Dual-polarization filtering antenna based on crossed dipoles and design method thereof

Abstract

The invention relates to the technical field of microwave communication, in particular to a dual-polarization filtering antenna based on crossed dipoles. The dual-polarization filtering antenna comprises a bottom layer dielectric plate, a vertical orthogonal dielectric substrate and a metal reflection back cavity. The bottom layer dielectric plate is coated with the metal grounding plate, the positioning pin is used for assembling the vertical orthogonal dielectric substrate in a horizontal gap of the bottom layer dielectric plate and a vertical gap of the metal reflection back cavity, a dipole antenna structure and a balun feed structure are printed on the vertical orthogonal dielectric substrate, and the metal reflection back cavity is installed on the bottom layer dielectric substrate. The metal reflection back cavity surrounds the periphery of the vertical orthogonal dielectric substrate. The antenna realizes out-of-band high suppression degree and in-band stable gain through the stepped feed structure, the fan-shaped impedance matching structure and the filtering branch generating the radiation zero point. The antenna balun feed structure has a filtering function, the antenna structure is easy to integrate, the system contour is reduced, and high frequency selectivity is achieved. The antenna has the filtering characteristic of high out-of-band roll-off degree, the dual-polarization performance of high isolation degree and the adjustable beam width.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave communications, and in particular relates to a cross-dipole-based dual-polarization filtering antenna with good out-of-band suppression and high isolation, and a design method thereof. Background Art

[0002] Mobile communication devices are constantly evolving, driving the demand for miniaturization and high integration. This, coupled with the increasing scarcity of electromagnetic spectrum resources, is gradually compressing the design space for RF front-end circuits. The traditional cascaded antenna and filter not only occupies a significant amount of space within the RF front-end but also creates a complex electromagnetic environment, making it difficult to meet the requirements for miniaturization and high integration. Therefore, collaborative filter and antenna design is crucial for development. Due to the poor frequency selectivity of monotonic antennas, filter antennas, as a key means of miniaturizing RF front-end devices, have become a hot topic of research within the industry.

[0003] Currently, the beam width of conventional filtering antennas on the market is difficult to freely adjust, which leads to its application scenarios being difficult to meet complex application requirements. Therefore, in order to solve the problems of poor selectivity and difficult beam width adjustment of conventional filtering antennas, a new type of filtering antenna is needed. Summary of the Invention

[0004] In order to solve the problems of poor selectivity and difficult beam width control of conventional filtering antennas, the present application provides a dual-polarization filtering antenna based on a cross dipole and a design method thereof. Dual polarization is a new antenna technology. By combining two antennas with mutually orthogonal polarization directions and working in a transmit-receive duplex mode at the same time, this design enables the dual-polarization antenna to simultaneously transmit and receive radio waves in the horizontal and vertical directions, thereby providing more stable and reliable communication quality. In addition, through a filtering branch and a stepped balun feeding structure, as well as a reflective back cavity of a specific size, the antenna achieves high selectivity, high isolation and controllable beam width.

[0005] The technical solution is to load high- and low-frequency filtering branches into the antenna's balun feed structure, resulting in a steep radiation attenuation of the antenna's upper and lower sidebands, creating multiple radiation nulls. Simultaneously, the three-stage stepped-feed balun structure maintains stable gain within the antenna's passband. By incorporating a metal reflective back cavity of specific size and structure, not only does it improve array element isolation, but it also allows for the beamwidth of antenna elements to be varied by adjusting the back cavity height, enabling flexible control of antenna performance.

[0006] The specific content is: In the first aspect, the example of the present invention designs a dual-polarization filtering antenna based on a cross dipole, including a bottom dielectric plate, a vertical orthogonal dielectric substrate, and a metal reflective back cavity. The bottom dielectric plate is coated with a metal ground plate, and the vertical orthogonal dielectric substrate is assembled using positioning pins in the horizontal gap of the bottom dielectric plate and the vertical gap of the metal reflective back cavity. The vertical orthogonal dielectric substrate is printed with a dipole antenna structure and a balun feeding structure. The metal reflective back cavity is installed on the bottom dielectric substrate, and the metal reflective back cavity surrounds the vertical orthogonal dielectric substrate.

[0007] Furthermore, the dipole antenna structure forms a dipole antenna, and the dipole antenna and the balun feeding structure constitute an antenna unit. The dipole antenna achieves a steep drop in out-of-band gain by the balun feeding structure with filtering characteristics.

[0008] Furthermore, the balun feeding structure includes a stepped matching filter structure, a filter branch structure, and a fan-shaped impedance matching structure. The fan-shaped impedance matching structure is located at the end, and the fan-shaped impedance matching structure includes a first fan-shaped impedance matching structure and a second fan-shaped impedance matching structure.

[0009] Furthermore, the stepped matching filter structure consists of a first-level stepped transmission line, a second-level stepped transmission line, and a third-level stepped transmission line. The three-level transmission line and the fan-shaped impedance matching structure at the end cooperate to adjust the antenna input impedance, so that the filtering antenna has a stable gain within the operating bandwidth, and cooperates with the resonant point of the filtering structure to form a steep drop in out-of-band gain, thereby improving the roll-off of the upper and lower sidebands.

[0010] Furthermore, the filtering branch structure includes: a high-frequency filtering resonant branch and a low-frequency filtering resonant branch; the filtering branch structure is a 90° bend line, and its resonant frequency corresponds to 1 / 4 of the wavelength. The high-frequency filtering resonant branch and the low-frequency filtering resonant branch resonate at 10.7GHz and 6.5GHz respectively, which basically correspond to the upper and lower sidebands of the working frequency band of the antenna without the resonant structure. Therefore, two radiation zero points are generated at both ends of the antenna working frequency to realize the filtering function.

[0011] The cross dipole antenna is printed on one layer of the vertical orthogonal dielectric substrate, and a balun feeding structure is printed on the other side. The vertical orthogonal dielectric substrate is fixed to the bottom dielectric substrate and the opening of the metal reflective back cavity by the positioning pins.

[0012] Furthermore, a metal grounding layer is applied on the upper side of the bottom dielectric substrate, and four gaps are opened in the horizontal direction for the dielectric substrate to pass vertically.

[0013] Furthermore, the metal reflective back cavity is provided with four vertical slots around its periphery for positioning and fixing the vertical dielectric substrate.

[0014] Furthermore, the filtering antenna is loaded with a metal reflector, and the height of the back cavity can change the beam width of the antenna, acting as a director; at the same time, the introduction of the metal cavity in the antenna array will increase the isolation between antenna units.

[0015] Furthermore, two pairs of crossed dipoles are placed orthogonally to form a +45° polarized dipole and a -45° polarized dipole respectively; the dual-polarized filter dipole supplies radio frequency signals to the ±45° polarized dipoles respectively through two radio frequency input ports.

[0016] Furthermore, the cross dual-polarization dipole is composed of two identical dipoles and a filtering balun feeding structure, with only the radiation polarization angle being different.

[0017] The present invention has the following advantages over traditional technologies: The antenna of the present invention loads filter branches onto the dipole balun feed structure. The long and short filter branches resonate at the antenna's lower and upper sidebands, respectively, and have a length of 1 / 4 of the corresponding frequency wavelength. This forms a short-circuit point at the corresponding frequency at the antenna feed line, reducing the antenna's radiated energy and generating a radiation zero point to achieve a high out-of-band gain roll-off. Furthermore, by adjusting the input impedance of the dipole unit through a third-order impedance matching transmission structure and a sector-shaped impedance, a stable in-band gain within the antenna's operating frequency band is achieved, improving the out-of-band suppression level. The present invention designs the filter onto the antenna feed structure. The antenna does not require additional cascaded filter components, and has high radiation efficiency and a small spatial size.

[0018] This invention incorporates a metal reflective back cavity around the dipole filter antenna to reduce back radiation and improve in-band gain. Changing the height of the reflective back cavity also modifies the antenna beamwidth, acting as a director. When this filter antenna is used to form an antenna array, the inclusion of the reflective back cavity significantly mitigates adverse factors such as antenna performance degradation and pattern distortion caused by electromagnetic coupling between elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The following is an explanation of the drawings in the embodiments, which is intended to more clearly illustrate the technical path of the present application. In order to explain the present application concisely and clearly, the following drawings describe specific details in detail.

[0020] Figure 1 This is a front view of a filter dipole in an embodiment of the present invention; Figure 2 This is a top view of the metal reflective back cavity in an embodiment of the present invention; Figure 3 A top view of a filter dipole in an embodiment of the present invention; Figure 4 The return loss of the simulated filter dipole port in the embodiment of the present invention is as follows; Figure 5The filtering dipole balun feeding structure in the embodiment of the present invention; Figure 6 The high-frequency filtering structure of the filtering dipole in the embodiment of the present invention; Figure 7 The low-frequency filter structure of the filter dipole in the embodiment of the present invention; Figure 8 Graph showing the variation of the gain of the simulated filter dipole with frequency in an embodiment of the present invention; Figure 9 This is a diagram showing the E-plane directional pattern of the simulated antenna changing with the high side of the back cavity in an embodiment of the present invention; Figure 10 Graph showing the change of the H-plane directional pattern of the simulated antenna along the high side of the back cavity in an embodiment of the present invention; Figure 11 Schematic diagram of the surface current of the filtering dipole in an embodiment of the present invention.

[0021] In the figure: 1. oscillator grounding terminal; 2. Microwave feed input port; 3. First-level step lower transmission line; 4. First-level step upper transmission line; 5. High-frequency filter resonant branch; 6. Second-level step transmission line; 7. Low-frequency filter resonant branch; 8. Third-level step transmission line; 9. Vertical longitudinal orthogonal dielectric plate; 10. First antenna oscillator; 11. First fan-shaped impedance matching structure; 12. Bottom dielectric plate; 13. Metal reflective back cavity; 14. Vertical slit in the back cavity; 15. Metal ground plate slit; 16. Metal ground plate; 17. Second antenna oscillator; 18. Vertical transverse dielectric plate; 19. Second fan-shaped impedance matching structure; 20. Positioning pin. DETAILED DESCRIPTION

[0022] The present invention is described below with reference to the accompanying drawings of the embodiments of the present invention. The following detailed description of the present application details the features of the present invention. It is obvious that the described embodiments are only a portion of the embodiments of the present invention; all other embodiments derived by persons of ordinary skill in the art without inventive effort based on the embodiments of the present invention are within the scope of protection of the present invention. The present invention proposes a method for designing a cross-dipole filter antenna operating in the 7.4 GHz to 9.5 GHz frequency range. This method is described in detail below with reference to the accompanying drawings and embodiments.

[0023] Furthermore, persons of ordinary skill in the art will appreciate that the figures provided herein are for illustration purposes only and are not necessarily drawn to scale.

[0024] As attached Figure 1 ,2,3,This embodiment provides a dual-polarization filtering antenna based on a cross dipole The invention comprises a bottom dielectric plate, a vertical orthogonal dielectric substrate, and a metal reflective back cavity 13. The bottom dielectric plate 12 is coated with a metal ground plate 16. The vertical orthogonal dielectric substrate is assembled in the horizontal gap of the bottom dielectric plate 12 and the vertical gap of the metal reflective back cavity 13 using positioning pins 20. The vertical orthogonal dielectric substrate is printed with a dipole antenna and a balun feeding structure. The metal reflective back cavity 13 is installed on the bottom dielectric substrate. The metal reflective back cavity 13 surrounds the vertical orthogonal dielectric substrate.

[0025] The horizontal gap of the bottom dielectric plate 12 is the metal ground plate slit 15 , the vertical gap of the metal reflective back cavity 13 is the back cavity vertical slit 14 , and the vertical orthogonal dielectric substrate includes a vertical longitudinal orthogonal dielectric plate 9 and a vertical transverse dielectric plate 18 .

[0026] The dipole antenna structure forms a dipole antenna, and the dipole antenna and the balun feeding structure constitute an antenna unit. In this embodiment, the dipole antenna is an antenna element, which includes a first antenna element 10 and a second antenna element 17. The two antenna elements are independently fed with radio frequency signals by the two independent balun feeding structures, so that the antenna produces dual-polarization performance. The element grounding terminal 1 is applied to a vertical orthogonal dielectric substrate and passes through the bottom dielectric plate 12 at the slit 15 of the metal ground plate.

[0027] The balun feeding structure includes a stepped matching filter structure, a filter branch structure, and a fan-shaped impedance matching structure, wherein the fan-shaped impedance matching structure is located at the end.

[0028] The stepped matching filter structure consists of a first-level stepped transmission line, a second-level stepped transmission line 6, and a third-level stepped transmission line 8. The first-level stepped lower transmission line 3 is below the metal ground plate 16, and the first-level stepped upper transmission line 4 is above the metal ground plate 16. The three-level transmission lines and the fan-shaped impedance matching structure cooperate to adjust the antenna input impedance, so that the filter antenna has a stable gain within the operating bandwidth, and cooperates with the resonant point of the filtering structure to form a steep drop in out-of-band gain, thereby improving the roll-off of the upper and lower sidebands.

[0029] The filter branch structure includes a high-frequency filter resonant branch 5 and a low-frequency filter resonant branch 7. The filter branch structure is a 90-degree bend line, with its resonant frequency corresponding to 1 / 4 of the wavelength. The high-frequency filter resonant branch 5 and the low-frequency filter resonant branch 7 resonate at 10.7 GHz and 6.5 GHz, respectively, roughly corresponding to the upper and lower sidebands of the operating frequency band of an antenna without a resonant structure. This creates two radiation nulls at both ends of the antenna's operating frequency, achieving a filtering function.

[0030] The width of the filtering branch structure is 0.12 mm, the high-frequency filtering resonance branch 5 is 3.7 mm long, and the sideband resonance branch is 6.9 mm long.

[0031] One end of the balun feeding structure is electrically connected to the microwave feed source input port 2 , and the other end is electrically connected to the first antenna element 10 and the second antenna element 17 .

[0032] It should be noted that the cross-dipole filtering antenna is composed of two identical pairs of dipole antennas and a balun feeding structure, the only difference being the placement positions.

[0033] As attached Figure 1 As shown, the balun feed line structure consists of a three-level stepped microstrip line structure. The three-level stepped structure achieves stable gain within the antenna operating band and increases the operating bandwidth of the filtering antenna to 7.4 GHz - 9.5 GHz, with a relative bandwidth of 25%.

[0034] Reference Attachment Figure 1 Two filtering branch structures are designed at the first-stage ladder transmission line of the balun feed to form two branch resonators to generate the filtering radiation zero point of the antenna; the filtering frequency of the antenna is generated by the filtering branch structure, and its length is 1 / 4 of the wavelength of the corresponding filtering frequency, forming a 1 / 4 wavelength resonator. The capacitive impedance at the end of the branch presents an inductive load to the feeding section loading point after impedance transformation; as shown in the following figure Figure 8 As shown in the figure, the radiation zero points appear at 10.7 GHz and 6.5 GHz. It can be seen that the gain drops sharply here, achieving rapid attenuation of the antenna out-of-band gain.

[0035] The filter branches are bent 90 degrees due to the size of the antenna to avoid taking up too much space. The width of the filter branches is 0.12 mm, the high-frequency filter branches are 3.7 mm long, and the low-frequency filter branches are 6.9 mm long.

[0036] It should be noted that the antenna radiation zero point can be controlled by adjusting the length of the filter branch and changing the resonant frequency, but at the same time, the matching problem of the antenna input impedance needs to be considered.

[0037] In practical applications, communication base station antennas usually need to be used in an array. In order to avoid the problems of impedance matching mismatch and pattern distortion caused by the electric coupling between antenna units in the array, the antenna is loaded with the metal reflective back cavity 1313, as shown in the attached figure. Figure 2 The use of the metal reflective back cavity 13 can effectively reduce the performance degradation caused by the complex electromagnetic environment behind the array.

[0038] In an embodiment, a fan-shaped impedance matching structure is provided at the end of the balun feeding structure of the cross-dipole filter antenna to achieve matching between the antenna input impedance and the 50-ohm coaxial line.

[0039] In some embodiments, the antenna arms 10 and 17 respectively form +45° polarized radiation and -45° polarized radiation. Figure 3 The filtering antenna uses two microwave source input ports, corresponding to the +45° polarization oscillator and the -45° polarization oscillator respectively.

[0040] In the embodiment provided in the present application, the vertical orthogonal dielectric substrate is provided with a positioning pin 20, which cooperates with the vertical slit 14 of the back cavity to achieve stable assembly of the structure. At the same time, the metal ground plate slit 15 on the bottom dielectric substrate allows the antenna element to pass through the metal ground plate 16, thereby realizing electromagnetic shielding of the feed structure by the element antenna through the metal ground plate 16.

[0041] The first antenna element 10, the second antenna element 17 and the balun feeding structure are printed on both sides of the vertical orthogonal dielectric substrate using printed circuit board technology; the microwave feed source input port 2 of the element balun feeding structure is connected to a 50-ohm coaxial cable to achieve excitation of the antenna.

[0042] It should be further explained that the dielectric substrates used in the antennas are all Rogers RO4350 plates with a relative dielectric constant of 3.66 and a loss tangent of 0.004.

[0043] The simulation performance of the cross-dipole filter antenna is shown in the attached figure. Figure 4 As shown, it can be seen that the antenna unit input end meets the port return loss greater than 10dB within the 7.4GHz - 9.5GHz bandwidth and the relative bandwidth meets 25%. At the same time, the port isolation of more than 20dB can be achieved within the operating bandwidth without the need for additional decoupling structure.

[0044] As attached Figure 5 ,6,7, respectively are the balun feeding structure of the filtering antenna, namely antenna 1, the balun feeding structure with only high-frequency resonant branches, namely antenna 2, and the balun feeding structure with only low-frequency resonant branches, namely antenna 3. The gain variation trend of the three within the operating bandwidth with frequency is shown in the attached figure. Figure 8 As shown in the figure, Antenna 1's gain exhibits steep attenuation at 6.9 GHz and 10.7 GHz, meeting the high out-of-band attenuation required for a filtering antenna. Antenna 2, loaded only with high-frequency filter resonant branch 5, exhibits a gradual gain change at low frequencies and lacks filtering characteristics in the lower sideband. Antenna 3, loaded only with low-frequency filter resonant branch 7, also exhibits a gradual gain change at high frequencies and similarly lacks filtering characteristics.

[0045] As attached Figure 8 It can be seen that within the operating bandwidth of the filtering antenna, the antenna gain fluctuates slightly and remains stable, decays rapidly outside the passband, and has strong performance stability within the operating bandwidth.

[0046] As attached Figure 9,10, shows the change of the antenna E-plane radiation pattern with the change of the height of the metal reflective back cavity 13. It can be seen that as the height of the metal reflective back cavity 13 increases, the antenna E-plane beam width also increases, achieving controllable adjustment of the antenna unit beam width.

[0047] In summary, an embodiment of the present invention proposes a cross-dipole filtering antenna, in which the dipole is loaded with a filtering branch to achieve high out-of-band suppression outside the passband, and a stepped microstrip line and a fan-shaped impedance matching structure are used to achieve stable gain within the passband. The antenna is loaded with a metal reflective back cavity 13 to improve the antenna isolation, thereby achieving a better decoupling effect.

[0048] The above description is merely an example of the present application, which is provided for illustrative purposes only and does not limit the embodiments. Those skilled in the art will appreciate that other variations can be made based on the above description. This list does not exhaustively describe all possible implementations, and any obvious variations derived therefrom are still within the scope of protection of the present invention.

Claims

1. A dual-polarization filtering antenna based on a cross dipole, characterized in that: The invention comprises a bottom dielectric plate (12), a vertical orthogonal dielectric substrate, and a metal reflective back cavity (13). The bottom dielectric plate (12) is coated with a metal ground plate (16). Positioning pins (20) are used to assemble the vertical orthogonal dielectric substrate in the horizontal gap of the bottom dielectric plate (12) and the vertical gap of the metal reflective back cavity (13). The vertical orthogonal dielectric substrate is printed with a dipole antenna structure and a balun feeding structure. The metal reflective back cavity (13) is installed on the bottom dielectric substrate. The metal reflective back cavity (13) surrounds the vertical orthogonal dielectric substrate.

2. The cross-dipole-based dual-polarization filtering antenna according to claim 1, characterized in that: The horizontal gap of the bottom dielectric plate is a metal ground plate slit (15), the vertical gap of the metal reflective back cavity (13) is a back cavity vertical slit (14), the vertical orthogonal dielectric substrate includes a vertical longitudinal orthogonal dielectric plate (9), a vertical transverse dielectric plate (18), a dipole antenna structure forms a dipole antenna, the dipole antenna and the balun feeding structure form an antenna unit, the dipole antenna is an antenna vibrator, the antenna vibrator includes a first antenna vibrator (10) and a second antenna vibrator (17), the two vibrator antennas are independently input with radio frequency signals by the two independent balun feeding structures, so that the antenna produces dual-polarization performance, the vibrator ground end (1) is applied on the vertical orthogonal dielectric substrate, passes through the bottom dielectric plate (12) from the metal ground plate slit (15), the antenna vibrator can pass through the metal ground plate (16), and the electromagnetic shielding of the vibrator antenna to the feeding structure is achieved through the metal ground plate (16).

3. The cross-dipole-based dual-polarization filtering antenna according to claim 2, characterized in that: The balun feeding structure includes a stepped matching filter structure, a filter branch structure, and a fan-shaped impedance matching structure. The fan-shaped impedance matching structure is located at the end. The fan-shaped impedance matching structure realizes the matching of the antenna input impedance and the 50-ohm coaxial line. One end of the balun feeding structure is electrically connected to the microwave feed source input port (2), and the other end is electrically connected to the first antenna element (10) and the second antenna element (17).

4. The cross-dipole-based dual-polarization filtering antenna according to claim 3, characterized in that: The stepped matching filter structure is composed of a first-stage stepped transmission line, a second-stage stepped transmission line (6), and a third-stage stepped transmission line (8). The three-stage transmission line and the sector-shaped impedance matching structure cooperate to adjust the antenna input impedance, so that the filter antenna has a stable gain within the operating bandwidth, and cooperates with the resonance point of the filter structure to form a steep drop in out-of-band gain, thereby improving the roll-off of the upper and lower sidebands.

5. The cross-dipole-based dual-polarization filtering antenna according to claim 3, characterized in that: The filtering branch structure comprises: a high-frequency filtering resonant branch (5), a low-frequency filtering resonant branch (7), and the filtering branch structure is a 90-degree bending line, which is 1 / 4 of the wavelength corresponding to its resonant frequency. The high-frequency filtering resonant branch (5) and the low-frequency filtering resonant branch (7) resonate at 10.7 GHz and 6.5 GHz respectively, which basically correspond to the upper and lower sidebands of the working frequency band of the antenna without the resonant structure. Therefore, two radiation zero points are generated at both ends of the antenna working frequency to achieve the filtering function.

6. The cross-dipole-based dual-polarization filtering antenna according to claim 4, characterized in that: The first-level ladder transmission line includes a first-level ladder lower transmission line (3) and a first-level ladder upper transmission line (4). The first-level ladder lower transmission line (3) is below the metal ground plate (16), and the first-level ladder upper transmission line (4) is above the metal ground plate (16). The fan-shaped impedance matching structure adjusts the antenna input impedance at the end of the feed line and, together with the step-type feeding branch, enables the antenna to operate stably within the working frequency band, reduces electromagnetic energy reflection, and achieves a relative bandwidth of 25%. The fan-shaped impedance matching structure includes a first fan-shaped impedance matching structure (11) and a second fan-shaped impedance matching structure (19).

7. The cross-dipole-based dual-polarization filtering antenna according to claim 2, characterized in that: The bottom dielectric plate and the metal ground plate (16) are horizontally slotted, and the metal reflective back cavity (13) is vertically slotted (14) and connected to the positioning pins (20) on the vertical longitudinal orthogonal dielectric plate (9) and the vertical transverse dielectric plate (18) to fix the vertically placed cross dual-polarization oscillator antenna to respectively realize +45° polarization radiation and -45° polarization radiation.

8. The cross-dipole-based dual-polarization filtering antenna according to claim 1, characterized in that: The bottom of the metal reflective back cavity (13) is attached to the bottom dielectric plate on all sides, thereby reducing the antenna's backward radiation and minimizing the electromagnetic coupling effect between units when forming an antenna array.

9. A design method for a dual-polarization filtering antenna based on a cross dipole, characterized in that: A cross-dipole-based dual-polarization filtering antenna according to any one of claims 1 to 8 is used. By loading high and low frequency filtering branches on the balun feeding structure, the upper and lower sidebands of the antenna experience a steep radiation attenuation, resulting in multiple radiation zeros. At the same time, the three-stage stepped feeding balun structure maintains a stable gain within the antenna passband. The balun feeding line structure is composed of a three-stage stepped microstrip line structure. The three-stage stepped structure realizes the antenna operating frequency band. Two filtering branch structures are designed at the first-stage stepped transmission line of the balun feeding to form two branch resonators for generating the filtering radiation zeros of the antenna. By adding a metal reflective back cavity (13) of a specific size and structure, not only can the isolation of the units in the array be improved, but the beam width of the antenna unit can also be changed by adjusting the back cavity height, thereby achieving flexible regulation of the antenna performance.

10. A design method for a dual-polarization filtering antenna based on a cross dipole, characterized in that: The antenna radiation zero point can be controlled by adjusting the length of the filter branch structure and changing the resonant frequency. However, the matching problem of the antenna input impedance needs to be considered at the same time. The use of a metal reflective back cavity (13) can effectively reduce the performance degradation caused by the complex electromagnetic environment after the array. The high-frequency filter resonant branch (5) and the low-frequency filter resonant branch (7) resonate at 10.7GHz and 6.5GHz respectively, which basically correspond to the upper and lower sidebands of the working frequency band of the antenna without a resonant structure. Therefore, two radiation zero points are generated at both ends of the antenna working frequency to achieve the filtering function. The filtering frequency of the antenna is generated by adjusting the filter branch structure. The length is 1 / 4 of the wavelength of the corresponding filtering frequency, forming a 1 / 4 wavelength resonator. The capacitive impedance at the end of the branch presents an inductive load to the feeding section loading after impedance transformation.

Images