TECHNICAL FIELD

The present disclosure relates to an antenna device. The antenna device is suitable for being used in an automotive radar antenna system. The disclosure is concerned with suppressing surface waves, which are created on an aperture plane of the antenna device.

BACKGROUND

Conventional antenna devices for automotive radar antenna systems are mainly divided into two groups. The first group includes printed circuit board (PCB) antenna devices. These antenna devices comprise metal-printed radiating planar structures (antennas) on a radio frequency (RF) substrate. The typical shapes of these antennas are zig-zag, combline, and patch. The second group includes waveguide antenna devices. These antenna devices comprise a waveguide (e.g., of a horn type), which is typically made of metal or metallized plastic. An antenna system consists usually of several such waveguide antenna devices, which are fabricated on a block together and work independently.

The radiation pattern of a conventional antenna device for an automotive radar antenna system suffers from the effect of surface waves, which are generated on the antenna aperture plane when the antennas of the antenna device radiate. These surface waves travel along the antenna aperture plane and create distortion on the radiation pattern of the antenna device. This effect is observed for both PCB antenna devices and waveguide antenna devices.

The effect may be addressed by adding blind antennas or electromagnetic bandgap (EBG) structures to the antenna device. This approach works for automotive radar antenna systems operating in the 76-77 GHz sub-band. However, future high-resolution radar antenna systems may use the whole assigned bandwidth up to 81 GHz, and may also comprise an increased number of antenna devices and antennas. The radar antenna systems become more complex, for example, they may have a higher density of antenna devices, may comprise waveguide antenna devices for providing sufficient bandwidth, and may include complex routing. In these scenarios, the conventional approach becomes more difficult to implement. Furthermore, the coupling between nearby antenna devices and antennas becomes critical as well, and is also negatively affected by the surface waves.

SUMMARY

In view of the above, this disclosure has the objective to provide an antenna device that is designed for suppressing or eliminating surface waves on the antenna aperture plane. The antenna device should be of low complexity and simple to fabricate. The antenna device should be suitable for an automotive radar antenna system, for instance, one that uses the entire bandwidth between 76-81 GHz. Another goal is to design the antenna device such that the number of antenna elements could be easily increased.

These and other objectives are achieved by the solution of this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

The solution of this disclosure is suitable for mm-wave automotive radar antenna systems, and can be applied on such antenna systems even if working between 76-81 GHz.

A first aspect of this disclosure provides an antenna device comprising: an antenna aperture plane; one or more antennas arranged on the antenna aperture plane, wherein each antenna is configured to radiate a radio wave in response to being fed with a radio frequency signal; and one or more resistive sheets arranged besides the antennas on the antenna aperture plane.

The use of the one or more resistive sheets, which are provided on the same antenna aperture plane than the antennas, results into a reduction or elimination of surface waves on the antenna aperture plane. This effect can be achieved for both PCB-based and waveguide-based antenna devices. The surface wave suppression leads to several advantages. For example, a smoother radiation pattern of the antenna device is exhibited in the azimuth plane. The radiation pattern may have smaller fluctuations on the amplitude of the radiation. This can help to relax requirements on the calibration of the automotive radar antenna system, which includes the antenna device, wherein the calibration is a potentially expensive and time consuming task in the automotive radar series development. Further, a mutual coupling between nearby antennas can be significantly reduced. This improves the overall performance of the antenna device and thus of the automotive radar antenna system, which includes the antenna device. Also, there is no need for any blind antennas or grooves on the antenna aperture plane, which makes the fabrication process of the antenna device easier. In addition, the solution of this disclosure provides the possibility to define more complex shapes of the resistive sheets, which may be used to optimize the surface wave reduction.

In an implementation form of the first aspect, each of the antennas is adapted to generate an electric surface wave that propagates along a respective path on the antenna aperture plane, when the antenna radiates the radio wave; and each resistive sheet is arranged in the respective path of at least one of the electric surface waves.

In this way, different surface waves, which would be or are generated on the antenna aperture plane, can be efficiently suppressed.

In an implementation form of the first aspect, the one or more antennas comprise a first antenna and a second antenna; and at least one of the resistive sheets is arranged between the first antenna and the second antenna.

In this way, surface waves are suppressed and additionally the coupling between the first antenna and the second antenna is reduced.

In an implementation form of the first aspect, the one or more resistive sheets comprise a first resistive sheet and a second resistive sheet; and at least one of the antennas is arranged between the first resistive sheet and the second resistive sheet.

In this way, surface waves created on both sides of the antenna on the antenna aperture plane can be suppressed.

In an implementation form of the first aspect, the first resistive sheet is arranged between the first antenna and the second antenna; the second antenna is arranged between the first resistive sheet and the second resistive sheet; and the second resistive sheet is arranged between the second antenna and a third antenna of the one or more antennas.

In this way, both surface waves on the aperture plane and coupling between antennas of the antenna device are reduced. In an implementation form of the first aspect, the first antenna and the second antenna are configured to radiate at the same wavelength; and a distance between the first antenna and the second antenna on the aperture antenna plane is in a range of 0.5 - 50 times the wavelength.

The distance between the antennas may be different for different designs of the antenna device. The antenna device shows a good performance over the whole range of distances according to this implementation form.

In an implementation form of the first aspect, several of the antennas are arranged one after the other along a direction on the antenna aperture plane; and at least one resistive sheet is arranged between each adjacent pair of the several antennas along the direction.

This reduces significantly the mutual coupling between the antennas.

In an implementation form of the first aspect, at least one of the antennas is arranged at or near an edge of the antenna aperture plane; and at least one resistive sheet is arranged besides the at least one antenna on the opposite side of the antenna than the edge of the antenna plane aperture.

The surface waves created by the antenna may be able to travel only in a direction away from the edge of the antenna aperture plane, and can thus be efficiently suppressed by the arrangement of the resistive sheet.

In an implementation form of the first aspect, the one or more resistive sheets are printed, and/or painted, and/or deposited on the antenna aperture plane.

This allows a simple fabrication process of the antenna device.

In an implementation form of the first aspect, the one or more resistive sheets each have a resistivity value in a range of 100-500 Q/square.

These resistivity values enable an efficient suppression or elimination of surface waves. In an implementation form of the first aspect, the antenna aperture plane comprises a surface plane of a PCB or of a metal waveguide, or of a metallized plastic waveguide.

That is, the solution of this disclosure is suitable for PCB antenna devices and for waveguide antenna devices.

In an implementation form of the first aspect, the one or more antennas comprise: at least one of a PCB zigzag antenna and a PCB combline antenna, if the antenna aperture plane comprises the surface plane of the PCB; and a horn antenna, if the antenna aperture plane comprises the surface plane of the metal waveguide or of the metallized plastic waveguide.

Accordingly, the solution of this disclosure is compatible with a wide range of antenna types.

In an implementation form of the first aspect, the one or more antennas comprise at least one automotive radar antenna; and/or the one or more antennas are each configured to radiate in a frequency range of 76-81 GHz.

Thus, the antenna device is suitable for an automotive radar antenna system that operates in a wide frequency range.

In an implementation form of the first aspect, the one or more resistive sheets comprise at least one of a graphite-based sheet, a graphene-based sheet, a copper-based sheet, and a nickel-based sheet.

In an implementation form of the first aspect, a thickness of each of the one or more resistive sheets is in a range of 1-50 pm.

Such resistive sheets can be fabricated without requiring a complex process, and are stable, and allow reducing the amplitude of surface waves efficiently.

In summary, this disclosure proposes a new solution for reducing surface waves on an antenna aperture plane of an antenna device, which may be used for a mm-wave automotive antenna system. The solution is based on the use of the one or more resistive sheets, which may be printed or painted or deposited on the same antenna aperture plane as the antennas of the antenna device. The use of the resistive sheets on the antenna aperture plane has proven beneficial both in simulations and measurements of real device. The resistive sheets affect advantageously the radiation pattern of the antenna device, which is a consequence of the reduction of the surface waves For instance, the resistive sheets lead to a reduction of ripples on the radiation pattern of the antenna device. Furthermore, a coupling between nearby antennas of the antenna device is also improved (reduced), when placing one or more resistive sheet between these antennas.

When applying the one or more resistive sheets, for example, a layer of a resistive material may be provided on one side or on both sides of an antenna of the antenna device. A surface wave that is created by the antenna may then induce an electrical current on the resistive material. Because of the lossy property of the resistive material, this induced current may be absorbed, and hence the surface wave amplitude reduced. The resistivity value of the resistive material may have a direct impact on the surface wave reduction. However, the effect of increasing the resistivity of a resistive sheet may be non-linear, and there may a maximum resistivity value, at which an improvement is not observed any further. This maximum resistivity value may also depend on the design (shape, distance, thickness) of the resistive sheet. Beneficial parameters and materials for the resistive sheets are provided in this disclosure.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms will be explained in the following description of specific implementations in relation to the enclosed drawings, in which

FIG. 1 shows two exemplary antenna devices according to this disclosure.

FIG. 2 shows an antenna device according to this disclosure with a PCB zig-zag antenna, and shows a radiation pattern of the antenna device.

FIG. 3 shows an antenna device according to this disclosure with a PCB combline antenna, and shows a radiation pattern of the antenna device.

FIG. 4 shows an antenna device according to this disclosure with a metal horn antenna, and shows a radiation pattern of the antenna device.

FIG. 5 shows an antenna device according to this disclosure with a metallized plastic horn antenna, and shows a radiation pattern of the antenna device.

FIG. 6 shows an antenna device according to this disclosure with two nearby antennas, and shows a coupling between the two antennas. DETAILED DESCRIPTION

FIG. 1 shows two antenna devices 100 according to this disclosure. One exemplary antenna device 100 is shown in FIG. 1(a) and another exemplary antenna device 100 is shown in FIG. 1(a). Like all antenna devices 100 of this disclosure, both antenna devices 100 are suitable for an automotive radar antenna system, and may operate in a frequency range of 76-81 GHz.

Each antenna device 100 of this disclosure comprises an antenna aperture plane 101, one or more antennas 102 arranged on the antenna aperture plane 101, and one or more resistive sheets 103 arranged besides the antennas 102 on the antenna aperture plane 101. The one or more antennas 102 are each configured to radiate a radio wave in response to being fed with a radio frequency signal. For instance, each antenna 102 may be configured to radiate in the frequency range of 76-81 GHz.

FIG. 1(a) shows an exemplary antenna device 100 with one antenna 102 and one resistive sheet 103. The antenna 102 is arranged at or near an edge of the antenna aperture plane 101. The resistive sheet 103 is arranged besides the antenna 102 and on the opposite side of the antenna

102 than the edge of the antenna plane aperture 101. A surface wave created by the radiating antenna 102 will travel towards the resistive sheet 103, and will be suppressed by the resistive sheet 103.

FIG. 1(b) shows an exemplary antenna device 100 with more than one antenna 102 and with more than one resistive sheet 103. As an example, three antennas 102 and four resistive sheets

103 are shown to be arranged on the aperture plane 101. The antennas 102 are arranged one after the other along a direction on the antenna aperture plane 101. One of the resistive sheets 103 is arranged between each adjacent pair of the antennas 102 along said direction. A distance between the antennas 102 on the aperture antenna plane may be in a range of 0.5 - 50 times the wavelength, at which the antennas 102 are configured to radiate. It is also possible that more than one resistive sheet 103 is arranged between each adjacent pair of antennas 102. Each antenna 102 may have a resistive sheet 103 arranged on each of its opposite sides, for instance as shown in FIG. 1(b).

The resistive sheets 103 in each antenna device 100 of this disclosure may be printed, or painted, or deposited, or formed by combinations thereof, on the antenna aperture plane 101. Each resistive sheet 103 may have a resistivity value in a range of 100-500 Q/square. Each resistive sheet 103 may have a thickness in a range of 1-50 gm. Each resistive sheet 103 may comprise at least one of graphite, graphene, copper, or nickel, or may be based on any one or any combination of these materials.

The use of the one or more resistive sheet 103 on the antenna aperture plane 101 next to the antennas 102 results in a reduction of surface waves and in a reduced coupling between nearby antennas 102. When placing the resistive sheets 103 besides the antennas 102, the surface waves induce electrical current on the resistive sheets 103, which is absorbed at least partly by the resistive sheets 103. This causes the surface wave amplitudes to be reduced. As a consequence, the effect of the surface waves on the radiation pattern of the antenna device 100 is also reduced. For example, the radiation pattern of the antenna device 100 may have smaller fluctuations on its amplitude.

The solution of this disclosure can be used in both PCB and waveguide antenna devices 100 as illustrated in the FIGs. 2-5. The resistive sheets 103 are easy to manufacture, without effecting the fabrication process of the antenna device 100 itself.

FIG. 2 shows an exemplary antenna device 100 according to this disclosure. Same elements in FIG. 2 and FIG. 1 are labelled with the same reference signs and may be implemented likewise. FIG. 2(a) shows an antenna device 100 with a PCB 201, which forms the antenna aperture plane 101 or wherein the antenna aperture plane 101 comprises the surface plane of the PCB 201. The antenna device 100 further comprises a PCB zig-zag antenna 102 formed in/on the PCB 201. The PCB zig-zag antenna 102 is, as an example, sandwiched by two resistive sheets 103, wherein one resistive sheet 103 is arranged on each side of the antenna 102. FIG. 2(b) shows the radiation pattern (gain in dB vs. zenith angle) of the antenna device 100 of FIG. 2(a) for angles 0° and 90° in the azimuth plane, in comparison with a similar antenna device that has no resistive sheet 103. It can be seen that ripples on the radiation pattern are reduced for the antenna device 100 of FIG. 2(a).

FIG. 3 shows an exemplary antenna device 100 according to this disclosure. Same elements in FIG. 3 and FIG. 1 are labelled with the same reference signs and may be implemented likewise. FIG. 3(a) shows an antenna device 100 with a PCB 201, which forms the antenna aperture plane 101 or wherein the antenna aperture plane 101 comprises the surface plane of the PCB 201. The antenna device 100 further comprises a PCB combline antenna 102 formed in/on the PCB 201. The PCB combline antenna 102 is, as an example, sandwiched by two resistive sheets 103, wherein one resistive sheet 103 is arranged on each side of the antenna 102. FIG. 3(b) shows the radiation pattern (gain in dB vs. zenith) of the antenna device 100 of FIG. 3(a) for angles 0° and 90° in the azimuth plane, in comparison with a similar antenna device that has no resistive sheet 103. It can be seen that ripples on the radiation pattern are reduced for the antenna device 100 of FIG. 3(a).

FIG. 4 shows an exemplary antenna device 100 according to this disclosure. Same elements in FIG. 4 and FIG. 1 are labelled with the same reference signs and may be implemented likewise. FIG. 4(a) shows an antenna device 100 with a metal block 401, which forms the antenna aperture plane 101 or wherein the antenna aperture plane 101 comprises the surface plane of the metal block 401. The antenna device 100 further comprises a horn antenna 102 formed in/on the metal block 401. The horn antenna 102 is, as an example, sandwiched by two resistive sheets 103, wherein one resistive sheet 103 is arranged on each side of the antenna 102. FIG. 4(b) shows the radiation pattern (gain in dB vs. zenith angle) of the antenna device 100 of FIG. 4(a) for angles 0° and 90° in the azimuth plane, in comparison with a similar antenna device that has no resistive sheet 103. It can be seen that ripples on the radiation pattern are reduced for the antenna device 100 of FIG. 4(a).

FIG. 5 shows an exemplary antenna device 100 according to this disclosure. Same elements in FIG. 5 and FIG. 1 are labelled with the same reference signs and may be implemented likewise. FIG. 5(a) shows an antenna device 100 with a metallization 501 of a plastic, which forms the antenna aperture plane 101 or wherein the antenna aperture plane 101 comprises the surface plane of the metallized plastic. The antenna device 100 further comprises a horn antenna 102 formed on the metallized plastic. The horn antenna 102 is, as an example, sandwiched by two resistive sheets 103, wherein one resistive sheet 103 is arranged on each side of the antenna 102. FIG. 5(b) shows the radiation pattern (gain in dB vs. zenith angle) of the antenna device 100 of FIG. 5(a) for angles 0° and 90° in the azimuth plane, in comparison with a similar antenna device that has no resistive sheet 103. It can be seen that ripples on the radiation pattern are reduced for the antenna device 100 of FIG. 5(a).

The antenna devices 100 shown in the FIGs. 2-5 enjoy at least the following advantages. Surface waves on the PCB-based and waveguide-based aperture planes 101 are reduced. This leads to a smoother radiation pattern in the azimuth plane. The antenna devices 100 do not need blind antennas or grooves on the horn antennas, making their fabrication processes easier. The antenna devices 100 provide the possibility to define more complex (e.g., printed) shapes of the resistive sheets 103, in order to optimize the surface wave reduction for each individual antenna device 100.

FIG. 6 shows an exemplary antenna device 100 according to this disclosure. Same elements in FIG. 6 and FIG. 1 are labelled with the same reference signs and may be implemented likewise. FIG. 6 shows that the surface wave reduction also improves the mutual coupling between nearby antennas 102, thus improving the overall antenna device/system performance. The exemplary antenna device 100 shown in FIG. 6(a) includes the PCB 201 and includes two PCB zig-zag antennas 102. The two antennas 102 are placed at a distance of 7.9mm (2k) from another. Further, the antenna device 100 comprises three resistive sheets 103, wherein one resistive sheet 103 is arranged between the antennas 102. As an example, this resistive sheet 103 has a resistivity of 250Q/square. FIG. 6(b) shows clearly that the coupling (scattering parameters in dB vs. frequency in GHz) is lower - in this example by approximately 5 dB at 76.5 GHz - compared to a similar antenna device that has no resistive sheet 103 between the antennas 102.

The reduction of the mutual coupling, which is obtained by exploiting the advantage of the surface wave reduction caused by the resistive sheets 103, may be important in an antenna radar system, for instance, for an automotive. For example, a strong coupling between a transmitter and a receiver can cause leakage in the receiver chain, and can block the detection of a target placed at a short distance with respect to the radar antenna system.

The solution of this disclosure is suitable for automotive radar antenna systems, either based on PCB antenna devices or waveguide antenna devices, as explained above. However, the solution of this disclosure can also been applied to any type of antenna device, which has a common antenna aperture plane 101, on which surface waves are excited, and on which it is possible to arrange one or more resistive sheets 103.

The way to apply these resistive sheets 103 is independent from the general solution of this disclosure, and is related to the manufacturing technology of the antenna device 100. For example, one or more graphene coatings may be used. However, more generally, any lossy material with any value of resistivity can be used to form a resistive sheet 103. Other examples to manufacture the one or more resistive sheets 103 include resistive pastes, lossy alloy(s), and special treatment(s) of metals that make the metals lossier (increase their resistivity value).

The present disclosure has been described in conjunction with various exemplary implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.