S / x / k / ka multi-band feed for vlbi

Abstract

The application discloses an S / X / K / Ka multi-band feed for VLBI, and relates to the technical field of satellite communication, comprising an S / X / K / Ka coaxial horn, an S-band circularly polarized feed network, an X-band integrated composite circularly polarized network, a K / Ka-band circular polarizer, a quadrature device and a diplexer. The S / X / K / Ka coaxial horn adopts a K / Ka-band dielectric horn which is coaxially nested in three layers from inside to outside, an X-band coaxial horn and an S-band corrugated horn, so that spatial separation receiving of four-band signals is realized. The S-band circularly polarized feed is composed of a magic T and an electric bridge; the X-band adopts integrated design to realize circularly polarized composition and miniaturization; the K / Ka-band completes polarization formation and band separation through the circular polarizer, the quadrature device and the diplexer. The application has compact structure, does not need mechanical feed switching, can realize simultaneous observation of S / X / K / Ka four bands, and is suitable for a new generation of VLBI system and a multi-band TT&C station.

Description

Technical Field

[0001] This invention belongs to the field of satellite communication technology, specifically relating to an S / X / K / Ka multi-band feed source for VLBI (Very Long Baseline Interferometry). Background Technology

[0002] Reflective parabolic antennas are widely used in radio astronomy, geodesy, satellite communications, and deep space exploration due to their high gain, high directivity, strong focusing ability, and simple and stable structure. With the rapid development of radio astronomy observation and satellite communications in recent years, especially the advancement of VLBI technology, there is a growing demand for high-frequency, broadband, and multi-band antenna technology. Since the frequency characteristics of reflective antennas depend on their feed source and feed network technology, the development of multi-band broadband feed sources is particularly important.

[0003] Traditional geodetic deep space exploration uses the S and X bands; the mainstream operating frequency band for geodetic VLBI stations based on the VLBI 2010 standard remains 3-14 GHz; astrometry and geodetic surveys in the East Asian VLBI network are conducted in the K band; satellite telemetry signals are often located in the S band; and next-generation deep space exploration and data transmission will operate in the Ka band. Currently available multi-band feed schemes mainly include S / X / Ka tri-band feeds and X / Ka dual-band feeds. S / X / Ka tri-band feeds typically employ a five-horn combination structure, with a central X / Ka dual-band corrugated horn surrounded by four S-band horns. X / Ka dual-band feeds often use a nested coaxial waveguide and circular waveguide configuration, combined with a composite structure of dielectric rod horns and corrugated horns to achieve dual-band operation.

[0004] However, existing dual-band or tri-band feeds are typically structurally complex and bulky, and can only cover a portion of the frequency bands, failing to simultaneously meet the observation requirements of all four bands (S, X, K, and Ka). In actual observations, researchers need to replace the feed equipment according to the target frequency band, a cumbersome and time-consuming process that not only reduces observation efficiency but also limits the realization of multi-band synchronous continuous observation. Furthermore, complex feed systems place high demands on the internal space of the antenna, contain numerous connecting components, impacting reliability and increasing maintenance costs. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides an S / X / K / Ka multi-band feed source for VLBI. The technical problem to be solved by this invention is achieved through the following technical solution:

[0006] This invention provides an S / X / K / Ka multi-band feed for VLBI, comprising: an S / X / K / Ka coaxial horn, an S-band circularly polarized feed network, an X-band demultiplexer and integrated synthesized circularly polarized network, a K / Ka band circularly polarizer, a K / Ka band quadrature, and a K / Ka band duplexer.

[0007] The S / X / K / Ka coaxial horn is used to radiate and receive electromagnetic wave signals in four frequency bands: S, X, K, and Ka.

[0008] The S-band circular polarization feed network is connected to the S-band output terminal of the S / X / K / Ka coaxial speaker, and is used to synthesize the received S-band electromagnetic wave signal into an S-band left-hand circular polarization signal and an S-band right-hand circular polarization signal.

[0009] The X-band demultiplexing and integrated synthesized circular polarization network is connected to the X-band output terminal of the S / X / K / Ka coaxial speaker, and is used to synthesize the received X-band electromagnetic wave signal into an X-band left-hand circular polarization signal and an X-band right-hand circular polarization signal.

[0010] The input terminal of the K / Ka band circular polarizer is connected to the K / Ka band output terminal of the S / X / K / Ka coaxial speaker to form a circular polarization signal from the received K-band electromagnetic wave signal and Ka-band electromagnetic wave signal.

[0011] The input of the K / Ka band quadrature is connected to the output of the K / Ka band circular polarizer, and is used to separate the circular polarization signal into two orthogonal polarization components.

[0012] The input of the K / Ka band duplexer is connected to the output of the K / Ka band quadrature, which is used to separate the two orthogonal polarization components to obtain the K-band left-hand circular polarization signal, the K-band right-hand circular polarization signal, the Ka-band left-hand circular polarization signal, and the Ka-band right-hand circular polarization signal.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] 1. The S / X / K / Ka multi-band feed for VLBI of the present invention integrates four key operating frequency bands (S, X, K, and Ka) within a single feed physical structure, fundamentally eliminating the need for mechanical feed switching between different observation missions. This enables telescopes equipped with this feed to simultaneously receive and process signals from four frequency bands, greatly improving observation efficiency and data acquisition synchronization. It is particularly suitable for complex VLBI missions requiring multi-band joint observation, satellite multi-band telemetry and control, and deep space exploration missions.

[0015] 2. The S / X / K / Ka multi-band feed for VLBI of this invention features a specially designed integrated synthetic circular polarization network for the X-band, which highly integrates wave division and polarization synthesis functions, significantly shortening the longitudinal length of the feed network. The K / Ka bands share the front-end dielectric horn and some processing channels, further reducing the number of components. The overall feed structure is compact, with a volume significantly smaller than traditional multi-feed system combinations.

[0016] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of an S / X / K / Ka multi-band feed for VLBI provided in an embodiment of the present invention;

[0018] Figure 2 This is a cross-sectional structural diagram of an S / X / K / Ka coaxial horn provided in an embodiment of the present invention;

[0019] Figure 3 This is a schematic diagram of an S-band corrugated horn provided in an embodiment of the present invention;

[0020] Figure 4 This is a block diagram illustrating the principle of an S-band circularly polarized feed network provided in an embodiment of the present invention.

[0021] Figure 5 This is a standing wave diagram of the S / X / K / Ka multi-band feed in each frequency band provided in the embodiments of the present invention;

[0022] Figure 6 The radiation pattern of the S / X / K / Ka multi-band feed provided in the embodiments of the present invention is shown in each frequency band.

[0023] Icons: 1 - S / X / K / Ka coaxial horn; 2 - X-band demultiplexing and integrated circular polarization network; 3 - K / Ka band circular polarizer; 4 - K / Ka band quadrature; 5 - K / Ka band duplexer; 6 - S-band corrugated horn; 7 - X-band coaxial horn; 8 - K / Ka band dielectric horn. Detailed Implementation

[0024] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description of an S / X / K / Ka multi-band feed source for VLBI proposed according to the present invention is provided in conjunction with the accompanying drawings and specific embodiments.

[0025] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0026] This invention provides an S / X / K / Ka multi-band feed for VLBI, which solves the problems of incomplete frequency band coverage, complex structure, and need for mechanical switching in existing technologies by combining an innovative coaxial nested horn structure with a highly integrated back-end signal processing network. It enables operation in the S-band (2.2-2.3GHz), X-band (7.5-9GHz), K-band (20.7-23.5GHz), and Ka-band (26.5-34GHz), meeting the requirements of next-generation VLBI systems for wide bandwidth, multi-band, and high-reliability synchronous observation.

[0027] The core design of this invention's S / X / K / Ka multi-band feedhorn lies in spatial hierarchical multiplexing and network function integration. By implementing the receiving functions of different frequency bands in a radial spatial hierarchy, the challenge of spatial separation reception of multi-band signals is solved. Based on this, optimal back-end polarization processing and frequency band separation networks are designed for the signal characteristics of each frequency band, and these networks are compactly laid out and directly connected, ultimately forming a fully functional, high-performance, and physically integrated four-band feedhorn system. This design maximizes system miniaturization and high reliability while ensuring performance.

[0028] Please see Figure 1 , Figure 1 This is a schematic diagram of the overall structure of an S / X / K / Ka multi-band feed for VLBI provided in an embodiment of the present invention. Figure 1 As shown, the S / X / K / Ka multi-band feed for VLBI in this embodiment includes: an S / X / K / Ka coaxial horn 1, an X-band demultiplexer and integrated synthetic circular polarization network 2, a K / Ka band circular polarizer 3, a K / Ka band quadrature 4, a K / Ka band duplexer 5, and an S-band circular polarization feed network (not shown separately in the figure, its functional components are integrated in the connecting waveguide).

[0029] In this embodiment, the S / X / K / Ka coaxial horn 1 is used to radiate and receive electromagnetic wave signals in four frequency bands: S, X, K, and Ka. After the electromagnetic wave signals are received by the S / X / K / Ka coaxial horn 1, the S, X, K / Ka frequency band signals are initially separated in space and sent to the corresponding back-end processing network to output the left-hand circularly polarized signal and the right-hand circularly polarized signal of the corresponding frequency band.

[0030] In this embodiment, the S-band circular polarization feed network is connected to the S-band output terminal of the S / X / K / Ka coaxial horn 1, and is used to synthesize the received S-band electromagnetic wave signal into an S-band left-hand circular polarization signal and an S-band right-hand circular polarization signal; the X-band demultiplexing and integrated circular polarization network 2 is connected to the X-band output terminal of the S / X / K / Ka coaxial horn 1, and is used to synthesize the received X-band electromagnetic wave signal into an X-band left-hand circular polarization signal and an X-band right-hand circular polarization signal; the input terminal of the K / Ka band circular polarizer 3 is connected to the S / X / K / Ka coaxial horn 1. The K / Ka band output terminal is used to form a circularly polarized signal from the received K-band and Ka-band electromagnetic wave signals; the input terminal of the K / Ka band quadrature 4 is connected to the output terminal of the K / Ka band circular polarizer 3, and is used to separate the circularly polarized signal into two orthogonal polarization components; the input terminal of the K / Ka band duplexer 5 is connected to the output terminal of the K / Ka band quadrature 4, and is used to separate the two orthogonal polarization components to obtain a K-band left-hand circularly polarized signal, a K-band right-hand circularly polarized signal, a Ka-band left-hand circularly polarized signal, and a Ka-band right-hand circularly polarized signal.

[0031] In this embodiment, the S / X / K / Ka coaxial horn 1 is the core antenna component of the present invention, employing a three-layer coaxial nested structure. Please refer to [link / reference needed]. Figure 2 , Figure 2 This is a cross-sectional structural diagram of an S / X / K / Ka coaxial horn provided in an embodiment of the present invention. Figure 2 As shown, the S / X / K / Ka coaxial speaker 1 includes a three-layer structure arranged coaxially and nested from the inside out: the innermost K / Ka band dielectric speaker 8, the middle X band coaxial speaker 7, and the outermost S band corrugated speaker 6.

[0032] This invention adopts a three-layer coaxial nested design of "medium horn - coaxial horn - corrugated horn", which integrates the receiving units of the four frequency bands into one unit in space, avoiding the lateral size expansion caused by the traditional multi-horn side-by-side layout.

[0033] Specifically, the innermost K / Ka band dielectric horn 8 is a circular waveguide horn filled with dielectric material, used to receive and radiate K-band and Ka-band electromagnetic wave signals. The dielectric material is used to increase the equivalent radiation aperture.

[0034] Optionally, the filling dielectric material is a low-loss dielectric material, such as polytetrafluoroethylene or ceramic matrix composites. Dielectric loading not only broadens the operating bandwidth and improves the radiation pattern symmetry, but more importantly, it increases the equivalent wavelength of electromagnetic waves within the horn, thus allowing for a smaller physical aperture while meeting electrical performance requirements. This leaves crucial space for the design of the outer horn, forming the basis for a compact structure. In this embodiment, the K / Ka band dielectric horn 8 is responsible for receiving and radiating electromagnetic wave signals in the 20.7-23.5 GHz (K band) and 26.5-34 GHz (Ka band) bands.

[0035] In this embodiment, the X-band coaxial horn 7 in the middle layer is a metal waveguide structure, coaxially nested outside the K / Ka band dielectric horn 8, and is used to receive and radiate X-band electromagnetic wave signals.

[0036] For example, a coaxial waveguide structure made of aluminum or copper can be tightly nested around the exterior of the K / Ka band dielectric horn 8. Its inner wall and the outer wall of the K / Ka band dielectric horn 8 form a propagation channel in the 7.5-9 GHz (X-band) range. This structure requires precise design to ensure good radiation characteristics for X-band signals while minimizing interference with the operation of both inner and outer horn layers.

[0037] In this embodiment, the outermost S-band corrugated horn 6 is a four-ridge fed corrugated horn, coaxially nested outside the X-band coaxial horn 7, and is used to receive and radiate S-band electromagnetic wave signals.

[0038] Optionally, the S-band corrugated horn 6 can be a conical corrugated horn made of metal, nested on the outermost side of the X-band coaxial horn 7, with its inner wall and the outer wall of the X-band coaxial horn 7 forming a 2.2-2.3 GHz (S-band) propagation channel. The inner wall of the horn is machined with periodic annular grooves (corrugations) to improve the aperture efficiency of the S-band and excite the desired mixed mode to achieve excellent radiation pattern and low cross-polarization over a wide bandwidth. Its feeding section adopts a four-ridge structure, which can simultaneously excite four port signals for subsequent circular polarization synthesis.

[0039] Please refer to the above. Figure 3 and Figure 4 , Figure 3 This is a schematic diagram of an S-band corrugated horn provided in an embodiment of the present invention; Figure 4 This is a block diagram illustrating the principle of an S-band circularly polarized feed network provided in an embodiment of the present invention. Figure 4 As shown, in this embodiment, the S-band circularly polarized feed network includes: two magic T-band circularly polarized feed networks. Figure 4 The two magic Ts are connected to the four-ridge feed port of the S-band corrugated speaker 6 in the S / X / K / Ka coaxial speaker 1 (including magic T-1 and magic T-2) and a bridge circuit; the input terminals of the two magic Ts are connected to the four-ridge feed port of the S-band corrugated speaker 6 in the S / X / K / Ka coaxial speaker 1 (including magic T-1 and magic T-2). Figure 3 (Ports a, b, c, and d in the circuit). Two magic transformers (MTs) are used to combine four signals into two spatially orthogonal linearly polarized signals; the input terminals of the bridge are connected to the output terminals of the two magic transformers respectively, which are used to introduce a 90-degree phase difference between the two linearly polarized signals and output S-band left-hand circularly polarized signals and S-band right-hand circularly polarized signals.

[0040] Specifically, such as Figure 4 As shown, the input terminals of Magic T-1 are connected to ports a and b of the S-band corrugated speaker 6, and the input terminals of Magic T-2 are connected to ports c and d of the S-band corrugated speaker 6. The bridge can be a 90° bridge.

[0041] The S-band electromagnetic wave signal processing procedure is as follows: The S-band electromagnetic wave signal is received by the S-band corrugated horn 6, i.e., a corrugated horn with a four-ridge feed, outputting four signals. These four signals are fed into the S-band circularly polarized feed network. Magic T-1 combines the two signals output from port a and port b into one signal, and Magic T-2 combines the two signals output from port c and port d into another signal. These two signals are spatially orthogonally polarized. Subsequently, these two orthogonal linearly polarized signals are fed into a 90° bridge. The bridge generates signals with equal amplitude and a 90-degree phase difference at its two output ports, which correspond to the left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) S-band signal outputs, respectively.

[0042] In this embodiment, the X-band demultiplexing and integrated synthesized circular polarization network 2 includes: an X-band demultiplexer and an integrated synthesizing network; the input end of the X-band demultiplexer is connected to the X-band coaxial horn 7 in the S / X / K / Ka coaxial horn 1, and is used to couple and separate the received X-band electromagnetic wave signal to four sub-waveguide branches; the input end of the integrated synthesizing network is connected to the four sub-waveguide branches, and is used to form a 90-degree phase difference between two orthogonal linear polarization modes in the signals of the four sub-waveguide branches, and output X-band left-hand circular polarization signal and X-band right-hand circular polarization signal.

[0043] Optionally, the X-band demultiplexer can be a multi-coupler or a waveguide slot coupling structure, and the integrated synthesis network can be a highly integrated passive microwave network, such as a miniaturized and integrated fabrication of a classic waveguide bridge (e.g., a branch line bridge or a coupled line bridge) and a phase adjustment segment.

[0044] The X-band electromagnetic wave signal processing procedure is as follows: After the X-band electromagnetic wave signal is received by the X-band coaxial horn 7, it first enters an X-band demultiplexer, which couples the energy in the main waveguide to the four sub-waveguide branches. The signals from these four sub-waveguide branches then enter the integrated synthesis network. This network can directly process the input signal internally, accurately generating a 90-degree phase difference between the two orthogonal polarization modes, thereby obtaining the left-hand circularly polarized and right-hand circularly polarized X-band signals at its two output ports, respectively. Compared with the traditional discrete component cascade scheme, this integrated design significantly reduces the size and insertion loss.

[0045] In this embodiment, the K / Ka band circular polarizer 3 generates the required phase difference to form circular polarization by means of a dielectric sheet or pin structure installed in the circular waveguide for the passing K-band and Ka-band electromagnetic wave signals.

[0046] Alternatively, a dielectric sheet of a specific length and dielectric constant can be inserted into the circular waveguide, or a carefully arranged set of metal pins can be loaded. These discontinuities will produce different phase shifts for the two orthogonal linear polarization modes, and when the phase difference is adjusted to 90 degrees, the conversion from linear polarization to circular polarization is achieved.

[0047] In this embodiment, the K / Ka band orthogonalizer 4 is a waveguide double-T or coupling aperture structure, used to separate the circularly polarized signal into two orthogonal polarization components, which correspond to the left-hand circularly polarized signal and the right-hand circularly polarized signal, respectively.

[0048] Optionally, the K / Ka band orthogonalizer 4 can adopt a waveguide hybrid-T (Hybrid-T) or sidewall coupling aperture structure. Its function is to decompose the input circularly polarized wave into two orthogonal linearly polarized components with equal energy and fixed phase relationship (or directly separate the left and right circularly polarized signals), and output them from two ports respectively.

[0049] In this embodiment, the K / Ka band duplexer 5 is a combination of a bandpass filter and a directional coupler, and its operating frequency bands correspond to the K band and the Ka band, respectively. It is used to separate the signal path containing the K band and the Ka band into independent K band signal output paths and Ka band signal output paths.

[0050] Optionally, the K / Ka band duplexer 5 can be constructed from bandpass filters designed separately for the K-band and Ka-band. For example, a waveguide cavity filter or a dielectric resonator filter can be used. The K-band filter allows signals from 20.7–23.5 GHz to pass through while suppressing Ka-band signals, while the Ka-band filter allows signals from 26.5–34 GHz to pass through while suppressing K-band signals.

[0051] The K / Ka band electromagnetic wave signal processing process is as follows: K and Ka band signals are received by the innermost K / Ka band dielectric horn 8. After being transmitted sequentially through a circular waveguide, they first pass through the K / Ka band circular polarizer 3 to achieve linear polarization to circular polarization conversion. The generated circularly polarized signal then enters the K / Ka band quadrature 4, which decomposes the input circularly polarized wave into two orthogonal linearly polarized components with equal energy and fixed phase relationship (or directly separates the left and right circularly polarized signals), and outputs them from two ports respectively. Finally, the signals output from these two ports (each port contains K and Ka band components) enter the K / Ka band duplexer 5. After passing through the K / Ka band duplexer 5, the left and right circularly polarized signals of the K and Ka bands are completely separated, forming four independent output channels.

[0052] Please see Figure 5 , Figure 5 This figure shows the standing wave ratio (VSWR) of the S / X / K / Ka multi-band feed provided in this embodiment of the invention at various frequency bands. The upper left of the figure shows the VSWR in the S band, the upper right shows the VSWR in the X band, the lower left shows the VSWR in the K band, and the lower right shows the VSWR in the Ka band. As can be seen from the figure, a low VSWR is achieved in each operating frequency band. For example, the VSWR in the S band is less than 1.45, in the X band it is less than 1.31, in the K band it is less than 1.28, and in the Ka band it is less than 1.2. That is, the VSWR of the S / X / K / Ka multi-band feed is at a low level throughout the entire S, X, K, and Ka operating frequency bands, demonstrating good impedance matching, ensuring efficient signal transmission, and reducing reflection loss.

[0053] Please see Figure 6 , Figure 6 The radiation patterns of the S / X / K / Ka multi-band feed provided in this embodiment of the invention are shown in each frequency band. The upper left of the figure shows the radiation pattern in the S band, the upper right shows the radiation pattern in the X band, the lower left shows the radiation pattern in the K band, and the lower right shows the radiation pattern in the Ka band. The horizontal axis represents the azimuth, and the vertical axis represents the amplitude. As can be seen from the figure, the E-plane and H-plane radiation patterns of each operating frequency band are highly homogeneous, with a high degree of agreement within the main lobe range. This ensures the antenna's illumination efficiency and polarization purity, meeting the requirements of high-performance antennas for feed illumination characteristics.

[0054] This invention presents a multi-band S / X / K / Ka feed for VLBI, which, through an ingenious multi-layer coaxial horn structure design and a highly integrated back-end signal processing network, successfully achieves miniaturization, high reliability, and high performance of a four-band S / X / K / Ka feed, providing key equipment support for next-generation multi-functional VLBI systems and satellite tracking stations. Furthermore, its compact structure and lightweight design make it easier to integrate with antenna subreflectors and subsequent low-noise amplifier systems. The miniaturization feature is particularly advantageous in placing the entire feed and even the front-end low-noise amplifier within a cryogenic refrigerator, effectively reducing system noise temperature, which is crucial for improving the sensitivity of radio astronomy observations.

[0055] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device comprising said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. The orientations or positional relationships indicated by terms such as "upper," "lower," "left," and "right" are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0056] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0057] The above description, in conjunction with specific preferred 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 multi-band S / X / K / Ka feed for VLBI, characterized in that, include: S / X / K / Ka coaxial horn, S-band circular polarization feed network, X-band demultiplexing and integrated synthetic circular polarization network, K / Ka band circular polarizer, K / Ka band quadrature, and K / Ka band duplexer. The S / X / K / Ka coaxial horn is used to radiate and receive electromagnetic wave signals in four frequency bands: S, X, K, and Ka. The S / X / K / Ka coaxial horn includes a K / Ka band dielectric horn, an X band coaxial horn, and an S band corrugated horn, which are coaxially nested from the inside out. The S-band circular polarization feed network is connected to the S-band output terminal of the S / X / K / Ka coaxial speaker, and is used to synthesize the received S-band electromagnetic wave signal into an S-band left-hand circular polarization signal and an S-band right-hand circular polarization signal. The X-band demultiplexing and integrated circular polarization network is connected to the X-band output of the S / X / K / Ka coaxial horn, and is used to synthesize the received X-band electromagnetic wave signal into an X-band left-hand circular polarization signal and an X-band right-hand circular polarization signal. The X-band demultiplexing and integrated circular polarization network includes an X-band demultiplexer and an integrated synthesis network. The input of the X-band demultiplexer is connected to the X-band coaxial horn in the S / X / K / Ka coaxial horn, and is used to couple and separate the received X-band electromagnetic wave signal to four sub-waveguide branches. The input of the integrated synthesis network is connected to the four sub-waveguide branches, and is used to form a 90-degree phase difference between two orthogonal linear polarization modes in the signals of the four sub-waveguide branches, and output the X-band left-hand circular polarization signal and the X-band right-hand circular polarization signal. The input terminal of the K / Ka band circular polarizer is connected to the K / Ka band output terminal of the S / X / K / Ka coaxial speaker to form a circular polarization signal from the received K-band electromagnetic wave signal and Ka-band electromagnetic wave signal. The input of the K / Ka band quadrature is connected to the output of the K / Ka band circular polarizer, and is used to separate the circular polarization signal into two orthogonal polarization components. The input of the K / Ka band duplexer is connected to the output of the K / Ka band quadrature, which is used to separate the two orthogonal polarization components to obtain the K-band left-hand circular polarization signal, the K-band right-hand circular polarization signal, the Ka-band left-hand circular polarization signal, and the Ka-band right-hand circular polarization signal.

2. The S / X / K / Ka multi-band feed for VLBI according to claim 1, characterized in that, The K / Ka band dielectric horn is a circular waveguide horn filled with dielectric material, used to receive and radiate K-band and Ka-band electromagnetic wave signals. The dielectric material is used to increase the equivalent radiation aperture.

3. The S / X / K / Ka multi-band feed for VLBI according to claim 1, characterized in that, The X-band coaxial horn is a metal waveguide structure, coaxially nested outside the K / Ka band dielectric horn, used to receive and radiate X-band electromagnetic wave signals.

4. The S / X / K / Ka multi-band feed for VLBI according to claim 1, characterized in that, The S-band corrugated horn is a four-ridge fed corrugated horn, coaxially nested outside the X-band coaxial horn, used to receive and radiate S-band electromagnetic wave signals.

5. The S / X / K / Ka multi-band feed for VLBI according to claim 1, characterized in that, The S-band circularly polarized feed network includes: two magic transistors and one bridge; The input terminals of the two Magic Ts are connected to the four-ridge feed port of the S-band corrugated horn in the S / X / K / Ka coaxial horn, which is used to combine the four signals into two spatially orthogonal linearly polarized signals. The input terminals of the bridge are respectively connected to the output terminals of the two magic Ts, which are used to introduce a 90-degree phase difference between the two line polarization signals and output the S-band left-hand circular polarization signal and the S-band right-hand circular polarization signal.

6. The S / X / K / Ka multi-band feed for VLBI according to claim 1, characterized in that, The K / Ka band circular polarizer generates the required phase difference to form circular polarization by means of a dielectric sheet or pin structure installed in a circular waveguide for the passing K-band and Ka-band electromagnetic wave signals.

7. The S / X / K / Ka multi-band feed for VLBI according to claim 1, characterized in that, The K / Ka band orthogonalizer is a waveguide double-T or coupling aperture structure used to separate the circularly polarized signal into two orthogonal polarization components, which correspond to the left-hand circularly polarized signal and the right-hand circularly polarized signal, respectively.

8. The S / X / K / Ka multi-band feed for VLBI according to claim 1, characterized in that, The K / Ka band duplexer is a combination of a bandpass filter and a directional coupler, with its operating frequency bands corresponding to the K band and the Ka band, respectively. It is used to separate signal paths containing both the K band and the Ka band into independent K band signal output paths and Ka band signal output paths.

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