Circularly polarized scanning grid array based on wideband 90° balun

Abstract

This invention discloses a circularly polarized scanning grating array based on a broadband 90° balun, belonging to the field of microwave antenna technology. The array consists of a grating array of circularly polarized antenna elements. Each circularly polarized antenna element includes, from top to bottom, a radiating patch layer, a first dielectric substrate, an air gap layer, a metal ground layer, a second dielectric substrate, and a feed network layer. This circularly polarized antenna element uses a rotated microstrip patch as the radiator and employs a metal back cavity to achieve stable unidirectional radiation. This structure effectively reduces coupling between elements after antenna array assembly. The lower-layer feed network uses a 180° power divider phase shifter combined with an ultra-wideband phase shifter, which can greatly achieve broadband phase shifting, thereby widening the impedance bandwidth and axial ratio bandwidth of the circularly polarized antenna.

Description

Technical Field

[0001] This invention belongs to the field of microwave antenna technology, specifically relating to a circularly polarized scanning grid array based on a broadband 90° balun. Background Technology

[0002] Wideband phased arrays have important applications in many fields. The rapid advancement of modern communication technology has led to increasingly wider frequency hopping ranges and higher hopping rates. If an antenna's performance only has a narrow operating bandwidth, it can no longer meet the requirements of various users for modern communication. In the radar field, wideband phased array technology is an important way to solve problems such as multi-target resolution, target identification, and attribute judgment. Its improvement in radar anti-jamming capabilities is of great significance to the military field. In the communications field, the increased bandwidth of phased arrays increases the channel capacity and avoids channel congestion. In multi-functional applications, the wider bandwidth allows phased arrays to perform detection, electronic countermeasures, and communication functions simultaneously, making multi-functional integrated phased arrays possible.

[0003] Based on the way the electric field direction changes, antennas can be classified into linear polarization, circular polarization, and elliptical polarization. Compared to linearly polarized antennas, circularly polarized antennas have many advantages. Linearly polarized waves are prone to polarization deflection and energy loss when passing through rain and fog, while circularly polarized waves, upon encountering obstacles in rain and fog, exhibit reverse polarization and are isolated from the incident wave, thus possessing strong anti-interference and anti-attenuation capabilities. Circularly polarized waves can be received simultaneously by both horizontally and vertically polarized antennas. Therefore, circularly polarized phased array antennas have better anti-interference and anti-rain / fog attenuation capabilities and are widely used in satellite communications.

[0004] Therefore, researching broadband circularly polarized phased array antennas, so that the array antennas composed of them can achieve large-angle circular polarization scanning, has significant research and engineering significance.

[0005] Patent application number 201910692191.5 discloses a broadband circularly polarized array antenna, whose central feed network includes a square patch with an opening. Each of the four corners of the square patch is connected to a branch-shaped patch, and these branch-shaped patches are arranged in a structure rotated 90°. This structure achieves advantages such as wide impedance matching bandwidth, wide axial ratio bandwidth, and good circular polarization characteristics. However, this antenna is relatively large, making it inconvenient to form an array antenna, and it does not consider the coupling between antenna elements, thus lacking the potential to form an antenna array.

[0006] Patent document CN114665254A (application number 202111446979.1) discloses a sequentially phase-fed broadband circularly polarized array antenna and its wearable device, wherein one side of the dielectric substrate is a radiating element and the other side is a coupling slot element. This antenna achieves the characteristics of low profile and stable performance, but its impedance bandwidth and axial ratio bandwidth are not wide enough, which limits its application in broadband applications.

[0007] Currently, there is relatively little research on ultra-wideband circularly polarized scanning arrays, and further in-depth research is needed on how to achieve wide-angle scanning with ultra-wideband circular polarization. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a circularly polarized scanning grid array based on a broadband 90° balun. The antenna array of this invention consists of a grid array of circularly polarized antenna elements. Each circularly polarized antenna element is divided into a radiator, a metal back cavity, and an ultra-wideband feed network. A rotating microstrip patch is used as the radiator, and a metal back cavity is employed to achieve stable unidirectional radiation. This structure can effectively reduce the coupling between elements after the antenna array is assembled. The lower-layer feed network uses a 180° power divider phase shifter combined with an ultra-wideband phase shifter, which can greatly improve the antenna impedance bandwidth and axial ratio bandwidth.

[0009] The technical solution adopted in this invention is:

[0010] A circularly polarized scanning grid array based on a broadband 90° balun is characterized in that the array is composed of a grid array of circularly polarized antenna elements.

[0011] The circularly polarized antenna unit includes, from top to bottom, a radiating patch layer, a first dielectric substrate, an air gap layer, a metal ground layer, a second dielectric substrate, and a feed network layer.

[0012] The radiating patch layer includes four 90° rotationally symmetrical radiating patches disposed on the upper surface of the first dielectric substrate; each radiating patch is provided with a feed point, and an annular coupling slit is provided outside the feed point, the equivalent parasitic capacitance is used to offset the inductive effect brought by the feed copper pillar.

[0013] The feed network layer has a centrally symmetrical structure and is used to feed signals of equal amplitude and phase difference of 90° to four radiating patches; it includes a 180° power divider phase shifter, two T-junction power dividers, two broadband 90° baluns, and two bent microstrip lines.

[0014] The center of the 180° power divider phase shifter coincides with the center of the circularly polarized antenna element, and includes a feed slot and two symmetrically arranged gradient microstrip lines on both sides of the feed slot; the two output terminals of the 180° power divider phase shifter are respectively connected to a T-junction power divider.

[0015] One output terminal of the T-junction power divider is connected to the input terminal of the bent microstrip line, and the other output terminal is connected to a broadband 90° balun.

[0016] The broadband 90° balun is composed of a first coupling line and a second coupling line with an electrical length of 90° arranged in parallel. One end of the first coupling line and the second coupling line is connected to the short-circuit point through a first microstrip line, the other end of the first coupling line is connected to the output terminal of the T-junction power divider, and the other end of the second coupling line is connected to the feed point of the radiating patch through a feed copper pillar.

[0017] The short-circuit point is connected to the metal grounding layer through a metal through-hole.

[0018] The output end of the bent microstrip line is connected to the feed point of the radiating patch via a feed copper pillar.

[0019] Furthermore, the radiating patch is a rectangular metal patch with an aspect ratio of 2.3-2.6; the feed point is located at the center of the short side of the rectangular patch adjacent to the edge of the circularly polarized antenna element.

[0020] Furthermore, the first dielectric substrate is of type R5880, has a dielectric constant of 2.2, and a dielectric substrate thickness of 5.2 mm; the second dielectric substrate is of type RO4350B, has a dielectric constant of 3.48, and a dielectric substrate thickness of 0.508 mm.

[0021] Furthermore, each bend in the bent microstrip line is a 90° bend, and the outer corner of the 90° bend is chamfered to reduce the discontinuity of the microstrip transmission line at the bend.

[0022] Furthermore, a metal fence is provided around the outer side of the circularly polarized antenna element to improve the stability of the antenna pattern, while reducing the coupling effect between the circularly polarized antenna elements in the array and improving the scanning effect of the antenna array.

[0023] In this invention, when the circularly polarized antenna element is fed through a feed slot, the excitation signal is split into two equal-amplitude signals with a 180° phase difference by a 180° power divider phase shifter. This 180° power divider phase shifter has a natural 180° phase difference and can maintain good phase consistency over a wide bandwidth. Combined with a T-junction power divider, it achieves four-way power division while widening the bandwidth. An ultra-wideband 90° balun can achieve ultra-wideband 90° phase shift with good phase consistency, but it is not an exact 90° phase shift; therefore, it is further adjusted and optimized by combining it with a bent microstrip line. Then, the aforementioned structures are combined to form a feed network that enables sequential rotational feeding of the antenna at 0°, 90°, 180°, and 270°, improving the axial ratio characteristics of the antenna element. Finally, the radiating patch is fed through copper pillars and metal vias to radiate a left-hand circularly polarized wave. Because the broadband feed network of this invention has broadband phase shift characteristics, the antenna has a very high axial ratio bandwidth.

[0024] The beneficial effects of this invention are:

[0025] (1) This invention proposes a circularly polarized scanning grid array based on a broadband 90° balun. Its unit structure is different from that of a general microstrip patch antenna. It adopts a metal back cavity structure, which can reduce the coupling effect between units in the array.

[0026] (2) The antenna unit proposed in this invention adopts a combination of 180° power divider phase shifter and broadband 90° balun feed to achieve ultra-wideband circular polarization, achieving 53% impedance bandwidth and 44% 3dB axial ratio bandwidth.

[0027] (3) The circularly polarized scanning grid array based on a broadband 90° balun proposed in this invention has a gain drop of less than 6dB when scanning to ±50°. Attached Figure Description

[0028] Figure 1 This is a structural diagram of the antenna element described in this invention;

[0029] Figure 2 This is a top view of the antenna element described in this invention;

[0030] Figure 3 This is a side view of the antenna element described in this invention;

[0031] Figure 4 This is a bottom view of the antenna unit described in this invention;

[0032] Figure 5 This is a top view of the antenna array described in this invention;

[0033] Figure 6 This is a bottom view of the antenna array described in this invention;

[0034] Figure 7 These are simulation curves of the S-parameters of the antenna element described in this invention;

[0035] Figure 8 This is a simulation curve showing the change in axial ratio of the antenna in the side-firing direction as a function of frequency for the port-fed antenna element described in this invention.

[0036] Figure 9 This is a simulated radiation pattern of the antenna element at 4GHz frequency on the E and H planes of the present invention;

[0037] Figure 10 This is a scan pattern of the antenna array described in this invention, scanning from -50 degrees to 0 degrees in the xoz plane at a frequency of 4 GHz.

[0038] Explanation of reference numerals: 1. First dielectric substrate; 2. Air layer; 3. Ground layer; 4. Second dielectric substrate; 5. Feed point; 6. 180° power divider phase shifter; 7. Bent output microstrip line; 8. T-junction power divider; 9. Wideband 90° balun; 10. Feed copper pillar; 11. Annular coupling seam; 12. Rectangular microstrip patch; 13. Short-circuit copper pillar; 14. First coupling line; 15. Second coupling line; 16. First microstrip line. Detailed Implementation

[0039] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0040] The circularly polarized scanning grid array based on a broadband 90° balun in this embodiment is composed of a grid array of circularly polarized antenna elements, such as... Figure 5 , Figure 6 As shown, the array is arranged in a 4×3 grid pattern, with an element spacing of 0.66 wavelengths in the x-direction and adjacent rows staggered by 0.33 wavelengths in the x-direction, achieving ±50-degree scanning on the xoz plane. Figure 1 , Figure 3 The circularly polarized antenna element of this invention comprises, from top to bottom, a radiating patch layer, a first dielectric substrate, an air gap layer, a metal ground layer, a second dielectric substrate, and a feed network layer. The first dielectric substrate is of type R5880, with a dielectric constant of 2.2 and a substrate thickness of 5.2 mm; the air gap layer has a thickness of 5.2 mm; the second dielectric substrate is of type RO4350B, with a dielectric constant of 3.48 and a substrate thickness of 0.508 mm.

[0041] The radiation patch layer, such as Figure 2 As shown, it includes four 90° rotationally symmetrical rectangular radiating patches disposed on the upper surface of the first dielectric substrate. The long side and short side are 20 mm and 2.1 mm, respectively. The long side is 2.3 mm away from the dielectric substrate, and the short side is 6.3 mm away from the dielectric substrate. A feed point is disposed at the center of the short side of the rectangular radiating patch near the edge of the circularly polarized antenna element. The distance between the feed point and the short side of the rectangular radiating patch is 1 mm. An annular coupling slot with a gap width of 0.3 mm is disposed on its outer side. The equivalent parasitic capacitance is used to cancel the inductive effect brought by the feed copper pillar.

[0042] The power supply network layer, such as Figure 4 As shown, it is a centrally symmetrical structure used to feed signals of equal amplitude and phase difference of 90° sequentially into four rectangular radiating patches; it includes a 180° power divider phase shifter, two T-junction power dividers, two broadband 90° baluns, and two bent microstrip lines.

[0043] The center of the 180° power divider phase shifter coincides with the center of the circularly polarized antenna element, and includes a feed slot and two tapered microstrip lines symmetrically arranged on both sides of the feed slot. The two output terminals of the 180° power divider phase shifter are each connected to a T-junction power divider. The tapered microstrip line is 12mm long, and the feed slot is 1.5mm long.

[0044] One output terminal of the T-junction power divider is connected to the input terminal of the bent microstrip line, and the other output terminal is connected to a broadband 90° balun. The length and width of the output terminal of the T-junction power divider are 11 mm and 0.7 mm, respectively.

[0045] The broadband 90° balun is composed of a first coupling line and a second coupling line with an electrical length of 90° arranged in parallel. One end of the first coupling line and the second coupling line is connected to the short-circuit point through a first microstrip line, the other end of the first coupling line is connected to the output terminal of the T-junction power divider, and the other end of the second coupling line is connected to the feed point of the radiating patch through a feed copper pillar.

[0046] The short-circuit point is connected to the metal grounding layer through a metal through-hole with a radius of 0.5 mm.

[0047] The output end of the bent microstrip line is connected to the feed point of the radiating patch through a feed copper pillar. The width of the bent microstrip line is 1.2 mm, its characteristic impedance is 50 ohms, and the chamfer of the bent microstrip line is 45°.

[0048] Figure 7 This figure shows the simulated S-parameter curves of a circularly polarized antenna element based on a broadband 90° balun, as described in this invention. The figure shows that the center frequency of the antenna element is 4 GHz, at which the input port achieves good matching. The antenna's impedance bandwidth is 53%.

[0049] Figure 8 The figure shows the simulation curve of the axial ratio of a circularly polarized antenna element based on a broadband 90° balun as described in this invention, as well as the frequency variation. As can be seen from the figure, the axial ratio at the center frequency (4GHz) is less than 1.5dB, and the 3dB axial ratio bandwidth is greater than 44%.

[0050] Figure 9 This is a simulated radiation pattern on the E and H planes of a circularly polarized antenna element based on a broadband 90° balun, as described in this invention, at a frequency of 4 GHz. It can be seen that the radiating wave is a left-hand circularly polarized wave with a gain of 8.84 dBi. The beamwidth of the E plane is 67°, the beamwidth of the H plane is 67°, and the radiation patterns of the E plane and the H plane are relatively consistent.

[0051] Figure 10This is a scan diagram of the phased array described in this invention, scanning from -50 degrees to 0 degrees in the xoz plane at 4 GHz. Due to the symmetry of the scan, only the scan results below zero degrees are given. In the figure, when the main beam points to 0°, the gain is 18.3 dBi. As shown in the figure, the array achieves circular polarization scanning covering the entire operating frequency band, with gain fluctuation of less than 6 dB.

[0052] In summary, this embodiment of a circularly polarized antenna element based on a broadband 90° balun achieves an impedance bandwidth greater than 53% and an axial ratio bandwidth of 44% using a 180° power divider phase shifter combined with an ultra-wideband 90° balun feed network. The 180° power divider phase shifter used in this embodiment has a natural 180° phase difference and maintains good phase consistency over a wide bandwidth. Combined with a T-junction power divider, it achieves four-way power division while broadening the bandwidth. The ultra-wideband 90° balun enables ultra-wideband 90° phase shifting and has good phase consistency. Combined with the aforementioned structure, it forms a feed network that allows for sequential rotational feeding of the antenna at 0°, 90°, 180°, and 270°, improving the axial ratio characteristics of the antenna element. The antenna array based on this element, using the grid array method provided in this embodiment, can achieve wide-bandwidth angle scanning of the xoz plane. When the main beam points to 0°, the gain is 19.3dBi, and when scanning to ±50°, the gain decreases by less than 6dB. This embodiment describes a circularly polarized scanning grid array based on a broadband 90° balun that can be applied to the field of S-band satellite communication.

Claims

1. A circularly polarized scanning grid array based on a broadband 90° balun, characterized in that, The array consists of a grid of circularly polarized antenna elements. The circularly polarized antenna unit includes, from top to bottom, a radiating patch layer, a first dielectric substrate, an air gap layer, a metal ground layer, a second dielectric substrate, and a feed network layer. The radiating patch layer includes four 90° rotationally symmetrical radiating patches disposed on the upper surface of the first dielectric substrate; each radiating patch is provided with a feed point, and an annular coupling seam is provided on the outside of the feed point. The feed network layer has a centrally symmetrical structure and is used to feed signals of equal amplitude and phase difference of 90° to four radiating patches; it includes a 180° power divider phase shifter, two T-junction power dividers, two broadband 90° baluns, and two bent microstrip lines. The center of the 180° power divider phase shifter coincides with the center of the circularly polarized antenna element, and includes a feed slot and two tapered microstrip lines symmetrically arranged on both sides of the feed slot; the two output terminals of the 180° power divider phase shifter are respectively connected to a T-junction power divider. One output terminal of the T-junction power divider is connected to the input terminal of the bent microstrip line, and the other output terminal is connected to a broadband 90° balun. The broadband 90° balun is composed of a first coupling line and a second coupling line with an electrical length of 90° arranged in parallel. One end of the first coupling line and the second coupling line is connected to the short-circuit point through the first microstrip line, the other end of the first coupling line is connected to the output terminal of the T-junction power divider, and the other end of the second coupling line is connected to the feed point of the radiating patch through the feed copper pillar. The short-circuit point is connected to the metal grounding layer through a metal through-hole; The output end of the bent microstrip line is connected to the feed point of the radiating patch through a feed copper pillar. The radiating patch is a rectangular metal patch with an aspect ratio of 2.3-2.6; the feed point is located at the center of the short side of the rectangular patch near the edge of the circularly polarized antenna element.

2. The circularly polarized scanning grid array based on a broadband 90° balun as described in claim 1, characterized in that, The first dielectric substrate is model R5880, with a dielectric constant of 2.2 and a dielectric thickness of 5.2 mm; the second dielectric substrate is model RO4350B, with a dielectric constant of 3.48 and a dielectric thickness of 0.508 mm.

3. The circularly polarized scanning grid array based on a broadband 90° balun as described in claim 1, characterized in that, Each bend in the bent microstrip line is a 90° bend, and the outer corner of the 90° bend is chamfered to reduce the discontinuity of the microstrip transmission line at the bend.

4. The circularly polarized scanning grid array based on a broadband 90° balun as described in claim 3, characterized in that, A metal fence is provided around the outside of the circularly polarized antenna element.

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