A broadband millimeter wave circularly polarized microstrip antenna

Abstract

This invention proposes a broadband millimeter-wave circularly polarized microstrip antenna, comprising a first dielectric substrate and a second dielectric substrate stacked on top of each other. The upper surface of the first dielectric substrate is printed with a radiating patch 3, which has a set of regular octagonal structures with rectangular slots on opposite sides. The lower surface is printed with a composite feeding structure consisting of two quasi-V-shaped slots with opposing openings on a feeding substrate and a cross-shaped slot located between the two quasi-V-shaped slots. The regular octagonal patch with rectangular slots can form multiple current paths, generating multiple resonant points to broaden the impedance bandwidth. The feeding structure generates two orthogonal currents, and its internal angle compensation structure stabilizes the 90° phase difference between the two currents. Through the combination of the above feeding structure and the set of regular octagonal radiating patches with rectangular slots on opposite sides, the impedance bandwidth and 3dB axial ratio bandwidth of the antenna are effectively broadened, enabling stable right-hand circularly polarized radiation within the 28GHz-33GHz range.

Description

Technical Field

[0001] This invention belongs to the field of antenna technology, and specifically relates to a microstrip antenna capable of achieving 28-33GHz wideband millimeter-wave circular polarization, which can be used in 5G millimeter-wave communication, short-range high-precision radar, IoT wireless transmission and other fields. Background Technology

[0002] Millimeter-wave communication and short-range detection systems have extremely high requirements for antenna operating bandwidth, polarization stability, gain consistency and miniaturization. As the mainstream application frequency band, 28-33GHz urgently needs a circularly polarized microstrip antenna with matching performance as the core radiating unit.

[0003] Circularly polarized microstrip antennas are a common low-profile antenna type used in the millimeter-wave band. They mainly consist of a dielectric substrate, a radiating patch, a feeding structure, and a ground plane. Through electromagnetic coupling via the patch slots, they excite electric field components with equal amplitude and orthogonal phase, forming stable circularly polarized radiation. This type of antenna has the advantages of small size, light weight, compact structure, and easy integration. At the same time, it can effectively suppress multipath fading and polarization mismatch, significantly improving the reliability of wireless transmission and detection.

[0004] For example, patent application CN109037938A discloses a millimeter-wave broadband circularly polarized microstrip antenna, including a substrate, a microstrip feed line, an impedance transformer, a radiating patch, and a bottom ground plane. The microstrip feed line, impedance transformer, and radiating patch are all located on the upper surface of the substrate, with the microstrip feed line located in the middle of the substrate and the radiating patch near the edge. The microstrip feed line and the radiating patch are connected by the impedance transformer. The bottom ground plane is located on the lower surface of the substrate, and a single circular slot structure is provided on the bottom ground plane, with the center of the single circular slot structure corresponding to the center of the radiating patch. This invention achieves high gain and good impedance matching, but because the coupling structure of the single circular slot and the radiating patch is simple, its impedance bandwidth and axial ratio bandwidth are relatively narrow. Specifically, the impedance bandwidth is less than -10dB in the 26GHz–29GHz frequency band, and the axial ratio is less than 3dB in the 27.7GHz–29GHz frequency band. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and propose a wideband millimeter-wave circularly polarized microstrip antenna to solve the technical problem of narrow impedance bandwidth and axial ratio bandwidth of circularly polarized microstrip antennas in the prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention includes a first dielectric substrate 1 and a second dielectric substrate 2 stacked on top of each other. The upper and lower surfaces of the first dielectric substrate 1 are respectively printed with a radiating patch 3 and a feeding structure 4. The radiating patch 3 adopts a regular octagonal structure with rectangular slots on opposite sides. The feeding structure 4 adopts a composite structure consisting of two quasi-V-shaped slots 42 with opposite openings on the feeding substrate 41 and a cross-shaped slot 43 located between the two quasi-V-shaped slots. One arm of the cross-shaped slot 43 is located at the projection position of the rectangular slot on the radiating patch 3.

[0007] Furthermore, the first dielectric substrate 1, the second dielectric substrate 2, and the power feeding substrate 41 are all square in shape.

[0008] Furthermore, the center of the radiating patch 3 is located on the center normal of the first dielectric substrate 1, and the rectangular slot provided on the regular octagonal structure is located on one diagonal of the first dielectric substrate 1; the side length of the regular octagonal structure is W2, 1.3mm≤W2≤1.6mm, and the width of the rectangular slot is S1, 0.15mm≤S1≤0.3mm.

[0009] Furthermore, in the composite structure, the two arms of the quasi-V-groove 42 are orthogonal and parallel to the two adjacent sides of the feed substrate 41, respectively. The lengths of the inner and outer arms are L5 and L4, respectively, with 0.8mm≤L5≤1.0mm and 1.8mm≤L4≤2.2mm, and the arm width is L6, with 0.2mm≤L6≤0.4mm. The inner angle of the quasi-V-groove 42 is provided with a triangular compensation structure.

[0010] Furthermore, in the composite structure, the length of the rectangular arm in the cross-shaped groove 42 located at the rectangular slot projection position on the radiating patch 3 is greater than the length of the other rectangular arm, wherein the length of the longer rectangular arm is L1, 3.0mm≤L1≤3.6mm, the length of the shorter rectangular arm is L2, 1.2mm≤L2≤1.8mm, and the width of the rectangular arm is L3, 0.2mm≤L3≤0.4mm.

[0011] Furthermore, the cross-shaped groove 42 has protrusions that bend counterclockwise at the free ends of its two rectangular arms, forming a swastika shape.

[0012] Furthermore, the center of the cross-shaped groove 42 is located on the center normal of the feeding substrate 41.

[0013] Furthermore, the second dielectric substrate 2 has a microstrip feed line 5 printed on its lower surface.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. The radiating patch of this invention adopts a set of regular octagonal structures with rectangular slots on opposite sides, which can construct multiple independent current paths, making the current distribution at different frequencies more stable and directly widening the impedance bandwidth. At the same time, it balances the amplitude of two orthogonal radiating currents across the entire frequency band. Circular polarization radiation requires that the amplitudes of the two orthogonal radiating currents be consistent. If the difference in the amplitude of the two currents at different frequencies is too large, the axial ratio value will increase. This structure suppresses the difference in current amplitude, providing a basis for widening the axial ratio bandwidth. The rectangular slots on the radiating patch and the cross-shaped slots in the lower feeding structure form vertical interlayer electromagnetic coupling. Relying on the combination of the patch slots and the cross-shaped slots, multiple resonant points are superimposed to expand the working frequency domain and synergistically widen the antenna impedance bandwidth.

[0016] 2. The feeding structure of this invention has two sets of quasi-V-shaped slots with opposite openings, which can extend the equivalent electrical length of the feed and widen the operating frequency band. At high millimeter-wave frequencies, the corners of the quasi-V-shaped slots are prone to parasitic effects, causing phase shifts in the two feed currents and disrupting the circular polarization conditions. The triangular compensation structure added at the inner corner can improve the local current distribution, offset the phase drift caused by parasitic effects, and ensure that the two feed currents maintain a stable 90° phase difference across the entire frequency band. Circular polarization requires simultaneous current amplitude balance and phase orthogonality. This feeding structure provides stable broadband phase characteristics. Combined with the top-layer patch to balance the current amplitude, experimental results show that the antenna's 3dB axial ratio bandwidth covers 28.5~33GHz, synergistically widening the impedance and axial ratio bandwidth. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0018] Figure 2 This is a top view of the first dielectric substrate of the present invention.

[0019] Figure 3 This is a schematic diagram of the power supply structure of the present invention.

[0020] Figure 4 This is a simulation curve of S11 for antenna embodiment 1 of the present invention.

[0021] Figure 5 This is a simulation curve of the axial ratio of antenna embodiment 1 of the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and specific examples:

[0023] Example 1

[0024] In this embodiment, the side length of the regular octagon is W2=1.45mm, the width of the rectangular slot is S1=0.2mm, the long arm of the cross-shaped slot is L1=3.3mm, the short arm is L2=1.5mm, the width of the rectangular arm is L3=0.3mm, the inner arm of the quasi-V slot is L5=0.9mm, the outer arm is L4=2.0mm, and the slot width is L6=0.3mm.

[0025] Reference Figure 1 The present invention includes a first dielectric substrate 1 and a second dielectric substrate 2 stacked on top of each other. The upper and lower surfaces of the first dielectric substrate 1 are respectively printed with a radiating patch 3 and a feeding structure 4. The radiating patch 3 adopts a regular octagonal structure with rectangular slots on opposite sides. The feeding structure 4 adopts a composite structure consisting of two quasi-V-shaped slots 42 with opposite openings on the feeding substrate 41 and a cross-shaped slot 43 located between the two quasi-V-shaped slots. One arm of the cross-shaped slot 43 is located at the projection position of the rectangular slot on the radiating patch 3.

[0026] The first dielectric substrate 1, the second dielectric substrate 2, and the feeding substrate 41 are all square in shape.

[0027] Reference Figure 2 The radiating patch 3 adopts a set of regular octagonal structures with rectangular slots on opposite sides. Its center is located on the center normal of the first dielectric substrate 1. The rectangular slots on the regular octagonal structure are located on one diagonal of the first dielectric substrate 1. The side length of the regular octagonal structure is W2, and the width of the rectangular slot is S1. The smooth contour of the regular octagon, combined with the rectangular slots that run through opposite sides, can form multiple independent current paths on the patch metal surface, suppress the drastic current distortion caused by frequency shift, make the current distribution at different frequency points more stable, expand the antenna resonance range to broaden the impedance bandwidth, and the multi-path current can also stabilize the amplitude of the two orthogonal radiation currents across the entire frequency band, reduce the current amplitude difference under frequency shift. Circular polarization radiation requires the two orthogonal current amplitudes to be equal. If the amplitude difference is too large, it will increase the axial ratio and compress the axial ratio bandwidth. This patch structure can maintain current balance in a wide frequency range, providing a basis for broadening the axial ratio bandwidth. At the same time, the rectangular slots of the patch and the cross slots of the lower layer form vertical interlayer electromagnetic coupling, and the superposition of multiple resonant points further expands the working frequency domain.

[0028] Reference Figure 3 The feeding structure 4 adopts a composite structure consisting of two quasi-V-shaped grooves 42 with opposite openings on the feeding substrate 41 and a cross-shaped groove 43 located between the two quasi-V-shaped grooves. One arm of the cross-shaped groove 43 is located at the projection position of the rectangular slot on the radiating patch 3. The two form a vertical interlayer electromagnetic coupling, opening up the energy transfer channel between the patch and the bottom layer feeding, superimposing multiple resonant points, and widening the impedance bandwidth. At the same time, it uniformly transmits feeding energy, suppresses the amplitude difference of the two orthogonal radiation currents caused by frequency offset, stabilizes the current amplitude, and reduces the axial ratio fluctuation.

[0029] The two arms of the quasi V-shaped slot 42 in the composite structure are orthogonal and parallel to two adjacent sides of the feed substrate 41 respectively. The lengths of the inner and outer arms are L5 and L4 respectively, and the arm width is L6. A triangular compensation structure is provided at the inner angle of the quasi V-shaped slot 42; Two groups of quasi V-shaped slots with opposite openings can extend the equivalent electrical length of the feed, weaken the bandwidth limitation caused by the single resonance frequency point, broaden the overall operating frequency band. Under the high-frequency working conditions of millimeter waves, parasitic capacitance will be generated at the V-shaped slot corner of the quasi V-shaped slot, causing phase drift of the two-way feed current and destroying the circular polarization condition of 90° orthogonality. The triangular compensation block at the inner angle fills the blank area at the corner, optimizes the local current path, cancels the phase shift caused by the parasitic effect, and ensures that the two-way feed current maintains a stable 90° phase difference in the whole frequency band, broadening the axial ratio bandwidth from the phase dimension;

[0030] The center of the cross-shaped slot 42 is located on the central normal line of the feed substrate 41, ensuring the global symmetry of the feed structure, and preventing the introduction of inherent deviation of the current amplitude due to eccentricity, thus avoiding the deterioration of the circular polarization axial ratio.

[0031] The length of the rectangular arm of the cross-shaped slot 42 located at the projection position of the rectangular slot on the radiation patch 3 is greater than the length of the other rectangular arm. The length of the longer rectangular arm is L1, the length of the shorter rectangular arm is L2, and the width of the rectangular arm is L3. The asymmetrical cross slot with different lengths can split out two independent orthogonal current paths, and the amplitudes of the two currents are regulated by the length difference between the long and short arms. The free ends of the two rectangular arms are provided with protrusions bent counterclockwise, forming a "卍"-shaped perturbation structure to guide the current to rotate and distribute counterclockwise. After the two orthogonal and equal-amplitude currents with a stable 90° phase difference are coupled to the top-layer patch, a right-handed circularly polarized wave is synthesized in the far field. At the same time, the long arm of the cross slot is perpendicularly coupled to the patch slot, enhancing the energy transfer between layers, and further broadening the impedance bandwidth by multi-resonance coupling.

[0032] Refer to as Figure 4 On the lower surface of the second dielectric substrate 2, a microstrip feeder 5 is printed. The radio frequency signal is transmitted through the microstrip feeder, sending energy into the composite feed structure, and then exciting the radiation patch to radiate electromagnetic waves outward.

[0033] The overall working principle of the antenna is as follows: RF signals are input to a microstrip feed line on the lower surface of the second dielectric substrate, which transfers energy to a composite feeding structure on the bottom surface of the first dielectric substrate. Unequal-length cross-shaped slots with swastika-shaped bends at the ends generate two independent orthogonal currents. These, combined with quasi-V-shaped slots with opposing openings, extend the equivalent electrical length and broaden the bandwidth. Triangular compensation structures at the inner corners of the quasi-V-shaped slots counteract the phase shift caused by high-frequency parasites, ensuring the two currents maintain a stable 90° phase difference across the entire frequency band. The slots in the feeding structure are vertically coupled with the rectangular slots of the top-layer octagonal radiating patch. The multi-path current distribution of the patch creates multiple resonant points, broadening the impedance bandwidth and stabilizing the amplitudes of the two radiated currents. The two radiated currents, with equal amplitudes and orthogonal phases, are spatially superimposed, ultimately radiating right-hand circularly polarized electromagnetic waves outwards.

[0034] Example 2

[0035] This embodiment has the same structure as Embodiment 1, except that the following parameters have been adjusted:

[0036] The side length of the regular octagon is W2=1.3mm, the width of the rectangular slot is S1=0.15mm, the long arm of the cross-shaped slot is L1=3.0mm, the short arm is L2=1.2mm, the width of the rectangular arm is L3=0.2mm, the inner arm of the quasi-V slot is L5=0.8mm, the outer arm is L4=1.8mm, and the slot width is L6=0.2mm.

[0037] Example 3

[0038] This embodiment has the same structure as Embodiment 1, except that the following parameters have been adjusted:

[0039] The side length of the regular octagon is W2=1.6mm, the width of the rectangular slot is S1=0.3mm, the long arm of the cross-shaped slot is L1=3.6mm, the short arm is L2=1.8mm, the width of the rectangular arm is L3=0.4mm, the inner arm of the quasi-V slot is L5=1.0mm, the outer arm is L4=2.2mm, and the slot width is L6=0.4mm.

[0040] The effects of this invention can be further illustrated by simulation results:

[0041] 1. Experimental conditions and simulation content

[0042] The electromagnetic simulation software HFSS19.0 was used to build a simulation model for Example 1, and two simulation calculations were performed: one was to simulate the return loss parameters of antenna S11, and the curves were obtained as shown in the figure. Figure 4 Secondly, simulations were performed on the antenna's axial ratio performance, and the axial ratio variation curves were obtained as follows: Figure 5 .

[0043] 2. Simulation Result Analysis

[0044] Figure 4The S11 return loss curve is shown, with the horizontal axis representing frequency in GHz and the vertical axis representing return loss in dB. Within the frequency range of 28 GHz to 33 GHz, the curve values ​​are all below -10 dB, indicating that the antenna has good impedance matching in the target frequency band and its impedance bandwidth fully covers 28 to 33 GHz.

[0045] Figure 5 The curve represents the axial ratio variation. The horizontal axis represents frequency in GHz, and the vertical axis represents the axial ratio in dB. Within the frequency range of 28.5 GHz to 33 GHz, the axial ratio value is less than 3 dB, which means that the circular polarization performance of the antenna in this frequency band meets the standard, has a wide 3 dB axial ratio bandwidth, and can stably achieve broadband right-hand circular polarization radiation.

[0046] The two sets of simulation curves show that this antenna achieves both wide impedance bandwidth and wide axial ratio bandwidth by relying on the coordinated design of the radiating patch and the feeding structure, effectively overcoming the narrow bandwidth defect of existing millimeter-wave circularly polarized antennas.

Claims

1. A broadband millimeter wave circularly polarized microstrip antenna, comprising a first dielectric substrate (1) and a second dielectric substrate (2) stacked one above the other, the upper and lower surfaces of the first dielectric substrate (1) being respectively printed with a radiating patch (3) and a feed structure (4); characterized in that: The radiating patch (3) adopts a regular octagon structure with rectangular slots provided on a pair of opposite sides; the feeding structure (4) adopts a composite structure composed of two quasi-V-shaped slots (42) with opposite openings provided on the feeding substrate (41) and a cross-shaped slot (43) located between the two quasi-V-shaped slots, and one arm of the cross-shaped slot (43) is located at the projection position of the rectangular slot on the radiating patch (3).

2. The microstrip antenna according to claim 1, characterized in that, The first dielectric substrate (1), the second dielectric substrate (2) and the feeding substrate (41) are all square in shape.

3. The microstrip antenna according to claim 2, characterized in that, The center of the radiating patch (3) is located on the central normal line of the first dielectric substrate (1), and the rectangular slots provided on the regular octagon structure are located on a diagonal line of the first dielectric substrate (1); the side length of the regular octagon structure is W2, 1.3 mm ≤ W2 ≤ 1.6 mm, and the width of the rectangular slot is S1, 0.15 mm ≤ S1 ≤ 0.3 mm.

4. The microstrip antenna according to claim 3, characterized in that, For the composite structure, the two arms of the quasi-V-shaped slot (42) are orthogonal and are respectively parallel to two adjacent sides of the feeding substrate (41), the lengths of the inner and outer arms are L5 and L4 respectively, 0.8 mm ≤ L5 ≤ 1.0 mm, 1.8 mm ≤ L4 ≤ 2.2 mm, the arm width is L6, 0.2 mm ≤ L6 ≤ 0.4 mm, and a triangular compensation structure is provided at the inner angle of the quasi-V-shaped slot (42).

5. The microstrip antenna according to claim 3, characterized in that, For the composite structure, the length of the rectangular arm of the cross-shaped slot (42) located at the projection position of the rectangular slot on the radiating patch (3) is greater than the length of the other rectangular arm. The length of the longer rectangular arm is L1, 3.0 mm ≤ L1 ≤ 3.6 mm, the length of the shorter rectangular arm is L(2), 1.2 mm ≤ L2 ≤ 1.8 mm, and the width of the rectangular arm is L3, 0.2 mm ≤ L3 ≤ 0.4 mm.

6. The microstrip antenna according to claim 5, characterized in that, For the cross-shaped slot (42), the free ends of its two rectangular arms are provided with protrusions bent in the counterclockwise direction, forming a "卍" shape.

7. The microstrip antenna according to claim 5, characterized in that, The center of the cross-shaped slot (42) is located on the central normal line of the feeding substrate (41).

8. The microstrip antenna according to any one of claims 1-7, characterized in that, The lower surface of the second dielectric substrate (2) is printed with a microstrip feeder (5).

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