A low axial ratio circularly polarized antenna with an isolation structure

Abstract

This invention discloses a low-axial-ratio, high-power-capacity circularly polarized antenna with an isolation structure, belonging to the field of high-power microwave measurement technology. This invention adds an isolation structure between the antenna's circular polarization generation structure and the feeding structure to suppress the influence of different connection structures at the antenna's rear end. A typical isolation structure is a rearward-expanding metal surface. On the one hand, through appropriate tilt angle design, it effectively suppresses the forward reflection of the isolation structure itself, reducing its impact on the front-end circular polarization generation structure and ensuring low-axial-ratio characteristics. On the other hand, by adopting appropriate depth and size design, it effectively suppresses the backward propagation of surface current and reflection from the rear-end metal surface, reducing the impact of the rear-end connection structure on the antenna's low-axial-ratio characteristics. Finally, experimental verification shows that a circularly polarized antenna with an ultra-low axial-ratio is obtained. The isolation structure added in this invention effectively suppresses the backward propagation of surface current and the reflection from the rear-end metal surface without affecting the antenna's low-axial-ratio characteristics.

Description

Technical Field

[0001] This invention belongs to the field of high-power microwave measurement technology, specifically relating to a low-axis-ratio circularly polarized antenna with an isolation structure. Background Technology

[0002] Antennas, as a key component of wireless communication systems, play a crucial role at both the signal transmission and reception ends. For linearly polarized antennas, the polarization matching requirements of the transmitting and receiving systems are quite stringent. When there is an angle between the polarization directions of the transmitting and receiving systems, the received signal will suffer some loss; when the polarization directions are perpendicular, the transmitting and receiving ends will be completely isolated. According to polarization theory, any linearly polarized wave can be decomposed into two circularly polarized waves with opposite directions of rotation and equal amplitude. Therefore, circularly polarized antennas can effectively receive any linearly polarized wave, showing a significant advantage in solving the polarization mismatch problem. Especially when the axial ratio of the circularly polarized antenna is sufficiently low, the received signal strength remains constant regardless of the direction of the linearly polarized incoming wave.

[0003] An ideal circularly polarized antenna maintains a constant polarization loss coefficient for linearly polarized waves in any direction, enabling reception of such waves without polarization mismatch. However, practical circularly polarized antennas are affected by manufacturing errors and environmental factors, typically exhibiting elliptical polarization characteristics with a certain axial ratio. When used for precise measurement of high-power microwave signals with unknown polarization directions, improving the axial ratio of the circularly polarized antenna, suppressing environmental influences, and simultaneously meeting high-power capacity requirements are key design considerations.

[0004] Currently, numerous studies on low-axial-ratio circularly polarized antennas have been conducted both domestically and internationally. Typical examples include circularly polarized antennas designed using circular polarization converters, corrugated horns, and waveguide slot structures. However, the circularly polarized antennas presented in relevant literature or examples are typically elliptical polarized antennas with axial ratios of 0.5dB-3dB. The measured axial ratio results are usually more than 1dB higher than the simulation results. The main reason for this is that designers focus only on the antenna's intrinsic performance, neglecting the impact of the back-end connection structure and the testing environment on the antenna's axial ratio characteristics during actual use. Therefore, a practical and effective low-axial-ratio circularly polarized antenna design scheme is still lacking to meet the high-precision measurement requirements of high-power microwave signals with unknown polarization directions. Summary of the Invention

[0005] The purpose of this invention is to provide a low axial ratio circularly polarized antenna with an isolation structure. The isolation structure effectively suppresses the backward propagation of surface current and the reflection from the rear metal surface, solving the problems of poor axial ratio characteristics and poor scattering suppression of current practical circularly polarized antennas due to factors such as processing errors and usage environment. At the same time, it has the characteristics of high power capacity and is suitable for the need for accurate measurement of high-power microwave signals with unknown polarization direction in different application scenarios.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A low-axis-ratio circularly polarized antenna with an isolation structure includes a circularly polarized feeding structure, a circularly polarized generating structure, a mounting flange, and an isolation structure.

[0008] The isolation structure is a rearward-expanding metallic emitting surface located at l2 behind the circular polarization generating structure and nested on the circular polarization feeding structure. By adjusting the tilt angle θ of the isolation structure and the dimensions (a1, b1) of the emitting surface of the isolation structure, where θ is the tilt angle formed by the emitting surface of the isolation structure and the circular polarization generating structure, a1 is the length of the emitting surface, and b1 is the width of the emitting surface, the antenna's low axial ratio characteristics are ensured while effectively suppressing the backward transmission of surface current and reflection from the rear metallic surface.

[0009] The distance between the isolation structure and the circular polarization generation structure is l2. The isolation structure is designed to slide back and forth on the circular polarization generation structure to achieve the frequency modulation function of the circular polarization antenna. When the size of the transmitting surface (a1, b1) of the isolation structure is larger than or approximately equal to the size of the rear metal reflector, the reflection suppression effect is better. Its size design is adapted according to the application scenario. The tilt angle θ of the isolation structure is determined by the length l3 of the isolation structure segment and the size of the transmitting surface (a1, b1). While keeping the size of the transmitting surface (a1, b1) unchanged, the larger the tilt angle of the isolation structure, the narrower the axial ratio beamwidth of the circular polarization antenna. In order to obtain better wide beam characteristics, the tilt angle of the isolation structure should be smaller than the value adapted to the application scenario.

[0010] The standard flange at the rear end of the circular polarization feed structure is used for antenna installation and fixation, while the front end is connected to the circular polarization generation structure to generate circular polarization waves. The combination of the circular polarization generation structure and the isolation structure achieves technical specifications such as low axial ratio, wide beam, and high power capacity.

[0011] Furthermore, the isolation structure can be truncated pyramidal, truncated cone, or other types suitable for the application scenario.

[0012] Furthermore, in the X-band, the isolation structure is selected as a rearward-expanding frustum-shaped metal emitting surface, the circular polarization feeding structure is a rectangular waveguide transmission section, and the BJ100 type waveguide is selected; the circular polarization generation structure is a waveguide slotted section, which includes a first irregular slot and a second irregular slot, and the two irregular slots are rotationally symmetric structures.

[0013] The beneficial effects of this invention are as follows:

[0014] 1. The X-band low axial ratio circularly polarized antenna structure based on the isolation structure proposed in this invention is simple and easy to implement. The added isolation structure effectively suppresses the back propagation of surface current and the reflection suppression of the rear metal surface without affecting the low axial ratio characteristics of the antenna.

[0015] 2. Simulation results of this invention show that when connecting different structures such as straight waveguides and enclosures, the axial ratio change at the antenna center frequency is less than 0.25dB; the calculated antenna power capacity is 270kW, which meets the requirements for use under high power conditions, realizing the design of a low axial ratio, high power capacity circularly polarized antenna; the measured results show that the main axial ratio at the antenna center frequency is 0.12dB, and the 0.25dB axial ratio beamwidth is greater than 20°, realizing the design of an ultra-low axial ratio circularly polarized antenna that is close to ideal circular polarization.

[0016] 3. The measured results of the main technical indicators of the antenna of this invention are consistent with the simulation results, and it has excellent engineering application value. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the low axial ratio circularly polarized antenna based on the isolation structure design of this invention;

[0018] 1(a) shows the three-dimensional structure of the circularly polarized antenna according to an embodiment of the present invention;

[0019] 1(b) is a schematic diagram showing the dimensions of the circularly polarized antenna according to an embodiment of the present invention;

[0020] Among them, 01-rectangular waveguide transmission section, 02-waveguide slotted section, 03-first irregular slot, 04-second irregular slot, 05-isolation structure, 06-mounting flange

[0021] Figure 2 A comparative analysis of the changes in axial ratio when the circularly polarized antenna is connected to waveguides of different lengths before and after adding the isolation structure in this embodiment of the invention:

[0022] 2(a) The effect of waveguide length variation on the axial ratio of a circularly polarized antenna without isolation structure;

[0023] 2(b) The effect of waveguide length variation on the axial ratio of a circularly polarized antenna with an isolated structure;

[0024] Figure 3 A comparative analysis of the changes in axial ratio when the circularly polarized antenna is connected to enclosures of different sizes before and after adding the isolation structure in this embodiment of the invention:

[0025] 3(a) The effect of the box width variation on the axial ratio of the circularly polarized antenna without isolation structure;

[0026] 3(b) The effect of housing height variation on the axial ratio of a circularly polarized antenna without isolation structure;

[0027] 3(c) The effect of the box width variation on the axial ratio of the isolated circularly polarized antenna;

[0028] 3(d) The effect of box height variation on the axial ratio of the isolated circularly polarized antenna;

[0029] Figure 4 The following are simulation analysis results of the influence of isolation structure parameters on antenna axial ratio characteristics in an embodiment of the present invention;

[0030] 4(a) The effect of changes in the location of the isolation structure on the axial ratio of the circularly polarized antenna;

[0031] 4(b) The effect of changes in the size of the emitting surface of the isolation structure on the axial ratio of the circularly polarized antenna;

[0032] 4(c) The effect of the tilt angle change of the isolation structure on the axial ratio of the circularly polarized antenna;

[0033] Figure 5 A physical image of a low-axis-ratio circularly polarized antenna based on an isolation structure design. Detailed Implementation

[0034] The present invention will now be explained and described in detail with reference to the accompanying drawings and embodiments.

[0035] The design concept of this invention is as follows: This invention adds an isolation structure between the antenna's circular polarization generation structure and the feeding structure to suppress the influence of different connection structures at the antenna's rear end. By integrating the circular polarization generation structure and the isolation structure design, it achieves technical specifications such as low axial ratio, wide beam, and high power capacity. A typical isolation structure is a rearward-expanding metallic emitting surface. On the one hand, through appropriate tilt angle design, it effectively suppresses the forward reflection of the isolation structure itself, reducing its impact on the front-end circular polarization generation structure and ensuring low axial ratio characteristics. On the other hand, by adopting appropriate depth and size design, it effectively suppresses the backward transmission of surface current and reflection from the rear-end metallic surface, reducing the impact of the rear-end connection structure on the antenna's low axial ratio characteristics. Finally, actual measurements verify that a circularly polarized antenna with an ultra-low axial ratio has been obtained.

[0036] The following detailed description of the specific implementation of the present invention, with reference to the accompanying drawings, takes the design of an X-band circularly polarized antenna as an example. It should be noted that the isolation structure proposed in this invention is also applicable to other circularly polarized antennas based on waveguide transmission structures. The isolation structure is not limited to the rearward expansion reflective surface of the frustum type in the embodiment, but can also be frustum type or other types.

[0037] In the X-band, a low-axis-ratio circularly polarized antenna based on an isolation structure design consists of a rectangular waveguide transmission section 01, a waveguide slotted section 02, an isolation structure 05, and a mounting flange 06. The waveguide slotted section 02 includes a first irregular slot 03 and a second irregular slot 04; the two irregular slots are rotationally symmetric structures. Figure 1As shown in 1(a). The rectangular waveguide transmission section uses a BJ100 type waveguide. The front end of the rectangular waveguide transmission section is connected to the slotted waveguide section to form a circularly polarized wave. The rear end of the rectangular waveguide transmission section is connected to a standard flange for antenna mounting and fixing. The slotted waveguide section is located at the very front of the circularly polarized antenna. The surface current at the upper and lower slot lines synthesizes the Ex field, and the current on the side wall forms the Ey field. By adjusting the slot depth l1 and the tilt angle (d2, d3, d4, d5), a 90° phase difference is formed to achieve a circularly polarized wave.

[0038] The isolation structure is a rearward-expanding metal emitting surface located at a certain distance l2 behind the slotted waveguide section, as shown in 1(b). It is nested on the rectangular waveguide transmission section. Through appropriate tilt angle θ and size (a1, b1) design, the low axial ratio characteristics of the antenna are ensured while effectively suppressing the backward transmission of surface current and the reflection of the rear metal surface.

[0039] The key parameters of the isolation structure were simulated and analyzed, and the results are as follows: Figure 4 As shown. First, there is the distance (l2) between the isolation structure and the waveguide slotted section, as... Figure 4 As shown in (a), simulations revealed that the movement of the isolation structure within a certain range can change the antenna's center frequency, with an adjustment range of up to 40MHz, without compromising the antenna's low axial ratio characteristics. If the isolation structure is designed to slide back and forth on the waveguide slotted section, the antenna's frequency modulation function can be achieved to a certain extent. Secondly, the dimensions of the isolation structure's transmitting surface (a1, b1), such as... Figure 4 As shown in (b), simulations revealed that the dimensional changes of the emitting surface of the isolation structure within a certain range had little impact on the antenna axial ratio. Figure 3 Simulation results in (c) and (d) show that when the size of the emitting surface of the isolation structure is larger than or roughly equal to the size of the rear metal reflective surface, the reflection suppression effect is better, and its size design can be adapted according to the application scenario; finally, the tilt angle θ of the isolation structure, such as Figure 4 As shown in (c), the tilt angle is mainly determined by the length l3 of the isolation structure segment and the dimensions of the transmitting surface (a1, b1). With the transmitting surface dimensions unchanged, the simulation results show the axial ratio beamwidth of the antenna when the length l3 of the isolation structure segment is 6mm (corresponding to tilt angle θ = 77.1°), 11mm (corresponding to tilt angle θ = 67.2°), 16mm (corresponding to tilt angle θ = 58.5°), and 21mm (corresponding to tilt angle θ = 51.2°). It is found that when the tilt angle of the isolation structure is large, the axial ratio beamwidth of the circularly polarized antenna obtained by repeated parameter optimization is narrow. In order to obtain better wide beam characteristics, the tilt angle of the isolation structure should be less than a certain angle.

[0040] Simulations were used to obtain the axial ratio versus frequency curves of a circularly polarized antenna connected to straight waveguides of different lengths. The results were compared with those of a circularly polarized antenna without isolation. Figure 2As shown. The results indicate that: Figure 2 As shown in (a), before adding the isolation structure, when the straight waveguide length l changes from 290 mm to 310 mm, the center frequency (the frequency corresponding to the lowest axial ratio) of the circularly polarized antenna shifts and exhibits a periodic variation, with the axial ratio at the center frequency increasing to a maximum of 0.45 dB; after adding the isolation structure, as shown in (a), the center frequency .... Figure 2 As shown in (b), the surface current distribution results show that the backward current is significantly reduced, the center frequency of the circularly polarized antenna is only slightly shifted, and the maximum axial ratio at the center frequency is less than 0.21dB.

[0041] Simulations were used to obtain the axial ratio versus frequency curves of a circularly polarized antenna connected to enclosures of different sizes. The results were compared with those of a circularly polarized antenna without isolation. Figure 3 As shown. The results indicate that before adding the isolation structure, as... Figure 3 As shown in (a) and 3(b), when the width a2 of the enclosure structure changes from 90mm to 110mm and the height b2 changes from 60mm to 80mm, the center frequency of the circularly polarized antenna will shift significantly, with the axial ratio at the center frequency increasing to a maximum of 1.4dB. After adding the isolation structure, as shown in 3(c) and 3(d), the surface current distribution results show that the reflection caused by the rear enclosure is effectively suppressed by the isolation structure, and the maximum axial ratio at the center frequency is less than 0.22dB.

[0042] The low axial ratio circularly polarized antenna was fabricated and tested. A photograph of the actual antenna is shown below. Figure 5 As shown in Table 1, the structural parameters are as follows. For axial ratio measurement, a standard pyramidal horn antenna is used as the source antenna. The center of the circularly polarized antenna aperture is aligned with the center of the pyramidal horn antenna aperture. The pyramidal horn antenna is rotated 360° along the axis. The measured maximum and minimum level difference is the axial ratio of the circularly polarized antenna. The measured axial ratio of the circularly polarized antenna is 0.12 dB. For axial ratio beamwidth measurement, the circularly polarized antenna is deflected at different angles along the axis. After each rotation, the position of the circularly polarized antenna is adjusted to ensure that its phase center axis is directly aligned with the center of the pyramidal horn antenna aperture. The pyramidal horn antenna is rotated 360° along the axis to obtain the axial ratio test results for different angles. The actual test data is shown in Table 2.

[0043] Table 1 Structural parameters of circularly polarized antenna

[0044] Structural parameters <![CDATA[a1]]> <![CDATA[b1]]> <![CDATA[l1]]> <![CDATA[l2]]> <![CDATA[l3]]> Unit (mm) 70.58 64.25 31.20 14.00 18.50 Structural parameters <![CDATA[d1]]> <![CDATA[d2]]> <![CDATA[d3]]> <![CDATA[d4]]> <![CDATA[d5]]> Unit (mm) 29.62 19.50 19.47 18.16 28.50

[0045] Table 2. Test results of beamwidth for circularly polarized antennas

[0046] Angle / ° Measured shaft ratio / dB Simulated shaft ratio / dB 0° 0.12 0.06 5° 0.14 0.05 10° 0.24 0.21 15° 0.30 0.35 20° 0.52 0.37 -5° 0.15 0.05 -10° 0.22 0.21 -15° 0.39 0.35 -20° 0.56 0.37

[0047] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A low axial ratio circularly polarized antenna with an isolation structure, comprising a circularly polarized feed structure, a circularly polarized generation structure, and a mounting flange, characterized in that, It also includes isolation structures; The isolation structure is a rearwardly expanding metallic emission surface located behind the circular polarization generating structure. At this location, nested within a circularly polarized feed structure, the tilt angle of the isolation structure is adjusted. and the size of the emitting surface of the isolation structure ( , This is used to ensure the antenna's low axial ratio characteristics while effectively suppressing back propagation of surface current and reflection from the rear metal surface; among which The tilt angle formed by the emitter surface of the isolation structure and the circular polarization structure. The length of the launching surface, The width of the emitting surface; The distance between the isolation structure and the circular polarization generating structure is The isolation structure is designed to slide back and forth on the circular polarization generation structure to achieve the frequency modulation function of the circular polarization antenna; the size of the emitting surface of the isolation structure ( , When the size is larger than or roughly equivalent to the size of the rear metal reflective surface, the reflection suppression effect is good; its size design should be adapted according to the application scenario; the tilt angle of the isolation structure. The length of the isolation structure segment and the size of the launching surface ( , They jointly decided to maintain the size of the launch surface ( , With the isolation structure tilt angle remaining unchanged, the larger the tilt angle, the narrower the axial ratio beamwidth of the circularly polarized antenna. The tilt angle of the isolation structure is taken to be smaller than the value required for the application scenario. The circular polarization feed structure is connected to a standard flange at the rear end for antenna installation and fixation, and connected to a circular polarization generating structure at the front end to generate circular polarization waves. The combination of the circular polarization generating structure and the isolation structure achieves technical specifications of low axial ratio, wide beam, and high power capacity.

2. The low-axis-ratio circularly polarized antenna with an isolation structure according to claim 1, characterized in that, The isolation structure adopts a truncated pyramid shape, a frustum shape, or other types suitable for the application scenario.

3. The low-axis-ratio circularly polarized antenna with an isolation structure according to claim 1, characterized in that, In the X-band, the isolation structure is a rearward-expanding frustum-shaped metal emitting surface, the circular polarization feeding structure is a rectangular waveguide transmission section, and a BJ100 type waveguide is used; the circular polarization generation structure is a waveguide slotted section, which includes a first irregular slot and a second irregular slot, and the two irregular slots are rotationally symmetric structures.

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