Radar array

Abstract

A radar array configured to transmit and receive radar waves with a center wavelength λ comprises a plurality of antenna arrays. Each of these arrays comprises a patch antenna with a plurality of notches and at least one pair of parasitic patches arranged mirror-symmetrically at opposite ends of the patch antenna. A radar array configured to transmit and receive radar waves comprises a plurality of such antenna arrays. The antenna arrays are arranged in two rows (R1, R2) as receiving antennas or in two rows (R1, R2) as transmitting antennas, with a spacing between the rows being λ and a spacing between two antenna arrays within a row being 2λ. All notches of the patch antennas are arranged on the same side of the radar array.The parasitic patches each have at least one incision on two opposite sides, these incisions being orthogonal to the longitudinal axis (L1, L2) of the row (R1, R2).

Description

[0001] The present invention relates to a radar array having the antenna arrangements required for a radar sensor. State of the art

[0002] Radar sensors for imaging require high operating bandwidths, as their resolution is defined by the frequency bandwidth. A higher bandwidth thus improves the separation of consecutive objects. This is why they are referred to as ultra-wideband applications. Arrays with multiple antennas are particularly suitable for such applications.

[0003] Implementing such radar sensors with external broadband antennas that cannot be integrated into a circuit board layout results in significant connectivity complexity, unsuitable overall system dimensions, and high costs. Current planar antennas for board integration have the following disadvantages: Spiral antennas have a high bandwidth, but are circularly polarized and ineffective in their radiation due to their traveling wave characteristics.

[0004] Bowtie antennas are broadband, but their main radiation direction is not orthogonal to the circuit board, which impairs suitable directivity for radar applications. Log-periodic planar antennas are broadband, but their individual arms are already on the order of magnitude of an antenna array, making multi-antenna grids unsuitable for them.

[0005] Different designs of patch antennas are described in Gatti et al., Single-Layer Line-Fed Broadband Microstrip Patch Antenna on Thin Substrates, Electronics 2021, 10, 1037. Such patch antennas have a limited bandwidth, which can only be inadequately increased by subdividing the pad with slots.

[0006] US 11 539 139 B1 describes radar arrays with patch antennas that have parasitic patches.

[0007] It is an object of the present invention to provide a radar array for imaging methods that has multiple antenna arrangements with a design that can be accommodated multiple times in a gridable array for an ultra-wideband application as a planar printed circuit board design, while not having a complicated geometry. It is intended to achieve a wider bandwidth than conventional patch antennas. Disclosure of the invention

[0008] This task is solved by a radar array with multiple antenna arrangements, each comprising a patch antenna with multiple notches. These notches divide the patch antenna into several resonators. At least one pair of parasitic patches is arranged mirror-symmetrically at opposite ends of the patch antenna. This allows a multitude of resonators of different lengths to be realized, resulting in a broadband multi-resonator structure that can be adjusted via geometric parameters. The different lengths enable the antenna arrangement to resonate over a wide frequency range, in particular from 57 to 64 GHz, and thus to operate actively as an antenna there. Adapting the resonators to other frequency ranges can be achieved by adjusting their length.The parasitic patches each have at least one notch on two opposite sides, with these notches running orthogonally to the longitudinal axis of the row. This allows the parasitic patches to be mirror-symmetrical.

[0009] The notches of the patch antenna are preferably arranged axially symmetrically to a feed line of the patch antenna. This also results in symmetrical radiation for the H-field. If the patch antenna is fed from the side rather than below, symmetry is not possible due to the one-sided feed from a feed line orthogonal to the feed line. The radiation pattern of the present antenna arrangement corresponds closely to that of a typical rectangular patch antenna, thus achieving the same rotationally symmetric radiation as with a pure patch.

[0010] Furthermore, it is preferred that the patch antenna has first notches that border the feed line and second notches that are arranged parallel to the first notches. The feed point of the patch antenna can be optimized via the length of the first notches. This adjustment is particularly preferably carried out such that the electrical impedance at the feed point of the patch antenna is in the range of 40 Ω to 60 Ω and most preferably is 50 Ω. Typically, a patch antenna has a high impedance at its edge, while the impedance in the center of the patch antenna is 0 Ω. Due to the length of the first notches, the impedance of the patch antenna can be adapted to the impedance of the feed line, which is in particular a microstrip line with inset feed. This eliminates the need for a transformation network to adapt the high impedance of the patch antenna to the impedance of the feed line.The second notches separate the resonators from each other. Their length allows the impedance matching of the outer resonators to be adjusted.

[0011] The parasitic patches allow the normally limited bandwidth of the patch antenna to be increased beyond the frequency limits that can be set for bandwidth adjustment simply by making cuts in the patch antenna.

[0012] It is preferred that the notches of the parasitic patches are arranged on sides that do not border the patch antenna. They run, in particular, parallel to the notches of the patch antenna. Furthermore, they run, in particular, parallel or orthogonal to a feed line of the patch antenna.

[0013] The parasitic patches are not electrically connected to the feed line. Rather, they are electrically isolated from the patch antenna by an air gap. The width of the air gap between the patch antenna and a parasitic patch is, in particular, less than 10% of the length of the side of the patch antenna facing the parasitic patch.

[0014] The antenna array is designed for easy integration into a printed circuit board layout. For this purpose, a conductive patterned layer is preferably provided, which is arranged on a dielectric substrate, in particular a single-layer one. On the back of the substrate, there is another full-surface conductive layer that serves as a ground plane. This design makes it possible to transmit and receive directional and rear-shielded signals, while the antenna array remains compact and cost-effective.

[0015] The radar array is configured to transmit and receive radar waves with a center wavelength λ. The antenna arrays can be used as transmitting antennas and / or as receiving antennas. These are preferably configured to form a MIMO (Multiple Input Multiple Output) system, thus providing a plurality of virtual antenna pairs.

[0016] The antenna arrays configured as receiving antennas are arranged in two rows. The antenna arrays configured as transmitting antennas can also be arranged in two rows. The spacing between the two rows is λ. The spacing between two antenna arrays within a row is 2λ. This can increase the resolution of the radar sensor and compensate for the effect that the antenna array has an increased width compared to a patch antenna without parasitic patches.

[0017] In each row, the patch antennas and the parasitic patches are preferably located on the longitudinal axis of the row.

[0018] All patch antenna notches are located on the same side of the radar array. This is the side of the row to which the feedlines extend. The feedlines of one row extend from the antenna arrays toward their edges, and the feedlines of the adjacent row extend between two antenna arrays in the first row in the same direction as the feedlines of the first row.

[0019] In all embodiments of the radar array, this enables high resolution and depth of field of radar images for imaging radar sensors. Short description of the drawings

[0020] Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Fig. 1 shows a patch antenna according to the prior art. Fig. Figure 2 shows another patch antenna according to the prior art. Fig. 3 shows an antenna arrangement for a radar array according to an embodiment of the invention. Fig. 4 shows a diagram in which the input reflection coefficients of the patch antennas are plotted according to the Fig. 1 and Fig. 2 and the antenna arrangement according to Fig. 3 can be compared with each other. Fig. 5 shows an array of multiple antenna arrangements for a radar sensor according to an embodiment of the invention. Fig. 6 shows a diagram of a possible implementation of the MIMO approach of the radar array according to Fig. 5. Embodiments of the invention

[0021] In the Fig. 1 and Fig. 2 shows microstrip fed patch antennas as known from Gatti et al., Single-Layer Line-Fed Broadband Microstrip Patch Antenna on Thin Substrates, Electronics 2021, 10, 1037. The patch antenna 10 according to Fig. 1 has a feed line 11 that terminates at a feed point 12 at one edge of the patch antenna 10. Through notches 13a, 13b on both sides of the feed line 11, the feed point 12 was adjusted to an electrical impedance of 50 Ω. Beyond the two notches 13a, 13b, the patch antenna 10 has two resonators 14a, 14b.

[0022] The patch antenna according to Fig. 2 differs from the patch antenna 10 according to Fig. 1 in that it has two further notches 15a, 15b, which run parallel to the first two notches 13a, 13b. This forms a pair of resonators 14a, 16a and 14b, 16b on each side of the feed line 11. The outer resonators 16a, 16b are shorter than the inner resonators 14a, 14b, which, compared to the patch antenna 10 according to Fig. 1 an increase in bandwidth is achieved.

[0023] Fig. Figure 3 shows an antenna arrangement for a radar array according to an embodiment of the invention. This comprises a patch antenna 10 as shown in Fig. 2. Beyond each of its two outer resonators 16a, 16b, a parasitic patch 20a, 20b is arranged. This patch has a first resonator 21a, 21b, which is separated from a second resonator 23a, 23b by a notch 22a, 22b. The two resonators 21a, 23a-b have different lengths. A further notch 24a-b is arranged opposite the first notch 22a-b, which points in the same direction as the notches 13a-b, 15a-b of the patch antenna, so that the two parasitic patches 20a-b are each mirror-symmetrical. Their second resonator 23a-b is separated from the outer resonator 16a-b of the patch antenna 10 by an air gap 25a-b. The air gap 25a-b has a width of 100 µm.

[0024] In Fig. 4 is for a first comparative example VB1 using the patch antenna according to Fig. 1, a second comparative example VB2 using the patch antenna according to Fig. 2 and an example B1 according to the invention using the antenna arrangement according to Fig. 3 shows the input reflection coefficient S11 in a frequency range f from 54 to 67 GHz. The input reflection coefficient represents a measure of the broadband capability of the antenna array. The bandwidth is defined as the range where S11 is less than -10 dB. The frequency ranges of lower reflection are the frequency ranges in which the antenna array actively radiates. Fig. 4 it can be seen that by providing the parasitic patches in the antenna arrangement according to the invention, the bandwidth of the patch antenna can be significantly increased.

[0025] In a radar array according to an embodiment of the invention, two parallel rows R1, R2 of mutually offset antenna arrangements according to Fig. 3. All patch antennas 10 and parasitic patches 20a, 20b are each located together on the longitudinal axis L1, L2 of their respective rows R1, R2. The distance between the two rows R1, R2 is λ, where λ is the mean wavelength of the radar waves emitted by the radar array. The distance between two antenna arrangements within each row is 2λ, with the two rows being offset from each other by the length λ. All feed lines 11 are continued in the radar array in the same direction, so that the feed lines of the first row R1 cross the second row R2, while the feed lines of the second row R2 are continued from the edge of the antenna arrangement array. This arrangement of antenna arrangements, which are in Fig. 5, can function as receiving antennas within the radar array. Another arrangement of antenna arrays, not shown, can function as transmitting antennas within the radar array.

[0026] This radar array functions as a MIMO system. Fig. Figure 6 shows the position of several antenna arrays in an xy coordinate system of the radar array. The transmitting antennas are arranged in a single row at the top and the receiving antennas are arranged in two rows at the bottom according to Fig. 5. A multitude of virtual antenna pairs are formed between the transmitting and receiving antennas, whose y-coordinates are located around a value of 0.050 m. These are derived from the centers of all connecting lines between each transmitting antenna and each receiving antenna. The virtual antenna pairs are substitute positions that act outwardly like a transmitting / receiving construct, as if a bidirectional antenna were present.

[0027] The radar array according to the embodiment can be used for imaging processes to separate objects lying one behind the other.

Claims

[1] A radar array configured to transmit and receive radar waves having a mean wavelength λ, comprising a plurality of antenna arrays, each comprising a patch antenna (10, 40) with a plurality of notches (13a-b, 15a-b, 43a-b, 44a-b, 46a-b, 47a-b) and at least one pair of parasitic patches (20a-b, 30a-d) arranged mirror-symmetrically at opposite ends of the patch antenna (10, 40), wherein the antenna arrays are arranged in two rows (R1, R2) as receiving antennas or in two rows (R1, R2) as transmitting antennas, wherein a distance between the rows is λ and a distance between two antenna arrays within a row is 2λ, characterized bythat all the notches (13a-b) of the patch antennas (10) are arranged on the same side of the radar array and the parasitic patches (20a-b) each have at least one notch (22a-b, 24a-b) on two opposite sides, these notches (22a-b, 24a-b) running orthogonal to the longitudinal axis (L1, L2) of the row (R1, R2). [2] Radar array according to claim 1, characterized by that the notches (13a-b, 15a-b, 43a-b, 44a-b, 46a-b, 47a-b) of the patch antenna (10, 40) are arranged axially symmetrically to a feed line (11, 41) of the patch antenna (10, 40). [3] Radar array according to claim 2, characterized by that the patch antenna (10, 40) has first notches (13a-b, 43a-b) which are adjacent to the feed line (11, 41) and second notches (15a-b, 46a-b) which are arranged parallel to the first notches (13a-b, 43a-b). [4] Radar array according to claim 3, characterized bythat an amount of electrical impedance at a feed point (12, 42) of the patch antenna is in the range of 40 Ω to 60 Ω. [5] Radar array according to one of claims 1 to 4, characterized by that the incisions (22a-b, 32a-d) of the parasitic patches (20a-b, 30a-d) are each arranged on sides which do not adjoin the patch antenna (10, 40). [6] Radar array according to one of claims 1 to 5, characterized by that a width of an air gap (25a-b) between the patch antenna (10) and a parasitic patch (20a-b) is in each case less than 10% of a length of the side of the patch antenna (10, 40) facing the parasitic patch (20a-b, 30a-d). [7] Radar array according to one of claims 1 to 6, characterized by that in each row (R1, R2) the patch antennas (10) and the parasitic patches (20a-b) are located on the longitudinal axis (L) of the row.

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