a tenth of a wavelength of a center frequency in a band of operation. According to further aspects, the parasitic patch has a length in a fist dimension which is similar to a length in one dimension of the patch antenna. This way, the electrical field can be affected similarly across that dimension. ln that case, the length in another dimension (e.g. perpendicular to the first dimension) may be significantly smaller, such as a tenth of the length in the first dimension. This provides a compact arrangement. The parasitic patch may be arranged in connection to a side ofthe patch antenna that is opposite to the side where the feed line feeds the patch antenna. This way, the parasitic patch can be aligned with the electrical field, which improves matching between the feed line 121 and the patch antenna and/or the coupling from the patch antenna in the waveguide aperture 140. The parasitic patch may be rectangular, rectangular with rounded corners, or any other planar shape.

Figures 6A-6H show various example patch antennas 120 and feed lines 121. Figures 6A-6C and 6G-6H show patch antennas fed by single-ended microstrip. Figures 6A- 6C show patch antennas fed by differential microstrip. ln Figures 6C and 6H, the patch antenna is fed from a corner 124 of the patch antenna 120. ln Figures 6A-6B and 6D- 6G, the patch antenna is fed from a center 122 of an edge 123 of the patch antenna 120. Figures 6B, 6D, and 6F show different types of matching 125. Figure 6G shows a parasitic patch 128 arranged to couple with the patch antenna The metamaterial arrangement 156 may comprises a first metamaterial structure 155 and a first ground plane. ln that case, the first metamaterial structure is arranged on the waveguide module 130. Furthermore, the first ground plane may be arranged onthe PCB 110, i.e., be a conductive layer of the PCB. Alternatively, the first metamaterial structure is arranged on the PCB 110. ln that case, the first ground plane may be arranged on waveguide module 130, i.e., be an integral part of the waveguide module, such as the surface around the waveguide aperture.

Metamaterial structures are sometimes called electromagnetic bandgap (EBG) structures. The metamaterial structure may be arranged to form a high-impedance surface, such as an artificial magnetic conductor (AMC). lf the high-impedance faces an electrically conductive surface (i.e., a low-impedance surface such as a perfect electric conductor, PEC, in the ideal case), and if the two surfaces are arranged at a distance apart less than a quarter of a wavelength at a center frequency, no electromagnetic waves in a frequency band of operation can, in the ideal case, propagate along or between the intermediate surfaces since all parallel plate modes are cut-off in that frequency band. ln other words, the high-impedance surface, and the low-impedance surface form an electromagnetic bandgap between the two surfaces. This way, electromagnetic energy can pass more or less unhindered along the intended waveguiding path, but not in any other direction. The two surfaces may also be arranged directly adjacent to each other, i.e., electrically connected to each other. ln other words, the first metamaterial structure 155 may be arranged in contact with or at a distance from the first ground plane, where the distance is smaller than a quarter of an operation wavelength. The operation wavelength can correspond to the center frequency in a band of operation.

The first metamaterial structure 155 may be arranged on the waveguide module 130 and the antenna ground plane 180 may constitute the first ground plane. An example of this is shown in Figure 1. ln an alternative example, a ground plane is arranged around the patch antenna and constitutes the first ground plane. ln a realistic scenario, the electromagnetic waves in the frequency band of operation are attenuated per length along the intermediate surfaces. Herein, to attenuate is interpreted as to significantly reduce an amplitude or power of electromagnetic signal propagation, such as a radio frequency signal. The attenuation is preferably complete, in which case attenuate and block are equivalent, but it is appreciated that such complete attenuation is not always possible to achieve.

The metamaterial arrangement 156 is arranged intermediate the waveguide module 130 and the PCB 110 and is arranged to at least partly surround the waveguide aperture 140 and/or and the patch antenna 120 to define a passage 145 from the patch antenna into the waveguide aperture 140. According to aspects, this corresponds to a metamaterial structure at least partly surround the waveguide aperture 140 and/or and the patch antenna 120. Herein, to surround is interpreted broadly, i.e., including surrounding at least a part of the passage. The metamaterial arrangement preferably completely surrounds the passage to provide high isolation. However, it is understood that if the metamaterial arrangement does not completely surround, the technical effect may still be achieved to some effect with some of the same technical advantage.

According to aspects, the metamaterial arrangement 156 comprises a first metamaterial structure and a second metamaterial structure arranged facing each other. For example, the first and the second metamaterial structures may comprise complementary protruding pins facing each other.

The use of metamaterial structures provides low and high isolation of the transition. Another advantage is that there is no need for electrical contact between the waveguide module and the PCB. This is an advantage since high precision assembly is not necessary since electrical contact need not be verified. Electrical contact between the layers is, however, also an option. ln addition, the metamaterial structure provides relaxed tolerances in the exact placement of the patch antenna due to the high isolation.

There exists a multitude of metamaterial structures. Such structures often comprise elements arranged in a periodic or quasi-periodic pattern in one, two or three dimensions. Herein, a quasi-periodic pattern is interpreted to mean a pattern that is locally periodic but displays no long-range order. A quasi-periodic pattern may be realized in one, two or three dimensions. As an example, a quasi-periodic pattern can be periodic at length scales below ten times an element spacing, but not at length scales over 100 times the element spacing.

A metamaterial structure may comprise at least two element types, the first type of element comprising an electrically conductive material and the second type of element comprising an electrically insulating material. Elements of the first type may be made from a metal such as copper or aluminum, orfrom a non-conductive material like PTFE or FR-4 coated with a thin layer of an electrically conductive material like gold or copper. Elements of the first type may also be made from a material with an electric conductivity comparable to that of a metal, such as a carbon nanostructure or electrically conductive polymer. As an example, the electric conductivity of elementsof the first type can be above 103 Siemens per meter (S/m). Preferably, the electric conductivity of elements of the first type is above 105 S/m. ln other words, the electric conductivity of elements of the first type is high enough that the electromagnetic radiation can induce currents in the elements of the first type, and the electric conductivity of elements of the second type is low enough that no currents can be induced in elements of the second type. Elements of the second type may optionally be non-conductive polymers, vacuum, or air. Examples of such non-conductive element types also comprise FR-4 PCB material, PTFE, plastic, rubber, and silicone.

Elements of the first and second type may be arranged in a pattern characterized by any of translational, rotational, or glide symmetry, or a periodic, quasi-periodic or irregular pattern.

The physical properties of the elements of the second type also determines the dimensions required to obtain attenuation of electromagnetic propagation past the metamaterial structure. Thus, if the second type of material is chosen to be different from air, the required dimensions of the first type of element changes.

The elements of the first type may be arranged in a periodic pattern with some spacing. The spaces between the elements of the first type constitute the elements of the second type. ln other words, the elements of the first type are interleaved with elements of the second type. lnterleaving of the elements of the first and second type can be achieved in one, two or three dimensions.

A size of an element of either the first or the second type, or both, is smaller than the wavelength in air of electromagnetic radiation in the frequency band. As an example, defining the center frequency as the frequency in the middle of the frequency band, the element size is between 1/5th and 1/50th of the wavelength in air of electromagnetic radiation at the center frequency. Here, the element size is interpreted as the size of an element in a direction where the electromagnetic waves are attenuated, e.g., along a surface that acts as a magnetic conductor. As an example, for an element comprising a vertical rod with a circular cross section and with electromagnetic radiation propagating in the horizontal plane, the size of the element corresponds to a length or diameter of the cross section of the rod.

A type of metamaterial structure comprises electrically conductive protrusions on an electrically conductive substrate. ln other words, the first and/or the second metamaterial structure may comprise a plurality of protruding conductive elements 150. Example protruding elements are shown in Figures 1-2B and 4A-B. Theprotrusions may optionally be encased in a dielectric material. lt is appreciated that the protrusions may be formed in many different shapes, like a square, circular, elliptical, rectangular, or more generally shaped cross sections. lf the first metamaterial structure 155 is arranged on the waveguide module 130 and comprises plurality of protruding conductive elements 150. These protrusions may be integrally formed on the waveguide module.

Figures 8A and 8B show an example transition arrangement 100 where the first metamaterial structure 155 is arranged on the waveguide module 130 and comprises plurality of protruding conductive elements 150. According to aspects, the first metamaterial structure 155 comprises at least one side pin 850 arranged to intersect with a direction along the electrical field direction of the patch antenna 120. A side pin 850 is a protruding conductive element 150. This improves the transition from the patch antenna into the waveguide aperture. Preferably there are two side pins symmetrically arranged with respect to the waveguide aperture. According to further aspects, the cross section of the side pin 850 overlaps with the cross section of patch antenna when looking a direction along the electrical field direction of the patch antenna. This overlap is preferably more than 40%, i.e., the at least 40% of the cross section of the side pin 850 overlaps with the cross section of the patch antenna when looking along a direction along the electrical field of the patch antenna. This is left- right in Figure 8A. ln Figure 8A the overlap is 100%.

According to aspects, at least one of the protruding conductive elements 150 is arranged such that a side wall of that protruding conductive element is aligned with a sidewall of the waveguide aperture 140. ln Figure 8B, the two side pins 850 are arranged such respective side walls are aligned with the waveguide aperture. This arrangement can improve the coupling from the patch antenna into the waveguide aperture. lt is also possible that the protrusions are mushroom shaped, as in, e.g., a cylindrical rod on an electrically conductive substrate with a flat electrically conductive circle on top of the rod, wherein the circle has a cross section larger than the cross section of the rod, but small enough to leave space for the second element type between the circles in the metamaterial structures. Such a mushroom-shaped protrusion may advantageously be formed in a PCB, wherein the rod comprises a via hole, which may or may not be filled with electrically conductive material.The protrusions have a length in a direction facing away from the electrically conductive substrate. lf the element of the second type is air, the protrusion length may correspond to a quarter of the wavelength in air at the center frequency. The surface along the tops of the protrusions is then close to a perfect magnetic conductor at the center frequency. Even though the protrusions are only a quarter wavelength long at a single frequency, it presents a high impedance surface at a frequency band around that single frequency. This type of metamaterial structure thus presents a band of frequencies where electromagnetic waves may be attenuated, when the metamaterial structure faces a low impedance surface. ln a non-limiting example, the center frequency is 15 GHz and electromagnetic waves in the frequency band 10 to 20 GHz propagating intermediate the metamaterial structure and an electrically conductive surface are attenuated.

As another example, a type of metamaterial structure comprises a single slab of electrically conductive material into which cavities have been introduced. The cavities may be air-filled or filled with a non-conductive material. lt is appreciated that the cavities may be formed in different shapes such as elliptical, circular, rectangular, or more general cross section shapes. ln general, the length (in a direction facing away from the electrically conductive substrate) corresponds to a quarter of the wavelength at the center frequency.

The waveguide aperture acts as an interface to a waveguide structure, such as in a distribution layer in an array antenna or a tubular waveguide attached to the external side of the module, while the passage allows for the patch antenna arranged on the PCB to couple electromagnetic waves into the waveguide structure and also to pick up radio signals exiting the waveguide.

According to some aspects, the first metamaterial structure is integrally formed with a flange of the waveguide. The repetitive structure may, e.g., be machined directly into a metal element forming the interface towards the waveguide and comprising the waveguide aperture. This is an advantage since such machining can be performed in a cost-effective manner with high mechanical precision. This type of integrally formed metamaterial structure is also mechanically stable, which is an advantage.

According to other aspects, the waveguide module 130 comprises a plurality of waveguide apertures 140 and the PCB comprise a plurality of patch antennas 120, where each waveguide aperture is arranged to interface a respective patch antenna.

Here, each waveguide aperture and/or each patch antenna may be surrounded (orpartly surrounded) by the same metamaterial arrangement or by separate arrangements. For example, each waveguide aperture may be surrounded by respective rings (or squares or such) of protruding pins. For example, ten pins symmetrically arranged around a waveguide aperture may constitute a ring. Alternatively, a single ring may surround both waveguide apertures. ln another example, each waveguide aperture is surrounded by respective ring of protruding pins, where some pins are shared by the respective rings. lf the waveguide module 130 comprises a plurality of waveguide apertures 140, at least two waveguide apertures may be arranged such that their respective electrical field directions are arranged extending in the same direction. ln other words, the electrical field directions extend along the same line if the fields are perfectly aligned. lf the waveguide apertures are rectangular, this means that the waveguide apertures are arranged with their respective wide sides facing each other. This also include slightly angled, e.g., angled within 20 degrees. This is a common arrangement in a distribution layer in an array antenna. Furthermore, at least two waveguide apertures 140 may be arranged less than a wavelength apart. Here, the wavelength can be free space or guided and can correspond to the center frequency of a band of operation. The spacing can be measured center to center. Preferably, the at least two waveguide apertures are spaced about half a wavelength apart, which is highly desirable in a distribution layer in an array antenna.

According to aspects, the waveguide module comprises one or more alignment holes configured to receive respective alignment taps soldered to the PCB. This alignment "tap and hole" configuration provides for an increased alignment precision and simplifies assembly of the waveguide module with the PCB. Alternatively, or in combination of, the waveguide module comprises guiding pins arranged to mate with alignment holes in the PCB.

Figures 2A-4C are computer-aided design-drawings showing various aspects of an example transition arrangement or parts of that example transition arrangements. ln this example, the metamaterial arrangement 156 comprises a first metamaterial structure 155 and a first ground plane. More specifically, the first metamaterial structure is arranged on the waveguide module 130 and the first ground plane is arranged on the PCB 110, where the antenna ground plane 180 constitutes the first ground plane. The first metamaterial structure comprises a plurality of protruding conductive elements 150 integrally formed on the waveguide module 130. The pins are arranged at a distance from the first ground plane, where the distance is smaller than a quarter of an operation wavelength. The patch antenna 120 is rectangular and is fed from a short side by a differential microstrip. A notch for matching purposes is arranged in the patch antenna between the two lines constituting the differential microstrip. The waveguide aperture is rectangular with rounded corners. ln the example embodiment of Figures 2A-4C, the transition is arranged to operate at 76 to 81 GHz. The patch antenna is 1.5x1 mm, where the notch is 0.8x0.15 mm. The protruding pins are 0.8 by 1 mm. The rectangular waveguide aperture is 2.5x1.2 mm. The PCB comprises a substrate with a dielectric constant of 3 and a thickness of 5 mils. The top conductor constituting the patch antenna and the differential microstrip comprises copper. The bottom conductor constituting the antenna ground plane and first ground plane of the metamaterial arrangement comprises copper. The other dimensions of the PCB match the waveguide module.

There is also disclosed herein an antenna arrangement comprising the transition arrangement 100 according to the discussion above. Furthermore, there is disclosed herein a radio or radar transceiver comprising the transition arrangement 100 and/or the antenna arrangement. ln addition, there is disclosed herein a vehicle comprising the transition arrangement 100, the antenna arrangement, and/or the radio or radar transceiver.

There is also disclosed herein a method for producing a transition arrangement 100 for a patch antenna to waveguide transition, as is shown in Figure 7. The method comprises providing S1 a printed circuit board (PCB) 110, comprising a patch antenna 120 fed by a feed line 121; arranging S2 an antenna ground plane 180 to face the patch antenna 120; arranging S3 a waveguide module 130 to interface with the PCB 110, the waveguide module comprising a waveguide aperture 140 arranged facing the patch antenna 120 such that an electric field direction of the patch antenna 120 is aligned with an electric field direction of the waveguide aperture 140, wherein the feed line 121 feeds the patch antenna 120 from a direction perpendicular to the electrical field of the patch antenna 120, and arranging S4 a metamaterial arrangement 156 intermediate the waveguide module 130 and the PCB 110, wherein the metamaterial arrangement is arranged to at leastpartly surround the waveguide aperture 140 and/or and the patch antenna to define a passage 145 from the patch antenna into the waveguide aperture 140, wherein the metamaterial arrangement 156 is arranged to attenuate electromagnetic signal propagation in a frequency band intermediate the waveguide module 130 and PCB 110 in any other direction than via the passage 145 and along the feed line 121.

Claims

1. A transition arrangement (100) for a patch antenna-to-waveguide transition, the transition arrangement comprising a waveguide module (130), a printed circuit board, PCB, (110), an antenna ground plane (180), and a metamaterial arrangement (156), the PCB comprising a patch antenna (120) fed by a feed line (121 ), the antenna ground plane (180) arranged facing the patch antenna (120), the waveguide module (130) arranged to interface with the PCB (110), the waveguide module comprising a waveguide aperture (140) arranged facing the patch antenna (120) such that an electric field direction of the patch antenna (120) is aligned with an electric field direction of the waveguide aperture (140), wherein the metamaterial arrangement (156) is arranged intermediate the waveguide module (130) and the PCB (110) and is arranged to at least partly surround the waveguide aperture (140) and/or and the patch antenna (120) to define a passage (145) from the patch antenna into the waveguide aperture (140), wherein the metamaterial arrangement (156) is arranged to attenuate electromagnetic signal propagation in a frequency band intermediate the waveguide module (130) and PCB (110) in any other direction than via the passage (145) and along the feed line (121), wherein the feed line (121) connects to the patch antenna (120) from a direction perpendicular to the electrical field direction of the patch antenna (140):

2. The transition arrangement (100) according to claim 1, wherein the feed line (121) comprises a planar transmission line.

3. The transition arrangement (100) according to claim 2, wherein the planar transmission line is a microstrip (126).

4. The transition arrangement (100) according to claim 2, wherein the planar transmission line (121) is differential microstrip (127).

5. The transition arrangement (100) according to any previous claim, wherein the patch antenna (120) is fed from a center (122) of an edge (123) of the patch antenna (120).

6. The transition arrangement (100) according to any previous claim, wherein the patch antenna (120) is fed from a corner (124) of the patch antenna (120).

7. The transition arrangement (100) according to any previous claim, wherein the metamaterial arrangement (156) comprises a first metamaterial structure (155) and a first ground plane, and wherein the first metamaterial structure is arranged on the waveguide module (130).

8. The transition arrangement (100) according to any previous claim, wherein the metamaterial arrangement (156) comprises a first metamaterial structure (155) and a first ground plane, and wherein the first metamaterial structure is arranged on the PCB (110).

9. The transition arrangement (100) according to any of claims 7-8, wherein the first metamaterial structure (155) is arranged in contact with or at a distance from the first ground plane, where the distance is smaller than a quarter of an operation wavelength.

10. The transition arrangement (100) according to any of claims 7 or 9, wherein the first metamaterial structure (155) is arranged on the waveguide module (130) and the antenna ground plane (180) constitutes the first ground plane.

11. The transition arrangement (100) according to any of claims 1-6, wherein the metamaterial arrangement (156) comprises a first metamaterial structure and a second metamaterial structure arranged facing each other.

12. The transition arrangement (100) according to any of claims 7-11, wherein the first and/or the second metamaterial structure comprises a plurality of protruding conductive elements (150).

13. The transition arrangement (100) according to claim 12, wherein the first metamaterial structure (155) comprises at least one side pin (850) arranged to intersect with a direction along the electrical field direction of the patch antenna (120).

14. The transition arrangement (100) according to claim 12 or 13, wherein at least one of the protruding conductive elements (150) is arranged such that a side wall of that protruding conductive element is aligned with a sidewall of the waveguide aperture (140).

15. The transition arrangement (100) according to any previous claim, wherein the PCB (110) comprises a parasitic patch (128) arranged to couple with the patch antenna (120). The transition arrangement (100) according to ef* _ wherein at least two waveguide apertures (140) are arranged such that their respective electrical field directions are arranged extending in the same direction. The transition arrangement (100) according to any of fi cIaims wherein at least two waveguide apertures (140) are arranged less than a wavelength apart. An antenna arrangement comprising the transition arrangement (100) according to any of claims and/or the radio.