A dual-band dual-polarized microstrip filtering antenna with differential feed

Abstract

The application discloses a differential feed dual-band dual-polarized microstrip filter antenna, which comprises three layers of dielectric substrates arranged in a top-down interval, and the lower surface of the first layer of dielectric substrate is loaded with an octagonal ring-shaped coupling parasitic structure; the upper surface of the second layer of dielectric substrate is printed with a rectangular radiation patch, the rectangular radiation patch is loaded with four unclosed rectangular slots which are square distributed and rotationally symmetrical to each other, and the lower surface of the second layer of dielectric substrate is printed with a cross-shaped parasitic branch and four L-shaped symmetrical open circuit branches which are of the same structure and extend outward along the diagonal direction of the rhombus; the lower surface of the third layer of 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; the differential feed technology is combined with the microstrip antenna, so that the dual-band dual-polarized filter antenna design with four radiation zeros is realized, the antenna has good edge selectivity and good out-of-band suppression capability, the in-band gain is stable, and the directional diagram has good symmetry and directivity.

Description

Technical Field

[0001] This invention belongs to the field of antenna technology, and specifically relates to a differentially fed dual-frequency dual-polarized microstrip filter antenna. Background Technology

[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 stringent. While traditional single-polarized antennas are widely used in many fields, they often prove insufficient when facing challenges such as multi-band, multi-protocol, spatial constraints, and signal interference. Dual-band dual-polarized antennas can simultaneously support two vertical electric field polarization modes in two operating frequency bands, significantly improving communication capacity and system anti-interference capabilities. In complex communication environments, dual-band dual-polarized filtering antennas can significantly reduce interference between signals and improve spectrum utilization efficiency.

[0003] Differential feeding is a common feeding method that offers higher noise and interference immunity compared to traditional single-ended feeding. By feeding two complementary signals, differential feeding effectively suppresses common-mode interference while improving antenna radiation characteristics and signal quality. Especially in high-frequency, high-speed signal transmission, differential feeding significantly enhances antenna performance and avoids the ground noise and uneven radiation problems that can be introduced by traditional single-ended feeding.

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

[0005] For differentially fed dual-polarized dual-frequency microstrip filter antennas, patent application CN118073840A discloses a small dual-band dual-polarized filter antenna. This invention provides communication in two frequency bands and does not require the integration of an additional filtering system. However, its dual polarization design is right-hand circular polarization radiation and omnidirectional linear polarization radiation, which is essentially still a single-polarization design. Furthermore, it has large gain fluctuations, poor edge selectivity, and poor out-of-band suppression capability within the operating frequency band.

[0006] Patent application CN117154401A discloses a high-performance dual-polarized filter antenna with differential feeding. It uses a parasitic square patch and a V-shaped metal strip to achieve the filtering response and uses a differential feeding method. It has high edge selectivity, but poor out-of-band suppression capability. Furthermore, due to the complexity of the dual-polarization design and the filtering structure, it cannot be designed for dual-frequency operation.

[0007] In summary, the design methods for filtered antennas can be divided into three types: The first method involves directly cascading the filter's output with the antenna signal input to impart the filter's low-pass, high-pass, or band-pass response to the antenna's radiation performance. This design avoids impedance mismatch to some extent, but the space constraints of the entire RF front-end are not further alleviated. The second method replaces the last stage of the filter with a resonant antenna. Adjusting the size of the resonant antenna ensures equal impedance before and after the replacement, allowing the filtered antenna to achieve a gain curve similar to the filter's transmission coefficient trajectory. This design method allows for flexible adjustment of parameters such as the filter's center frequency, reflection coefficient, insertion loss, and operating bandwidth according to actual application requirements, before finally attaching the resonant antenna. Compared to the first method, the second method reduces space requirements to some extent, but the antenna may be affected by the filter's insertion loss, leading to a significant reduction in efficiency and a marked deterioration in radiation performance. The third design method involves using electromagnetic coupling to design the filter and antenna without introducing a filter circuit structure. This allows the filter antenna to have both in-band radiation and out-of-band filtering characteristics, seamlessly connecting them to achieve overall miniaturization, high integration, and multi-functionality. However, it is greatly affected by the antenna structure and may encounter problems such as poor edge selectivity and unstable in-band radiation gain due to inappropriate radiated null loading.

[0008] Current dual-band microstrip filter antenna designs often face challenges due to the difficulty of implementing dual-band dual-polarization. Instead, they typically rely on single-polarization microstrip antennas or employ non-traditional dual-polarization methods, such as combining circular and linear polarization. Such dual-polarization inherently cannot simultaneously support two perpendicular electric field polarization modes, resulting in limited application prospects. Furthermore, current dual-band filter antennas suffer from poor edge selectivity and unstable in-band radiation gain due to inappropriate null loading. Summary of the Invention

[0009] To overcome the shortcomings of the prior art, the present invention aims to provide a differentially fed dual-frequency dual-polarized microstrip filter antenna. By loading four unclosed rectangular slots onto the dual-polarized microstrip antenna, a normal resonant point is introduced at high frequencies, realizing the design of a dual-frequency dual-polarized microstrip antenna. Furthermore, a radiation null is introduced near the low-frequency stopband of the high-frequency operating band, improving the out-of-band suppression capability of the near-low-frequency stopband. Simultaneously, by loading an octagonal ring-coupled parasitic structure, an L-shaped symmetrical open-circuit stub, and a cross-shaped parasitic stub, three radiation nulls are introduced at the out-of-band stopbands of the two operating frequency bands, further improving the antenna's edge selectivity and out-of-band suppression capability. Ultimately, a differentially fed dual-frequency dual-polarized microstrip filter antenna design with four radiation nulls, good edge selectivity and good out-of-band suppression capability, and stable in-band gain is formed.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A differentially fed dual-frequency dual-polarized microstrip filter antenna includes a first dielectric substrate 1, a second dielectric substrate 2, and a third dielectric substrate 3 spaced apart from top to bottom. An octagonal annular coupling parasitic structure 4 is loaded on the lower surface of the first dielectric substrate 1. A rectangular radiating patch 5 is printed on the upper surface of the second dielectric substrate 2. Four unclosed rectangular slots 9, arranged in a square distribution and rotate symmetrically with each other, are loaded on the rectangular radiating patch 5. A cross-shaped parasitic stub 7 and four identical L-shaped symmetrical open-circuit stubs 6, arranged in a rhomboid distribution and extending outward along the diagonal of the rhomboid, are printed on the lower surface of the third dielectric substrate 3. The second dielectric substrate 2 and the third dielectric substrate 3 are connected by a coaxial feed line 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 through the metal inner core 8 of the coaxial feed line 18, and the metal ground plane 16 is connected to the metal outer shell 17 of the coaxial feed line 18.

[0013] The octagonal ring-coupled parasitic structure 4 is a rectangular ring with chamfered corners. The octagonal ring-coupled parasitic structure 4 introduces a radiation null point in the high-frequency stopband near the low-frequency operating frequency band.

[0014] The unclosed rectangular slits 9 are symmetrical structures, including long sides 11 and short sides 10 that are connected to each other. The four unclosed rectangular slits 9 introduce a resonant point for normal operation at high frequencies and introduce a radiation null point near the low-frequency stopband of the high-frequency operating band.

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

[0016] The L-shaped symmetrical open-circuit stub 6 includes a rectangular main stub 12 and two subordinate L-shaped stubs 15 symmetrical about the rectangular main stub 12. The subordinate L-shaped stubs 15 are composed of a long rectangular stub 13 and a short rectangular stub 14 connected vertically. The subordinate L-shaped stubs 15 are connected vertically to the rectangular main stub 12 through the long rectangular stub 13. The rectangular main stub 12 is connected to the metal core 8 of the coaxial feed line 18. The L-shaped symmetrical open-circuit stub 6 introduces a radiation null point at the low-frequency stopband of the low-frequency operating frequency band.

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

[0018] The metal core 8 of the coaxial feeder 18 passes through the third dielectric substrate 3 and is connected to the rectangular radiating 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 has four feed ports arranged in a rhombus shape, located at the four vertices of the rhombus. The two ports on the diagonal parallel to the y-axis are the first feed port 16-1 and the second feed port 16-2, which together form differential port A. The two ports on the diagonal parallel to the x-axis are the third feed port 16-3 and the fourth feed port 16-4, which together form differential port B. When the first feed port 16-1 and the second feed port 16-2 input signals of the same magnitude but with a phase difference of 180°, the third feed port 16-3 and the fourth feed port 16-4 are connected to a matched load, and the antenna operates normally. The operation of the third feed port 16-3 and the fourth feed port 16-4 is similar. 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 S is the reflection coefficient of differential port A under differential mode signal. dd22 The reflection coefficient of differential port B under differential mode signal, S dd12 and S dd21 S is the transmission coefficient between two differential ports under differential mode signaling. mn (m,n=1,2,3,4) are the standard S-parameters of a four-port network structure.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This invention introduces a normal resonant point at high frequencies by loading four unclosed rectangular slots 9 on a rectangular radiating patch 5 on the upper surface of the second dielectric substrate 2, thus realizing the design of a dual-frequency dual-polarized microstrip antenna. Furthermore, it introduces a radiation null point near the low-frequency stopband of the high-frequency operating band, improving the antenna's out-of-band suppression capability and edge selectivity near the low-frequency stopband of the high-frequency operating band. Moreover, the gain is stable within both operating bands, overcoming the difficulty of achieving mutually perpendicular dual-polarization design in ordinary dual-polarized microstrip antennas in the prior art.

[0027] 2. This invention introduces a radiation null in the high-frequency stopband of the low-frequency operating band by loading an octagonal ring-coupled parasitic structure 4 on the lower surface of the first dielectric substrate 1; by loading an L-shaped symmetrical open-circuit stub 6 on the lower surface of the second dielectric substrate 2, a radiation null is introduced in the low-frequency stopband of the low-frequency operating band; and by loading a cross-shaped parasitic stub 7 on the lower surface of the second dielectric substrate 2, a radiation null is introduced in the high-frequency stopband of the high-frequency operating band. The loading of these three radiation nulls enables the antenna to have strong out-of-band suppression capability and high edge selectivity outside the operating frequency band, without affecting the dual-frequency dual-polarization design and stable radiation of the antenna. This overcomes the problems of poor edge selectivity and out-of-band suppression capability and unstable in-band radiation gain caused by unsuitable loading of radiation nulls in the prior art.

[0028] In summary, this invention overcomes the difficulty of achieving mutually perpendicular dual-polarization design in conventional dual-polarized microstrip antennas by loading four unclosed rectangular slots 9 on the rectangular radiating patch 5 on the upper surface of the second dielectric substrate 2. This enables a dual-frequency dual-polarized microstrip antenna with stable gain within the dual-frequency operating band and introduces a radiation null near the low-frequency stopband in the high-frequency operating band. Together with the three radiation nulls introduced by loading an octagonal ring-coupled parasitic structure 4 on the lower surface of the first dielectric substrate 1 and L-shaped symmetrical open-circuit stubs 6 and cross-shaped parasitic stubs 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. Ultimately, a dual-frequency dual-polarized microstrip filter antenna with four radiation nulls is formed. This invention has good edge selectivity and good out-of-band suppression capability and achieves a differentially fed dual-frequency dual-polarized microstrip filter antenna design with stable in-band gain. Attached Figure Description

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

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

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

[0032] Figure 4 This is a 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 This is a schematic diagram of the lower surface structure of the third dielectric substrate 3 of the present invention.

[0034] Figure 6 The differential mode emission coefficient S of this invention dd11 Result image.

[0035] Figure 7 This is a graph showing the gain results of the antenna of this invention.

[0036] Figure 8 This is the differential mode emission coefficient S of the antenna in Example 1. dd11 And gain result graph.

[0037] Figure 9 This is the differential mode emission coefficient S of the antenna in Example 2. dd11 And gain result graph.

[0038] Figure 10 This is the differential mode emission coefficient S of the antenna in Example 3. dd11And gain result graph.

[0039] Figure 11 This is the differential mode emission coefficient S of the antenna in Example 4. dd11 And gain result graph.

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

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

[0042] The components are as follows: 1. First dielectric substrate; 2. Second dielectric substrate; 3. Third dielectric substrate; 4. Octagonal ring-coupled parasitic structure; 5. Rectangular radiating patch; 6. L-shaped symmetrical open-circuit stub; 7. Cross-shaped parasitic stub; 8. Metal core; 9. Unclosed rectangular slot; 10. Short side; 11. Long side; 12. Rectangular main stub; 13. Long rectangular stub; 14. Short rectangular stub; 15. Auxiliary L-shaped stub; 16. Metal ground plane; 16-1. First feed port; 16-2. Second feed port; 16-3. Third feed port; 16-4. Fourth feed port; 17. Metal casing; 18. Coaxial feed line. Detailed Implementation

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

[0044] Current microstrip filter antennas, when designed for dual-band operation, often face challenges due to the difficulty of implementing dual-band dual-polarization. Instead, they typically employ single-polarization microstrip antennas, or use non-traditional polarization techniques, such as combining circular and linear polarization. Such dual polarization, inherently unable to simultaneously support two perpendicular electric field polarization modes, has limited application prospects. Furthermore, current dual-band filter antennas suffer from poor edge selectivity and instability in in-band radiation due to inappropriate null loading. This invention proposes a differentially fed dual-frequency dual-polarized microstrip filter antenna. It combines differential feeding technology with microstrip antenna design and achieves the design of dual-polarized dual-frequency microstrip antenna through slot loading technology. By loading open-circuit stubs and parasitic structures, radiation nulls are loaded on both sides of the dual-frequency operating band. Combined with the radiation nulls introduced by the feeding method, a dual-frequency dual-polarized filter antenna design with four radiation nulls is achieved. This antenna has good edge selectivity and good out-of-band suppression capability, stable in-band gain, and good symmetry and directivity in its radiation pattern.

[0045] Specifically, the present invention proposes a differentially fed dual-frequency dual-polarized microstrip filter antenna, the structure of which is as follows: Figure 1 As shown, it consists of three dielectric substrates, a metal cladding layer, and a power supply structure. The first dielectric substrate 1 has a thickness of 3 mm, the second dielectric substrate 2 has a thickness of 4 mm, and the third dielectric substrate 3 has a thickness of 1 mm. The spacing between the first dielectric substrate 1 and the second dielectric substrate 2 is 5 mm, and the spacing between the second dielectric substrate 2 and the third dielectric substrate 3 is 6 mm. The materials of the first dielectric substrate 1, the second dielectric substrate 2, and the third dielectric substrate 3 are F4B with a relative permittivity of 2.65, and their side length is 80 mm.

[0046] Figure 2 The side view of the antenna structure shows the relative positions of the three dielectric substrates. It can also be seen that the third dielectric substrate 3 and the second dielectric substrate 2 are connected by the metal core 8 of the coaxial feed line 18. The metal core 8 of the coaxial feed line 18 passes through the third dielectric substrate 3 and is connected to the rectangular radiating patch 5 on the upper surface of the second dielectric substrate 2, and is connected to the L-shaped symmetrical open-circuit stub 6 on the lower surface of the second dielectric substrate 2.

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

[0048] Figure 4 A schematic diagram of the second dielectric substrate 2 is provided. A rectangular radiating patch 5, with a side length L2 of 45 mm, is placed on the upper surface of the second dielectric substrate 2. Four unclosed rectangular slots 9, each 1 mm wide, are loaded onto the patch. These slots are symmetrical, consisting of a long side 11 (12 mm) and a short side 10 (5 mm) that are connected to each other. The loading of these four unclosed rectangular slots 9 enables the design of a dual-band, dual-polarized microstrip antenna, and introduces a radiation null at 3.28 GHz. On the lower surface of the second dielectric substrate 2, cross-shaped parasitic stubs 7 and four L-shaped symmetrical open-circuit stubs 6 are printed. The L-shaped symmetrical open-circuit stubs 6 are directly connected to the metal core 8 of the coaxial feed line 18 at a point 1 mm from the antenna center. The L-shaped symmetrical open-circuit stubs 6 and the cross-shaped parasitic stubs 7 do not contact each other. The four L-shaped symmetrical open-circuit branches 6 have identical structures. Each L-shaped symmetrical open-circuit branch 6 includes a rectangular main branch 12 and two subordinate L-shaped branches 15 symmetrical about the rectangular main branch 12. The subordinate L-shaped branches 15 are composed of a long rectangular branch 13 and a short rectangular branch 14 connected perpendicularly. The identical rectangular main branch 12 has a length of 20.5 mm and a width of 2.5 mm. The subordinate L-shaped branches 15 are symmetrically loaded on both sides of the rectangular main branch 12, and are connected through the long rectangular branch 13. 3 is perpendicularly connected to the rectangular main branch 12, which is connected to the metal core 8 of the coaxial feed line 18. The distance L3 between the loading position of the auxiliary L-shaped branch 15 and the end connected to the metal core 8 of the rectangular main branch 12 and the coaxial feed line 18 is 11.5mm. The long rectangular branch 13 has a length of 5.75mm and a width of 2.5mm. The short rectangular branch 14 has a length of 4mm and a width of 2.5mm. The L-shaped symmetrical open-circuit branch 6 introduces a radiation null point at 1.68GHz.

[0049] The length L4 of the cross-shaped parasitic stub 7 is 27 mm. It is chamfered at the center and both ends to improve 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 stub 7 introduces a radiation null at 3.96 GHz.

[0050] Figure 5A schematic diagram of the third dielectric substrate 3 is given. The lower surface of the third dielectric substrate 3 is a metal ground plane 16, which is connected to the metal casing 17 of the coaxial feed line 18. The lower surface of the third dielectric substrate 3 has four feed ports arranged in a rhombus shape, located at the four vertices of the rhombus. The two ports on the diagonal of the rhombus parallel to the y-axis are the first feed port 16-1 and the second feed port 16-2, which together form differential port A. The two ports on the diagonal of the rhombus parallel to the x-axis are the third feed port 16-3 and the fourth feed port 16-4, which together form differential port B. When the first feed port 16-1 and the second feed port 16-2 input signals of the same magnitude but with a phase difference of 180°, the third feed port 16-3 and the fourth feed port 16-4 are connected to a matched load, and the antenna operates normally. The operation of the third feed port 16-3 and the fourth feed port 16-4 is similar. 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 S is the reflection coefficient of differential port A under differential mode signal. dd22 The reflection coefficient of differential port B under differential mode signal, S dd12 and S dd21 S is the transmission coefficient between two differential ports under differential mode signaling. mn (m,n=1,2,3,4) are the standard S-parameters of a four-port network structure.

[0056] Figure 6 The differential mode reflection coefficient S of the antenna of this invention is given. dd11Its differential mode reflection coefficient is less than -10dB in both the 1.78-2.1GHz and 3.72-3.84GHz bands, and it works normally in both bands. Figure 7 Regarding the gain of the antenna of this invention, the gain is stable in the operating frequency bands of 1.78-2.1 GHz and 3.72-3.84 GHz, with average gains of 7.8 dBi and 8.2 dBi, respectively. Furthermore, it can be seen that the antenna of this invention has good edge selectivity, with out-of-band rejection exceeding 14 dB.

[0057] To better demonstrate the design effect of this invention, four comparative examples are presented. Comparative example 1 is a basic differential-fed microstrip antenna, such as... Figure 8 As shown, it has a corresponding single resonant point, but it cannot work properly and shows no signs of dual-frequency operation. Comparative Example 2 is based on Comparative Example 1 with an unclosed rectangular slit 9 added, as shown... Figure 9 As shown, the number of resonant points changes from one to two, exhibiting dual-frequency characteristics. Furthermore, the radiation null point caused by the loading of the unclosed rectangular slit 9 at 3.28 GHz can be observed. Comparative Example 3 adds an L-shaped symmetrical open-circuit stub 6 to Comparative Example 2, as shown... Figure 10 As shown, the L-shaped symmetrical open-circuit stub 6 significantly improves antenna matching and introduces a radiation null at 1.68 GHz. Comparative Example 4 adds a cross-shaped parasitic stub 7 to Comparative Example 3, as shown... Figure 11 As shown, the addition of the cross-shaped parasitic stub 7 introduces a radiation null at 3.96 GHz. Adding the octagonal ring-coupled parasitic structure 4 based on Comparative Example 4 yields the dual-frequency dual-polarized microstrip filter antenna proposed in this invention.

[0058] Figure 12 and Figure 13 The radiation patterns of the antenna in the E-plane and H-plane at the operating frequencies of 1.94 GHz and 3.78 GHz within two operating frequency bands are presented. It can be seen that the radiation patterns have good symmetry and directivity, with no dips or distortions. The cross-polarization is below -28 dB.

[0059] In summary, this invention combines differential feeding technology with a microstrip antenna and utilizes slot loading technology to design a dual-polarized dual-frequency microstrip antenna. By loading open-circuit stubs and parasitic structures, radiating nulls are added to both sides of the dual-frequency operating band. Combined with the radiating nulls introduced by slot loading, a filter antenna design with four radiating nulls is achieved. This antenna exhibits good edge selectivity and good out-of-band suppression capability, stable in-band gain, and a good symmetry and directivity in its radiation pattern.

[0060] The key points and protection points of this invention are as follows:

[0061] The rectangular radiating patch 5 of the present invention is located on the upper surface of the second dielectric substrate 2. The rectangular radiating patch 5 is loaded with an unclosed rectangular slit 9 with a long side 11 of 12 mm and a short side 10 of 5 mm. The four unclosed rectangular slits 9 introduce a resonant point for normal operation at high frequency, realizing the design of a dual-frequency dual-polarized microstrip antenna, and introducing a radiation null point in the low-frequency stopband near the high-frequency operating band.

[0062] The octagonal ring-coupled parasitic structure 4 of the present invention is located on the lower surface of the first dielectric substrate 1. It can be regarded as a structure after the chamfering of a rectangular ring, with a corresponding rectangular side length of 37mm. It can introduce a radiation null point in the adjacent high-frequency stopband of the low-frequency operating frequency 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 out-of-band suppression capability and impedance matching. The cross-shaped parasitic branch 7 has a symmetrical structure and its single branch length is 27mm. It introduces a radiation null point in the high-frequency stopband of the high-frequency operating band.

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

[0065] The metal outer shell 17 of the coaxial feed line 18 of the present invention is connected to the metal ground plane 16 on the lower surface of the third dielectric substrate 3. The metal inner core 8 of the coaxial feed line 18 passes through the third dielectric substrate 3 and the second dielectric substrate 2 and is connected to the rectangular radiating patch 5 for power feeding. At the same time, the metal inner core 8 of the coaxial feed line 18 is also connected to the L-shaped symmetrical open-circuit stub 6. The two feed ports located on the straight line of the L-shaped symmetrical open-circuit stub 6 simultaneously feed signals of the same magnitude but with a phase difference of 180°, thereby realizing the operation of the antenna.

[0066] Application prospects of this invention:

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

[0068] Current microstrip filter antennas face challenges in dual-band design due to the high difficulty of implementing dual-band dual-polarization. Many designs rely solely on single-polarization microstrip antennas, or employ non-traditional dual-polarization methods, such as combining circular and linear polarization. Such dual-polarization inherently cannot simultaneously support two perpendicular electric field polarization modes, resulting in limited application prospects. Furthermore, current dual-band filter antennas suffer from poor edge selectivity and instability in in-band radiation due to inappropriate null loading.

[0069] This invention proposes a differentially fed dual-frequency dual-polarized microstrip filter antenna. It combines differential feeding technology with a microstrip antenna design, utilizing slot loading technology to achieve the dual-polarized dual-frequency microstrip antenna design. By loading open-circuit stubs and parasitic structures, radiating nulls are added to both sides of the dual-frequency operating band. Combined with the radiating nulls introduced by the feeding method, a filter antenna design with four radiating nulls is achieved. This antenna exhibits good edge selectivity and good out-of-band suppression capability, stable in-band gain, and a good symmetry and directivity in its radiation pattern, demonstrating promising application prospects.

[0070] The differential-fed dual-frequency dual-polarized microstrip filter antenna proposed in this invention uses a differential feeding method. It introduces a radiation null by loading parasitic structures such as an octagonal ring-coupled parasitic structure 4, an L-shaped symmetrical open-circuit stub 6, and a cross-shaped parasitic stub 7. When the dimensions of the parasitic structure, the radiating patch, and the loading gap change, the operating frequency changes, but the structure can still achieve the purpose of the invention.

Claims

1. A differentially fed dual-frequency dual-polarized microstrip filter antenna, comprising a first dielectric substrate (1), a second dielectric substrate (2), and a third dielectric substrate (3) spaced apart from top to bottom, characterized in that, An octagonal ring-shaped parasitic coupling structure (4) is loaded on the lower surface of the first dielectric substrate (1); a rectangular radiating patch (5) is printed on the upper surface of the second dielectric substrate (2), and four unclosed rectangular slots (9) distributed in a square and rotate symmetrically are loaded on the rectangular radiating patch (5); a cross-shaped parasitic branch (7) and four L-shaped symmetrical open-circuit branches (6) with the same structure distributed in a rhombus and extending outward along the diagonal of the rhombus are printed on the lower surface of the second dielectric substrate (2); the lower surface of the third dielectric substrate (3) is a metal ground plane (16); the second dielectric substrate (2) and the third dielectric substrate (3) are connected by a coaxial feed line (18); The coaxial feed line (18) includes a metal core (8) and a metal shell (17). The third dielectric substrate (3) and the second dielectric substrate (2) are connected through the metal core (8) of the coaxial feed line (18). The metal floor (16) is connected to the metal shell (17) of the coaxial feed line (18). The octagonal ring coupling parasitic structure (4) is a rectangular ring with chamfered corners. The octagonal ring coupling parasitic structure (4) introduces a radiation null point near the high-frequency stopband in the low-frequency operating band. The unclosed rectangular slits (9) are symmetrical structures, including long sides (11) and short sides (10) that are connected to each other. The four unclosed rectangular slits (9) introduce the resonant point of normal operation at high frequency and introduce the radiation null point near the low frequency stopband of the high frequency operating band. The L-shaped symmetrical open-circuit stub (6) is connected to the metal core (8) of the coaxial feed line (18) at one end near the center of the antenna. The other end of the L-shaped symmetrical open-circuit stub (6) is in an open-circuit state. The cross-shaped parasitic stub (7) is located at the center of the four L-shaped symmetrical open-circuit stubs (6). The L-shaped symmetrical open-circuit stub (6) and the cross-shaped parasitic stub (7) do not contact each other. The direction of the cross-shaped parasitic stub (7) forms a 45° angle with the direction of the L-shaped symmetrical open-circuit stub (6). The L-shaped symmetrical open-circuit stub (6) includes a rectangular main stub (12) and two subordinate L-shaped stubs (15) symmetrical about the rectangular main stub (12). The subordinate L-shaped stub (15) is composed of a long rectangular stub (13) and a short rectangular stub (14) connected vertically. The subordinate L-shaped stub (15) is connected vertically to the rectangular main stub (12) through the long rectangular stub (13). The rectangular main stub (12) is connected to the metal core (8) of the coaxial feed line (18). The L-shaped symmetrical open-circuit stub (6) introduces a radiation null point at the low-frequency stopband of the low-frequency operating frequency band.

2. The differentially fed dual-frequency dual-polarized microstrip filter antenna according to claim 1, characterized in that, The cross-shaped parasitic branch (7) is chamfered at both the center and both ends, and the cross-shaped parasitic branch (7) introduces a radiation null point at the high-frequency stopband of the high-frequency operating band.

3. The differentially fed dual-frequency dual-polarization microstrip filter antenna according to claim 1, characterized in that, The metal core (8) of the coaxial feed (18) passes through the third dielectric substrate (3) and is connected to the rectangular radiating 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).

4. The differentially fed dual-frequency dual-polarization microstrip filter antenna according to claim 1, characterized in that, The metal floor (16) has four feed ports arranged in a rhombus shape. The four feed ports are located at the four vertices of the rhombus. The two ports on the diagonal of the rhombus parallel to the y-axis are the first feed port (16-1) and the second feed port (16-2), which together form differential port A. The two ports on the diagonal of the rhombus parallel to the x-axis are the third feed port (16-3) and the fourth feed port (16-4), which together form differential port B. When the first feed port (16-1) and the second feed port (16-2) input signals of the same magnitude but with a phase difference of 180°, the third feed port (16-3) and the fourth feed port (16-4) are connected to a matched load, and the antenna works normally. The same applies when the third feed port (16-3) and the fourth feed port (16-4) are working. Their differential mode S-parameters are: in, S dd11 The reflection coefficient of differential port A under differential mode signal. S dd22 The reflection coefficient of differential port B under differential mode signal. S dd12 and S dd21 The transmission coefficient between two differential ports under differential mode signaling. S mn (m,n=1,2,3,4) are the standard S-parameters of a four-port network structure.

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