Polarization converter with end-capped filter circuit controlling frequency characteristics
By introducing a filter circuit into the polarization converter, the frequency characteristics can be controlled independently, solving the problem of insufficient flexibility in traditional designs and achieving improved frequency adjustability and stability under large-angle oblique incidence.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV OF SCI & TECH
- Filing Date
- 2022-01-19
- Publication Date
- 2026-05-12
AI Technical Summary
In traditional polarization converter designs, frequency and polarization characteristics are difficult to control independently, resulting in insufficient design flexibility and unstable performance under large-angle oblique incidence.
By loading a filter circuit on the back of the dual-polarized antenna array floor and controlling the frequency characteristics through the filter circuit, an ultra-wideband or dual-band polarization converter can be designed independently of the polarization characteristics.
This technology improves the frequency adjustability and stability of polarization converters, enabling them to maintain good performance under large-angle oblique incidence, and enhancing the flexibility and freedom of design.
Smart Images
Figure CN116505281B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polarization converters, and in particular a polarization converter that utilizes a termination filter circuit to control frequency characteristics. Background Technology
[0002] Polarization is a crucial characteristic of electromagnetic waves. When the polarization of the incident electromagnetic wave differs from the desired polarization, a polarization converter is required. Polarization converters have significant applications in antenna design and RCS reduction. Traditional polarization converter designs typically utilize birefringence and gratings, which require long propagation distances to achieve the desired phase change. Consequently, polarization converters designed using this approach are bulky and have narrow bandwidths. In recent years, with the increasing maturity of metamaterials / metasurface technologies, polarization converters designed using these technologies have found applications in both microwave and optical bands. Among these, reflective linear cross-polarization converters designed using anisotropic metasurfaces have numerous applications. Many researchers have designed ultra-wideband, low-profile, and high-efficiency polarization converters using anisotropic metasurfaces. Furthermore, by rationally designing the unit structure of anisotropic metasurfaces, such as using bi-square open resonant ring structures, double-C-shaped narrow ring structures, and double-cut slotted metal ring structures, dual-band, high-efficiency polarization converters can be designed. However, designing using anisotropic metasurfaces requires comprehensive consideration of polarization conversion and frequency characteristics. This approach necessitates meticulous design of the unit cell pattern in ultra-wideband or multi-band polarization converters to simultaneously meet polarization and frequency requirements, posing a significant design challenge. Furthermore, the entire unit cell structure needs to be redesigned when the required frequency characteristics change. Additionally, the polarization conversion performance of polarization converters designed using anisotropic metasurfaces is easily altered under large-angle oblique incidence waves, making them largely unsuitable for applications requiring large-angle illumination. Summary of the Invention
[0003] The purpose of this invention is to provide a polarization converter that utilizes a filter circuit to control its frequency characteristics. This scheme designs the polarization characteristics and frequency characteristics separately, allowing the frequency characteristics to be controlled independently. The polarization converter designed using this scheme exhibits excellent oblique incidence angle characteristics. This scheme can serve as a good supplement to polarization converter design schemes.
[0004] The technical solution to achieve the purpose of this invention is: a polarization converter that uses a termination filter circuit to control frequency characteristics, the polarization converter including a dual-polarized antenna array and a filter circuit disposed on the back of the floor of the dual-polarized antenna array;
[0005] The dual-polarized antenna array is used to receive x-polarized or y-polarized linearly polarized incident waves and convert them into y-polarized or x-polarized waves.
[0006] The filtering circuit is used to control the full-pass / band-pass filtering characteristics to achieve an ultra-wideband / dual-band frequency response.
[0007] Furthermore, the dual-polarized antenna array includes several antenna elements, each antenna element comprising, from top to bottom, a wide-angle matching layer, a metal vibrator dielectric substrate, a support layer, and a common ground plane; a horizontal metal vibrator radiating plate and a vertical metal vibrator radiating plate located on the same horizontal plane are disposed between the wide-angle matching layer and the metal vibrator dielectric substrate, and a coupling metal disc is disposed between the metal vibrator dielectric substrate and the support layer; the coupling metal disc is connected to the common ground plane through a vertical through-hole; the horizontal metal vibrator radiating plate and the vertical metal vibrator radiating plate are respectively connected to the common ground plane through two vertical short-circuit through-holes; the horizontal metal vibrator radiating plate passes through the common ground plane through a first vertical signal through-hole and connects to the input terminal of a filter circuit, and the output terminal of the filter circuit is connected to the vertical metal vibrator radiating plate through a second vertical signal through-hole.
[0008] Furthermore, the metal oscillator dielectric plate and the support layer have an asymmetrical cross-shaped structure.
[0009] Furthermore, the horizontal metal oscillator radiating plate and the vertical metal oscillator radiating plate are located on the two arms of the cross-shaped structure of the metal oscillator dielectric plate, thereby forming an asymmetrical cross-shaped structure.
[0010] Furthermore, the horizontal metal oscillator radiator and the vertical metal oscillator radiator each include two oscillator arms, one of which is the feed end and the other is grounded.
[0011] Furthermore, the coupling metal disc is disposed at the intersection of the cross structure.
[0012] Furthermore, the center of the coupling metal disc is connected to the common ground via a vertical through-hole; the grounding arms of the horizontal and vertical metal radiating plates are respectively connected to the common ground via vertical short-circuit through-holes; the feed end of the horizontal metal radiating plate is connected to the input end of the filter circuit through a first vertical signal through-hole penetrating the common ground, and the output end of the filter circuit is connected to the feed end of the vertical metal radiating plate via a second vertical signal through-hole.
[0013] Furthermore, the filtering circuit includes an all-pass filter or a band-stop filter, respectively achieving ultra-wideband / dual-band frequency response.
[0014] Furthermore, the band-stop filter includes an input microstrip line, a first microstrip line, a second microstrip line, a third microstrip line, and an output microstrip line connected in sequence on the main transmission line, as well as a fourth microstrip line, a fifth microstrip line, and a sixth microstrip line, which are respectively located at the front end, the middle, and the end of the second microstrip line.
[0015] Furthermore, the all-pass filter is a 50-ohm microstrip line.
[0016] Compared with the prior art, the significant advantages of this invention are:
[0017] (1) This invention provides a novel design scheme for polarization converters. By loading a filter circuit on the back of the dual-polarized antenna array floor, the polarization characteristics and frequency characteristics of the polarization converter can be designed separately. This is completely different from the previous reflective polarization converters based on anisotropic metasurface designs, and this scheme improves the design flexibility and freedom.
[0018] (2) This invention introduces an RF filter circuit into the design of a polarization converter. By changing the frequency characteristics of the filter circuit, polarization converters with different frequency characteristics can be obtained. For example, if it is necessary to design single-band and multi-band polarization converters, the antenna can be kept unchanged, and only the structure of the filter can be changed. This feature increases the frequency tunability of the polarization converter.
[0019] (3) The filter circuit in this invention is not affected by the oblique incident angle. As long as the antenna can receive the incident wave, the polarization converter can still maintain good performance at large angles.
[0020] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description
[0021] Figure 1 This is a structural diagram of the dual-band polarization converter that uses a terminated band-stop filter to control the frequency characteristics in Example 1.
[0022] Figure 2 This is a structural diagram of the metal vibrator and dielectric substrate of the dual-polarized antenna in Example 1.
[0023] Figure 3 This is a structural diagram of the support layer for the dual-polarized antenna in Example 1.
[0024] Figure 4 This is a structural diagram of the shared ground plane of the dual-polarized antenna and the filter circuit in Example 1.
[0025] Figure 5 This is a structural diagram of the band-stop filter in the dual-band polarization converter that uses a terminated band-stop filter to control the frequency characteristics in Example 1.
[0026] Figure 6 This is a schematic diagram of the reflection coefficient of a dual-band polarization converter that uses a terminated band-stop filter to control the frequency characteristics in Example 1, under linear x-polarized incident waves at different incident angles.
[0027] Figure 7This is a schematic diagram of the polarization conversion ratio of the dual-band polarization converter in Example 1, which uses a terminated band-stop filter to control the frequency characteristics, under linear x-polarized incident waves at different incident angles.
[0028] Figure 8 This is a schematic diagram of the polarization azimuth angle of the dual-band polarization converter that uses a terminated band-stop filter to control the frequency characteristics in Example 1 under a vertically incident linear x-polarized incident wave.
[0029] Figure 9 This is a structural diagram of the ultrawideband polarization converter that utilizes terminated microstrip lines to control frequency characteristics in Example 2.
[0030] Figure 10 This is a structural diagram of the microstrip line in the ultra-wideband polarization converter that utilizes a terminated microstrip line to control frequency characteristics, as shown in Example 2.
[0031] Figure 11 This is a schematic diagram of the reflection coefficients of the ultrawideband polarization converter with frequency control characteristics using a terminated microstrip line in Example 2, under linear x-polarized incident waves at different incident angles.
[0032] Figure 12 This is a schematic diagram of the polarization conversion ratio of the ultrawideband polarization converter that uses a terminated microstrip line to control the frequency characteristics under different incident angles in Example 2.
[0033] Figure 13 This is a schematic diagram of the polarization azimuth angle of the ultra-wideband polarization converter that uses a terminated microstrip line to control the frequency characteristics in Example 2 under a vertically incident linear x-polarized incident wave. Detailed Implementation
[0034] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.
[0035] Combination Figure 1 A polarization converter that uses a termination filter circuit to control frequency characteristics includes a dual-polarized antenna array and a filter circuit disposed on the back of the floor of the dual-polarized antenna array.
[0036] The dual-polarized antenna array is used to receive x-polarized or y-polarized linearly polarized incident waves and convert them into y-polarized or x-polarized waves.
[0037] The filtering circuit is used to control the full-pass / band-pass filtering characteristics to achieve an ultra-wideband / dual-band frequency response.
[0038] The design concept of this invention is as follows: First, a broadband dual-polarization antenna array is selected, which can receive incident waves of either x-polarization or y-polarization. Then, a filter circuit is loaded between the feed ports of the two polarizations of the antenna array to achieve frequency selection of the received signal. This filter is loaded on the back of the antenna array floor and isolated from the antenna. Finally, the signal that can pass through the filter circuit can be transmitted into free space either y-polarized or x-polarized, achieving cross-polarization conversion.
[0039] Specifically, such as Figure 1 As shown, a polarization converter that utilizes a termination filter circuit to control frequency characteristics includes a dual-polarized antenna array and a filter circuit disposed on the back of the antenna array floor. The dual-polarized antenna array includes several antenna elements, each antenna element comprising a wide-angle matching layer 1, a metal vibrator dielectric substrate 2, a support layer 3, and a common ground plane 9 arranged sequentially. A horizontal metal vibrator radiator 5 and a vertical metal vibrator radiator 6 are disposed between the wide-angle matching layer 1 and the metal vibrator dielectric substrate 2; each of the horizontal and vertical metal vibrator radiators 5 and 6 consists of two vibrator arms, one arm serving as the feed terminal and the other arm grounded, as shown. Figure 2 As shown. The support layer 3 is an asymmetrical cross-shaped structure, as... Figure 3 As shown. A coupling metal disc 7 is disposed above the cross-shaped position of the support layer 3; the center of the coupling metal disc 7 is connected to the common ground plane 9 through a vertical through hole 8; the grounding arms of the horizontal metal radiator plate 5 and the vertical metal radiator plate 6 are respectively connected to the common ground plane 9 through vertical short-circuit through holes 10 and 11. The feed end of the horizontal metal radiator plate 5 is connected to the input end of the filter circuit through a vertical signal through hole 12 penetrating the common ground plane 9, and the output end of the filter circuit is connected to the feed end of the vertical metal radiator plate 6 through a vertical signal through hole 16.
[0040] Specifically, the filters are an all-pass filter and a band-stop filter. The all-pass filter is a 50-ohm microstrip line. The band-stop filter includes an input microstrip line 14, a first microstrip line 17, a second microstrip line 18, a third microstrip line 19, and an output microstrip line 15 connected in sequence on the main transmission line, as well as a fourth microstrip line 20, a fifth microstrip line 21, and a sixth microstrip line 22, which are respectively located at the front, middle, and end of the second microstrip line 18.
[0041] Example 1
[0042] This embodiment describes a polarization converter that utilizes a termination filter circuit to control its frequency characteristics; specifically, it is a dual-band polarization converter that utilizes a termination band-stop filter to control its frequency characteristics. When the incident wave is a linear x-polarized or y-polarized electromagnetic wave, it can achieve dual-band cross-polarization conversion. The polarization converter in this embodiment operates in the 6.5-10 GHz and 15-19 GHz bands, with relative bandwidths of 42.4% and 23.5%, respectively. Furthermore, this polarization converter exhibits a polarization conversion ratio exceeding 90% and good stability at the oblique incidence angle. A more detailed description follows with reference to the accompanying drawings.
[0043] See Figure 1 A dual-band polarization converter that utilizes a terminated band-stop filter to control frequency characteristics includes a dual-polarized antenna array and a band-stop filter disposed on the back of the antenna array floor. The dual-polarized antenna array transmits received electromagnetic wave signals to the band-stop filter, which controls its frequency characteristics. The dual-polarized antenna element includes a wide-angle matching layer 1, a metal dipole dielectric substrate 2, a support layer 3, horizontal and vertical metal dipole radiating plates 5 and 6, a coupling metal disc 7, a vertical via 8, a common floor 9, two vertical short-circuit vias 10 and 11, and two vertical signal vias 12 and 16. The wide-angle matching layer 1 is 7.58mm long and wide, made of Teflon, and 2.7mm thick. The dielectric substrate 2 of the metal vibrator is made of Rogers RT5880 and 0.254mm thick. The support layer 3 is made of Teflon and 2.7mm thick. The common ground plane 8 is the copper-clad metal on the back of the band-stop filter, serving as the ground plane for both the dual-polarized antenna array and the band-stop filter. The dielectric substrate 4 of the band-stop filter is made of Rogers RO3003 and 0.254mm thick. To achieve good matching with the metal vibrator radiating plates 5 and 6, four dielectric blocks with dimensions of 0.85mm*0.85mm, 0.85mm*4.53mm, 4.53mm*0.85mm, and 4.53mm*4.53mm, and a thickness of 2.7mm, were removed from the upper left, upper right, lower left, and lower right corners of the support layer 3, respectively. The horizontal and vertical metal vibrator radiating plates 5 and 6 are shaped as follows... Figure 3 As shown. The diameter of the coupling metal disc 7 is 1.88 mm. The diameter of the vertical through-hole 8 is 0.4 mm. The diameters of the two vertical short-circuit through-holes 10 and 11 and the two vertical signal through-holes 12 and 16 are all 0.5 mm. The dimensions of each part of the metal oscillator radiating plate are as follows: p = 7.58, l d1 =1.4,l d2 =0.88,l d3 =0.8,l d4 ,l d5 =0.1,l d6 =0.85l d7 =4.53,w d1=2,w d2 =1.24,w d3 =0.68,r f =r g1 =0.25,r g2 =0.15,r g3 =0.25,r g4 =0.5,l d8 =4.84,l d9 =1.45,r f =0.25,w m =0.7 (unit: mm).
[0044] See Figure 5 This is a schematic diagram of a band-stop filter in a dual-band polarization converter that utilizes a terminated band-stop filter to control frequency characteristics. The input microstrip line 14 of the band-stop filter is connected to the horizontal metal radiator 5 via a vertical signal via 12, and the output microstrip line 15 is connected to the vertical metal radiator 6 via a vertical signal via 16. The dielectric substrate material of the band-stop filter is Rogers RO3003 with a thickness of 0.254 mm. The width w of the input and output transmission lines of the band-stop filter on the main transmission line is shown. m =0.7mm, width w of the first and third microstrip lines b1 =0.15mm, length l b1 =0.15mm, second microstrip line width w b2 = 0.54mm, length l b2 =7.9mm, the width w of the fourth and sixth transmission lines located on the branch line b4 =0.15mm, length l b4 = 4.85mm, fifth transmission line width w b3 = 0.58mm, length l b3 =3.96mm.
[0045] See Figure 6 Let be the reflection coefficient of the polarization converter at different oblique incidence angles, where the incident wave is x-polarized linearly polarized. As shown in the figure, within the first operating frequency band of 6.5-10 GHz, the reflection coefficient r of the polarization converter increases until the oblique incidence angle increases to 45 degrees. xx It can still stay below -10dB, r yx All are above -1dB. Among them, r xx =|E xr / E xi |,r yx =|E yr / E xi |,E xi E represents the electric field of the incident wave with x-polarization.xr and E yr These represent the x-polarized emission electric field and the y-polarized reflection electric field, respectively. Within the second operating frequency band of 15-19 GHz, when the incoming wave illuminates perpendicularly, r... xx Below -10dB, r yx Above -1dB. When the oblique incident angle increases to 45 degrees, the operating bandwidth at high frequencies decreases to 17.75GHz, but it can still maintain good polarization conversion performance.
[0046] See Figure 7 Let be a linearly polarized wave with x-polarization as the incident wave. The polarization conversion ratio (PCR) of this polarization converter at different oblique incidence angles is given by PCR = r. yx 2 / (r yx 2 +r xx 2 For vertically incident waves, PCR was above 90% in both the 6.5-10 GH and 15-19 GH operating frequency bands. When the oblique incident angle increased to 45 degrees, the bandwidth at high frequencies decreased slightly, but PCR remained above 90% in both operating frequency bands.
[0047] See Figure 8 Let be the polarization azimuth angle θ of the polarization converter when the incident wave is an x-polarized linearly polarized wave and is incident perpendicularly. The polarization azimuth angle θ is defined as θ = arctan(r xy / r xx It represents the relative rotation angle between the reflected wave and the incident wave. As shown in the figure, the polarization azimuth angle θ is higher than 75 degrees in the ranges of 6.62-9.85 GHz and 15.17-19 GHz, and approaches 90 degrees at 7.2 GHz and 9.5 GHz. These results demonstrate that the polarization converter exhibits good linear cross-polarization conversion performance.
[0048] Example 2
[0049] This embodiment describes a polarization converter that utilizes a termination filter circuit to control frequency characteristics; specifically, it is an ultra-wideband polarization converter that utilizes a termination microstrip line to control frequency characteristics. When the incident wave is a linear x- or y-polarized electromagnetic wave, ultra-wideband cross-polarization conversion can be achieved. The polarization converter in this embodiment operates in the 6-19 GHz frequency band, with a relative bandwidth of 104%. Furthermore, this polarization converter exhibits a polarization conversion ratio exceeding 90% and good stability at the oblique incidence angle. A more detailed description follows with reference to the accompanying drawings.
[0050] See Figure 9An ultrawideband polarization converter utilizing terminated microstrip lines to control frequency characteristics includes a dual-polarized antenna array and microstrip lines disposed on the back of the antenna array floor. The dual-polarized antenna elements and... Figure 2 The structures used are exactly the same.
[0051] See Figure 10 This is a schematic diagram of a microstrip line in an ultra-wideband polarization converter that utilizes a terminated microstrip line to control its frequency characteristics. The microstrip line has a characteristic impedance of 50 ohms and a width w. m =0.7mm.
[0052] See Figure 11 Let be the reflection coefficient of the polarization converter at different oblique incidence angles, where the incident wave is x-polarized linearly polarized. As shown in the figure, under perpendicular incidence, the reflection coefficient r of the polarization converter is [value missing] within the frequency range of 6-19 GHz. xx Below -10dB, r yx Above -0.6dB. When the oblique incidence angle increases to 30 degrees, the reflection coefficient r in the 6-18GHz range... xx It remains below -10dB. When the oblique incidence angle increases to 45 degrees, the reflection coefficient r at 18GHz... xx -8.35Db, r yx All are within -2dB.
[0053] See Figure 12 , representing the polarization conversion ratio of the polarization converter at different oblique incidence angles for an x-polarized linearly polarized incident wave. For vertically incident waves, within the range of 6-19 GH, PCR remains above 90% when the oblique incidence angle increases to 30 degrees. When the oblique incidence angle increases to 45 degrees, the PCR remains greater than 84.5% across the entire operating frequency band.
[0054] See Figure 13 Let be the incident x-polarized linearly polarized wave, and let θ be the polarization azimuth angle θ of the polarization converter when it is incident perpendicularly. As can be seen from the figure, the polarization azimuth angle θ is greater than 72 degrees in the range of 6-19 GHz, and at 11.7 GHz, the polarization azimuth angle θ is close to 90 degrees.
[0055] This invention designs a reflective polarization converter with ultra-wideband and dual-frequency band characteristics. When a linearly x-polarized or y-polarized electromagnetic wave irradiates the surface of this polarization converter, the reflected wave becomes orthogonally polarized. This invention can be used in antenna design, radar cross section (RCS) reduction, and wireless communication technology.
[0056] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.
Claims
1. A polarization converter that utilizes a termination filter circuit to control frequency characteristics, characterized in that, The polarization converter includes a dual-polarized antenna array and a filter circuit disposed on the back of the floor of the dual-polarized antenna array; The dual-polarized antenna array is used to receive... x- polarization or y- Polarized linearly polarized incident wave, and convert it into y- polarization or x- polarization; The filtering circuit is used to control the full-pass / band-pass filtering characteristics to achieve an ultra-wideband / dual-band frequency response; The dual-polarized antenna array includes several antenna elements, each antenna element comprising, from top to bottom, a wide-angle matching layer (1), a metal vibrator dielectric substrate (2), a support layer (3), and a common ground plane (9); a horizontal metal vibrator radiator (5) and a vertical metal vibrator radiator (6) located on the same horizontal plane are disposed between the wide-angle matching layer (1) and the metal vibrator dielectric substrate (2), and a coupling metal disc (7) is disposed between the metal vibrator dielectric substrate (2) and the support layer (3); the coupling metal disc (7) is connected to the common ground plane (9) through a vertical through-hole (8); the horizontal metal vibrator radiator (5) and the vertical metal vibrator radiator (6) are connected to the common ground plane (9) through two vertical short-circuit through-holes (10, 11); the horizontal metal vibrator radiator (5) is connected to the input terminal of the filter circuit through a first vertical signal through-hole (12) penetrating the common ground plane (9), and the output terminal of the filter circuit is connected to the vertical metal vibrator radiator (6) through a second vertical signal through-hole (16). The metal oscillator dielectric plate (2) and the support layer (3) are asymmetrical cross-shaped structures; The horizontal metal oscillator radiating plate (5) and the vertical metal oscillator radiating plate (6) are located on the two arms of the cross structure of the metal oscillator dielectric plate (2), thereby forming an asymmetrical cross structure. The coupling metal disc (7) is disposed at the intersection of the cross structure.
2. The polarization converter with frequency characteristics controlled by a termination filter circuit according to claim 1, characterized in that, The horizontal metal oscillator radiator (5) and the vertical metal oscillator radiator (6) each include two oscillator arms, one of which is the feed end and the other is grounded.
3. The polarization converter with frequency characteristics controlled by a termination filter circuit according to claim 1, characterized in that, The center of the coupling metal disc (7) is connected to the common floor (9) through a vertical through hole (8); the grounding arms of the horizontal metal radiator (5) and the vertical metal radiator (6) are connected to the common floor (9) through vertical short-circuit through holes (10, 11); the feed end of the horizontal metal radiator (5) is connected to the input end of the filter circuit through the common floor (9) through the first vertical signal through hole (12), and the output end of the filter circuit is connected to the feed end of the vertical metal radiator (6) through the second vertical signal through hole (16).
4. The polarization converter with frequency characteristics controlled by a termination filter circuit according to claim 1, characterized in that, The filtering circuit includes an all-pass filter or a band-stop filter, which respectively achieves the frequency response of ultra-wideband / dual-band.
5. The polarization converter with frequency characteristics controlled by a termination filter circuit according to claim 4, characterized in that, The band-stop filter includes an input microstrip line (14), a first microstrip line (17), a second microstrip line (18), a third microstrip line (19), and an output microstrip line (15) connected in sequence on the main transmission line, as well as a fourth microstrip line (20), a fifth microstrip line (21), and a sixth microstrip line (22) located at the front, middle, and end of the second microstrip line (18), respectively.
6. The polarization converter with frequency characteristics controlled by a termination filter circuit according to claim 4, characterized in that, The all-pass filter is a 50-ohm microstrip line.