Differential feed dual-frequency dual-polarization microstrip filtering antenna

Abstract

A differential feed dual-frequency dual-polarization microstrip filtering antenna comprises three layers of dielectric substrates which are arranged at intervals from top to bottom, and an octagonal annular coupling parasitic structure is loaded on the lower surface of the first layer of dielectric substrate; a rectangular radiation patch is printed on the upper surface of the second dielectric substrate and is loaded with four non-closed rectangular gaps which are distributed in a square shape and are mutually rotationally symmetrical. A cross-shaped parasitic branch knot and four L-shaped symmetrical open-circuit branch knots which are distributed in a rhombus shape and extend outwards along the diagonal direction of the rhombus are printed on the lower surface of the second dielectric substrate layer; the lower surface of the third dielectric substrate is a metal floor; the second layer of dielectric substrate and the third layer of dielectric substrate are connected through a coaxial feeder line; according to the dual-frequency dual-polarization filtering antenna, the mode of combining the differential feed technology and the microstrip antenna is adopted, the design of the dual-frequency dual-polarization filtering antenna with four radiation zero points is achieved, the antenna has good edge selectivity and good out-of-band rejection capacity, in-band gain is stable, and a directional diagram has good symmetry and directionality.

Description

Technical Field

[0001] The invention belongs to the technical field of antennas, and in particular relates to a differentially fed dual-frequency dual-polarization microstrip filtering antenna. Background Art

[0002] With the rapid development of wireless communication technology, spectrum resources are becoming increasingly scarce, especially in applications such as wireless communication, satellite communication, and the Internet of Things (IoT), where the requirements for frequency selectivity and out-of-band suppression capabilities are becoming increasingly high. Although traditional single-polarization antennas are widely used in many fields, they often show their shortcomings when faced with challenges such as multi-band, multi-protocol, space limitations, and signal interference. Dual-band dual-polarization antennas can simultaneously support two vertical electric field polarization modes in two working frequency bands, greatly improving communication capacity and system anti-interference. In complex communication environments, dual-band dual-polarization filter antennas can significantly reduce interference between signals and improve spectrum utilization efficiency.

[0003] Differential feeding technology is a common feeding method. Compared with traditional single-ended feeding, it has higher anti-noise and anti-interference capabilities. Differential feeding can effectively suppress common-mode interference and improve the radiation characteristics and signal quality of the antenna by feeding two complementary signals. Especially in high-frequency and high-speed signal transmission, differential feeding technology can significantly improve the performance of the antenna and avoid the ground noise and uneven radiation problems that may be introduced by traditional single-ended feeding.

[0004] When differential feeding technology is combined with a dual-frequency dual-polarization microstrip filter antenna, efficient signal transmission, strong anti-interference ability and frequency selectivity can be achieved simultaneously. Differential feeding effectively improves the common-mode suppression capability of the antenna and reduces the impact of feeder line loss and noise on the signal, while the dual-frequency dual-polarization design enhances the antenna's multi-band signal reception and transmission capabilities and improves the overall performance of the system. It has broad application prospects in wireless communication systems such as 5G communications, satellite communications, the Internet of Things and radar systems.

[0005] For the differentially fed dual-polarized dual-frequency microstrip filter antenna, the patent application document with publication number CN118073840A discloses a small dual-band dual-polarized filter antenna. The invention provides two-band communications and does not require the integration of an additional filtering system. However, the dual polarization designed is right-handed circularly polarized radiation and omnidirectional linearly polarized radiation, which is essentially a single-polarization design. In addition, the gain fluctuation is large within the working frequency band, the edge selectivity is poor, and the out-of-band suppression capability is poor.

[0006] The patent application document with publication number CN117154401A discloses a high-performance dual-polarization filtering antenna with differential feeding, which adopts parasitic square patches and V-shaped metal strips to achieve filtering response and uses differential feeding. It has high edge selectivity, but poor out-of-band suppression capability, and is limited by the complexity of dual-polarization design and filtering structure, and cannot be designed for dual frequency.

[0007] In summary, the design methods of filtering antennas can be divided into the following three types: The first method is to directly cascade the filter end with the same impedance and the antenna signal input end, and instill the low-pass, high-pass or band-pass response of the filter into the radiation performance of the antenna. This design will avoid the occurrence of certain impedance mismatches, but the space size pressure of the entire RF front end has not been further alleviated. The second method is to replace the last order of the filter with a resonant antenna, adjust the size of the resonant antenna to ensure that the impedance before and after the replacement is equal, so that the filtering antenna can obtain a gain curve trend similar to the filter transmission coefficient trajectory. This design method can freely adjust the filter center frequency, reflection coefficient, insertion loss and working bandwidth parameters according to actual application requirements, and finally graft the resonant antenna. Compared with the first method, the space resources occupied by the second method will be reduced to a certain extent, but the antenna may be affected by the insertion loss of the filter, which will greatly reduce the efficiency to a certain extent and significantly deteriorate the radiation performance. The third design method is to use electromagnetic coupling to design the filter and antenna without introducing the filtering circuit structure, so that the filtering antenna has the characteristics of in-band radiation / out-of-band filtering, seamlessly connected, and ultimately achieve an overall miniaturization, high integration and multi-function. However, it is greatly affected by the antenna structure, and there will be problems such as poor edge selectivity due to inappropriate radiation zero point loading and unstable in-band radiation gain.

[0008] At present, when designing dual-frequency microstrip filter antennas, due to the high difficulty of dual-frequency design of dual-polarized antennas, dual-frequency design is usually only performed through single-polarized microstrip antennas, or the dual-frequency dual-polarization designed is dual-polarization in non-traditional communication fields, such as dual-polarization combining circular polarization and linear polarization. This kind of dual-polarization is essentially not able to support two perpendicular electric field polarization modes at the same time, and its application prospects are poor. In addition, the current dual-frequency filter antennas have problems such as poor edge selectivity and unstable in-band radiation gain caused by improper radiation zero point loading. Summary of the invention

[0009] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a differentially fed dual-frequency dual-polarized microstrip filter antenna. By loading four unclosed rectangular gaps on the dual-polarized microstrip antenna, a normal working resonance point is introduced at high frequency, the design of the dual-frequency dual-polarized microstrip antenna is realized, and a radiation zero point is introduced at the low-frequency stop band adjacent to the high-frequency working band, thereby improving the out-of-band suppression capability of the low-frequency stop band adjacent to the high-frequency working band; at the same time, by loading an octagonal annular coupled parasitic structure, an L-shaped symmetrical open-circuit branch and a cross-shaped parasitic branch, three radiation zero points are introduced at the out-of-band stop band of the two working bands, thereby further improving the edge selectivity and out-of-band suppression capability of the antenna; finally, a differentially fed dual-frequency dual-polarized microstrip filter antenna design with four radiation zero points, good edge selectivity and good out-of-band suppression capability, and stable in-band gain is formed.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] A differentially fed dual-frequency dual-polarized microstrip filtering antenna comprises a first dielectric substrate 1, a second dielectric substrate 2 and a third dielectric substrate 3 which are arranged in intervals from top to bottom, wherein the lower surface of the first dielectric substrate 1 is loaded with an octagonal annular coupling parasitic structure 4; the upper surface of the second dielectric substrate 2 is printed with a rectangular radiation patch 5, and the rectangular radiation patch 5 is loaded with four non-enclosed rectangular gaps 9 which are distributed in a square and rotationally symmetrical with each other; the lower surface of the second dielectric substrate 2 is printed with a cross-shaped parasitic branch 7 and four L-shaped symmetrical open branches 6 of the same structure which are distributed in a diamond shape and extend outward along the diagonal direction of the diamond shape; the lower surface of the third dielectric substrate 3 is a metal floor 16; the second dielectric substrate 2 and the third dielectric substrate 3 are connected by a coaxial feeder 18.

[0012] The coaxial feed line 18 includes a metal inner core 8 and a metal outer shell 17 . The third dielectric substrate 3 and the second dielectric substrate 2 are connected via the metal inner core 8 of the coaxial feed line 18 . The metal floor 16 is connected to the metal outer shell 17 of the coaxial feed line 18 .

[0013] The octagonal annular coupling parasitic structure 4 is a rectangular annular structure with chamfered corners. The octagonal annular coupling parasitic structure 4 introduces a radiation zero point in the high-frequency stop band adjacent to the low-frequency working band.

[0014] The non-closed rectangular slots 9 are symmetrical structures, including long sides 11 and short sides 10 connected to each other. The four non-closed rectangular slots 9 introduce a normal working resonance point at high frequency and introduce a radiation zero point at the low frequency stop band adjacent to the high frequency working band.

[0015] The L-shaped symmetrical open-circuit branch 6 is connected to the metal core 8 of the coaxial feed line 18 at one end close to the center of the antenna, and the other end of the L-shaped symmetrical open-circuit branch 6 is in an open-circuit state. The cross-shaped parasitic branch 7 is located at the center of the four L-shaped symmetrical open-circuit branches 6. The L-shaped symmetrical open-circuit branch 6 and the cross-shaped parasitic branch 7 do not contact each other, and the direction of the cross-shaped parasitic branch 7 forms an angle of 45° with the direction of the L-shaped symmetrical open-circuit branch 6.

[0016] The L-shaped symmetrical open-circuit branch 6 includes a rectangular main branch 12 and two subsidiary L-shaped branches 15 symmetrical about the rectangular main branch 12, wherein the subsidiary L-shaped branch 15 is composed of a long rectangular branch 13 and a short rectangular branch 14 vertically connected, the subsidiary L-shaped branch 15 is vertically connected to the rectangular main branch 12 through the long rectangular branch 13, the rectangular main branch 12 is connected to the metal core 8 of the coaxial feed line 18, and the L-shaped symmetrical open-circuit branch 6 introduces a radiation zero point at the low-frequency stop band of the low-frequency working band.

[0017] The cross-shaped parasitic branch 7 is chamfered at the center and both ends, and the cross-shaped parasitic branch 7 introduces a radiation zero point at the high-frequency stop band of the high-frequency working frequency band.

[0018] The metal core 8 of the coaxial feed line 18 passes through the third dielectric substrate 3 to be connected to the rectangular radiation patch 5 on the upper surface of the second dielectric substrate 2 , and is connected to the L-shaped symmetrical open branch 6 on the lower surface of the second dielectric substrate 2 .

[0019] The metal floor 16 is provided with four feeding ports distributed in a rhombus, and the four feeding ports are respectively located at the four vertices of the rhombus, wherein the two ports on the rhombus diagonal parallel to the y-axis are the first feeding port 16-1 and the second feeding port 16-2, and the two together constitute the differential port A, and the two ports on the rhombus diagonal parallel to the x-axis are the third feeding port 16-3 and the fourth feeding port 16-4, and the two together constitute the differential port B. When the first feeding port 16-1 and the second feeding port 16-2 input the same signal with a phase difference of 180°, the third feeding port 16-3 and the fourth feeding port 16-4 are connected to the matching load, and the antenna works normally at this time, and the third feeding port 16-3 and the fourth feeding port 16-4 work in the same way, and their differential mode S parameters are:

[0020] S dd11 =(S 11 -S 12 -S 21 +S 22 ) / 2

[0021] S dd22 =(S 33 -S 34 -S 43 +S 44 ) / 2

[0022] S dd12 =(S 13 -S 14 -S 23 +S 24 ) / 2

[0023] S dd21 =(S 31 -S 41 -S 32 +S 42 ) / 2

[0024] Among them, S dd11 is the reflection coefficient of differential port A under differential signal, S dd22 Reflection coefficient of differential port B under differential signal, S dd12 and S dd21 is the transmission coefficient between the two differential ports under differential mode signal, S mn (m,n=1,2,3,4) are the standard S parameters of the four-port network structure.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention loads four unclosed rectangular slots 9 on the rectangular radiation patch 5 on the upper surface of the second dielectric substrate 2, introduces a normal working resonance point at high frequency, realizes the design of a dual-frequency dual-polarization microstrip antenna, and introduces a radiation zero point at the low-frequency stop band adjacent to the high-frequency working band, improves the out-of-band suppression capability and edge selectivity of the antenna at the low-frequency stop band adjacent to the high-frequency working band, and stabilizes the gain in the two working bands, thereby overcoming the difficulty of the ordinary dual-polarization microstrip antenna in the prior art to perform mutually perpendicular dual-polarization design.

[0027] 2. The present invention introduces a radiation zero point in the high-frequency stop band adjacent to the low-frequency working band by loading an octagonal annular coupled parasitic structure 4 on the lower surface of the first dielectric substrate 1; loads an L-shaped symmetrical open-circuit branch 6 on the lower surface of the second dielectric substrate 2 to introduce a radiation zero point at the low-frequency stop band of the low-frequency working band; and loads a cross-shaped parasitic branch 7 on the lower surface of the second dielectric substrate 2 to introduce a radiation zero point at the high-frequency stop band of the high-frequency working band; the loading of three radiation zero points enables the antenna to have a strong out-of-band suppression capability and a high edge selectivity outside the working frequency band, and does not affect the dual-frequency dual-polarization design of the antenna and the stable radiation of the antenna, thereby overcoming the problems of poor edge selectivity and out-of-band suppression capability and unstable in-band radiation gain caused by inappropriate loading of radiation zero points in the prior art.

[0028] In summary, the present invention overcomes the difficulty of mutually perpendicular dual-polarization design of ordinary dual-polarization microstrip antennas in the prior art by loading four unclosed rectangular gaps 9 on the rectangular radiation patch 5 on the upper surface of the second dielectric substrate 2, realizes a dual-frequency dual-polarization microstrip antenna with stable gain in the dual-frequency working frequency band, and introduces a radiation zero point at the low-frequency stop band adjacent to the high-frequency working frequency band; together with the three radiation zero points introduced by loading an octagonal annular coupling parasitic structure 4 on the lower surface of the first dielectric substrate 1 and loading an L-shaped symmetrical open-circuit branch 6 and a cross-shaped parasitic branch 7 on the lower surface of the second dielectric substrate 2, the edge selectivity and out-of-band suppression capability of the antenna are improved, and finally a device with four radiation zero points is formed. The present invention has good edge selectivity and good out-of-band suppression capability, and realizes the design of a differentially fed dual-frequency dual-polarization filter microstrip antenna with stable in-band gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the overall structure of the antenna of the present invention.

[0030] Figure 2 is a side view of the antenna of the present invention.

[0031] Figure 3 It is a schematic structural diagram of the first dielectric substrate 1 of the present invention.

[0032] Figure 4 Schematic diagram of the structure of the second dielectric substrate 2 of the present invention, wherein: Figure 4 (a) is a schematic diagram of the upper surface structure of the second dielectric substrate 2. Figure 4 (b) is a schematic diagram of the lower surface structure of the second dielectric substrate 2.

[0033] Figure 5 It is a schematic diagram of the lower surface structure of the third dielectric substrate 3 of the present invention.

[0034] Figure 6 is the differential mode emission coefficient S of the present invention dd11 Result graph.

[0035] Figure 7 Graph showing the gain results of the antenna of the present invention.

[0036] Figure 8 is the differential mode radiation coefficient S of the antenna of comparative example 1 dd11 and gain result graph.

[0037] Fig. 9 is the differential mode radiation coefficient S of the antenna of comparative example 2 dd11 and gain result graph.

[0038] Fig.10 is the differential mode radiation coefficient S of the antenna of comparative example 3 dd11and gain result graph.

[0039] Fig.11 is the differential mode radiation coefficient S of the antenna of comparative example 4 dd11 and gain result graph.

[0040] Fig.12 is the radiation pattern of the present invention at 1.94 GHz, wherein, Fig.12 (a) is the E-plane directional diagram, Fig.12 (b) is the H-plane orientation diagram.

[0041] Fig.13 is the radiation pattern of the present invention at 3.78 GHz, wherein, Fig.13 (a) is the E-plane directional diagram, Fig.13 (b) is the H-plane orientation diagram.

[0042] Among them, 1. the first layer of dielectric substrate; 2. the second layer of dielectric substrate; 3. the third layer of dielectric substrate; 4. the octagonal annular coupled parasitic structure; 5. the rectangular radiation patch; 6. the L-shaped symmetrical open-circuit branch; 7. the cross-shaped parasitic branch; 8. the metal inner core; 9. the unclosed rectangular gap; 10. the short side; 11. the long side; 12. the rectangular main branch; 13. the long rectangular branch; 14. the short rectangular branch; 15. the auxiliary L-shaped branch; 16. the metal floor; 16-1. the first feeding port; 16-2. the second feeding port; 16-3. the third feeding port; 16-4. the fourth feeding port; 17. the metal shell; 18. the coaxial feed line. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0044] When designing dual-frequency filter antennas, the current microstrip filter antennas are generally designed with single-polarized microstrip antennas, because of the high difficulty of dual-frequency design of dual-polarized antennas. Or the dual polarization they design is non-traditional communication dual polarization, such as the dual polarization that combines circular polarization and linear polarization. This type of dual polarization is essentially not able to support two vertical electric field polarization modes at the same time, and its application prospects are poor. In addition, the current dual-frequency filter antennas have problems such as poor edge selectivity and unstable in-band radiation caused by improper radiation zero point loading. The present invention proposes a dual-frequency dual-polarization microstrip filter antenna with differential feeding, which realizes the design of dual-polarization dual-frequency microstrip antenna by combining differential feeding technology with microstrip antenna, and realizes the design of dual-polarization dual-frequency microstrip antenna by slot loading technology. Radiation zero points are loaded on both sides of the dual-frequency working band by loading open-circuit branches and parasitic structures, and combined with the radiation zero points introduced by the feeding method, a dual-frequency dual-polarization filter antenna design with four radiation zero points is realized. The antenna has good edge selectivity and good out-of-band suppression capability, and the in-band gain is stable, and the radiation pattern has good symmetry and directivity.

[0045] Specifically, the present invention proposes a differentially fed dual-frequency dual-polarized microstrip filtering antenna, the structure of which is as follows: Figure 1 As shown, it consists of three layers of dielectric substrates, metal coatings thereon, and a feeding structure, wherein the thickness of the first dielectric substrate 1 is 3 mm, the thickness of the second dielectric substrate 2 is 4 mm, the thickness of the third dielectric substrate 3 is 1 mm, the interval between the first dielectric substrate 1 and the second dielectric substrate 2 is 5 mm, the interval between the second dielectric substrate 2 and the third dielectric substrate 3 is 6 mm, and the material of the first dielectric substrate 1, the second dielectric substrate 2, and the third dielectric substrate 3 is F4B with a relative dielectric constant of 2.65, and the side length is 80 mm.

[0046] Figure 2 It is a side view of the antenna structure, and the relative position relationship of the three-layer dielectric substrate can be seen. It can be seen that the third-layer dielectric substrate 3 and the second-layer dielectric substrate 2 are connected through the metal core 8 of the coaxial feed line 18, and the metal core 8 of the coaxial feed line 18 passes through the third-layer dielectric substrate 3 and is connected to the rectangular radiation patch 5 on the upper surface of the second-layer dielectric substrate 2, and is connected to the L-shaped symmetrical open branch 6 on the lower surface of the second-layer dielectric substrate 2.

[0047] Figure 3 A structural schematic diagram of the first dielectric substrate 1 is given. The lower surface of the first dielectric substrate 1 is an octagonal annular coupling parasitic structure 4, which can be regarded as a rectangular annular structure with chamfers at four corners. The corresponding rectangular side length L1 is 37 mm, the annular width T1 is 2.5 mm, the side length D1 of the outer ring chamfer is 10 mm, and the side length D2 of the inner ring chamfer is 10 mm. The octagonal annular coupling parasitic structure 4 introduces a radiation zero point at 2.24 GHz.

[0048] Figure 4 A schematic diagram of the structure of the second dielectric substrate 2 is given. On the upper surface of the second dielectric substrate 2 is a rectangular radiation patch 5, the side length L2 of the rectangular radiation patch 5 is 45 mm, and four unclosed rectangular slots 9 are loaded thereon. The width of the unclosed rectangular slots 9 is 1 mm. The unclosed rectangular slots 9 are symmetrical structures, including long sides 11 and short sides 10 connected to each other. The long side 11 is 12 mm, and the short side 10 is 5 mm. The loading of the four unclosed rectangular slots 9 realizes the design of a dual-frequency dual-polarization microstrip antenna, and the loading of the unclosed rectangular slots 9 introduces a radiation zero point at 3.28 GHz. A cross-shaped parasitic branch 7 and four L-shaped symmetrical open-circuit branches 6 are printed on the lower surface of the second dielectric substrate 2, wherein the L-shaped symmetrical open-circuit branch 6 is directly connected to the metal core 8 of the coaxial feeder 18 at 1 mm near one end of the center of the antenna, and the L-shaped symmetrical open-circuit branch 6 and the cross-shaped parasitic branch 7 do not contact each other. The four L-shaped symmetrical open branches 6 have the same structure. The L-shaped symmetrical open branches 6 include a rectangular main branch 12 and two subsidiary L-shaped branches 15 symmetrical about the rectangular main branch 12, wherein the subsidiary L-shaped branch 15 is composed of a long rectangular branch 13 and a short rectangular branch 14 connected vertically, and the same rectangular main branch 12 has a length of 20.5 mm and a width of 2.5 mm. The subsidiary L-shaped branches 15 are symmetrically loaded on both sides of the rectangular main branch 12, and the subsidiary L-shaped branches 15 are connected by the long rectangular branches 13 and the short rectangular branches 14. 3 is vertically connected to the rectangular main branch 12, the rectangular main branch 12 is connected to the metal inner core 8 of the coaxial feed line 18, the distance L3 between the loading position of the auxiliary L-shaped branch 15 and the connected end of the rectangular main branch 12 and the metal inner core 8 of the coaxial feed line 18 is 11.5 mm, the long rectangular branch 13 is 5.75 mm long and 2.5 mm wide, the short rectangular branch 14 is 4 mm long and 2.5 mm wide, and the L-shaped symmetrical open-circuit branch 6 introduces a radiation zero point at 1.68 GHz.

[0049] The length L4 of the cross-shaped parasitic branch 7 is 27 mm, and it is chamfered at the center and both ends to improve the out-of-band suppression capability. The chamfer width W1 at the center is 2.26 mm, and the chamfer side length at both ends is 0.8 mm. The cross-shaped parasitic branch 7 introduces a radiation zero point at 3.96 GHz.

[0050] Figure 5A schematic diagram of the structure of the third dielectric substrate 3 is given. The lower surface of the third dielectric substrate 3 is a metal floor 16, which is connected to the metal shell 17 of the coaxial feed line 18. The lower surface of the third dielectric substrate 3 is provided with four feeding ports distributed in a rhombus, and the four feeding ports are respectively located at the four vertices of the rhombus, wherein the two ports on the diagonal line of the rhombus parallel to the y-axis are the first feeding port 16-1 and the second feeding port 16-2, which together constitute the differential port A, and the two ports on the diagonal line of the rhombus parallel to the x-axis are the third feeding port 16-3 and the fourth feeding port 16-4, which together constitute the differential port B. When the first feeding port 16-1 and the second feeding port 16-2 input the same signal with a phase difference of 180°, the third feeding port 16-3 and the fourth feeding port 16-4 are connected to a matching load, and the antenna works normally at this time. The third feeding port 16-3 and the fourth feeding port 16-4 work in the same way, and their differential mode S parameters are:

[0051] S dd11 =(S 11 -S 12 -S 21 +S 22 ) / 2

[0052] S dd22 =(S 33 -S 34 -S 43 +S 44 ) / 2

[0053] S dd12 =(S 13 -S 14 -S 23 +S 24 ) / 2

[0054] S dd21 =(S 31 -S 41 -S 32 +S 42 ) / 2

[0055] Among them, S dd11 is the reflection coefficient of differential port A under differential signal, S dd22 Reflection coefficient of differential port B under differential signal, S dd12 and S dd21 is the transmission coefficient between the two differential ports under differential mode signal, S mn (m,n=1,2,3,4) are the standard S parameters of the four-port network structure.

[0056] Figure 6 The differential mode reflection coefficient S of the antenna of the present invention is given dd11Its differential mode reflection coefficient is less than -10dB in both 1.78-2.1GHz and 3.72-3.84GHz, and it works normally in these two frequency bands. Figure 7 The gain of the antenna of the present invention is shown in Figure 1. The gain of the antenna in the working frequency bands of 1.78-2.1 GHz and 3.72-3.84 GHz is stable, and the average gain is 7.8 dBi and 8.2 dBi respectively. It can be seen that the antenna of the present invention has good edge selectivity, and the out-of-band suppression capability exceeds 14 dB.

[0057] In order to better reflect the design effect of the present invention, four comparative examples are proposed. Comparative example 1 is a basic differentially fed microstrip antenna. Figure 8 As shown, it has a corresponding single resonance point, but it cannot work normally and there is no sign of dual frequency. Comparative Example 2 is to load an unclosed rectangular gap 9 based on Comparative Example 1, as shown in FIG. Fig. 9 As shown, it can be seen that the number of resonance points changes from one to two, with dual-frequency characteristics, and the radiation zero point caused by the loading of the unclosed rectangular gap 9 at 3.28GHz can be seen. Comparative Example 3 adds an L-shaped symmetrical open branch 6 based on Comparative Example 2, as shown in FIG. Fig.10 As shown in FIG. 1 , it can be seen that after the L-shaped symmetrical open-circuit branch 6 is loaded, the matching of the antenna is significantly improved, and a radiation zero point is introduced at 1.68 GHz. Comparative Example 4 is based on Comparative Example 3 and a cross-shaped parasitic branch 7 is loaded. Fig.11 As shown, the loading of the cross-shaped parasitic branch 7 introduces a radiation zero point at 3.96 GHz. Based on the comparative example 4, the octagonal annular coupling parasitic structure 4 is loaded to obtain the dual-frequency dual-polarization microstrip filtering antenna proposed by the present invention.

[0058] Fig.12 and Fig.13 The E-plane and H-plane radiation patterns of the antenna at the operating frequencies of 1.94 GHz and 3.78 GHz in two operating frequency bands are given. It can be seen that the radiation patterns have good symmetry and directivity, without pits and distortion. The cross polarization is below -28 dB.

[0059] In summary, the present invention realizes the design of a dual-polarization dual-frequency microstrip antenna by combining differential feeding technology with a microstrip antenna through slot loading technology, loads radiation zeros on both sides of the dual-frequency working band by loading open-circuit branches and parasitic structures, and combines with the radiation zeros introduced by slot loading to realize the design of a filtering antenna with four radiation zeros. The antenna has good edge selectivity and good out-of-band suppression capability, and the in-band gain is stable, and the radiation pattern has good symmetry and directivity.

[0060] The key points and protection points of the present invention are:

[0061] The rectangular radiation patch 5 of the present invention is located on the upper surface of the second dielectric substrate 2. The rectangular radiation patch 5 is loaded with an unclosed rectangular gap 9 with a long side 11 of 12 mm and a short side 10 of 5 mm. The four unclosed rectangular gaps 9 introduce a normal working resonance point at high frequency, thereby realizing the design of a dual-frequency dual-polarization microstrip antenna and introducing a radiation zero point in the low-frequency stop band adjacent to the high-frequency working band.

[0062] The octagonal annular coupling parasitic structure 4 of the present invention is located on the lower surface of the first dielectric substrate 1, which can be regarded as a structure after the rectangular loop is chamfered, and the corresponding rectangular side length is 37mm. It can introduce a radiation zero point in the high-frequency stop band adjacent to the low-frequency working band.

[0063] The cross-shaped parasitic branch 7 of the present invention is located on the lower surface of the second dielectric substrate 2. The center and edge positions of the cross-shaped parasitic branch 7 are chamfered to improve the out-of-band suppression capability and impedance matching. The cross-shaped parasitic branch 7 is a symmetrical structure, and the length of a single branch is 27 mm. It introduces a radiation zero point in the high-frequency stop band of the high-frequency working band.

[0064] The L-shaped symmetrical open-circuit branch 6 of the present invention is located on the lower surface of the second-layer dielectric substrate 2, and is located on the same surface as the cross-shaped parasitic branch 7, but is not connected. The L-shaped symmetrical open-circuit branch 6 is connected to the metal core 8 of the coaxial feed line 18 1 mm near one end of the antenna center, and introduces a radiation zero point in the low-frequency stop band of the low-frequency working band.

[0065] The metal shell 17 of the coaxial feed line 18 of the present invention is connected to the metal floor 16 on the lower surface of the third dielectric substrate 3, and the metal core 8 of the coaxial feed line 18 passes through the third dielectric substrate 3 and the second dielectric substrate 2 to be connected to the rectangular radiation patch 5 for feeding. At the same time, the metal core 8 of the coaxial feed line 18 is also connected to the L-shaped symmetrical open-circuit branch 6, and the two feeding ports located on the straight line where the L-shaped symmetrical open-circuit branch 6 is located simultaneously feed signals of the same magnitude and a phase difference of 180° to realize antenna operation.

[0066] Application prospects of the present invention:

[0067] The differentially fed dual-frequency dual-polarized microstrip filter antenna proposed in the present invention can simultaneously support two vertical electric field polarization modes in two working frequency bands, greatly improving the communication capacity and anti-interference performance of the system. In a complex communication environment, the dual-frequency dual-polarized filter antenna can significantly reduce interference between signals and improve spectrum utilization efficiency. The present invention can play an important role in wireless communications, satellite networks, radars, and Internet of Things applications.

[0068] When designing dual-frequency filtering antennas, the current microstrip filter antennas are difficult to design dual-frequency antennas, so they are only designed with single-polarized microstrip antennas, or the dual-frequency dual-polarization they design is non-traditional communication dual-polarization, such as the dual-polarization that combines circular polarization and linear polarization. This type of dual polarization is not able to support two vertical electric field polarization modes at the same time, and its application prospects are poor. In addition, the current dual-frequency filtering antennas have problems such as poor edge selectivity and unstable in-band radiation caused by improper radiation zero point loading.

[0069] The present invention proposes a differentially fed dual-frequency dual-polarized microstrip filtering antenna, which adopts a method of combining differential feeding technology with microstrip antenna, realizes the design of dual-polarized dual-frequency microstrip antenna through slot loading technology, loads radiation zero points on both sides of the dual-frequency working band by loading open-circuit branches and parasitic structures, and combines with the radiation zero points introduced by the feeding method to realize the design of a filtering antenna with four radiation zero points. The antenna has good edge selectivity and good out-of-band suppression capability, and the in-band gain is stable, the radiation pattern has good symmetry and directivity, and has good application prospects.

[0070] The differentially fed dual-frequency dual-polarization microstrip filter antenna proposed in the present invention uses a differential feeding method and introduces a radiation zero point by loading with parasitic structures such as an octagonal ring-coupled parasitic structure 4, an L-shaped symmetrical open-circuit branch 6 and a cross-shaped parasitic branch 7. When the sizes of the parasitic structure, the radiation patch and the loading gap change, the operating frequency changes, and the structure can still achieve the purpose of the invention.

Claims

1. A differentially fed dual-frequency dual-polarized microstrip filtering antenna, comprising a first dielectric substrate (1), a second dielectric substrate (2) and a third dielectric substrate (3) arranged in a spaced relationship from top to bottom, characterized in that: The lower surface of the first dielectric substrate (1) is loaded with an octagonal annular coupling parasitic structure (4); the upper surface of the second dielectric substrate (2) is printed with a rectangular radiation patch (5), and the rectangular radiation patch (5) is loaded with four non-enclosed rectangular gaps (9) that are distributed in a square and rotationally symmetrical with each other; the lower surface of the second dielectric substrate (2) is printed with cross-shaped parasitic branches (7) and four L-shaped symmetrical open branches (6) of the same structure that are distributed in a diamond shape and extend outward along the diagonal direction of the diamond shape; the lower surface of the third dielectric substrate (3) is a metal floor (16); and the second dielectric substrate (2) and the third dielectric substrate (3) are connected via a coaxial feeder (18).

2. The differentially fed dual-frequency dual-polarized microstrip filtering antenna according to claim 1, characterized in that: The coaxial feed line (18) comprises a metal inner core (8) and a metal outer shell (17); the third layer dielectric substrate (3) and the second layer dielectric substrate (2) are connected via the metal inner core (8) of the coaxial feed line (18); and the metal floor (16) is connected to the metal outer shell (17) of the coaxial feed line (18).

3. The differentially fed dual-frequency dual-polarized microstrip filtering antenna according to claim 1, characterized in that: The octagonal annular coupling parasitic structure (4) is a rectangular annular structure with chamfered corners at four corners. The octagonal annular coupling parasitic structure (4) introduces a radiation zero point at a high-frequency stop band adjacent to a low-frequency working band.

4. The differentially fed dual-frequency dual-polarized microstrip filtering antenna according to claim 1, characterized in that: The non-enclosed rectangular slots (9) are of symmetrical structure, comprising long sides (11) and short sides (10) connected to each other. The four non-enclosed rectangular slots (9) introduce a normal working resonance point at a high frequency and introduce a radiation zero point at a low frequency stop band adjacent to the high frequency working band.

5. The differentially fed dual-frequency dual-polarized microstrip filtering antenna according to claim 1, characterized in that: The L-shaped symmetrical open-circuit branch (6) is connected to the metal inner core (8) of the coaxial feeder (18) at one end close to the center of the antenna, and the other end of the L-shaped symmetrical open-circuit branch (6) is in an open-circuit state. The cross-shaped parasitic branch (7) is located at the center of the four L-shaped symmetrical open-circuit branches (6). The L-shaped symmetrical open-circuit branches (6) and the cross-shaped parasitic branches (7) do not contact each other, and the direction of the cross-shaped parasitic branch (7) forms an angle of 45° with the direction of the L-shaped symmetrical open-circuit branch (6).

6. A differentially fed dual-frequency dual-polarization microstrip filtering antenna according to claim 1 or 5, characterized in that: The L-shaped symmetrical open-circuit branch (6) comprises a rectangular main branch (12) and two subsidiary L-shaped branches (15) symmetrical about the rectangular main branch (12), wherein the subsidiary L-shaped branch (15) is composed of a long rectangular branch (13) and a short rectangular branch (14) vertically connected, the subsidiary L-shaped branch (15) is vertically connected to the rectangular main branch (12) through the long rectangular branch (13), the rectangular main branch (12) is connected to the metal core (8) of the coaxial feed line (18), and the L-shaped symmetrical open-circuit branch (6) introduces a radiation zero point at a low-frequency stop band of a low-frequency working frequency band.

7. A differentially fed dual-frequency dual-polarization microstrip filtering antenna according to claim 1 or 5, characterized in that: The cross-shaped parasitic branch (7) is chamfered at the center and both ends, and the cross-shaped parasitic branch (7) introduces a radiation zero point at a high-frequency stop band of a high-frequency working frequency band.

8. The differentially fed dual-frequency dual-polarized microstrip filtering antenna according to claim 2, characterized in that: The metal inner core (8) of the coaxial feed line (18) passes through the third dielectric substrate (3) to be connected to the rectangular radiation patch (5) on the upper surface of the second dielectric substrate (2), and is connected to the L-shaped symmetrical open-circuit branch (6) on the lower surface of the second dielectric substrate (2).

9. The differentially fed dual-frequency dual-polarized microstrip filtering antenna according to claim 1, characterized in that: The metal floor (16) is provided with four feeding ports distributed in a rhombus shape, and the four feeding ports are respectively located at the four vertices of the rhombus, wherein two ports on the rhombus diagonal line parallel to the y-axis are the first feeding port (16-1) and the second feeding port (16-2), and the two together constitute a differential port A, and two ports on the rhombus diagonal line parallel to the x-axis are the third feeding port (16-3) and the fourth feeding port (16-4), and the two together constitute a differential port B. When the first feeding port (16-1) and the second feeding port (16-2) input signals of the same magnitude and a phase difference of 180°, the third feeding port (16-3) and the fourth feeding port (16-4) are connected to a matching load, and the antenna works normally at this time, and the third feeding port (16-3) and the fourth feeding port (16-4) work in the same manner, and their differential mode S parameters are: S dd11 =(S 11 -S 12 -S 21 +S 22 ) / 2 S dd22 =(S 33 -S 34 -S 43 +S 44 ) / 2 S dd12 =(S 13 -S 14 -S 23 +S 24 ) / 2 S dd21 =(S 31 -S 41 -S 32 +S 42 ) / 2 Among them, S dd11 is the reflection coefficient of differential port A under differential signal, S dd22 Reflection coefficient of differential port B under differential signal, S dd12 and S dd21 is the transmission coefficient between the two differential ports under differential mode signal, S mn (m,n=1,2,3,4) are the standard S parameters of the four-port network structure.

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