A differential-fed dual-frequency circularly polarized substrate integrated waveguide back cavity antenna array

Abstract

The application discloses a differential feed dual-frequency circularly polarized substrate integrated waveguide back cavity antenna array, which comprises an array structure composed of 2*2 antenna units, the antenna unit contains a substrate integrated waveguide cavity, the substrate integrated waveguide cavity is enclosed by an array of metal through holes penetrating through the first and second lower dielectric substrates, a differential feed network comprising a plurality of improved ring couplers is arranged on the third bottom dielectric substrate, and the differential feed network provides the antenna unit with differential signals with a phase difference of 175-185 degrees; a differential feed probe is connected to a port + and a port - respectively; a circular radiation hole is etched on the top copper layer of the substrate integrated waveguide cavity; the antenna unit has a radiation structure arranged on the surface of the first dielectric substrate and comprising a pair of arc-shaped microstrip lines and two groups of symmetrically distributed elliptical stubs; the two groups of elliptical stubs are symmetrically distributed on the arc-shaped microstrip line at an included angle θ r of 50-70 degrees; and the input signals of the port + and the port - have a phase difference of 180±5 degrees.

Description

Technical Field

[0001] This invention relates to the field of microwave antenna technology, specifically to a differentially fed dual-frequency circularly polarized substrate integrated waveguide (SIW) cavity antenna array and its design method, applicable to, but not limited to, 5G communication, satellite navigation and millimeter-wave radar system applications. Background Technology

[0002] Circularly polarized antennas offer advantages such as reduced polarization mismatch and adjustable azimuth angles between transmitting and receiving antennas, and have been widely used in various fields including satellite and wireless communications. Research has focused extensively on broadband, dual-band, multi-band, low-profile, high-gain, dual-circularly polarized radiation, and low-cross-polarization circularly polarized antennas. Dual-band circularly polarized antennas, in particular, can operate in two different frequency bands while being naturally isolated from each other. This characteristic is especially beneficial for the design of full-duplex systems, as it simplifies the design process and supports device miniaturization.

[0003] Cavity-backed antenna structures can improve the gain of dual-band circularly polarized antennas. However, the large thickness of the metal cavity and its high manufacturing cost pose challenges to its integration with compact circuitry. Combining substrate-integrated waveguide technology with dual-band circularly polarized antennas offers several advantages, such as smaller form factor, easier circuit integration, lower manufacturing cost, and lighter structure. Existing literature proposes a flat substrate-integrated waveguide cavity-backed antenna with a substrate thickness of 0.03λ0 (free-space wavelength), achieving dual-band circularly polarized radiation using a single-layer PCB. Furthermore, existing literature describes a compact millimeter-wave substrate-integrated waveguide cavity-backed antenna whose array configuration achieves gains of 18.2 dBic and 18.5 dBic in two different operating frequency bands. Additionally, existing literature demonstrates a magnetoelectric dipole antenna integrated with a substrate-integrated waveguide cavity, enabling dual-band dual-circularly polarized radiation.

[0004] On the other hand, differential circuits can be applied to dual-band substrate-integrated waveguide cavity antennas, which helps improve the antenna's cross-polarization performance and eliminates the need for baluns or other phase shifters. For example, existing literature has proposed a low-profile, dual-band, dual-polarization differential cavity antenna characterized by two simple differential feed networks placed vertically and horizontally on a single-layer substrate. Furthermore, existing literature has also proposed a novel dual-band, dual-polarization filter antenna and array utilizing a differential feed scheme, achieving antenna element gains of 8.34 dBi and 8.7 dBi, and array gains of 13.5 dBi and 15.1 dBi, respectively, in dual-band operation. Additionally, existing literature has introduced a dual-band phased array employing a differential feed network, which can perform wide-angle scanning while maintaining isolation between the two ports below -13.14 dB in the θ = 0° plane.

[0005] The differential antennas or arrays discussed above are limited to achieving linear polarization in dual-band applications. In contrast, circularly polarized antennas and arrays have a wider range of applications in communications. Although the literature on dual-band dual-circularly polarized antennas or arrays demonstrates good performance, these designs rarely incorporate differential circuitry. A review of current research indicates that little attention has been paid to differentially circuit-excited dual-band dual-circularly polarized substrate-integrated waveguide cavity-backed antenna elements and arrays, making this an important area for further exploration.

[0006] Based on the above analysis, existing literature reports indicate the following problems with this type of antenna:

[0007] 1) Few studies have focused on the research of differential circuit-excited dual-frequency dual-circularly polarized substrate integrated waveguide cavity antenna elements and arrays. However, as mentioned above, the combination of several technologies will give the antenna superior performance.

[0008] 2) Improvement of the power supply network: Some existing technologies use differential power supply but require external baluns or phase shifters, resulting in additional losses;

[0009] 3) High cross-polarization: In some existing technologies, the cross-polarization level is only below -10dB, which is difficult to meet the requirements of high resolution.

[0010] There is a need in this field for improved differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna arrays and their design techniques, in order to overcome the aforementioned shortcomings of existing technologies and achieve more beneficial technical effects.

[0011] The information included in this background section of the specification of this invention, including any references cited in this invention and any descriptions or discussions thereof, is included for technical reference purposes only and is not intended to limit the scope of the invention. Summary of the Invention

[0012] This invention improves the broadband circularly polarized substrate integrated waveguide cavity antenna by using an improved ring coupler to generate differential signals to feed the antenna array. It excites the cavity in two modes through dual-mode resonance, distinguishes the resonant frequencies of the two modes through the radiation structure, and achieves a high frequency ratio between the resonant frequencies of the two modes, further simplifying the differential feeding network. This enables the antenna element to operate independently in two different modes, solving the above and other technical problems.

[0013] According to one or more embodiments of the present invention, the present invention enables increased bandwidth, reduced design complexity of the feed network, and reduced cross-polarization ratio; by improving a simple microstrip ring coupler, approximately 180 degrees of power distribution and phase shift can be generated within the required operating frequency band of the antenna; furthermore, existing technologies and antenna designs generally use broadband baluns, which suffer from severe losses at high frequencies due to the need to weld balancing resistors into the balun structure, the present invention eliminates the need for balancing resistors; by adding a pair of arc-shaped microstrip lines and two pairs of elliptical stubs to extend the surface current flow path, the electric field strength is increased in areas where the electric field is insufficient, thereby meeting the requirements of circular polarization, compensating for the circular polarization characteristics of the antenna, and contributing to the realization of broadband circular polarization radiation; compared with existing technologies, the proposed array has the characteristics of wide bandwidth, high gain, simple feed method, compact design, and low profile, making it particularly suitable for applications in compact integrated circuits.

[0014] More specifically, to address the aforementioned and other problems, according to one aspect of the present invention, the present invention aims to provide a differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array, comprising: an array structure composed of 2×2 antenna elements, wherein each antenna element includes a substrate integrated waveguide cavity, the substrate integrated waveguide cavity comprising a first upper dielectric substrate and a second lower dielectric substrate stacked vertically, the substrate integrated waveguide cavity being enclosed by an array of metal vias penetrating the first upper dielectric substrate and the second lower dielectric substrate, wherein the diameter of each metal via in the metal via array is d, and the spacing between them is p; wherein the substrate integrated waveguide cavity has a diameter of d R A circular radiating aperture is etched into the top copper layer of the integrated waveguide cavity on the substrate; wherein, the antenna unit has a radiating structure disposed on the surface of the first upper dielectric substrate, including a pair of arc-shaped microstrip lines and two symmetrically distributed sets of elliptical stubs; wherein, the length of the arc-shaped microstrip lines is l1 and the width is w1, the major semi-axis of the two sets of elliptical stubs are R1 and R2 respectively, the ratios of their major semi-axis to minor semi-axis are Ratio1 and Ratio2 respectively, and the two sets of elliptical stubs are arranged at an angle θ. r Symmetrically distributed on the arc-shaped microstrip line; a differential feed network, including four improved ring couplers disposed on the third bottom dielectric substrate, for providing differential signals with a phase difference in the range of 175°-185° to the antenna element; a differential feed probe, penetrating the second bottom dielectric substrate of the substrate integrated waveguide cavity, including a pair of coaxially arranged probes, respectively connected to the first differential port + and the second differential port -, wherein the diameter of the differential feed probe is d. s The corresponding coaxial hole diameter is d. cThe substrate-integrated waveguide cavity has a diameter of C1, which is formed by a set of metallized vias with a diameter of d along the circumferential direction. The spacing p satisfies the necessary condition for the formation of the substrate-integrated waveguide cavity, i.e., p / d < 2, to avoid electromagnetic leakage. The included angle θ of the elliptical stubs... r The phase difference between the input signals of the first differential port + and the second differential port - is 180°±5°, with a range of 50°-70°, in order to achieve dual-frequency circular polarization radiation in both low-frequency and high-frequency bands.

[0015] According to one or more embodiments of the present invention, the differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array operates in the low-frequency band of 15.5-19.595 GHz and the high-frequency band of 21.93-24.76 GHz.

[0016] According to one or more embodiments of the present invention, the center frequency of the low-frequency band is 17.6 GHz, and the high-frequency band is 23.4 GHz.

[0017] According to one or more embodiments of the present invention, the spacing between the antenna elements is 0.6-0.8 times the free space wavelength corresponding to the center frequency of the high-frequency band.

[0018] According to one or more embodiments of the present invention, the included angle θ of the elliptical branch r It is 60°±2°.

[0019] According to one or more embodiments of the present invention, the annular coupler is disposed on the bottom copper layer of the third bottom dielectric substrate and is connected to the radiating structure through the differential feed probe.

[0020] According to one or more embodiments of the present invention, the first upper dielectric substrate, the second lower dielectric substrate, and the third lower dielectric substrate are bonded together by an adhesive sheet; and

[0021] The output port of the ring coupler corresponds one-to-one with the differential feed probe.

[0022] According to one or more embodiments of the present invention, the resonant frequency ratio between the fundamental mode and the first higher-order mode of the substrate integrated waveguide cavity is 1:1.3-1.5, and the electric field distribution of the higher-order mode is orthogonal to the fundamental mode.

[0023] According to one or more embodiments of the present invention, the parameters of the elliptical branch satisfy the following relationship:

[0024] θ r =60°±2°, Ratio1=0.7±0.05, Ratio2=0.6±0.05, and R1=3.0-3.4mm, R2=3.0-3.2mm.

[0025] According to one or more embodiments of the present invention, the antenna element has an axial ratio bandwidth of 4.09% and 4.20% in the two frequency bands of 15.34-15.98 GHz and 23.05-24.04 GHz, respectively, a cross-polarization level of less than -20 dB, and an impedance bandwidth of 23.34% and 12.12%, respectively.

[0026] According to one or more embodiments of the present invention, the parameters of the substrate integrated waveguide cavity are:

[0027] -C1=10±0.5mm, d=0.7±0.1mm, p=1.0472±0.1mm,

[0028] - The diameter d of the circular radiating aperture R = 4.5 ± 0.2 mm, center hole diameter d M =1±0.2mm.

[0029] According to one or more embodiments of the present invention, the dielectric substrate is made of F4BM, and its dielectric constant ε r =2.2, loss tangent tanδ=0.001, thickness of each substrate layer h1=h2=2.286±0.1mm.

[0030] According to one or more embodiments of the present invention, the phase imbalance of the output port of the improved ring coupler is ≤ ±5° and the amplitude imbalance is ≤ 0.5dB in the dual frequency band, and the power supply network does not require an external balun or phase shifter.

[0031] According to one or more embodiments of the present invention, the thickness h3 of the third bottom dielectric substrate is 0.508 mm.

[0032] According to one or more embodiments of the present invention, the arc-shaped microstrip line spacing d1 of the radiating structure is 5 ± 0.2 mm, and the antenna element generates left-hand circularly polarized radiation in the low-frequency band and the high-frequency band, respectively.

[0033] According to one aspect of the present invention, the present invention is committed to providing a design method for an antenna array comprising a plurality of antenna elements, the method comprising: designing a radiating structure for the antenna elements, the radiating structure comprising a pair of arc-shaped microstrip lines and two sets of symmetrically distributed elliptical stubs; adjusting the included angle θ of the elliptical stubs... rThe fundamental and higher-order resonant frequencies of the substrate-integrated waveguide cavity are separated by the ratios of the long semi-axis R1 / R2 and the short semi-axis Ratio1 / Ratio2. The position and diameter of the differential feed probes are optimized to ensure that the impedance matching bandwidth of port + and port - covers the dual frequency bands. A 2×2 array of differential feed networks is constructed using an improved ring coupler, and the phase and amplitude balance is verified by simulation.

[0034] According to one or more embodiments of the present invention, the improved ring coupler connects the feed probe via a copper pad, and the differential feed probe connects the arc-shaped microstrip line to the differential feed network.

[0035] According to one or more embodiments of the present invention, the improved ring coupler is designed to replace the conventional balun.

[0036] According to one or more embodiments of the present invention, the improved ring coupler is integrated on a third underlying dielectric substrate.

[0037] According to one or more embodiments of the present invention, each antenna element has a radiation hole on the top layer of the substrate integrated waveguide cavity and two matching holes on the bottom layer; and each antenna element has a central hole at its geometric center.

[0038] According to one or more embodiments of the present invention, the phase difference is 180°.

[0039] According to one or more embodiments of the present invention, the thickness of the third bottom dielectric substrate of the improved annular coupler is 0.254 mm, and the copper pad with a diameter of 0.5 mm is etched on its surface to enhance connection reliability.

[0040] According to another aspect of the present invention, a method for manufacturing a differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array is also provided, comprising the following steps: constructing an array structure composed of 2×2 antenna elements, each antenna element comprising: a substrate integrated waveguide cavity, which is composed of a first upper dielectric substrate and a second lower dielectric substrate stacked vertically, and is formed by an array of metal vias, the diameter of which is d, and the spacing p satisfies p / d<2 to avoid electromagnetic leakage; etching a copper layer with a diameter of d on the top layer of the substrate integrated waveguide cavity. R A circular radiating aperture; a radiating structure is disposed on the surface of the first upper dielectric substrate, including a pair of arc-shaped microstrip lines and two symmetrically distributed sets of elliptical branches, the included angle of the elliptical branches being θ. r The phase angle is 50°-70°, with the ratios of the major and minor semi-axis being Ratio1 and Ratio2, respectively. An integrated differential feed network, including four improved ring couplers, is located on the bottom copper layer of the third bottom dielectric substrate, providing a differential signal with a phase difference of 175°-185°. Differential feed probes are installed penetrating the second lower dielectric substrate, with a probe diameter of d.s The corresponding coaxial hole diameter is d c Connect to the differential port ±, with an input signal phase difference of 180°±5° to achieve dual-frequency circularly polarized radiation.

[0041] According to one or more embodiments of the present invention, the antenna array operates in a low-frequency band of 15.5-19.595 GHz and a high-frequency band of 21.93-24.76 GHz, wherein the center frequency of the low-frequency band is 17.6 GHz and the high-frequency band is 23.4 GHz.

[0042] According to one or more embodiments of the present invention, the first, second and third dielectric substrates are bonded together by adhesive sheets, and the output port of the annular coupler corresponds one-to-one with the differential feed probe.

[0043] According to one or more embodiments of the present invention, the ratio of the fundamental mode to the first higher-order mode resonant frequency of the substrate integrated waveguide cavity is 1:1.3-1.5, and the electric field distribution of the higher-order mode is orthogonal to that of the fundamental mode.

[0044] According to one or more embodiments of the present invention, the antenna element has an axial ratio bandwidth of 4.09% and 4.20% in the 15.34-15.98 GHz and 23.05-24.04 GHz bands, respectively, a cross-polarization level of less than -20 dB, and an impedance bandwidth of 23.34% and 12.12%, respectively.

[0045] According to one or more embodiments of the present invention, the differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array is suitable for feeding 5G networks / millimeter waves, suitable for 5G communication networks and satellite navigation systems, and suitable for communication systems in microwave and millimeter wave bands. It features dual-band operation, wide bandwidth, high gain, low profile and low cross-polarization.

[0046] According to one or more embodiments of the present invention, the antenna array of the present invention reduces the complexity of the feeding network, reduces the cross-polarization level of the antenna, and improves the performance of the antenna by simplifying the differential feeding mechanism.

[0047] Further embodiments of the present invention can also achieve other beneficial technical effects not listed one by one. These other beneficial technical effects may be partially described below and can be expected and understood by those skilled in the art after reading the present invention. Attached Figure Description

[0048] The above-described features and advantages, as well as other features and advantages, and the ways in which they are implemented, of the embodiments of the present invention will become more apparent and better understood by referring to the following description in conjunction with the accompanying drawings, in which:

[0049] Figure 1(a)-1(b)An antenna element according to an embodiment of the present invention is schematically illustrated. FIG1(a) schematically shows the three-dimensional structure of the antenna element according to the embodiment, and FIG1(b) schematically shows an exploded top view of the antenna element, illustrating the exploded components of the antenna element. The radiation aperture (14 mm), metallized vias (1.0472 mm spacing), arcuate microstrip line (6.9813 mm × 0.1 mm), and elliptical stubs (R1 = 3.2 mm, Ratio1 = 0.7, R2 = 3.0 mm, Ratio2 = 0.6, θ) of the antenna element are labeled. r =60°).

[0050] Figure 2 (a)- Figure 2 (c) The evolution of the antenna element involved in the present invention, as illustrated in the simulation design, is shown schematically. Figure 2 (a) shows an antenna element consisting of only one set of curved microstrip lines; Figure 2 (b) shows an antenna element consisting of a set of curved microstrip lines and a set of elliptical stubs; Figure 2 (c) shows an antenna element consisting of a set of arcuate microstrip lines and two sets of elliptical stubs;

[0051] Figure 3 The illustration shows a simulation result obtained according to an embodiment of the present invention. Figure 2 (a)- Figure 2 (c) Differential S-parameters |S_t of each antenna element dd11 |, (b) Axial ratio bandwidth AR and left-hand circular polarization gain LHCP Gain (select the plane defined by phi = 0° and theta = 0°).

[0052] Figure 4 The diagram schematically illustrates the electric field distribution of a dual-band substrate integrated waveguide cavity antenna element according to an embodiment of the present invention at different times, wherein, Figure 4 (a) shows the electric field distribution of the fundamental mode at f1 = 15.5 GHz and the first higher-order mode at f2 = 22.5 GHz at time t = 0; Figure 4 (b) shows the electric field distribution of the fundamental mode at f1 = 15.5 GHz and the first higher-order mode at f2 = 22.5 GHz at time t = T / 4; Figure 4 (c) shows the electric field distribution of the fundamental mode at f1 = 15.5 GHz and the first higher-order mode at f2 = 22.5 GHz at time t = T / 2; Figure 4 (d) shows the electric field distribution of the fundamental mode at f1 = 15.5 GHz and the first higher-order mode at f2 = 22.5 GHz at time t = 3T / 4.

[0053] Figure 5The diagram schematically illustrates the horizontal electric field distribution of the fundamental mode of a dual-frequency substrate integrated waveguide cavity antenna element according to an embodiment of the present invention at f1 = 15.5 GHz and the first higher-order mode at f2 = 22.5 GHz.

[0054] Figure 6 The schematic diagram illustrates the included angle θ of a dual-band substrate integrated waveguide cavity antenna element in different elliptical stubs according to an embodiment of the present invention. r Simulation results under the conditions Figure 6 (a) Difference S-parameters |S dd11 |, Figure 6 (b) Axial ratio bandwidth AR and left-hand circular polarization gain LHCP Gain (select the plane defined by phi = 0° and theta = 0°).

[0055] Figure 7 The illustration schematically shows the simulation results of a dual-frequency substrate integrated waveguide cavity antenna element according to an embodiment of the present invention under different semi-major axes R1 and R2 of elliptical stubs. Figure 7 (a) Difference S-parameters |S dd11 |, Figure 7 (b) Axial ratio bandwidth AR and left-hand circular polarization gain LHCP Gain (select the plane defined by phi = 0° and theta = 0°).

[0056] Figure 8 The illustration schematically shows the simulation results of a dual-frequency substrate integrated waveguide cavity antenna element according to an embodiment of the present invention under different ratios of the major and minor axes of elliptical stubs, Ratio1 and Ratio2. Figure 8 (a) Difference S-parameters |S dd11 |, Figure 8 (b) Axial ratio bandwidth AR and left-hand circular polarization gain LHCP Gain (select the plane defined by phi = 0° and theta = 0°).

[0057] Figure 9 The diagram schematically illustrates the normalized radiation patterns of a dual-band substrate integrated waveguide cavity antenna element in the low-frequency and high-frequency bands corresponding to the E-plane and H-plane, respectively, with the main lobe direction and cross-polarization level marked. Figure 9 (a) shows the radiation pattern of the antenna element in the E plane at 15.5 GHz; Figure 9 (b) shows the radiation pattern of the antenna element in the H plane at 15.5 GHz; Figure 9 (c) shows the radiation pattern of the antenna element in the E-plane at 22.5 GHz; Figure 9 (d) shows the radiation pattern of the antenna element in the H plane at 22.5 GHz.

[0058] Figure 10(a) schematically shows an exploded view of an antenna array according to an embodiment of the present invention, Figure 10(b) schematically shows the antenna array located on a third bottom dielectric substrate and consisting of a feed network of four improved ring couplers, and Figure 10(c) schematically shows a side cross-sectional view of the antenna array.

[0059] Figure 11 (a)-(b) schematically illustrate the (a) differential S-parameters |S, obtained by simulation of an antenna array according to an embodiment of the present invention under conditions with and without a feed network. dd11 |, (b) Axial ratio bandwidth AR and left-hand circular polarization gain LHCP Gain (select the plane defined by phi = 0° and theta = 0°). Detailed Implementation

[0060] In the following description of specific embodiments, taken in conjunction with the accompanying drawings, details of one or more embodiments of the invention will be set forth. Other features, objects, and advantages of the invention will become apparent from these descriptions, drawings, and claims.

[0061] It should be understood that the illustrated and described embodiments are not limited in application to the details of the configurations set forth in the following description or illustrated in the accompanying drawings. The illustrated examples may be other embodiments and can be implemented or performed in various ways. The examples are provided by way of explanation rather than limitation of the disclosed embodiments. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments of the invention without departing from the scope or spirit of the disclosure. For example, features illustrated or described as part of one embodiment may be used with another first embodiment to still produce another embodiment. Therefore, this disclosure covers such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0062] Similarly, it is understood that the phrases and terms used in this invention are for descriptive purposes and should not be considered restrictive. The use of "comprising," "including," or "having" and variations thereof in this invention is intended to include, in an open-ended manner, the items listed thereafter, their equivalents, and any additional items.

[0063] In this invention, taking a 2×2 antenna array constructed based on antenna elements as an example, a differential signal is generated by using an improved ring coupler to power the antenna array. This invention further simplifies the differential feeding network and other technologies and inventive concepts by using dual-mode resonant excitation and distinguishing the resonant frequencies of the two modes through a radiating structure, thus solving the aforementioned and other technical problems.

[0064] The present invention will now be described in more detail with reference to several embodiments thereof.

[0065] The structure of an antenna element according to an exemplary embodiment of the present invention is shown in FIG1, for example. This structure utilizes F4BM(ε r The system consists of two substrates (tanδ = 2.2, tanδ = 0.001). The upper layer, referred to as substrate #I, has a thickness of h1, the same as substrate #II, with a thickness of h2. To achieve dual-frequency circularly polarized radiation, a pair of arc-shaped microstrip lines (length l1, width w1) with two sets of elliptical stubs are etched onto the upper surface of substrate #I, forming the main radiation structure. The spacing between the pair of arc-shaped microstrip lines and the two sets of elliptical stubs is d1. The major semi-axis of these two sets of elliptical stubs are R1 and R2, respectively, and their ratios to their minor semi-axis are Ratio1 and Ratio2, respectively. The elliptical stubs are symmetrically distributed on the two arc-shaped microstrip lines, with an included angle θ between each arc-shaped microstrip line. r A diameter d is set at the geometric center of the antenna element. M A central hole is used to ensure good impedance matching. The substrate-integrated waveguide cavity has a diameter of C1 and consists of a series of metal vias with a diameter of d and a spacing of p, penetrating each dielectric substrate and copper layer. To ensure sufficient radiation, a via with a diameter of d is etched on the top layer of the antenna element. R A circular hole. A pair of holes with a diameter of d. s The feed probe passes through two copper layers on the bottom surface of substrate #I with a diameter of d. c The coaxial aperture is used to feed the antenna element. The differential ports are set as port + and port -, corresponding to the feed probe (in subsequent analysis, the signal phase at port + is set to 0°, and the signal phase at port - is set to 180°). The specific parameter values ​​of the antenna element are shown in Table I.

[0066] The dimensions of the antenna elements mentioned in Table I

[0067]

[0068] Antenna element structural design: like Figure 2 As shown, the antenna element proposed in the embodiment of the present invention, such as Figure 1, can be designed according to the following evolution process. All results can be simulated by ANSYS HFSS software. First, a pair of arc-shaped microstrip lines are inserted into the substrate integrated waveguide cavity, which are regarded as antenna #1. The simulated differential S-parameters and the corresponding axial ratio (AR) and gain are as follows. Figure 3As shown, the impedance bandwidth of antenna #1 is 26.2% (16.34-21.26 GHz). However, the corresponding axial ratio is greater than 3 dB over the entire impedance bandwidth, which does not meet the requirements for circular polarization radiation. To compensate for the circular polarization characteristics of antenna #1, a pair of elliptical stubs can be introduced to extend the surface current flow path, thereby increasing the electric field strength in areas where the electric field is insufficient, thus satisfying the requirements for circular polarization. Based on this, the final structure of antenna #2 is obtained, as shown... Figure 2 As shown in (b), compared to antenna #1, the impedance bandwidth of antenna #2 is divided into two parts (16.11-20.66 GHz and 20.90-24.58 GHz). Furthermore, antenna #2 exhibits two frequency bands with axial ratios less than 3 dB (15.05-15.89 GHz and 21.76-22.67 GHz), and the 3-dB gain bandwidth is increased by 2.8%. To further balance the electric field distribution of antenna #2, another set of elliptical stubs can be introduced to ensure that the axial ratio of antenna #2 increases further in both frequency bands, thus obtaining the structure of antenna #3. The other set of introduced elliptical stubs shares a value θ with the first set of elliptical stubs in antenna #2. r Compared to antenna #2, the proposed antenna #3 exhibits an increase in impedance bandwidth of 3.2% and 0.8% in the two different frequency bands, respectively. Regarding axial bandwidth, antenna #3 and antenna #2 have almost the same axial bandwidth in the low-frequency band, but in the high-frequency band, antenna #3 shows a 1.7% increase in axial bandwidth compared to antenna #2. In terms of 3-dB gain bandwidth, antenna #3 shows an increase of more than 2% compared to antenna #2. Therefore, the designed antenna #3 can achieve dual-frequency circularly polarized radiation and demonstrates a significant performance improvement compared to the two proposed reference antenna elements.

[0069] The working principle of an antenna element: The electric field distribution of the proposed dual-frequency substrate integrated waveguide cavity antenna element at different times is as follows: Figure 4 As shown. In the low-frequency range, the fundamental mode of the excitation cavity has electric field principal vectors that are perpendicular to each other at t=0 and t=T / 4 (indicated by black arrows). As time progresses, the electric field direction rotates clockwise, resulting in left-handed circularly polarized radiation. In the high-frequency range, through... Figure 4 (b) and Figure 5 It can be observed that another mode is excited within the cavity. At t=0, the direction of the principal electric field vector is opposite to that of the fundamental mode, but the electric field vector directions at t=0 and t=T / 4 remain orthogonal. As time progresses, the electric field direction continues to rotate clockwise, thus achieving left-handed circularly polarized radiation in the high-frequency range.

[0070] Parametric analysis:The introduction of elliptical stubs induces dual-frequency circularly polarized radiation in the substrate-integrated waveguide cavity, meaning that certain parameters of these stubs can significantly impact the antenna element's performance. These parameters include the included angle θ between the elliptical stubs. r The lengths of the major semi-axis of the two sets of elliptical branches, R1 and R2, and the ratios of their corresponding major and minor semi-axis, Ratio1 and Ratio2.

[0071] Figure 6 It shows the different θ r The difference S-parameters |S0 are obtained by simulation on the plane defined by phi = 0° and theta = 0°. dd11 |, axial ratio bandwidth and left-hand circular polarization gain. From Figure 5 As can be seen from (a), at θ r At 60°, the antenna element achieves the widest impedance bandwidth across both frequency bands. Figure 5 In (b), although the antenna element is at θ r At θ = 50°, the widest axial ratio bandwidth is achieved, but the overlap bandwidth (i.e., the common part of the impedance bandwidth, axial ratio bandwidth, and left-hand circular polarization bandwidth) is not as good as θ. r Performance at 60°. Therefore, the included angle between the elliptical branches is θ. r Performance is better at 60°.

[0072] Figure 7 The difference S-parameters |Si| are shown, obtained from simulations on the plane defined by phi = 0° and theta = 0°, with different combinations of R1 and R2. dd11 | Axial ratio bandwidth and left-hand circular polarization gain. When R1 is fixed at 3.0mm, the impedance bandwidth expands with increasing R2 in both frequency bands, indicating that the antenna element performs better when R1 = 3.0mm and R2 = 3.2mm. However, changing R1 while keeping R2 at 3.2mm results in a narrower impedance bandwidth, preventing further performance improvements. Figure 6 As shown in (b), when R1 remains constant at 3.0 mm, the axial ratio bandwidth and left-hand circular polarization gain are almost identical. Conversely, when R2 is fixed at 3.2 mm, increasing R1 leads to a decrease in axial ratio bandwidth. This indicates that R1 plays a dominant role in the circular polarization characteristics of the antenna element.

[0073] Figure 8 This describes the difference S-parameters |S| obtained from simulations under different ratios of the major and minor axes, Ratio1 and Ratio2, on a plane defined by phi = 0° and theta = 0°. dd11| Axial ratio bandwidth and left-hand circular polarization gain. When Ratio1 remains constant at 0.7, the impedance bandwidth, axial ratio bandwidth, and left-hand circular polarization gain decrease as Ratio2 increases. Conversely, when Ratio2 is set to 0.6, increasing Ratio1 leads to a decrease in the low-frequency impedance bandwidth and an increase in the high-frequency impedance bandwidth. The trends of axial ratio bandwidth and left-hand circular polarization gain are similar to those of impedance bandwidth.

[0074] Based on the above analysis, after determining the optimal parameters of the antenna element, we can confirm its dual-frequency circular polarization radiation characteristics by analyzing and verifying the radiation pattern of the antenna element. Figure 9 (a) and Figure 9 (b) shows the E-plane and H-plane radiation patterns of the proposed antenna element at 15.605 GHz. Both radiation patterns exhibit a symmetrical shape, with the cross-polarization level (i.e., right-hand circular polarization level) remaining below -20 dB. This low cross-polarization level is attributed to the use of a differential feeding mechanism. At higher frequencies, although the cross-polarization level of the antenna element increases slightly, it still remains below -20 dB. This demonstrates that this antenna element can achieve circularly polarized radiation in both frequency bands while maintaining a low cross-polarization level.

[0075] Antenna array design: According to one or more embodiments of the present invention, a 2×2 differential antenna array was designed using the proposed antenna elements to improve the gain of dual-band circularly polarized radiation. As shown in Figure 10(a), the spacing between the two antenna elements is 9.8 mm, approximately equivalent to 0.7 times the free-space wavelength at the high-frequency center frequency of 22.885 GHz. To achieve differential feeding, the antenna array employs four improved ring couplers forming a differential feeding network. These ring couplers are located at the bottom of substrate #III, with a thickness h3 of 0.508 mm. The top layer of substrate #III is covered with a copper layer and forms a common ground with the 2×2 antenna array. Figure 10(b) and 10(c) As shown, each annular coupler is connected to a feed probe at the bottom of substrate #III, which in turn connects to an arc-shaped microstrip line and an elliptical stub to generate dual-frequency circularly polarized radiation. Semi-cured adhesive sheets (ε-type), such as FR-25, are used between the substrate layers. r =2.43, loss tangent tanδ=0.0017) are bonded together, thereby connecting the substrate layers and copper layers.

[0076] Figure 11 The performance comparison of the proposed 2×2 antenna array with and without a feed network is shown. After inputting a signal at port 1, the two output signals of equal power can maintain nearly equal amplitudes and a phase difference of 180°. The phase imbalance can be maintained within ±5° in the two frequency bands in which the array operates.

[0077] With a power supply network, the impedance bandwidths of the two frequency bands are (23.34%, 15.5-19.595GHz and 12.12%, 21.93-24.76GHz), respectively; without a power supply network, the impedance bandwidths are (24.47%, 15.46-19.77GHz and 18.37%, 20.49-24.635GHz), respectively. Compared to the former, adding a power supply network reduces the impedance bandwidths of the two frequency bands by 1.13% and 6.25%, respectively. With a power supply network, the axial ratio bandwidths of the two frequency bands are (4.09%, 15.34-15.98GHz and 4.20%, 23.05-24.04GHz), respectively; without a power supply network, the impedance bandwidths are (3.46%, 15.36-15.90GHz and 2.57%, 22.64-23.23GHz), respectively. Compared to the previous setup, adding a feed network increased the axial ratio bandwidth by 0.63% and 2.05% in the two frequency bands, respectively. With the feed network, the antenna array's peak gain was 10.72 dBi at 20.75 GHz, while without the feed network, the peak gain was 14.85 dBi at 24.25 GHz. This represents a 4.13 dBi decrease in peak gain after adding the feed network. Analysis of the three key parameters—impedance bandwidth, axial ratio bandwidth, and peak gain—concludes that the overall performance degradation of the antenna array after introducing a differential feed network is minimal and within acceptable limits. Furthermore, the introduced differential feed network has a simple structure and does not require the balancing resistors found in structures like baluns, making it more suitable for high-frequency array applications. Therefore, the differential feed network in this design is effective.

[0078] Performance comparison and technical advantages: This invention improves upon a broadband circularly polarized substrate integrated waveguide cavity antenna, exciting the cavity in two modes and achieving a high frequency ratio between the resonant frequencies of the two modes, thereby enabling the antenna element to operate independently in two different modes. A 2×2 antenna array is constructed based on this antenna element, and a modified ring coupler is used to generate a differential signal to feed the antenna array. This invention solves the aforementioned and other technical problems by using dual-mode resonant excitation and distinguishing the resonant frequencies of the two modes through a radiating structure, further simplifying the differential feeding network and other inventive concepts.

[0079] Compared to existing technologies, the bandwidth improvement of this invention is significant, and it eliminates the need for an external balun, allowing direct integration into the front end of a compact RF circuit. Table II summarizes the performance and key specifications of the antenna array of this invention compared to other similar designs.

[0080] Table II compares the antenna array of the present invention with similar antenna structures in other prior art.

[0081]

[0082] Note: λ0 refers to the wavelength of free space corresponding to the center frequency, and NG indicates that it is not given in the text.

[0083] Compared with antenna sample [1], the present invention can achieve circular polarization radiation in two frequency bands. In contrast, although antenna sample [1] uses a differential feeding method, it can only achieve linear polarization radiation, and the radiation direction of the antenna is limited. Compared with antenna samples [2] and [3], the present invention can achieve a wider impedance bandwidth, and the axial ratio bandwidth is more advantageous than that of antenna sample [3]. The present invention uses fewer antenna elements, and the overall size of the antenna array is smaller. Compared with antenna samples [4] and [5], the present invention has a greater advantage in both impedance bandwidth and axial ratio bandwidth, and the peak gain is close to that of antenna sample [5]. At the same time, antenna samples [2], [3], [4] and [5] do not use differential feeding networks, which will lead to a high level of cross-polarization in high-frequency applications. In contrast, the present invention uses a differential feeding network, which has a significant technical advantage in reducing the level of cross-polarization.

[0084] In summary, according to one or more embodiments of the present invention, this invention combines the advantages of substrate-integrated waveguide cavity antennas and differential circuits. By introducing arc-shaped microstrip lines and elliptical stubs, the structure is very simple, and broadband circularly polarized radiation in two frequency bands is achieved. Furthermore, it simplifies the feed network, making it suitable for high-frequency applications and reducing cross-polarization levels. Because it can achieve dual-frequency circularly polarized radiation, the antenna array of this invention has a wider range of applications and can operate over a wider frequency band, which is also an advantage of this antenna array.

[0085] The foregoing description of several embodiments of the invention has been provided for illustrative purposes. This foregoing description is not intended to be exhaustive, nor is it intended to limit the invention to the specific forms and / or configurations disclosed. The invention is not limited to the illustrative embodiments described above. Those skilled in the art will understand that other modifications and alterations can be made to the embodiments disclosed herein without departing from the scope and spirit of the invention, and such modifications and alterations are all within the scope of the invention.

Claims

1. A differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array, characterized in that, include: An array structure consisting of 2×2 antenna elements, wherein each antenna element includes a substrate integrated waveguide cavity, the substrate integrated waveguide cavity comprising a first upper dielectric substrate and a second lower dielectric substrate stacked vertically, the substrate integrated waveguide cavity being enclosed by an array of metal vias penetrating the first upper dielectric substrate and the second lower dielectric substrate, each metal via in the metal via array having a diameter of d and a spacing of p between them; wherein the substrate integrated waveguide cavity has a diameter of d R A circular radiating aperture is etched into the top copper layer of the integrated waveguide cavity on the substrate; wherein, the antenna unit has a radiating structure disposed on the surface of the first upper dielectric substrate, including a pair of arc-shaped microstrip lines and two symmetrically distributed sets of elliptical stubs; wherein, the length of the arc-shaped microstrip lines is l1 and the width is w1, the major semi-axis of the two sets of elliptical stubs are R1 and R2 respectively, the ratios of their major semi-axis to minor semi-axis are Ratio1 and Ratio2 respectively, and the two sets of elliptical stubs are arranged at an angle θ. r Symmetrically distributed along the arc-shaped microstrip line; A differential feed network, comprising four improved ring couplers disposed on a third bottom dielectric substrate, is used to provide differential signals with a phase difference in the range of 175°–185° to the antenna element; and A differential feed probe, penetrating the second lower dielectric substrate of the substrate integrated waveguide cavity, includes a pair of coaxially arranged probes connected to a first differential port + and a second differential port -, wherein the diameter of the differential feed probe is d. s The corresponding coaxial hole diameter is d. c ; The substrate-integrated waveguide cavity has a diameter of C1 and is surrounded by a set of metallized vias of diameter d along the circumferential direction. The spacing p satisfies the necessary condition for the formation of the substrate-integrated waveguide cavity, i.e., p / d < 2, to avoid electromagnetic leakage. The included angle θ of the elliptical stubs... r The phase difference between the input signals of the first differential port + and the second differential port - is 180°±5°, with a range of 50°-70°, in order to achieve dual-frequency circular polarization radiation in both low-frequency and high-frequency bands.

2. The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array according to claim 1, characterized in that, The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array operates in the low-frequency band of 15.5-19.595GHz and the high-frequency band of 21.93-24.76GHz.

3. The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array according to claim 2, characterized in that, The center frequency of the low-frequency band is 17.6 GHz, and the high-frequency band is 23.4 GHz.

4. The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array according to claim 1, characterized in that, The included angle θ of the elliptical branch r It is 60°±2°.

5. The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array according to claim 1, characterized in that, The spacing between the antenna elements is 0.6-0.8 times the free space wavelength corresponding to the center frequency of the high-frequency band.

6. The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array according to any one of claims 1-5, characterized in that, The annular coupler is disposed on the bottom copper layer of the third bottom dielectric substrate and is connected to the radiating structure through the differential feed probe.

7. The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array according to any one of claims 1-5, characterized in that, The first upper dielectric substrate, the second lower dielectric substrate, and the third bottom dielectric substrate are bonded together by an adhesive sheet; and The output port of the ring coupler corresponds one-to-one with the differential feed probe.

8. The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array according to any one of claims 1-5, characterized in that, The ratio of the resonant frequency of the fundamental mode to the first higher-order mode of the substrate integrated waveguide cavity is 1:1.3-1.5, and the electric field distribution of the higher-order mode is orthogonal to that of the fundamental mode.

9. The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array according to any one of claims 1-5, characterized in that, The parameters of the elliptical branch satisfy the following relationship: θ r =60°±2°, Ratio1=0.7±0.05, Ratio2=0.6±0.05, and R1=3.0-3.4mm, R2 = 3.0-3.2 mm.

10. The differentially fed dual-frequency circularly polarized substrate integrated waveguide cavity antenna array according to any one of claims 1-5, characterized in that, The antenna element has an axial ratio bandwidth of 4.09% and 4.20% in the 15.34-15.98GHz and 23.05-24.04GHz frequency bands, respectively, a cross-polarization level of less than -20dB, and impedance bandwidths of 23.34% and 12.12%, respectively.

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