RU2622488C1 - Subsurface sensing antenna - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: according to the invention the microwave wideband antenna contains, at least, two conductive layers: the lower emitting layer of the type "Butterfly" and the current redistributing layer, having slots ending with cutouts of arbitrary shape, and also contains microstrips to power the antenna located on the current redistributing layer in isolation from the rest part of the current redistributing layer, at least, two feeding vertical connectors interconnecting between the lower layer and the current redistributing layer, and the vertical connectors grounding the antenna layers.

EFFECT: preserving the working frequency range of microwave wideband antennas with a substantial reduction in its size.

11 cl, 3 dwg

Description

FIELD OF THE INVENTION

This invention relates to ultra-wideband microwave antennas, in particular for use in non-contact ultra-wideband subsurface radars, for 3D or 2D visualization of subsurface structures.

State of the art

The problem of using ultra-wideband (UWB) microwave antennas in various radio frequency devices is that the characteristics of UWB microwave antennas, such as antenna dimensions, reflection coefficient from the power port, isolation between the receiving and transmitting paths, and matching with the external environment, on all the basic properties of the devices themselves, such as the overall dimensions of the device, the isolation between the receiving and transmitting paths, the level of spurious surface reflections of the emitted signal, agreed e microwave antennas and radio paths, transmit power, etc.

On the one hand, the dimensions of UWB microwave antennas should be minimal due to the lack of free space inside modern electronic devices, but on the other hand, UWB microwave antennas should be larger in order to maintain the required characteristics of signal reception and transmission.

At the moment, in most subsurface radars for sensing soil, roads, bridges, buildings, structures, etc. Dipole UWB microwave antennas are used, having the form of two symmetrical triangular diverging conductive monopole surfaces. Such dipole antennas are known under the conditional name “bow tie” (in English terminology “bow-tie”, ie “bow tie”). The principal broadband of these antenna structures is physically explained by the increase, with increasing length of the radio wave, of the current electric exciting (or received for the receiving antenna) current along the length of the radiating triangle as it moves away from the power points. That is, the longer the working wavelength, the greater the realized effective length of the radiating structure. However, some radars and applications require improvements in the performance of such dipole antennas. The requirements are due to the small size of the devices into which the UWB microwave antennas are embedded, and, as a result, the UWB microwave antennas must have a smaller size, have stable matching in a wide frequency range, reliable isolation between the receiving and transmitting paths to prevent the receiver input from being overloaded with a direct signal ( signal) of the transmitter to the input of the radar receiver and achieve good energy conservation. The more stable the antenna matching, the less energy is lost when reflected from its port. Therefore, less generator power and lower overall power consumption are required. Similarly, suppressing radiation backward reduces the energy loss due to backward radiation and leads to the same positive result. In addition, suppressing the radiation back increases the reliability of the received data and prevents the influence of nearby objects (for example, the operator’s hand) on the signal received by the receiver.

The minimum dimensions (length, width, thickness) of UWB microwave antennas are required, first of all, in mobile (wearable) devices, for example, such as mobile phones, since these devices have small dimensions (length, width, thickness) and a small internal space for placement of electronic components.

Thus, a particularly important parameter for UWB microwave antennas in mobile (wearable) devices is thickness, because Mobile (wearable) devices themselves, as a rule, have a small thickness (from 0.5 cm). Also, from the design point of view, with small sizes of UWB, microwave antennas should have increased noise immunity from other electronic units of the mobile device to ensure the simultaneous operation of all units. Therefore, shielding in the form of a metallization layer is usually installed on the UWB microwave antennas from the rear side, which prevents the influence of external spurious signals on the antenna, and vice versa. In addition, additional requirements are imposed on the operating frequency range of UWB microwave antennas. Usually, the larger the antenna, the lower its operating frequency range, and vice versa (a general rule for all antennas). Attempts to reduce the size of UWB UHF antennas of existing structures by merely introducing materials with a high coefficient of dielectric constant do not give the desired result, because this leads to a narrowing of the operating frequency range. Therefore, reducing the size of UWB microwave antennas should be provided with a more integrated approach.

In the prior art, solutions are known that solve the problem of increasing the dielectric constant of a UWB UHF antenna with preserving its dimensions, for example, in US Pat. This is a traditional butterfly dipole antenna made on a standard dielectric substrate with a metal shield on the back.

The specified technical solution is the closest prototype to the proposed invention. The main disadvantage of the invention according to the patent US 5,563,616 A lies in the fact that no methods are proposed for maintaining an increase in the coefficient of dielectric constant while reducing the dimensions of the antenna. This drawback is especially critical if the UWB microwave antenna is used to operate at frequencies of 3 GHz or less.

US Pat. No. 7,123,207 B2 proposes a UWB UHF butterfly type antenna. This is the traditional design of antennas of this class, manufactured on a dielectric substrate in conjunction with resistance matching circuits. The main disadvantages of existing inventions, such as US 7,123,207 B2:

- no method for reducing the dimensions of the antenna;

- the absence of a screen on the back of the antenna leads to a significant effect of surrounding objects on the characteristics of the UWB microwave antenna.

With these drawbacks, the antenna proposed in US 7,123,207 B2 will have a larger size than that required for use in mobile and wearable devices. It will also be affected by the surrounding electronic components of the mobile device. Such an effect can be removed only by additional shielding.

US Pat. No. 7,372,409 B2 proposes a UWB UHF patch antenna in the form of slit-loaded triangular slots with shielded reverse radiation. This antenna has been enhanced with special slots as an additional load. Such an improvement leads to a decrease in the width and length of the antenna. However, the invention has a significant disadvantage in that no method for reducing the thickness of the antenna is proposed.

UWB microwave antenna with the indicated drawback. proposed in the patent US 7,372,409 B2, has a thickness of the order of 0.07λ and can only be used in mobile devices with a large thickness of the case.

As follows from the foregoing, one of the main problems of modern electronic devices, in particular mobile and wearable devices, is the lack of internal free space. For this reason, the problem of developing UWB UHF antennas of minimum dimensions with maintaining and enhancing their performance is particularly acute. However, such characteristics of the antennas as the operating frequency range, bandwidth, directly depend on the size of the antenna. Those. the larger the size, the higher, for example, the lower limit of the working frequency range.

SUMMARY OF THE INVENTION

The claimed technical solution discloses a microwave broadband antenna while maintaining the lower boundary of the working frequency range of 3.1 GHz, as well as the bandwidth of the working frequency range of 2.9 GHz with dimensions 25-30% less than that of analogues.

According to the present invention, an ultra-wideband microwave antenna comprises at least two conductive layers: a bottom “butterfly” type emitting layer and a current redistribution layer having slits ending in cutouts of arbitrary shape; a microstrip for powering the antenna located on the current redistribution layer in isolation from the rest of the current redistribution layer; at least two energizing vertical connectors connecting the lower layer and the current redistribution layer; and at least two vertical connectors, grounding layers of the antenna.

In an embodiment, the antenna comprises at least three grounding vertical connectors, wherein the grounding vertical connectors are either at equal distances from each other, either in an exponential distribution, or depending on the distribution of current density, or by any other law.

In an embodiment, the bottom “butterfly” type emitting layer contains elements of arbitrary shape symmetrical and / or asymmetric with respect to the axis of the antenna.

In an embodiment, the antenna has an arbitrary external shape.

In an embodiment, the antenna is fabricated on a standard microwave dielectric flexible or inflexible substrate, or using antenna-on-chip technology.

In an embodiment, the antenna further comprises an upper shielding layer.

In an embodiment, slots and cutouts are arranged symmetrically with respect to the axis of the antenna.

In an embodiment, the cutouts are located on the side of the slots closest to the axis of the antenna.

In an embodiment, the slots are rectangular and the cuts are circular.

In an embodiment, the microstrip is located along the axis of the antenna and extends from the edge of the current redistribution layer to its center.

In an embodiment, at least one power connector connects the microstrip to at least one of the radiating elements of the lower layer, and at least one other power connector connects the microstrip to at least one other of the radiating elements of the lower layer.

The technical result of the claimed invention is to maintain the working frequency range (for example, the lower and upper boundaries of the working frequency range of 3.1 and 6 GHz, respectively) of a microwave broadband antenna, while significantly reducing its size (length and width - dimensions in the plane of the antenna layers and thickness - maximum vertical distance between the radiating and screen layers of the antenna).

The main improvements to achieve the claimed technical result and the required characteristics of the operating frequency range of the microwave broadband antenna are indicated below:

- inner metal layer with special cutouts redistributing induced currents. It is located between the lower radiating layer and the upper screen. Due to the creation of special cutouts in this layer, the current paths on it are lengthened, which, in turn, leads to the possibility of increasing the working wavelength and, accordingly, reducing the working frequencies down the range;

- the lower radiating metal layer, made in the form of an antenna-dipole of the "butterfly" type with elements of arbitrary shape;

- interlayer grounding connections arranged in a row on the sides of the antenna and having a density equal to the current density in a given section of the antenna;

- UWB microwave antenna is designed with the possibility of manufacturing in the form of a multilayer printed circuit board from ordinary material or in the form of an antenna on a chip. To do this, all the metallization of the antenna is made on parallel layers, for the connection between the layers exclusively vertical connectors standard for printed circuit boards are used.

The above is a brief, non-limiting summary of the objectives, aspects, and advantages of the present invention. Additional features and advantages of the present invention will become apparent from the following detailed description of the invention.

Brief Description of the Drawings

Further, the present invention will be described in detail with reference to the accompanying drawings, in which:

In FIG. 1 shows the main layers and elements of a microwave broadband antenna:

- in FIG. 1A shows an internal current redistribution layer;

- in FIG. 1B shows an upper metal shielding layer;

- in FIG. 1C shows inter-level grounding connectors arranged linearly with a distance inversely proportional to the current distribution density;

- in FIG. 1D depicts a lower butterfly emitting layer.

In FIG. 2 shows an example of shifting the operating frequency range of UWB microwave antennas down the spectrum:

- in FIG. 2A shows the operating range of a classic implementation of an antenna with an upper shielding layer;

- in FIG. 2B shows the operating range of the proposed microwave broadband antenna with the same dimensions.

In FIG. 3 shows various possible forms of a microwave broadband antenna.

Description of Embodiments

In FIG. 1 shows the main conductive layers and elements of a microwave broadband antenna in a preferred embodiment of the invention.

In FIG. 1A shows the inner layer 110 of the current redistribution of UWB microwave antennas 100. This layer 110 is located between the upper metal shielding layer 120 (see further in Fig. 1B) and the lower emitting layer 130 of the butterfly type (see further in Fig. 1D). The inner layer 110 redistribution of currents has cutouts 111 in the form of narrow slits ending in a circular cut, designed to lengthen the paths of the flow of currents and to expand the operating frequency range towards lower frequencies. The configuration of the slots and cutouts can be changed for technological reasons or to optimize the characteristics of the antenna in any sub-band of operating frequencies. Lengthening the current paths increases the working wavelength of the UWB microwave antenna 100. In one non-limiting example, the slots may have a rectangular shape and the cuts may have a circular shape. Slots and cutouts can be located symmetrically or asymmetrically with respect to the axis of the antenna. The cutouts can be located on the side of the slots that is closest to the axis of the antenna.

Also, the inner layer 110 of the current redistribution may include a microstrip supply line 112 for UWB microwave antennas 100, going from the edge of the inner layer 110 to its center and then connected to the lower radiating layer 130 using energizing (vertical) connectors 113. The edges of the inner layer 110 of the redistribution currents must be grounded using inter-level grounding connectors 140 in the form of hollow cylinders.

In FIG. 1B, the upper metal shielding layer 120 of UWB UHF antenna 100 is shown. The layer 120 is electrically grounded using inter-level grounding connectors 140 with layers 110 and 130.

The upper metal shielding layer 120 is made on the UWB microwave antenna 100 optionally, depending on the number of layers on the board of the target device, and allows for maximum simplicity and manufacturability. Its use is justified if it is necessary to suppress radiation in the rear half-space of a mobile device by more than 10 dB and, if necessary, shielding from surrounding elements. In cases where shielding from surrounding objects is not required, for example, in stand-alone radars that are not built into electronic devices, the UWB microwave antenna 100 can be made without the upper metal shielding layer 120 and, thus, contain only two layers.

UWB UHF antenna 100, implemented without the upper metal shielding layer 120, has characteristics similar to the antenna in the preferred embodiment of the present invention (i.e., operates in the frequency range 3.1-10 GHz), except for a smaller thickness and the need for only two layers, which makes it popular for most devices made on two-layer printed circuit boards.

In FIG. 1C shows the implementation of UWB microwave antennas 100 with inter-level grounding connectors 140 located not at an equal distance, but with distances inversely proportional to the current distribution density, to reduce losses during the flow of currents between the layers. This embodiment of the UWB microwave antenna 100 is used in cases where the antennas are used to transmit a high-power radio signal, or when it is necessary to provide minimal resistance to currents flowing between the layers of the antenna.

In FIG. 1D shows the lower radiating layer 130 with two symmetric radiating parts of the dipole 131 and 132 made in the form of two triangles with a feed point in the center of the lower radiating layer 130 (a kind of UWB antenna dipole of the butterfly type). This type and arrangement of radiating elements provides a wide operating frequency range and a uniform radiation pattern of UWB microwave antennas 100.

In FIG. 2A, 2B are graphs of reflection coefficient from the antenna port S21. Horizontal is the frequency in GHz, vertical is the reflection coefficient S21 in dB. As a threshold for determining the working frequency band selected level S21≤-6 dB. The operating frequency range is additionally highlighted in a gray rectangle. In FIG. 2A shows the operating range of a classic implementation of an antenna with an upper shielding layer (for example, as in US 5,563,616 A). In FIG. 2B shows the operating range of the proposed microwave broadband antenna with the same dimensions.

As shown in the graphs of FIG. 2, the proposed antenna allows you to push the lower limit of the operating frequency range from 4.4 GHz to 3.3 GHz without increasing the dimensions of the antenna.

The inner layer 110 of the redistribution of currents can have cutouts in the form of narrow slits ending in a cut in the form of various geometric shapes: circle, triangle, square, polygon. In addition, the microstrip supply line 112 can be located on the layer 110, or on the upper metal shielding layer 120, or the antenna can be powered by a soldered microwave coaxial cable.

A preferred embodiment of the invention is as follows.

UWB microwave antenna 100 consists of three layers: the inner layer 110 redistribution of currents, the upper metal shielding layer 120, the lower emitting layer 130 of the type "butterfly". The inner current redistribution layer 110 has cuts 111, which are thin cuts extending from the edge of the layer to its line of symmetry and ending with round cuts near the axis of symmetry of the UWB microwave antenna 100. Also, the UWB microwave antenna 100 contains inter-level grounding connectors 140 that electrically connect all three layer on two or four sides of the UWB microwave antenna 100. On the inner layer of the current redistribution 110, there is a power line 112 extending from the edge of the current redistribution layer 110 to its center and then connected to the lower radiation the laminating layer 130 using the supply (vertical) connectors 113.

The proposed technical solution - UWB microwave antenna 100 is applicable in the problems of subsurface sounding for medical purposes, healthcare, fitness. In biomedical applications, UWB UHF antenna 100 can be used for non-invasive sensing of the body tissue structure. In this case, direct electrical contact, as well as the use of special gels, is not required. UWB microwave antennas 100 can also be used in motion detectors (palpitations, respiration, etc.).

UWB UHF antenna 100 can have a rectangular shape, or the shape of other geometric shapes: a circle, a triangle polygon, or have a shape corresponding to the shape of the space allocated in the device for this antenna, suitable for the internal dimensions of the target device, which is achieved through the use of flexible material with making a microwave broadband antenna. The material from which the UWB microwave antenna 100 is made may be one of the well-known microwave dielectrics, for example FR-4, Rogers, or based on flexible printed circuit boards, or in accordance with antenna-on-chip technology, or the antenna may have an air-filled internal spaces to reduce the cost of construction. UWB microwave antenna 100 can be made on a standard microwave dielectric substrate (including flexible).

UWB UHF antenna 100 can perform the functions of receiving / transmitting in the case of a single-antenna circuit or the function of receiving or transmitting separately, in the case of multi-antenna radars.

Multi-antenna radars with UWB microwave antennas 100 can be used, for example, in car collision avoidance systems, medical scans without moving the phone on the surface, etc.

The upper shielding layer 120 is important in case of increased requirements to minimize backward radiation of UWB microwave antennas 100, as well as for protection from external components. Even with the use of the upper shielding layer 120, the most critical antenna size - thickness - can be reduced to 1 mm in the frequency range 3.1-10 GHz by using the inventive UWB microwave antenna design.

In the absence of such requirements, the upper shielding layer 120 may not be used. In this case, the UWB microwave antenna 100 will have only two layers.

Grounding connectors 140 can be located both on both sides of the UWB microwave antenna 100, and on all four sides, depending on the requirements for the strength of the side lobes of spurious radiation. The location of the grounding connectors 140 can be either with the same distance between them, or with a variable distance, for example, by an exponential distribution, or depending on the distribution of current density, or by any other law. For example, the distance between the connectors can be reduced (to place them denser) in places with a higher concentration of currents in order to reduce the resistive loss of currents when flowing in the antenna.

The lower radiating layer 130 of the butterfly type has two halves 131 and 132. They can be in the form of triangles or other shapes that allow the flow of current from the lower radiating layer to the upper. In addition, the bottom emitting layer 130 of the type "butterfly" can have both symmetrical and asymmetric with respect to the axis of the antenna elements.

UWB microwave antenna 100, built-in, for example, in a mobile phone, allows for subsurface sounding of the thickness of the adipose tissue of a person’s body and displays the measurement result on the screen of the same mobile phone.

UWB UHF antenna 100 in a mobile phone works as follows: the antenna emits a microwave signal coming from the transmitter into the object under study. This signal undergoes multiple reflections inside the object, which come back. Reflections that hit the antenna are transmitted to the receiver. After processing in the receiver and in the digital block, the results of measuring the reflections in the depth of the investigated object are presented on the phone screen.

Industrial applicability

The proposed invention describes an antenna for receiving / transmitting UWB radio signal and does not concern the principles of generation, detection, modulation / demodulation, digital signal transformations. The proposed antenna was originally designed for a radar for non-invasively displaying the subsurface structure of human body tissues in the tasks of periodically monitoring the effectiveness of physical exercises. In this case, in a general sense, the use of the present invention in radars for measuring the thickness of body tissues (for example, fat, etc.) is provided for subsurface non-invasive sounding of medical and non-medical purposes. The structure of the proposed UWB antenna in this context can be applied equally efficiently in various RF devices. These include subsurface sounding radars, radar devices, wireless data transmission systems, wireless energy transmission systems.

Claims (17)

1. An ultra-wideband microwave antenna, comprising: at least two conductive layers: - the bottom emitting layer of the type "butterfly" containing at least two radiating elements, and - a current redistribution layer having slots ending with cutouts of arbitrary shape; a microstrip for powering the antenna located on the current redistribution layer in isolation from the rest of the current redistribution layer; at least two energizing vertical connectors connecting the bottom layer and the current redistribution layer; and at least two vertical connectors, grounding layers of the antenna. 2. The ultra-wideband microwave antenna according to claim 1, comprising at least three grounding vertical connectors, wherein the grounding vertical connectors are either at equal distances from each other, either in an exponential distribution, or depending on the distribution of current density, or any other the law. 3. The ultra-wideband microwave antenna according to claim 1, in which the lower emitting layer of the type "butterfly" contains symmetric and / or asymmetric relative to the axis of the antenna elements of arbitrary shape. 4. The ultra-wideband microwave antenna according to claim 1, having an arbitrary external shape. 5. The ultra-wideband microwave antenna according to claim 1, made on a standard microwave dielectric flexible or inflexible substrate or using antenna-on-chip technology. 6. The ultra-wideband microwave antenna according to claim 1, further comprising an upper shielding layer. 7. The ultra-wideband microwave antenna according to claim 1, wherein the slots and cutouts are located symmetrically with respect to the axis of the antenna. 8. The ultra-wideband microwave antenna according to claim 1, wherein the cutouts are located on the side of the slots closest to the axis of the antenna. 9. The ultra-wideband microwave antenna according to claim 1, wherein the slots are rectangular in shape and the cutouts are circular. 10. The ultra-wideband microwave antenna according to claim 1, wherein the microstrip is located along the axis of the antenna and extends from the edge of the current redistribution layer to its center. 11. The ultra-wideband microwave antenna according to claim 1, in which at least one power connector connects the microstrip to at least one of the radiating elements of the lower layer, and at least one other power connector connects the microstrip to at least one other of the radiating elements bottom layer.

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