Antenna structure for a radar sensor

Abstract

The invention relates to an antenna structure (10) for a radar sensor, having rows of antenna patches (14, 16) arranged in a comb, which are constructed in microstrip technology on a substrate (18) in a single layer, the width of the antenna patches, measured in the row direction, varying along the row, characterized in that the antenna patches (14, 16) overlap one another in a direction transverse to the rows, a feed network (12) switching on the antenna patches alternately on opposite sides.

Description

Technical Field

[0001] The present invention relates to an antenna structure for a radar sensor having rows of antenna patches arranged in a comb shape and constructed in a single layer on a substrate using microstrip technology, wherein the width of the antenna patches, measured in the row direction, varies along the row.

[0002] In particular, the present invention relates to an antenna structure for a radar sensor disposed in a corner of a motor vehicle body for monitoring traffic conditions in front of and to one side of the vehicle. Correspondingly, the radar sensor should have the widest possible azimuth angle range with the most uniform sensitivity, while the radar beam should be well focused in terms of elevation, thereby achieving high sensitivity for objects located at the radar sensor height in an almost horizontal plane. Background Technology

[0003] Two basic types of antenna structures suitable for this application are known from practice.

[0004] In the first basic type, the antenna patch, similar to the teeth of a comb, is arranged only on one side of a straight feed line that extends vertically in the mounting position. Therefore, this arrangement has a large aperture along the vertical line, through which good focusing of radar radiation is achieved in the elevation angle. Conversely, in the azimuth angle, this arrangement has a very small aperture and correspondingly a wide azimuth angle range. However, a disadvantage is that detection performance is unstable in real-world installations because distortion in the antenna profile can easily occur due to refraction or obstruction of radar radiation caused by other vehicle components or by the radar sensor radome.

[0005] In the second basic type, antenna patches are alternately arranged on opposite sides of the feed line. Since the spacing between antenna patches on the same side of the feed line should approximately correspond to the wavelength of the radar radiation, the total number of antenna patches in this embodiment is approximately twice that in the first basic type, making the structure less susceptible to localized near-field radar interference. However, the dual-sided arrangement of the antenna patches creates a larger aperture in terms of azimuth, resulting in stronger radar radiation focusing, which is undesirable for the application purposes described here.

[0006] Antenna structures are also known in which the feed network has two parallel feed lines and the antenna patches are comb-shaped and interlocked (A. Pirhadi, “DESIGN OF MODIFIED MICROSTRIP COMBLINEARRAY ANTENNA FOR AVIONIC APPLICATION”, Progress In Electromagnetics Research Letters, Vol. 14, pp. 31-40, 2010). If the antenna patches are fed in series from one end of the feed lines, a load for impedance matching is required at the opposite end of the feed lines, resulting in power loss. In other antenna structures of this type (Mohammad Mosalanejad, Ilja Ocket, Charlotte Soens and Guy AEVandenbosch: "Wideband Compact Comb-Line Antenna Array for 79GHz Automotive Radar Applications", IEEE ANTENNAS AND WIRELESS PROPAGATIONLETTERS, Vol. 17, No. 9, September 2018), multi-layered high-frequency substrates are required. Summary of the Invention

[0007] The objective of this invention is to provide an antenna structure that has a small aperture in terms of azimuth angle and enables stable operation of a radar sensor with a simple construction.

[0008] According to the present invention, this task is accomplished by having antenna patches overlap each other in a direction transverse to the row, and a feed network alternately connecting the antenna patches from opposite sides.

[0009] By varying the width of the patches, the amplitude curve along the row can be controlled in such a way that side-beams are largely suppressed in terms of elevation. Furthermore, the configuration of the feed network allows for tuning of the antenna patches fed alternately on opposite sides, eliminating the need for impedance matching and thus avoiding power loss. Since the antenna patches are essentially arranged in a single row, a small aperture in terms of azimuth is achieved, similar to that in a single-sided antenna structure with only one feed line. However, the number of antenna patches is similarly high to that in a double-sided structure, resulting in high detection stability. In this way, all the requirements for corner radar used in motor vehicles are met with a single-layer antenna structure.

[0010] The following describes the advantageous configurations.

[0011] In one embodiment, the feed network has two parallel feed lines that alternately connect to the antenna patch every other antenna patch.

[0012] In another embodiment, the feed network has two parallel feed lines, which are connected to a common signal input terminal at one end via a power branching element.

[0013] In another embodiment, the feed network has only a single feed line; however, this feed line is either zigzag or meandering. The feed line is extended so that the antenna patches are alternately connected on opposite sides. In this case, the construction and operating principle of the antenna structure are roughly similar to the conventional structure, in which the antenna structure is arranged on both sides. However, this is achieved by extending the feed line in a zigzag pattern: the antenna patches overlap each other, thus significantly reducing the aperture in terms of azimuth.

[0014] In another embodiment, the single feed line extends in a straight line through the section that connects the two successive antenna patches.

[0015] In another embodiment, the single feed line is connected to the feed point at one end via an impedance matching unit.

[0016] In another embodiment, the overlap between antenna patches is at least 30%, preferably at least 40%, in the direction transverse to the row.

[0017] The following describes the embodiments in more detail based on the drawings. Attached Figure Description

[0018] The attached diagram shows:

[0019] Figure 1 An antenna structure according to a first embodiment of the present invention is shown;

[0020] Figure 2 and Figure 3 An example of a conventional antenna structure is shown;

[0021] Figure 4 An antenna structure according to another embodiment of the present invention is shown;

[0022] Figure 5 Showing for according to Figures 1 to 4 The power / frequency curve of the antenna structure;

[0023] Figure 6 Showing for according to Figures 1 to 4 An elevation angle curve diagram of the antenna structure;

[0024] Figure 7 Showing for according to Figures 1 to 4 An azimuth antenna curve diagram of the antenna structure. Detailed Implementation

[0025] Figure 1 An antenna structure 10 according to a first embodiment of the present invention is shown. This antenna structure is configured for a corner radar of a motor vehicle and is formed by rows of a feed network 12 and antenna patches 14, 16, which are constructed as a single layer on a substrate 18 using microstrip technology. In the radar sensor mounting position, the rows of antenna patches 14, 16 extend vertically. The feed network 12 has two parallel, linearly extending feed lines 20, 22, which are connected at one end to a common feed point 26 via a power branch element 24.

[0026] Antenna patch 14 is perpendicular to feed line 20 in the direction toward feed line 22 and has almost the same length. Figure 1 The width of the antenna patch 14 (measured horizontally) varies and generally decreases from the center of the feed line 20 towards both ends. The spacing between the antenna patches 14 is approximately the wavelength λ of the transmitted signal propagating in the feed line 20. At the free ends (in... Figure 1 In the upper part, the feed line 20 terminates at one of the antenna patches 14, and the feed line is not terminated by an impedance matching mechanism there, causing the radar signal to be reflected at this end of the feed line. Thus, a standing wave is generated in the feed line, the antinode of which is located at the position of the antenna patch 14 through which the radar signal is transmitted. Due to the large aperture of the antenna patch 14, the emitted signal is well focused in terms of elevation. The width of the antenna patch 14 determines the amplitude curve in the vertical direction, and this width is chosen such that sidebeams are largely suppressed.

[0027] Antenna patch 16 is positioned at a right angle away from the other feed line 22, more specifically away in the direction toward feed line 20, such that antenna patches 14 and 16 are comb-shaped and interlocked. The overlap of antenna patches 14 and 16 in the direction transverse to feed lines 20 and 22 is at least 30%, preferably at least 40%. Antenna patches 16 are also arranged at a spacing of wavelength λ, having the same length but varying widths, such that the beam is also suppressed therein. At the free end, feed line 22 also terminates at one of the antenna patches 16 and does not terminate there via an impedance matching unit, such that a standing wave is also generated in that feed line, with the antinodes of the standing wave located at the position of antenna patch 16. The first antenna patch 16 and the power branch element 24 are connected by a tuning unit 28 (a component of feed line 22), the length of which determines the phase relationship between the oscillations in antenna patch 16 (on the one hand) and the oscillations in antenna patch 14 (on the other hand). Generally, the length of the tuning unit 28 is chosen such that the oscillation at a location on the feed line is out of phase with the oscillation in the feed line 20, where the antenna patch 16 is located away from the feed line. However, since the antenna patch is located away from its corresponding feed line in the opposite direction, the emitted radar radiation is in phase.

[0028] Since the overlapping antenna patches 14 and 16 form essentially a single row in the vertical direction, the antenna arrangement has a small aperture in the azimuth angle, resulting in a wide positioning angle range for the radar sensor.

[0029] For comparison, Figure 2 and Figure 3 Two conventional antenna structures are shown.

[0030] exist Figure 2 The image shows an antenna structure 30 with antenna patches 34, all of which are oriented to the same side away from the straight feed line 40. This arrangement is similar to... Figure 1 The right branch (Ast) of the antenna structure 10 shown is similar. Here, the antenna patches 34 also form only a single row, which has a small aperture in terms of azimuth, thus producing a wide positioning angle range. However, the number of antenna patches 34 (five in this embodiment) is only approximately Figure 1 The antenna patches 14 and 16 account for half of the total number, which makes the detection performance less stable under real-world usage conditions when the antenna structure 30 is used.

[0031] Figure 3 An antenna structure 50 with antenna patches 54 and 56 is shown, the antenna patches being oriented away from a common feed line 60 towards opposite sides. Transmission performance and... Figure 1The transmission performance of antenna structure 10 in the model is roughly similar; however, Figure 3 The structure in the middle has a larger aperture in terms of azimuth angle, which makes the radar radiation more focused and thus produces a narrower positioning angle range.

[0032] Figure 4 An antenna structure 70 according to another embodiment of the present invention is shown. This antenna structure has a feed network 72 and antenna patches 74, 76, said antenna patches being connected to… Figure 3 Similarly, they originate from a common feed line 80, facing opposite sides. However, this feed line 80 extends in a zigzag pattern, allowing antenna patches 74 and 76 to be connected to alternately opposite sides. Figure 4 In this configuration, the patches are connected by straight sections of the feed line. However, the feed line can optionally be curved.

[0033] The vertical spacing between two adjacent antenna patches 74 and 76 is approximately λ / 2. The feed line 80 is in... Figure 4 The lower end of the feed line is connected to the feed point 86 via an impedance matching unit 84. The free (upper) end of the feed line terminates at one of the antenna patches 74, and there is no termination via an impedance matching element, resulting in a standing wave with antinodes at the locations of antenna patches 74 and 76. The total number of antenna patches 74 and 76 (with the same aperture in terms of elevation angle) is... Figure 1 and Figure 3 The total number of elements is the same, ensuring stable performance. However, due to the zigzag extension of the feed line 80, the aperture ratio in terms of azimuth angle is different. Figure 3 The small in the middle makes it comparable to Figure 1 Similarly, a wide range of positioning angles can be obtained.

[0034] exist Figure 5 In the middle, for in Figures 1 to 4 The antenna structures 10, 30, 50, and 70 shown are plotted relative to the frequency, representing the strength (in dB) of the signal generated by reflections at the free ends of the feed lines. The smaller the reflection, the greater the power transmitted through the antenna patch. Therefore, in the operating frequency band of the radar sensor (between 76 GHz and 77 GHz), the reflection should be less than -10 dB. It can be seen that this condition is satisfied not only for conventional antenna structures 30 (thin solid line) and 50 (thin dashed line), but also for antenna structure 10 (thick solid line) and antenna structure 70 (thick dashed line).

[0035] exist Figure 6In the diagram, for four antenna configurations of 10, 30, 50, and 70°, antenna curves (antenna gain in dB as a function of elevation angle) are shown. It can be seen that for all four antenna configurations, good focusing of the radar signal is achieved around an elevation angle of 0°, with only relatively insignificant sidebeams. Furthermore, it can be seen that, according to... Figure 4 With the antenna structure 70 (thick dashed line), particularly effective suppression of side beams is achieved.

[0036] exist Figure 7 In the diagram, antenna curves in terms of azimuth are shown for four antenna structures 10, 30, 50, and 70. It can be seen that for antenna structures 10 and 70 according to the invention (thick solid and thick dashed lines), due to the smaller aperture, significantly less focusing is produced compared to antenna structure 50, resulting in a wider positioning range. On the other hand, in the case of antenna structures 10 and 70 according to the invention, the overall gain is greater than in the case of antenna structure 30, especially at azimuth angles between +20° and +40° and between -20° and -40°.

Claims

1. An antenna structure (70) for a radar sensor, the antenna structure having rows of comb-shaped antenna patches (74, 76) constructed monolayer on a substrate (18) using microstrip technology, the width of the antenna patches, measured in the row direction, varying along the row, wherein, The antenna patches (74, 76) overlap each other in a direction transverse to the row, and a feed network (72) alternately connects the antenna patches from opposite sides, wherein the feed network (72) has a single feed line (80) that extends in a zigzag pattern, such that the single feed line alternately connects the antenna patches (74, 76) from opposite sides, wherein the overlap of the antenna patches (74, 76) is achieved by the zigzag extension of the feed line (80).

2. The antenna structure (70) according to claim 1, wherein, The feed line (80) extends linearly through the sections that connect two successive antenna patches (74, 76).

3. The antenna structure (70) according to claim 1 or 2, wherein, The feed line (80) is connected to the feed point (86) at one end via an impedance matching unit (84).

4. The antenna structure (70) according to claim 1 or 2, wherein, The overlap between the antenna patches (74, 76) is at least 30% in the direction transverse to the row.

5. The antenna structure (70) according to claim 4, wherein, The overlap between the antenna patches (74, 76) is at least 40% in the direction transverse to the row.

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