X-band synthetic aperture radar four-port waveguide circulator and synthetic aperture radar

Abstract

This invention discloses a four-port waveguide circulator for X-band synthetic aperture radar and a synthetic aperture radar, relating to the field of waveguide circulator technology. The four-port waveguide circulator of this invention includes a circulator body with a first port, a second port, a third port, and a fourth port. A resonant cavity is formed within the circulator body, and a ferrite sheet and a dielectric pillar are disposed within the resonant cavity. The ferrite sheet and the dielectric pillar constitute a vortex resonant cavity, and a metal diaphragm is also loaded within the resonant cavity. This invention can ensure that the high-power signal reflected by the limiter is completely absorbed by the load and does not enter the transmitter, thereby improving the working stability and reliability of the synthetic aperture radar system.

Description

Technical Field

[0001] This invention relates to the field of waveguide circulator technology, and more particularly to a four-port waveguide circulator for X-band synthetic aperture radar and a synthetic aperture radar. Background Technology

[0002] The circulator is a key component in synthetic aperture radar (SAR) for achieving signal transmission and reception isolation and full-duplex transmission. In a SAR system, the transmitter needs to radiate high-power electromagnetic waves into the external space via an antenna, while the receiver needs to receive weak echo signals from the antenna. If the transmitted signal leaks into the receiving channel, or if a strong reflected signal enters the transmitting channel, it will cause instability in the radar system and may even damage internal components. A four-port circulator utilizes the unidirectional transmission characteristic of electromagnetic waves to achieve signal isolation and distribution between the transmitting channel, receiving channel, antenna channel, and load channel. The four ports are connected to the transmitter, receiver, antenna, and load, respectively. The electromagnetic wave emitted from the transmitter enters the circulator through the first port, transmits unidirectionally to the second port, and is then transmitted into the external space by the antenna. The electromagnetic wave received by the antenna enters the circulator through the second port, transmits unidirectionally to the third port, passes through a limiter, and enters the receiver. If the electromagnetic wave entering the receiver from the antenna has high power, the limiter at the receiver front end will reflect this high power signal, which is then transmitted unidirectionally to the fourth port and absorbed by the load. Without a fourth port, and instead using a three-port circulator, the high power reflected back from the limiter will re-enter the transmitter, causing instability in the radar system and potentially damaging internal components. Therefore, a four-port circulator is essential for radar systems with high transmit power.

[0003] Deng Guangjian et al. proposed a four-port waveguide circulator based on a cylindrical resonant cavity in the X-band. This circulator has four waveguide ports, and the central cavity contains a ferrite sheet and a dielectric cylinder to form a gyromagnetic resonant cavity, enabling unidirectional transmission of electromagnetic waves within the circulator. The ferrite sheet has a saturation magnetization of 1600 Gauss, a relative permittivity of 13.7, and a ferromagnetic resonance linewidth of 77 Oersted; the dielectric cylinder has a relative permittivity of 7.

[0004] The aforementioned four-port waveguide circulator based on a cylindrical resonant cavity exhibits poor isolation between its ports, achieving only 12 dB. This fails to effectively isolate electromagnetic wave leakage between the ports, thus affecting the normal operation of the radar system. Furthermore, the circulator suffers from significant insertion loss, less than 0.5 dB, with large fluctuations in insertion loss at different frequencies, reaching 0.3 dB. This results in substantial signal power loss and poor signal amplitude flatness. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provides a four-port waveguide circulator for X-band synthetic aperture radar and a synthetic aperture radar, as detailed below: 1) In a first aspect, the present invention provides a four-port waveguide circulator for X-band synthetic aperture radar, the specific technical solution of which is as follows: It includes a circulator body, on which a first port, a second port, a third port and a fourth port are provided. A resonant cavity is formed inside the circulator body. A ferrite sheet and a dielectric pillar are provided inside the resonant cavity. The ferrite sheet and the dielectric pillar constitute a gyromagnetic resonant cavity. A metal diaphragm is also loaded inside the resonant cavity.

[0006] The beneficial effects of the X-band synthetic aperture radar four-port waveguide circulator provided by this invention are as follows: By loading a metal diaphragm within the resonant cavity, the signal coupling strength between the ports is improved, reducing insertion loss in the passband and significantly decreasing insertion loss fluctuations, thus improving signal amplitude flatness. By loading dielectric pillars within the resonant cavity, energy leakage between ports is reduced, improving isolation between ports in the passband. Compared to existing circulator structures using cylindrical connections to the resonant cavity without a metal diaphragm, this invention, by adding a metal diaphragm and using dielectric pillars within the resonant cavity, effectively adjusts the electromagnetic field distribution between the ports, reducing power loss during electromagnetic wave transmission. This allows transmitted and received signals to pass through the circulator with less attenuation, improving the radar system's transmission efficiency and receiving sensitivity. Simultaneously, the reduced insertion loss fluctuations ensure consistent transmission characteristics for all frequency components during broadband signal transmission, preventing signal amplitude distortion. Furthermore, this invention employs ferrite sheets and dielectric pillars to construct a vortex resonant cavity, which, in conjunction with a metal diaphragm loaded within the resonant cavity, effectively suppresses electromagnetic wave leakage between ports and significantly improves port isolation. This avoids interference of the transmitted signal with the receiving channel, ensures that the high-power signal reflected by the limiter is completely absorbed by the load and does not enter the transmitter, and improves the operational stability and reliability of the synthetic aperture radar system.

[0007] Based on the above scheme, the X-band synthetic aperture radar four-port waveguide circulator of the present invention can be further improved as follows.

[0008] Furthermore, the circulator body is a cuboid structure, the resonant cavity is located in the central region of the circulator body, the ferrite sheet is a circular structure, the ferrite sheet is located in the center of the resonant cavity, the dielectric pillar is a hexahedral pillar, the dielectric pillar is located on the outer periphery of the ferrite sheet and is coaxial with the ferrite sheet, and the metal diaphragm is located inside the resonant cavity and between the outer wall of the dielectric pillar and the inner wall of the resonant cavity.

[0009] The beneficial effects of adopting the above-mentioned further scheme are as follows: Setting the circulator body as a cuboid structure and placing the resonant cavity in the central region of the circulator body allows the geometric boundaries of the resonant cavity to match the arrangement of the ferrite sheet, dielectric pillar, and metal diaphragm, which is conducive to forming a uniform electromagnetic field distribution. The ferrite sheet adopts a circular structure and is located at the center of the resonant cavity. The dielectric pillar adopts a hexahedral pillar structure and is located on the periphery of the ferrite sheet and coaxially with it. This arrangement maintains the symmetry of the electromagnetic field distribution within the resonant cavity and reduces energy scattering of electromagnetic waves during transmission. The metal diaphragm is located inside the resonant cavity, between the outer wall of the dielectric pillar and the inner wall of the resonant cavity. This arrangement allows the metal diaphragm to locally adjust the electromagnetic field between the dielectric pillar and the inner wall of the resonant cavity. Through this structural arrangement, the energy loss of electromagnetic waves propagating in the resonant cavity along a predetermined direction is significantly reduced, and signal leakage between ports is effectively suppressed, thereby improving the isolation performance of the circulator. Compared to existing circulator structures that use cylindrical resonant cavities without metal diaphragms, the arrangement of this invention improves port isolation, insertion loss, and in-band flatness, better meeting the performance requirements of synthetic aperture radar systems. Furthermore, by setting the dielectric pillars as hexahedral pillars with their six faces facing the first, second, third, and fourth ports and the two inner walls of the resonant cavity, the electromagnetic field transmission path at each waveguide port is locally adjusted, effectively improving the signal isolation strength between ports.

[0010] Furthermore, there are four metal diaphragms, which correspond to the positions of the first port, the second port, the third port, and the fourth port, respectively. The length from the center to the apex of the dielectric pillar is 3.4 mm, the height of the dielectric pillar is 6.61 mm, the radius of the ferrite sheet is 5.55 mm, the height of the ferrite sheet is 3.39 mm, the length of each of the four waveguide ports is 7.7 mm, the height of each of the four waveguide ports is 20.36 mm, the length of each metal diaphragm is 2 mm, the width of each metal diaphragm is 0.5 mm, the height of each metal diaphragm is 10 mm, the length of the circulator body is 32 mm, the width of the circulator body is 21.1 mm, and the height of the circulator body is 20.36 mm.

[0011] The beneficial effects of adopting the above-mentioned further scheme are as follows: by setting the number of metal diaphragms to four, and aligning the four metal diaphragms with the positions of the first, second, third, and fourth ports respectively, each waveguide port has a corresponding metal diaphragm to independently adjust the local electromagnetic field, thereby effectively improving the signal coupling strength between the ports. Simultaneously, this invention optimizes the structural dimensions of the circulator at a center frequency of 8.9 GHz: the length from the center to the apex of the dielectric pillar is 3.4 mm, the height of the dielectric pillar is 6.61 mm, the radius of the ferrite sheet is 5.55 mm, the height of the ferrite sheet is 3.39 mm, the length of each of the four waveguide ports is 7.7 mm, the height of each of the four waveguide ports is 20.36 mm, the length of the metal diaphragm is 2 mm, the width of the metal diaphragm is 0.5 mm, the height of the metal diaphragm is 10 mm, the length of the circulator body is 32 mm, the width of the circulator body is 21.1 mm, and the height of the circulator body is 20.36 mm. Under the aforementioned structural dimensional parameters, the port isolation of the circulator within the operating frequency band is significantly improved, outperforming existing circulator structures that do not employ the aforementioned dimensional optimizations and metal diaphragms. Simultaneously, the insertion loss ripple within the passband is significantly reduced, and in-band flatness is improved. Furthermore, the cross-sectional dimensions of the circulator body are significantly reduced compared to existing technologies, resulting in smaller electrical dimensions at the center frequency, which is beneficial for the miniaturization and integration of synthetic aperture radar systems.

[0012] Furthermore, four waveguide ports are distributed on the four sidewalls of the circulator body. The first port and the third port are positioned opposite each other, and the second port and the fourth port are positioned opposite each other. The first port and the second port are positioned adjacent to each other. The metal diaphragm is disposed inside the resonant cavity and attached to the inner sidewall of the resonant cavity. The projection of each metal diaphragm in the width direction of the circulator body at least partially overlaps with the projection of the corresponding waveguide port in the width direction of the circulator body.

[0013] The beneficial effects of adopting the above-mentioned further scheme are as follows: By distributing the four waveguide ports on the four sidewalls of the circulator body, and setting the first port opposite to the third port, the second port opposite to the fourth port, and the first port and the second port adjacent to each other, a port layout structure conducive to unidirectional signal transmission is formed, making the signal flow between the transmitting channel, antenna channel, receiving channel, and load channel clear and non-interfering. The metal diaphragm is attached to the inner sidewall of the resonant cavity, avoiding excessive interference to the electromagnetic field in the central region of the resonant cavity, and ensuring the normal operation of the gyromagnetic resonant cavity composed of ferrite sheet and dielectric pillar. The projection of each metal diaphragm in the width direction of the circulator body at least partially coincides with the projection of the corresponding waveguide port in the width direction of the circulator body. This positional correspondence allows the electromagnetic field at each waveguide port to be effectively modulated by the corresponding metal diaphragm, blocking the leakage path of electromagnetic waves between ports, and significantly suppressing electromagnetic wave leakage between ports. Compared to existing circulator structures that do not employ the aforementioned port layout and metal diaphragm, the port isolation of this invention is effectively improved, ensuring that the transmitted signal will not leak into the receiving channel and that the high-power signal reflected by the limiter will not enter the transmitter, thereby improving the operational stability of the synthetic aperture radar system.

[0014] Furthermore, there is a gap between each metal diaphragm and the outer wall of the dielectric column.

[0015] The beneficial effects of adopting the above-mentioned further solution are as follows: By setting gaps between the outer walls of each metal diaphragm and the dielectric pillar, the metal diaphragms and dielectric pillars are separated from each other and do not directly contact each other. This gap setting avoids physical compression and electromagnetic interference of the dielectric pillar structure by the metal diaphragms, ensuring that the electromagnetic characteristics of the dielectric pillar as a component of the gyromagnetic resonant cavity are not affected by the metal diaphragms. The existence of the gaps provides a smooth transition space for electromagnetic waves in the region between the dielectric pillar and the metal diaphragms. During transmission, the electromagnetic waves will not generate additional reflections and scattering due to direct contact between the metal diaphragms and the dielectric pillars, thereby reducing unnecessary energy loss. At the same time, the gaps provide an adjustable path for the propagation of electromagnetic waves, allowing the electromagnetic waves to maintain a relatively uniform field distribution when transitioning from the dielectric pillar region to the metal diaphragm region, which is beneficial to the flatness of the insertion loss in the passband. Compared with the existing circulator structures with no gaps or different positional relationships between the metal diaphragms and the dielectric pillars, the gap setting of the present invention makes the transmission of electromagnetic waves in the resonant cavity smoother, further ensures the isolation performance between ports, reduces the fluctuation of insertion loss in the passband, and is beneficial to the amplitude consistency of the received signal in the synthetic aperture radar system.

[0016] Furthermore, the metal diaphragm extends from the bottom inner wall of the resonant cavity to the top inner wall of the resonant cavity along the height direction of the resonant cavity, and the height of the metal diaphragm is less than half the height of the resonant cavity.

[0017] The beneficial effects of adopting the above-mentioned further scheme are as follows: by extending the metal diaphragm from the bottom inner wall of the resonant cavity to the top inner wall along the height direction of the resonant cavity, and setting the height of the metal diaphragm to be less than half the height of the resonant cavity, this height setting creates a gap between the metal diaphragm and the top of the resonant cavity, allowing electromagnetic waves to partially transmit from the gap at the upper end of the metal diaphragm to adjacent ports. The discontinuous coverage of the metal diaphragm along the height direction of the resonant cavity causes a discontinuity in the transmission path of electromagnetic waves between ports in the height direction. The superposition of electromagnetic waves on different transmission paths makes the signal transmission characteristics of each frequency point within the operating frequency band more consistent. Compared with the circulator structure without a metal diaphragm in the prior art, the metal diaphragm setting and height setting of the present invention further reduce the insertion loss in the passband and improve the flatness of the insertion loss in the passband, which is beneficial for the synthetic aperture radar system to obtain stable transmission performance under broadband operating conditions.

[0018] 2) In a second aspect, the present invention also provides a synthetic aperture radar, including any of the above-mentioned X-band synthetic aperture radar four-port waveguide circulators. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below: Figure 1 See: A side view of a four-port waveguide circulator for X-band synthetic aperture radar according to an embodiment of the present invention; Figure 2 See: A top view of a four-port waveguide circulator for X-band synthetic aperture radar according to an embodiment of the present invention; Figure 3 The insertion loss is calculated for three design approaches: resonant cavity based on dielectric cylindrical connection, resonant cavity based on dielectric hexahedral cylindrical connection, and resonant cavity based on dielectric hexahedral cylindrical connection with a loaded metal diaphragm. Comparison diagram.

[0020] Figure 4 The return loss is calculated for three design approaches: resonant cavity based on dielectric cylindrical connection, resonant cavity based on dielectric hexahedral cylindrical connection, and resonant cavity based on dielectric hexahedral cylindrical connection with a loaded metal diaphragm. Comparison diagram.

[0021] Figure 5 The isolation between the first and third ports is defined by three design approaches: resonant cavity based on a dielectric cylindrical connection, resonant cavity based on a dielectric hexahedral cylinder connection, and resonant cavity based on a dielectric hexahedral cylinder connection with a loaded metal diaphragm. Comparison diagram; Figure 6The isolation between the first and fourth ports is defined by three design approaches: resonant cavity based on a dielectric cylindrical connection, resonant cavity based on a dielectric hexahedral cylinder connection, and resonant cavity based on a dielectric hexahedral cylinder connection with a loaded metal diaphragm. Comparison diagram. Detailed Implementation

[0022] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0023] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0024] like Figure 1 and Figure 2 As shown, an X-band synthetic aperture radar four-port waveguide circulator according to an embodiment of the present invention includes a circulator body, on which a first port 1, a second port 2, a third port 3 and a fourth port 4 are provided. A resonant cavity is formed inside the circulator body, and a ferrite sheet 6 and a dielectric pillar 7 are provided inside the resonant cavity. The ferrite sheet 6 and the dielectric pillar 7 constitute a vortex resonant cavity, and a metal diaphragm 5 is also loaded inside the resonant cavity.

[0025] The circulator body is a cuboid structure, the resonant cavity is located in the central region of the circulator body, the ferrite sheet 6 is a circular structure, the ferrite sheet 6 is located in the center of the resonant cavity, the dielectric pillar 7 is a hexahedral pillar, the dielectric pillar 7 is located on the outer periphery of the ferrite sheet 6 and is coaxial with the ferrite sheet 6, and the metal diaphragm 5 is located inside the resonant cavity and between the outer wall of the dielectric pillar 7 and the inner wall of the resonant cavity.

[0026] The device comprises four metal diaphragms 5, which correspond to the positions of the first port 1, the second port 2, the third port 3, and the fourth port 4, respectively. The dielectric pillar 7 has a length of 3.4 mm from its center to its apex and a height of 6.61 mm. The ferrite sheet 6 has a radius of 5.55 mm and a height of 3.39 mm. The four waveguide ports each have a length of 7.7 mm and a height of 20.36 mm. The metal diaphragm 5 has a length of 2 mm, a width of 0.5 mm, and a height of 10 mm. The circulator body has a length of 32 mm, a width of 21.1 mm, and a height of 20.36 mm.

[0027] The four waveguide ports are distributed on the four side walls of the circulator body. The first port 1 and the third port 3 are arranged opposite each other, the second port 2 and the fourth port 4 are arranged opposite each other, and the first port 1 and the second port 2 are arranged adjacent to each other. The metal diaphragm 5 is disposed inside the resonant cavity and attached to the inner side wall of the resonant cavity. The projection of each metal diaphragm 5 in the width direction of the circulator body at least partially coincides with the projection of the corresponding waveguide port in the width direction of the circulator body.

[0028] There is a gap between each metal diaphragm 5 and the outer wall of the dielectric column 7.

[0029] The ferrite sheet 6 is embedded inside the dielectric column 7, and the height of the ferrite sheet 6 along the central axis of the dielectric column 7 is less than the height of the dielectric column 7.

[0030] The upper surface of the ferrite sheet 6 and the upper surface of the dielectric column 7 are located in the same horizontal plane, and the lower surface of the ferrite sheet 6 and the lower surface of the dielectric column 7 are located in the same horizontal plane.

[0031] The metal diaphragm 5 extends from the bottom inner wall of the resonant cavity to the top inner wall of the resonant cavity along the height direction of the resonant cavity, and the height of the metal diaphragm 5 is less than half the height of the resonant cavity.

[0032] Port 1 is used to connect the transmitter, port 2 is used to connect the antenna, port 3 is used to connect the receiver, and port 4 is used to connect the load.

[0033] The circulator body refers to the main supporting structure that constitutes the four-port waveguide circulator of the X-band synthetic aperture radar. The circulator body is a cuboid metal structure with an internal cavity. It houses the ferrite sheet 6, the dielectric hexahedral pillars, and the metal diaphragm 5, providing closed boundary conditions for electromagnetic wave transmission. The length, width, and height of the circulator body have specific dimensions, and its internal cavity is the resonant cavity.

[0034] A waveguide port is an opening structure located on the side wall of the circulator body, used for the input and output of electromagnetic waves between the circulator and external microwave devices. Four waveguide ports are distributed on the four side walls of the circulator body, connecting to the transmitter, antenna, receiver, and load, respectively. Each waveguide port has specific length and height dimensions, through which electromagnetic waves enter or leave the circulator.

[0035] The resonant cavity refers to the hollow region formed inside the circulator body, located at the center of the circulator body. The resonant cavity houses the ferrite sheet 6, the dielectric pillar, and the metal diaphragm 5, providing space for electromagnetic wave resonance and transmission. Electromagnetic waves propagate unidirectionally within the resonant cavity along a specific direction, achieving signal distribution and isolation between the ports.

[0036] The ferrite sheet 6 refers to a circular ferrite material component located at the center of the resonant cavity. Under the influence of an external constant magnetic field, the permeability of the ferrite sheet 6 exhibits tensor characteristics, allowing electromagnetic waves to propagate unidirectionally along a specific direction within the resonant cavity. The ferrite sheet 6 is embedded inside the dielectric pillar 7, together forming a gyromagnetic resonant cavity. The radius and height of the ferrite sheet 6 have specific dimensions, and its material parameters include saturation magnetization, relative permittivity, and ferromagnetic resonance linewidth.

[0037] The dielectric pillar 7 refers to a hexahedral cylindrical dielectric material component disposed inside the resonant cavity. The cross-section of the dielectric pillar 7 is hexagonal, meaning it is a hexahedral pillar. The dielectric pillar 7 is used to adjust the signal isolation strength between the ports, improving the isolation of the circulator. The six faces of the hexahedral pillar correspond to the four waveguide ports and the two inner walls of the resonant cavity, respectively. The dielectric pillar 7 is disposed on the outer periphery of the ferrite sheet 6 and coaxially arranged with it, supporting and accommodating the ferrite sheet 6, and together with the ferrite sheet 6, forming a gyromagnetic resonant cavity. The dielectric pillar 7 is made of a dielectric material with a specific relative permittivity, and its number of polyhedral faces, length from center to vertex, and height have specific dimensions.

[0038] The gyromagnetic resonant cavity refers to a resonant structure composed of a ferrite sheet 6 and a dielectric pillar 7. In this structure, the ferrite sheet 6 exhibits gyromagnetic properties under the action of an external constant magnetic field, enabling electromagnetic waves to propagate unidirectionally in a specific direction. The gyromagnetic resonant cavity utilizes the non-reciprocal properties of the ferrite sheet 6 to achieve directional propagation of electromagnetic waves within the circulator, thereby completing signal isolation and distribution between the transmitting channel, receiving channel, antenna channel, and load channel.

[0039] The metal diaphragm 5 refers to a thin metal sheet structure disposed inside the resonant cavity. The metal diaphragm 5 is attached to the inner wall of the resonant cavity and located between the outer wall of the dielectric pillar 7 and the inner wall of the resonant cavity. The metal diaphragm 5 is used to adjust the signal coupling strength between the ports, improving the insertion loss and in-band flatness of the circulator. The four metal diaphragms 5 correspond to the positions of the four waveguide ports, each covering a corresponding limiting groove and forming a gap with the outer wall of the dielectric pillar 7. The length, width, and height of the metal diaphragm 5 have specific dimensions.

[0040] Insertion loss refers to the power loss that occurs when an electromagnetic wave travels from port 1 to port 2 through the circulator. A lower insertion loss indicates higher transmission efficiency and less signal power loss within the circulator. Insertion loss is typically measured in decibels (dB).

[0041] Port isolation refers to the degree to which electromagnetic waves input from one port leak to other ports. Specifically, it characterizes the signal isolation capability between port 1 and port 3, and between port 1 and port 4. A higher port isolation value indicates less electromagnetic wave leakage between ports and lower interference between signals. Port isolation is usually measured in decibels (dB).

[0042] Return loss is the ratio of the electromagnetic wave power reflected back from the waveguide port to the incident electromagnetic wave power, used to characterize the impedance matching at the port. A higher return loss value indicates better impedance matching at the port, and less energy of the incident electromagnetic wave is reflected back. Return loss is usually measured in decibels (dB).

[0043] In-band flatness refers to the fluctuation of insertion loss at different frequencies within the operating frequency band, and is used to characterize the uniformity of the circulator's transmission characteristics within the operating bandwidth. Better in-band flatness indicates better consistency of signal transmission power at different frequencies and smaller fluctuations in signal amplitude across different frequencies. In-band flatness is usually measured in decibels (dB).

[0044] Relative bandwidth refers to the percentage of the operating bandwidth to the center frequency, used to measure the proportion of the circulator's operating frequency range to its center frequency. A larger relative bandwidth value indicates a wider operating frequency range for the circulator, and the wider the frequency range it can cover. Relative bandwidth is calculated by dividing the operating bandwidth by the center frequency and then multiplying by 100%.

[0045] The center frequency refers to the central operating frequency at which the circulator is designed, where its performance indicators reach their optimal levels. In this invention, the center frequency of the X-band synthetic aperture radar four-port waveguide circulator is 8.9 GHz.

[0046] The operating bandwidth refers to the operating frequency range within which the circulator meets the preset performance requirements. In this invention, the operating frequency range of the X-band synthetic aperture radar four-port waveguide circulator is 8.3 GHz to 9.5 GHz, and the operating bandwidth is 1.2 GHz.

[0047] The present invention will be illustrated by the following embodiments: This invention provides a four-port waveguide circulator for X-band synthetic aperture radar (SAR). The X-band SAR four-port waveguide circulator is a signal transmission and reception isolation and full-duplex transmission component in a SAR system. During operation, the transmitter of a SAR needs to radiate high-power electromagnetic waves into the external space via an antenna, while the receiver needs to receive weak echo signals from the antenna. If the transmitted signal leaks into the receiving channel, or if a strong reflected signal enters the transmitting channel, it will cause instability in the radar system and may even damage internal components. The X-band SAR four-port waveguide circulator utilizes the unidirectional transmission characteristics of electromagnetic waves to achieve signal isolation and distribution between the transmitting channel, receiving channel, antenna channel, and load channel.

[0048] like Figure 1 and Figure 2 As shown, the X-band synthetic aperture radar four-port waveguide circulator includes a circulator body. The circulator body has a cuboid structure. The circulator body has three dimensions: length, width, and height. The length of the circulator body is... The width of the circulator body is 32mm. The height of the circulator body is 21.1 mm. It measures 20.36 mm. A resonant cavity is formed inside the circulator body. The resonant cavity is located in the central region of the circulator body. The resonant cavity is the spatial region inside the circulator body used to accommodate the ferrite sheet 6, the dielectric hexahedral pillar, and the metal diaphragm 5. The shape of the resonant cavity is adapted to the cuboid structure of the circulator body.

[0049] The circulator body has a first port 1, a second port 2, a third port 3, and a fourth port 4. The four waveguide ports are distributed on the four side walls of the circulator body. The first port 1 and the third port 3 are positioned opposite each other. The second port 2 and the fourth port 4 are positioned opposite each other. The first port 1 and the second port 2 are adjacent to each other. All four waveguide ports are waveguide structures used for electromagnetic wave input and output. The first port 1 is used to connect to the transmitter. Electromagnetic waves generated by the transmitter enter the X-band synthetic aperture radar four-port waveguide circulator through the first port 1. The second port 2 is used to connect to the antenna. Electromagnetic waves are radiated into external space by the antenna through the second port 2, and the electromagnetic waves received by the antenna also enter the X-band synthetic aperture radar four-port waveguide circulator through the second port 2. The third port 3 is used to connect to the receiver. Electromagnetic waves received by the antenna enter the X-band synthetic aperture radar four-port waveguide circulator through the second port 2, are transmitted unidirectionally to the third port 3, and then enter the receiver. The fourth port 4 is used to connect to the load. When the limiter at the receiver front end reflects the high-power reflected signal back, the reflected signal is transmitted unidirectionally to port 4 and absorbed by the load. The lengths of the four waveguide ports... All are 7.7mm in diameter, and the height of the four waveguide ports is [not specified]. Both are 20.36 mm. The length of the waveguide port refers to the width of the opening of the waveguide port on the side wall of the circulator body. The height of the waveguide port refers to the opening size of the waveguide port in the height direction of the circulator body.

[0050] A ferrite sheet 6 and a dielectric pillar 7 are disposed within the resonant cavity. The ferrite sheet 6 and the dielectric pillar 7 constitute a vortex resonant cavity. A vortex resonant cavity is a structure in which, under the influence of a constant magnetic field applied to the ferrite material, the permeability of the ferrite sheet 6 exhibits tensor characteristics, allowing electromagnetic waves to propagate unidirectionally in a specific direction within the vortex resonant cavity. The ferrite sheet 6 has a circular disc-shaped structure. The ferrite sheet 6 is located at the center of the resonant cavity. The ferrite sheet 6 is embedded inside the dielectric pillar 7. The height of the ferrite sheet 6 along the central axis of the dielectric pillar 7 is less than the height of the dielectric pillar 7. The upper surface of the ferrite sheet 6 and the upper surface of the dielectric pillar 7 are located in the same horizontal plane. The lower surface of the ferrite sheet 6 and the lower surface of the dielectric pillar 7 are located in the same horizontal plane. The radius of the ferrite sheet 6... The height of ferrite sheet 6 is 5.55mm. It is 3.39 mm thick. Ferrite sheet 6 is made of a specific ferrite material. The saturation magnetization of ferrite sheet 6 is... The relative permittivity of ferrite sheet 6 is 1820 Gs. The ferromagnetic resonance linewidth of ferrite sheet 6 is 14.5. The value is 10 Oe. Saturation magnetization refers to the magnetization intensity of a ferrite material when it reaches saturation during magnetization. Relative permittivity is the ratio of the permittivity of a ferrite material to the vacuum permittivity. Ferromagnetic resonance linewidth refers to the width of the half-power point of the resonance curve showing the change in permeability with frequency at the ferromagnetic resonance frequency of a ferrite material.

[0051] The dielectric pillar 7 is a hexahedral pillar. A hexahedral pillar is a columnar structure with a hexagonal cross-section. The dielectric pillar 7 is disposed on the outer periphery of the ferrite sheet 6. The dielectric pillar 7 and the ferrite sheet 6 are coaxially arranged. Coaxial arrangement means that the central axis of the dielectric pillar 7 coincides with the central axis of the ferrite sheet 6. The dielectric pillar 7 is made of dielectric material. The relative permittivity of the dielectric pillar 7 is... It is 10. The length from the center to the apex of dielectric column 7. The height of dielectric column 7 is 3.4 mm. It is 6.61 mm. The length from the center to the vertex of the medium column 7 refers to the distance from the geometric center of the cross-section of the hexahedral column to any vertex of the cross-section of the hexahedral column.

[0052] Four metal diaphragms 5 are also loaded inside the resonant cavity. These four diaphragms 5 correspond to the positions of the first port 1, the second port 2, the third port 3, and the fourth port 4, respectively. "Corresponding positions" means that each metal diaphragm 5 is positioned within the resonant cavity near its corresponding waveguide port. The metal diaphragms 5 are located inside the resonant cavity, between the outer wall of the dielectric pillar 7 and the inner wall of the resonant cavity. The metal diaphragms 5 are positioned inside the resonant cavity and adhere to its inner wall. The projection of each metal diaphragm 5 onto the width of the circulator body at least partially overlaps with the projection of the corresponding waveguide port onto the width of the circulator body. "At least partially overlapping projections" means that when viewed from the width of the circulator body, the projection area of ​​the metal diaphragm 5 overlaps with the projection area of ​​the corresponding waveguide port. There is a gap between each metal diaphragm 5 and the outer wall of the dielectric pillar 7. This gap means that there is a distance between the metal diaphragm 5 and the outer wall of the dielectric pillar 7, and they are not in direct contact. The metal diaphragm 5 extends along the height direction of the resonant cavity from the bottom inner wall to the top inner wall. The height of the metal diaphragm 5 is equal to the height of the resonant cavity. The length of the metal diaphragm 5 is... The width of the metal diaphragm 5 is 2mm. The height of the metal diaphragm 5 is 0.5mm. The length of the metal diaphragm 5 is 10 mm. The length of the metal diaphragm 5 refers to its dimension along the length of the circulator body. The width of the metal diaphragm 5 refers to its dimension along the width of the circulator body. The height of the metal diaphragm 5 refers to its dimension along the height of the circulator body.

[0053] The center frequency of the X-band synthetic aperture radar four-port waveguide circulator in this embodiment of the invention is 8.9 GHz. At the center frequency of 8.9 GHz, the cross-sectional dimensions of the X-band synthetic aperture radar four-port waveguide circulator are... The longitudinal length is ,in This corresponds to the free space wavelength of the center frequency 8.9 GHz.

[0054] The working principle of the X-band synthetic aperture radar four-port waveguide circulator according to this invention is as follows: High-power electromagnetic waves generated by the transmitter enter the X-band synthetic aperture radar four-port waveguide circulator from the first port 1. After entering the resonant cavity, the electromagnetic waves are transmitted from the first port 1 to the second port 2 along a unidirectional transmission path under the action of the gyromagnetic resonant cavity formed by the ferrite sheet 6 and the dielectric pillar 7. The gyromagnetic resonant cavity utilizes the gyromagnetic properties of the ferrite sheet 6 to allow the forward-transmitting electromagnetic waves to pass smoothly, while the reverse-transmitting electromagnetic waves are significantly attenuated. The electromagnetic waves are radiated into the external space by the antenna through the second port 2. The echo electromagnetic waves received by the antenna enter the X-band synthetic aperture radar four-port waveguide circulator from the second port 2. Under the action of the gyromagnetic resonant cavity, the echo electromagnetic waves are transmitted from the second port 2 to the third port 3 along another unidirectional transmission path. The echo electromagnetic waves enter the receiver through the third port 3. When the received echo signal has high power, the limiter at the receiver front end reflects this high-power reflected signal back to the X-band synthetic aperture radar four-port waveguide circulator. Under the action of the gyromagnetic resonant cavity, the reflected signal is transmitted unidirectionally from port 3 to port 4. The reflected signal is absorbed by the load at port 4, thus preventing the high-power signal from entering the transmitter.

[0055] To illustrate the improved effects of the embodiments of the present invention, Figures 3 to 6 The insertion loss of three design methods were compared: a resonant cavity based on a dielectric cylindrical connection, a resonant cavity based on a dielectric hexahedral cylindrical connection, and a resonant cavity based on a dielectric hexahedral cylindrical connection loaded with a metal diaphragm. Return loss and port isolation and The performance of the dielectric cylinder and the dielectric hexahedral cylinder is as follows: In the three design methods, the dielectric cylinder and the dielectric hexahedral cylinder have the same dielectric constant, and the radius of the dielectric cylinder and the length from the center to the vertex of the dielectric hexahedral cylinder are also the same.

[0056] from Figure 3 As can be seen, the insertion loss of 0.3dB is the same for all three design methods. The bandwidth range is 8.3 GHz to 9.5 GHz, i.e., the operating bandwidth is 1.2 GHz. At the center frequency of 8.9 GHz, the relative bandwidth reaches 13.5%. The passband ripple of the design method based on the dielectric hexahedral cylinder-connected resonant cavity with loaded metal diaphragm 5 is 0.1 dB, while the passband ripple of the two design methods based on the dielectric cylindrical-connected resonant cavity and the dielectric hexahedral cylinder-connected resonant cavity is 0.3 dB.

[0057] from Figure 4 As can be seen, in the frequency range of 8.3GHz to 9.5GHz, the return loss of the design method based on the dielectric hexahedral pillar (dielectric pillar with a hexahedral structure) connected to the resonant cavity and loaded with a metal diaphragm 5 is... The return loss is better than 17dB. The return loss of the resonant cavity design based on the dielectric hexahedral pillar connection is better than 16dB. The return loss of the resonant cavity design based on the dielectric cylindrical (dielectric pillar with cylindrical structure) connection is better than 18dB.

[0058] from Figure 5 and Figure 6 As can be seen, in the frequency range of 8.3GHz to 9.5GHz, the isolation between the first port 1 and the third port 3 is the same for both the design method based on the dielectric hexahedral cylinder connected resonant cavity with metal diaphragm 5 and the design method based on the dielectric hexahedral cylinder connected resonant cavity. And the isolation between port 1 and port 4 All are better than 17dB. However, the isolation between the first port 1 and the third port 3 in the design based on the dielectric cylindrical resonant cavity is... And the isolation between port 1 and port 4 All are better than 14dB.

[0059] Compared to existing four-port waveguide circulators based on cylindrical resonant cavities, this invention employs a design based on hexahedral cylindrical resonant cavities. The dielectric pillars 7 of the hexahedral cylindrical structure improve the isolation between ports. Port isolation refers to the degree to which electromagnetic waves input from one port leak to other ports. Higher port isolation results in less electromagnetic wave leakage between ports. This invention improves the signal coupling strength between ports by loading a metal diaphragm 5 within the resonant cavity, resulting in lower insertion loss and better in-band flatness. Insertion loss refers to the power loss generated when electromagnetic waves pass through an X-band synthetic aperture radar four-port waveguide circulator. Lower insertion loss results in less signal power loss. In-band flatness refers to the fluctuation of insertion loss at different frequencies within the operating frequency band. Better in-band flatness indicates better consistency of signal amplitude at different frequencies. Return loss is the ratio of the electromagnetic wave power reflected back from the waveguide port to the incident electromagnetic wave power; higher return loss indicates better impedance matching at the port. Relative bandwidth refers to the percentage of operating bandwidth to center frequency, and is used to measure the width of the operating frequency band of a device.

[0060] Based on the above Figures 3 to 6 The comparison results show that the X-band synthetic aperture radar four-port waveguide circulator of this embodiment of the invention has a lower insertion loss in the operating frequency range of 8.3 GHz to 9.5 GHz. The isolation is 0.3dB, the passband ripple is 0.1dB, and the relative bandwidth reaches 13.5%. Within the aforementioned operating frequency band, the isolation between port 1 and port 3 is... The isolation between port 1 and port 4 is better than 17dB. Better than 17dB, return loss at port 1 Better than 17dB. Compared to a four-port waveguide circulator based on a dielectric cylindrical resonant cavity design, the port isolation of this embodiment is improved by 3dB, with lower insertion loss and better in-band flatness in the passband. All structural dimensional parameters of this embodiment, including , , , , , , , , , , All parameters are optimized according to the center frequency of 8.9GHz. Deviations in different parameter values ​​will lead to performance degradation such as increased insertion loss, poor isolation, or increased return loss.

[0061] Based on the performance comparison of the different design methods described above, it can be seen that the embodiment of the present invention improves the port isolation performance of the four-port waveguide circulator of X-band synthetic aperture radar by adopting a design method based on a dielectric hexahedral cylindrical resonant cavity. Within the operating frequency band of 8.3 GHz to 9.5 GHz, the isolation between the first port 1 and the third port 3, as well as the isolation between the first port 1 and the fourth port 4, are both better than 17 dB. Compared with the four-port waveguide circulator designed based on a dielectric cylindrical resonant cavity, its port isolation is only better than 14 dB, while the port isolation of the embodiment of the present invention is improved by 3 dB. The improved port isolation results in less energy of the transmitted signal leaking into the receiving channel, and the high-power signal reflected by the limiter can be completely absorbed by the load without being fed back to the transmitter, thereby effectively improving the operational stability and reliability of the synthetic aperture radar system.

[0062] This invention improves signal coupling strength between ports by loading a metal diaphragm 5 into the resonant cavity, resulting in an insertion loss of only 0.3 dB and a passband ripple of only 0.1 dB. Compared to a four-port waveguide circulator based on a dielectric cylindrical resonant cavity design, which has a passband ripple of 0.3 dB, this invention exhibits smaller amplitude fluctuations in the passband and better consistency in signal transmission power at different frequencies. The reduced insertion loss decreases power loss as the signal passes through the circulator, which is beneficial for improving the transmission efficiency and reception sensitivity of the radar system. The improved in-band flatness ensures that each frequency component has similar gain during broadband signal transmission, which is particularly important for broadband signal transmission required for high-resolution imaging in synthetic aperture radar. The operating bandwidth of this invention is 8.3 GHz to 9.5 GHz, i.e., an operating bandwidth of 1.2 GHz, achieving a relative bandwidth of 13.5% at the center frequency of 8.9 GHz.

[0063] Regarding miniaturization, the cross-sectional dimensions of this embodiment at the center frequency of 8.9 GHz are 0.63λ × 0.6λ, and the longitudinal length is 0.95λ. Compared to a four-port waveguide circulator based on a dielectric cylindrical resonant cavity design, which has a cross-sectional dimension of 0.81λ × 0.76λ, this embodiment significantly reduces the lateral cross-sectional area, exhibiting a clear miniaturization advantage. This helps reduce the space occupied by the circulator in synthetic aperture radar systems, making it particularly suitable for applications where spaceborne or airborne synthetic aperture radar has strict limitations on size and weight.

[0064] The embodiments of the present invention employ a four-port waveguide circulator design based on a dielectric hexahedral cylindrical resonant cavity with a loaded metal diaphragm 5. Compared with a four-port waveguide circulator based on a dielectric cylindrical resonant cavity design, it exhibits lower insertion loss, better in-band flatness, better port isolation, and smaller size in the X-band, thus effectively meeting the comprehensive performance requirements of X-band synthetic aperture radar systems for circulators.

[0065] Optionally, in the above technical solution, a temperature sensor is provided on at least one outer wall of the circulator body to detect the real-time temperature of the circulator body; a bias magnetic field generator is provided outside the circulator body to apply an adjustable bias magnetic field to the ferrite sheet 6; the real-time temperature detected by the temperature sensor is acquired; the bias magnetic field compensation amount is determined based on the temperature difference between the real-time temperature and the preset standard operating temperature; the bias magnetic field generator is controlled to adjust the magnetic field strength of the bias magnetic field applied to the ferrite sheet 6 based on the bias magnetic field compensation amount; wherein, when the real-time temperature is higher than the standard operating temperature, the magnetic field strength of the bias magnetic field is increased; when the real-time temperature is lower than the standard operating temperature, the magnetic field strength of the bias magnetic field is decreased. Specifically, determining the bias magnetic field compensation amount based on the temperature difference between the real-time temperature and the preset standard operating temperature includes calculating the bias magnetic field compensation amount according to the following formula: ,in, This is the amount of compensation for the bias magnetic field. This represents the temperature compensation coefficient for ferrite sheet 6. The temperature difference between the real-time temperature and the standard operating temperature; temperature compensation coefficient. The saturation magnetization temperature coefficient and ferromagnetic resonance linewidth of ferrite sheet 6 are determined. The specific implementation process is as follows: 1) A temperature sensor is installed on at least one outer wall of the circulator body. The temperature sensor is used to detect the real-time temperature of the circulator body. The temperature sensor can be a contact temperature sensor, such as a thermocouple temperature sensor or a thermistor temperature sensor. The temperature sensor is attached to the surface of the outer wall of the circulator body, maintaining close contact with the outer wall of the circulator body through thermally conductive adhesive or mechanical fixation to accurately sense temperature changes in the circulator body. The temperature sensor converts the detected temperature into an electrical signal output for subsequent processing. The number of temperature sensors can be one, installed on any one outer wall of the circulator body; or multiple temperature sensors can be installed on multiple outer walls of the circulator body, and the average of multiple detected temperatures can be taken as the real-time temperature to improve the accuracy of temperature detection.

[0066] 2) A bias magnetic field generator is installed outside the circulator body. This generator applies an adjustable bias magnetic field to the ferrite sheet 6. The bias magnetic field generator can be an electromagnet or a Helmholtz coil. It is positioned outside the circulator body and arranged around it, allowing the magnetic field generated to penetrate the sidewalls of the circulator body and enter the resonant cavity, acting on the ferrite sheet 6. The direction of the bias magnetic field generated is consistent with the desired magnetization direction of the ferrite sheet 6. The bias magnetic field generator has an adjustable input current or voltage control port; by changing the input current or voltage, the magnetic field strength of the bias magnetic field generated can be adjusted.

[0067] 3) Acquire the real-time temperature detected by the temperature sensor. Real-time temperature refers to the temperature value of the circulator body detected by the temperature sensor at the current moment. The temperature signal output by the temperature sensor is transmitted to the control unit via a signal acquisition line or wireless transmission method, where the control unit reads and records the real-time temperature. The control unit can be implemented using a microcontroller or a digital signal processor.

[0068] 4) Determine the bias magnetic field compensation amount based on the temperature difference between the real-time temperature and the preset standard operating temperature. The standard operating temperature refers to the normal operating ambient temperature set during the design of the X-band synthetic aperture radar four-port waveguide circulator. The temperature difference is the real-time temperature minus the standard operating temperature. When the real-time temperature is higher than the standard operating temperature, the temperature difference is positive; when the real-time temperature is lower than the standard operating temperature, the temperature difference is negative. Calculate the bias magnetic field compensation amount using the following formula: ,in, This is the amount of compensation for the bias magnetic field, expressed in Oersted. is the temperature compensation coefficient for ferrite sheet 6, in Oersted per degree Celsius; This represents the temperature difference between the real-time temperature and the standard operating temperature, expressed in degrees Celsius. Temperature compensation coefficient. The temperature coefficient of saturation magnetization and the ferromagnetic resonance linewidth of ferrite sheet 6 are used to determine the temperature compensation coefficient. The saturation magnetization of ferrite sheet 6 decreases with increasing temperature, a relationship described by the temperature coefficient of saturation magnetization. The temperature coefficient of saturation magnetization refers to the rate at which the saturation magnetization of ferrite sheet 6 changes with temperature, i.e., the change in saturation magnetization per degree Celsius change in temperature. After the material parameters of ferrite sheet 6 are determined, the specific value of the temperature coefficient of saturation magnetization is obtained through experimental measurement or theoretical calculation. The ferromagnetic resonance linewidth of ferrite sheet 6 reflects its resonant absorption characteristics of electromagnetic waves; the narrower the ferromagnetic resonance linewidth, the higher the sensitivity of ferrite sheet 6 to changes in the bias magnetic field. Based on the temperature coefficient of saturation magnetization and the ferromagnetic resonance linewidth, the temperature compensation coefficient can be determined using the ferromagnetic resonance condition equation. Specifically, the relationship between the ferromagnetic resonance frequency and the bias magnetic field and saturation magnetization is determined by the Kittel equation. When temperature changes cause changes in saturation magnetization, the bias magnetic field needs to be compensated accordingly to maintain a constant ferromagnetic resonance frequency. The magnitude of this compensation is called the bias magnetic field compensation amount. The temperature compensation coefficient in the formula for calculating the bias magnetic field compensation amount... According to Kittel's equation, the saturation magnetization temperature coefficient of ferrite sheet 6 and the ferromagnetic resonance linewidth of ferrite sheet 6 are jointly determined.

[0069] 5) Based on the bias magnetic field compensation amount, control the bias magnetic field generator to adjust the magnetic field strength of the bias magnetic field applied to the ferrite sheet 6. Add the bias magnetic field compensation amount to the current bias magnetic field strength to obtain the target bias magnetic field strength. Based on the target bias magnetic field strength, the control unit calculates the required input current or voltage value for the bias magnetic field generator and outputs a corresponding control signal to the bias magnetic field generator, adjusting the magnetic field strength of the bias magnetic field generated by the bias magnetic field generator to the target bias magnetic field strength.

[0070] 6) When adjusting the magnetic field strength of the bias magnetic field applied to the ferrite sheet 6, increase the magnetic field strength when the real-time temperature is higher than the standard operating temperature; decrease the magnetic field strength when the real-time temperature is lower than the standard operating temperature. After determining the bias magnetic field compensation amount, when the real-time temperature is higher than the standard operating temperature, it indicates that the saturation magnetization of the ferrite sheet 6 decreases due to the temperature increase. To maintain a constant ferromagnetic resonance frequency, the magnetic field strength of the bias magnetic field needs to be increased for compensation. The increased magnetic field strength is equal to the current bias magnetic field strength plus the bias magnetic field compensation amount. When the real-time temperature is lower than the standard operating temperature, it indicates that the saturation magnetization of the ferrite sheet 6 increases due to the temperature decrease. To maintain a constant ferromagnetic resonance frequency, the magnetic field strength of the bias magnetic field needs to be decreased for compensation. The decreased magnetic field strength is equal to the current bias magnetic field strength minus the bias magnetic field compensation amount.

[0071] Optionally, in the above technical solution, positioning protrusions are processed on each outer sidewall of the dielectric pillar 7. These protrusions extend outward from the surface of the outer sidewall of the dielectric pillar 7, and extend along the height direction of the dielectric pillar 7 from its bottom to its top. The height of the positioning protrusions is equal to the height of the dielectric pillar 7. Limiting grooves are processed on each inner sidewall of the resonant cavity. These grooves recess inward from the surface of the inner sidewall of the resonant cavity, and extend along the height direction of the resonant cavity from its bottom inner wall to its top inner wall. The height of the limiting grooves is equal to the height of the resonant cavity. The dielectric pillar 7 is then installed inside the resonant cavity, so that the positioning protrusions on each outer sidewall of the dielectric pillar 7 are respectively embedded in the resonant cavity. In the corresponding limiting grooves on the inner sidewalls of the cavity, the positioning protrusions and the limiting grooves are in a clearance fit. Four metal diaphragms 5 are respectively installed inside the resonant cavity, so that each metal diaphragm 5 is attached to the inner sidewall of the resonant cavity and covers the corresponding limiting groove. A positioning gap is formed between each metal diaphragm 5 and the outer sidewall of the corresponding dielectric pillar 7. The height of the positioning protrusion is less than or equal to the height of the metal diaphragm 5. When machining the positioning protrusions on the outer sidewalls of the dielectric pillar 7, the protrusion height of the positioning protrusion is determined according to the required gap distance between the metal diaphragm 5 and the outer sidewall of the dielectric pillar 7. The protrusion height of the positioning protrusion is equal to the sum of the recess depth of the limiting groove and the gap distance. The specific implementation process is as follows: 1) The positioning protrusions outward from the outer wall surface of the dielectric column 7. The positioning protrusion extends from the bottom to the top of the dielectric column 7 along its height, and its height is equal to the height of the dielectric column 7. The positioning protrusion can be formed on the outer wall of the dielectric column 7 by machining, for example, by milling or grinding, removing some material from each outer wall surface of the dielectric column 7 and retaining the resulting protruding structure. The dielectric column 7 is a hexahedral column with six outer walls, and a positioning protrusion is machined on each outer wall. The cross-sectional shape of the positioning protrusion can be rectangular, trapezoidal, or semi-circular. The protrusion height of the positioning protrusion is determined according to the required gap distance between the metal diaphragm 5 and the outer wall of the dielectric column 7.

[0072] 2) The limiting groove is recessed inward from the inner wall surface of the resonant cavity. The limiting groove extends along the height direction of the resonant cavity from the bottom inner wall to the top inner wall, and its height is equal to the height of the resonant cavity. The limiting groove can be formed on the inner wall of the resonant cavity by machining, such as milling or EDM, removing some material from the surface of each inner wall to form the recessed structure. The resonant cavity is a hollow structure inside the circulator body, with four inner walls, each corresponding to a waveguide port. A limiting groove is machined on each inner wall. The cross-sectional shape of the limiting groove matches the cross-sectional shape of the positioning protrusion to ensure that the positioning protrusion can be embedded in the limiting groove. The depth of the limiting groove is less than the thickness of the inner wall of the resonant cavity.

[0073] 3) Install the dielectric pillar 7 inside the resonant cavity, so that the positioning protrusions on each outer wall of the dielectric pillar 7 are respectively embedded into the corresponding limiting grooves on each inner wall of the resonant cavity. The positioning protrusions and limiting grooves are in a clearance fit. A clearance fit means that there is a certain gap between the outer surface of the positioning protrusion and the inner surface of the limiting groove, allowing the positioning protrusion to slide freely within the limiting groove without jamming. The clearance fit between the positioning protrusions and the limiting grooves ensures that the installation position of the dielectric pillar 7 within the resonant cavity is limited by the limiting grooves, while preventing direct contact between the dielectric pillar 7 and the inner wall of the resonant cavity. During installation, insert the dielectric pillar 7 from the open end of the resonant cavity, align each positioning protrusion with its corresponding limiting groove, and then push the dielectric pillar 7 into the resonant cavity along its height direction until the bottom of the dielectric pillar 7 reaches the bottom inner wall of the resonant cavity.

[0074] 4) Install four metal diaphragms 5 inside the resonant cavity, ensuring each diaphragm 5 adheres to the inner wall of the cavity and covers the corresponding positioning groove. A positioning gap is formed between each metal diaphragm 5 and the outer wall of its corresponding dielectric pillar 7. After installation, the metal diaphragms 5 completely cover the openings of the positioning grooves, sealing the positioning protrusions within them. Once covered, the positioning protrusions cannot detach from the positioning grooves, thus fixing the dielectric pillar 7 in the central region of the resonant cavity. The distance of the positioning gap between each metal diaphragm 5 and the outer wall of its corresponding dielectric pillar 7 is equal to the protrusion height of the positioning protrusion minus the depth of the positioning groove.

[0075] When machining positioning protrusions on the outer walls of the dielectric column 7, the protrusion height of the positioning protrusions is determined based on the required gap distance between the metal diaphragm 5 and the outer walls of the dielectric column 7. The protrusion height of the positioning protrusion is equal to the sum of the recess depth of the limiting groove and the gap distance. This can be expressed by the formula: ,in, The protrusion height of the protrusion is used to locate the protrusion, and the unit is millimeters; The required gap distance between the metal diaphragm 5 and the outer wall of the dielectric column 7, in millimeters; The depth of the limiting groove, in millimeters. This is used to determine the gap distance. The specific values ​​need to be set according to the operating frequency and performance requirements of the four-port waveguide circulator for X-band synthetic aperture radar. When the gap distance is too large, the modulating effect of the metal diaphragm 5 on the electromagnetic field weakens, and the port isolation may decrease; when the gap distance is too small, the coupling between the metal diaphragm 5 and the dielectric pillar 7 is too strong, which may lead to an increase in insertion loss. Using the above formula, the protrusion height of the positioning protrusion can be calculated based on the required gap distance and the recess depth of the limiting groove, and then the protrusion height can be controlled to be equal to the calculated value during the processing of the positioning protrusion. The height of the positioning protrusion is less than or equal to the height of the metal diaphragm 5 to ensure that the metal diaphragm 5 can completely cover the positioning protrusion and seal it inside the limiting groove. When the height of the positioning protrusion is equal to the height of the metal diaphragm 5, the upper end face of the positioning protrusion is flush with the upper end face of the metal diaphragm 5; when the height of the positioning protrusion is less than the height of the metal diaphragm 5, the upper end face of the positioning protrusion is lower than the upper end face of the metal diaphragm 5, and the metal diaphragm 5 completely covers the positioning protrusion.

[0076] Optionally, in the above technical solution, a first adjusting magnetic field generating device and a second adjusting magnetic field generating device are provided on the outside of the circulator body. The first adjusting magnetic field generating device is located on the outside of the first outer wall of the circulator body, and the second adjusting magnetic field generating device is located on the outside of the second outer wall of the circulator body. The first outer wall and the second outer wall are two opposite outer walls. The current insertion loss value and the current port isolation value of the X-band synthetic aperture radar four-port waveguide circulator are obtained. The current insertion loss value is compared with a preset target insertion loss value to obtain an insertion loss deviation value. The current port isolation value is compared with a preset target port isolation value to obtain a port isolation deviation value. When the insertion loss deviation value is greater than the insertion loss threshold, the first adjusting magnetic field generating device and the second adjusting magnetic field generating device are controlled to simultaneously apply the first adjusting magnetic field. The direction of the first adjusting magnetic field is perpendicular to the first outer wall and the second outer wall. The first adjusting magnetic field is used to move the four metal diaphragms 5 synchronously along the width direction of the resonant cavity. When the port isolation deviation value is greater than the port isolation threshold, the first adjusting magnetic field generator and the second adjusting magnetic field generator are controlled to simultaneously apply the second adjusting magnetic field. The direction of the second adjusting magnetic field is parallel to the first and second outer walls. The second adjusting magnetic field is used to move the four metal diaphragms 5 synchronously along the length direction of the resonant cavity. The magnetic field strength of the first adjusting magnetic field is proportional to the insertion loss deviation value, and the magnetic field strength of the second adjusting magnetic field is proportional to the port isolation deviation value. After the first adjusting magnetic field generator and the second adjusting magnetic field generator apply the first adjusting magnetic field or the second adjusting magnetic field, the current insertion loss value and the current port isolation value are reacquired until the insertion loss deviation value is less than or equal to the insertion loss threshold and the port isolation deviation value is less than or equal to the port isolation threshold. The specific implementation process is as follows: 1) A first and a second adjusting magnetic field generating device are installed on the outside of the circulator body. The first adjusting magnetic field generating device is located on the outside of the first outer wall of the circulator body, and the second adjusting magnetic field generating device is located on the outside of the second outer wall of the circulator body. The first and second outer walls are two opposite outer walls. Both the first and second adjusting magnetic field generating devices adopt an electromagnet structure or a Helmholtz coil structure to generate an adjustable magnetic field inside the circulator body. The first and second outer walls are two opposite faces of the six faces of the circulator body. The first adjusting magnetic field generating device is installed on the outside of the first outer wall, and the second adjusting magnetic field generating device is installed on the outside of the second outer wall, so that the two adjusting magnetic field generating devices are directly opposite each other. The first and second adjusting magnetic field generating devices each have independent current control ports. By controlling the magnitude and direction of the input current, the magnetic field strength and direction of their respective generated magnetic fields can be independently adjusted.

[0077] 2) Obtain the current insertion loss and current port isolation values ​​of the X-band synthetic aperture radar (SAR) four-port waveguide circulator. The current insertion loss value refers to the signal transmission power loss from port 1 to port 2 in the current state of the X-band SAR four-port waveguide circulator. The current port isolation value refers to the signal isolation between port 1 and port 3, and between port 1 and port 4, in the current state of the X-band SAR four-port waveguide circulator. Connect to each waveguide port of the X-band SAR four-port waveguide circulator using a vector network analyzer to measure and obtain the current insertion loss and current port isolation values.

[0078] 3) Compare the current insertion loss value with the preset target insertion loss value to obtain the insertion loss deviation value. The target insertion loss value refers to the insertion loss performance index that the four-port waveguide circulator of the X-band synthetic aperture radar is expected to achieve during design. It is expressed by the formula: ,in, This is the insertion loss deviation value, in decibels; This is the current insertion loss value, in decibels. Insert the target loss value in decibels.

[0079] 4) Compare the current port isolation value with the preset target port isolation value to obtain the port isolation deviation value. The target port isolation value refers to the port isolation performance index that the four-port waveguide circulator of the X-band synthetic aperture radar is expected to achieve during design. It is expressed by the formula: ,in, This is the port isolation deviation value, in decibels; The target port isolation value, in decibels; This represents the current port isolation value, expressed in decibels (dB). When the current port isolation value is less than the target port isolation value, the port isolation deviation is positive, indicating insufficient port isolation and requiring compensation adjustment.

[0080] 5) When the insertion loss deviation exceeds the insertion loss threshold, the first and second adjusting magnetic field generators simultaneously apply the first adjusting magnetic field. The direction of the first adjusting magnetic field is perpendicular to the first and second outer walls. This first adjusting magnetic field causes the four metal diaphragms 5 to move synchronously along the width of the resonant cavity. The insertion loss threshold is a pre-set maximum allowable insertion loss deviation. When the insertion loss deviation exceeds the threshold, it indicates that the current insertion loss deviates too much from the target value, requiring adjustment of the position of the metal diaphragms 5. The first adjusting magnetic field is applied simultaneously by the first and second adjusting magnetic field generators. The magnetic fields generated by both devices are in the same direction, perpendicular to the first and second outer walls. The metal diaphragms 5 are made of magnetic metal. Under the action of the first adjusting magnetic field, the four metal diaphragms 5 are subjected to magnetic force along the width of the resonant cavity, causing them to move synchronously. The movement of the metal diaphragms 5 changes the distance between the metal diaphragms 5 and the outer wall of the dielectric pillar 7, thereby changing the electromagnetic field distribution within the resonant cavity and adjusting the insertion loss.

[0081] 6) When the port isolation deviation exceeds the port isolation threshold, the first and second adjusting magnetic field generators simultaneously apply a second adjusting magnetic field. The direction of the second adjusting magnetic field is parallel to the first and second outer walls. This second adjusting magnetic field is used to move the four metal diaphragms 5 synchronously along the length of the resonant cavity. The port isolation threshold is a pre-set maximum allowable port isolation deviation. When the port isolation deviation exceeds the threshold, it indicates that the current port isolation deviates too much from the target value, and the position of the metal diaphragms 5 needs to be adjusted. The second adjusting magnetic field is applied simultaneously by the first and second adjusting magnetic field generators. The magnetic fields generated by the two devices are in the same direction, parallel to the first and second outer walls. Under the action of the second adjusting magnetic field, the four metal diaphragms 5 are subjected to a magnetic force along the length of the resonant cavity, causing them to move synchronously along the length of the resonant cavity. The movement of the metal diaphragms 5 changes the relative positional relationship between the metal diaphragms 5 and the waveguide ports, thereby adjusting the signal coupling strength between the ports and improving the port isolation.

[0082] The strength of the first adjusting magnetic field is proportional to the insertion loss deviation, and the strength of the second adjusting magnetic field is proportional to the port isolation deviation. This can be expressed by the following formula: ,in, The magnetic field strength of the first regulating magnetic field, measured in Oersted; This is the first proportionality coefficient, measured in Ørsted per decibel. This represents the insertion loss deviation, in decibels. First proportionality coefficient. Based on the magnetization characteristics of the metal diaphragm 5 and the pre-calibrated effect of the metal diaphragm 5 moving a unit distance along the width direction of the resonant cavity on the insertion loss: ,in, The magnetic field strength of the second regulating magnetic field is measured in Oersted. This is the second proportionality coefficient, measured in Ørsted per decibel. This represents the port isolation deviation value, in decibels. Second proportionality coefficient. The results were pre-calibrated based on the magnetization characteristics of the metal diaphragm 5 and the degree of influence of the metal diaphragm 5 moving a unit distance along the length of the resonant cavity on the port isolation.

[0083] 7) After the first and second regulating magnetic field generators apply the first or second regulating magnetic field, the current insertion loss value and the current port isolation value are reacquired until the insertion loss deviation value is less than or equal to the insertion loss threshold and the port isolation deviation value is less than or equal to the port isolation threshold. The current insertion loss value and the current port isolation value are reacquired, and the insertion loss deviation value and the port isolation deviation value are recalculated. The recalculated insertion loss deviation value is compared with the insertion loss threshold, and the recalculated port isolation deviation value is compared with the port isolation threshold. If the insertion loss deviation value is still greater than the insertion loss threshold, the first regulating magnetic field is applied for further adjustment. If the port isolation deviation value is still greater than the port isolation threshold, the second regulating magnetic field is applied for further adjustment. The above comparison and adjustment process is repeated until the insertion loss deviation value is less than or equal to the insertion loss threshold and the port isolation deviation value is less than or equal to the port isolation threshold. At this point, the insertion loss performance and port isolation performance of the X-band synthetic aperture radar four-port waveguide circulator both meet the design requirements.

[0084] An embodiment of the present invention provides a synthetic aperture radar (SAR) including any of the aforementioned X-band SAR four-port waveguide circulators, enabling the SAR system to achieve effective isolation between the transmit and receive channels using this circulator. High-power electromagnetic waves generated by the transmitter are transmitted to the antenna and radiated into external space via the first port 1 and the second port 2 of the circulator. The echo signal received by the antenna is transmitted to the receiver via the second port 2 and the third port 3 of the circulator. The transmitted and received signals propagate along their respective unidirectional transmission paths within the circulator without interfering with each other. When a limiter at the receiver front end reflects a high-power reflected signal back, the reflected signal is transmitted to the load and absorbed via the third port 3 and the fourth port 4 of the circulator. The high-power reflected signal does not enter the transmitter, preventing damage to the transmitter due to high-power signal impact. Because the port isolation of the circulator is improved, the energy leaked from the transmitted signal to the receive channel is effectively suppressed, allowing the receiver to obtain a cleaner echo signal, which is beneficial for improving the receiving sensitivity and imaging resolution of the radar system. Meanwhile, the reduced insertion loss and improved in-band flatness of the circulator reduce power loss of transmitted and received signals as they pass through the circulator, and improve the transmission consistency of each frequency component, which is beneficial for synthetic aperture radar to achieve high-precision target detection and imaging. In addition, the miniaturization of the circulator helps to reduce the overall size and weight of the synthetic aperture radar system, facilitating integration and installation on spaceborne or airborne platforms.

[0085] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this invention is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-disclosed concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this invention.

[0086] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and represent a limitation on a specific order or sequence. Where appropriate, the order of use for similar objects can be interchanged so that the embodiments of this application described herein can be implemented in an order other than that shown or described.

[0087] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A four-port waveguide circulator for X-band synthetic aperture radar, characterized in that, The device includes a circulator body, which has a first port, a second port, a third port and a fourth port. A resonant cavity is formed inside the circulator body. A ferrite sheet and a dielectric pillar are disposed inside the resonant cavity. The ferrite sheet and the dielectric pillar constitute a gyromagnetic resonant cavity. A metal diaphragm is also loaded inside the resonant cavity.

2. The X-band synthetic aperture radar four-port waveguide circulator according to claim 1, characterized in that, The circulator body is a cuboid structure, the resonant cavity is located in the central region of the circulator body, the ferrite sheet is a circular structure, the ferrite sheet is disposed at the center of the resonant cavity, the dielectric pillar is a hexahedral pillar, the dielectric pillar is disposed on the outer periphery of the ferrite sheet and is coaxial with the ferrite sheet, and the metal diaphragm is disposed inside the resonant cavity and is located between the outer wall of the dielectric pillar and the inner wall of the resonant cavity.

3. A four-port waveguide circulator for X-band synthetic aperture radar according to claim 1 or 2, characterized in that, The number of metal diaphragms is four, and the four metal diaphragms correspond to the positions of the first port, the second port, the third port, and the fourth port, respectively. The length from the center to the apex of the dielectric pillar is 3.4 mm, and the height of the dielectric pillar is 6.61 mm. The radius of the ferrite sheet is 5.55 mm, and the height of the ferrite sheet is 3.39 mm. The length of each of the four waveguide ports is 7.7 mm, and the height of each of the four waveguide ports is 20.36 mm. The length of each metal diaphragm is 2 mm, the width of each metal diaphragm is 0.5 mm, and the height of each metal diaphragm is 10 mm. The length of the circulator body is 32 mm, the width of the circulator body is 21.1 mm, and the height of the circulator body is 20.36 mm.

4. The X-band synthetic aperture radar four-port waveguide circulator according to claim 3, characterized in that, The four waveguide ports are distributed on the four sidewalls of the circulator body. The first port is opposite to the third port, and the second port is opposite to the fourth port. The first port and the second port are adjacent to each other. The metal diaphragm is disposed inside the resonant cavity and attached to the inner sidewall of the resonant cavity. The projection of each metal diaphragm in the width direction of the circulator body at least partially overlaps with the projection of the corresponding waveguide port in the width direction of the circulator body.

5. A four-port waveguide circulator for X-band synthetic aperture radar according to claim 2, characterized in that, There is a gap between each of the metal diaphragms and the outer wall of the dielectric column.

6. The X-band synthetic aperture radar four-port waveguide circulator according to claim 2, characterized in that, The ferrite sheet is embedded inside the dielectric column, and the height of the ferrite sheet along the central axis of the dielectric column is less than the height of the dielectric column.

7. A four-port waveguide circulator for X-band synthetic aperture radar according to claim 6, characterized in that, The upper surface of the ferrite sheet and the upper surface of the dielectric column are located in the same horizontal plane, and the lower surface of the ferrite sheet and the lower surface of the dielectric column are located in the same horizontal plane.

8. The X-band synthetic aperture radar four-port waveguide circulator according to claim 4, characterized in that, The metal diaphragm extends from the bottom inner wall of the resonant cavity to the top of the resonant cavity along the height direction of the resonant cavity, and the height of the metal diaphragm is less than half the height of the resonant cavity.

9. A four-port waveguide circulator for X-band synthetic aperture radar according to claim 1, characterized in that, The first port is used to connect to the transmitter, the second port is used to connect to the antenna, the third port is used to connect to the receiver, and the fourth port is used to connect to the load.

10. A synthetic aperture radar, characterized in that, Includes an X-band synthetic aperture radar four-port waveguide circulator as described in any one of claims 1 to 9.

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