A high time-delay stability antenna applied to an inter-satellite micrometer-level ranging system

Abstract

The present invention discloses a high-delay-stability antenna applied to an inter-satellite micrometer-level ranging system, comprising: an axially slotted loaded optical-wall shaped horn, an orthomode coupler, a frequency duplexer-like complex waveguide component, and a standard waveguide transmission system. The antenna disclosed by the present invention has extremely high co-frequency polarization isolation, delay stability, and multipath suppression performance, solves the technical bottleneck of the antenna design for the micrometer-level microwave ranging system, and has important significance for improving the ranging and velocity measurement accuracy of radar and navigation systems. The antenna designed by the invention is not only applicable to satellite payloads, but also applicable to ground systems. At the same time, the optimization methods for co-frequency polarization isolation, phase center stability, and multipath suppression can also be extended to other antenna designs, thus having strong practicability and broad market application prospects.

Description

Technical Field

[0001] The present invention relates to a high time-delay stability antenna applied to an inter-satellite micrometer-level ranging system, belonging to the technical field of spaceborne antennas. Background Art

[0002] The precise measurement of the Earth's gravity field plays an extremely important role in aspects such as military and geophysical sciences. The gravity field measurement technology based on low-orbit satellite-to-satellite tracking technology has been considered the most accurate test method after years of exploration. This technology consists of two low-orbit satellites in the same orbit. By measuring the distance and the rate of change of the distance between the two satellites, and then subtracting the influence of non-conservative forces, the Earth's gravity field model can be restored through multiple measurements. To achieve the accuracy of high-order gravity field inversion, the satellite needs to provide a ranging ability with micrometer-level accuracy. And the antenna, as the entrance of the microwave signal in the entire ranging system, its phase center is the reference point for microwave ranging. If the position of the antenna phase center on the whole satellite deviates from the centroid and is constantly changing, then the ranging and velocity measurement values will introduce this changing error amount, and this change amount is not the orbital perturbation caused by gravity anomaly, so it will ultimately lead to errors in gravity field inversion.

[0003] First of all, according to the mission requirements, the two satellites need to construct a K / Ka dual-frequency two-way ranging and velocity measurement link, and the errors are eliminated through the comparison of the dual-frequency two-way link. Therefore, each satellite needs to transmit and receive simultaneously in two frequency bands. Due to the extremely high sensitivity requirements of the system, the antenna is required to provide very high co-frequency isolation performance to meet the carrier-to-noise ratio requirements for the normal operation of the system. The usual method is to use two antennas to work in the transmit and receive modes at the same frequency respectively, and separate them by a certain distance to provide a certain isolation degree through the spatial distance. However, the background mission requires that the phase centers of the four ranging links must be on the line connecting the centroids of the two satellites. Since the line connecting the centroids of the two satellites is unique, it is necessary to design a K / Ka dual-frequency two-line polarization common antenna that can simultaneously provide four RF channels to ensure that the four ranging links work simultaneously and independently. Obviously, it is a very challenging task to simultaneously achieve high polarization isolation of the antenna in the K / Ka frequency band. After reviewing the literature, it is found that the highest value of its polarization isolation can only reach -60 dB, which cannot meet the requirements of the system. Therefore, it is necessary to carry out research on high polarization isolation antenna technology and conduct design.

[0004] Secondly, the phase center stability of the antenna determines the ranging accuracy of the entire system. Previous domestic and international research on phase centers mainly focused on the navigation antennas of GNSS satellites such as GPS and Beidou. Although research on antenna phase stability has been carried out, due to the ranging magnitude being in the millimeter level, no targeted design for high phase stability has been carried out at the antenna design level. When the ranging accuracy reaches the micron level, many error terms that were previously ignored will have a significant impact on the ranging accuracy, and at the antenna design level, it is necessary to conduct high-precision analysis of the phase center stability of the antenna and optimize the antenna design, which goes beyond the conventional cognitive scope of the antenna design field. There is no relevant literature reporting the related technologies and design methods of the antenna for the micron-level ranging system. Therefore, in order to meet the requirements of the development task of the gravity measurement satellite and achieve the inter-satellite ranging accuracy at the micron level, it is necessary to carry out research on the antenna design technology with high phase center stability.

[0005] Finally, since microwave ranging uses the method of measuring the phase of the signal (or called signal time delay) to invert the distance, obviously the introduction of multipath signals will cause changes in the phase of the measured signal, and this change directly affects the ranging accuracy. Therefore, for the antenna, it is necessary to suppress the multipath signals to ensure the ranging accuracy. Without increasing the system complexity, suppressing the far side lobes of the antenna radiation pattern is an effective method. However, for a conventional horn antenna, further suppression of the far side lobes cannot be achieved only by optimizing the pattern, so it is necessary to carry out innovative design on it.

[0006] In summary, for the research on the related technologies and design methods of high co-frequency polarization isolation, high phase stability, and multipath suppression required by the antenna of the micron-level ranging system for the application background, due to the lack of relevant literature reports and it being the first time in the design of spaceborne antennas in China, there is a technical gap. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: aiming at the deficiencies of the prior art, a high time delay stability antenna design method applied to the inter-satellite micron-level ranging system is proposed, which ensures the normal operation and ranging accuracy of the double-satellite micron-level microwave ranging system, and meets the technical requirements of extremely high co-frequency polarization isolation, high phase center stability, and high multipath suppression.

[0008] The solution adopted by the present invention to solve the above technical problem is:

[0009] The present invention discloses a high time delay stability antenna applied to the inter-satellite micron-level ranging system, including: a horn, an orthomode coupler, a frequency duplexer, and a connecting waveguide, where:

[0010] The frequency duplexer includes a first frequency duplexer and a second frequency duplexer;

[0011] As a transmitting or receiving end, the mirror-image design of a dual-star antenna is adopted to achieve dual-star two-way dual-frequency communication;

[0012] When acting as a receiving end, the horn receives the linearly polarized signal and transmits the linearly polarized signal to the orthomode coupler; the orthomode coupler separates the linearly polarized signal to obtain a horizontally polarized signal and a vertically polarized signal; the horizontally polarized signal is further separated by the first frequency duplexer to obtain K-band and Ka-band horizontally polarized signals, and the vertically polarized signal is separated by the second frequency duplexer and the connecting waveguide to obtain K-band and Ka-band vertically polarized signals;

[0013] When acting as a transmitting end, the transmitter sends K-band and Ka-band signals to two frequency duplexers respectively. The first frequency duplexer synthesizes K-band and Ka-band signals into a horizontally polarized signal and transmits it to the horizontal polarization port of the orthomode coupler. The second frequency duplexer synthesizes K-band and Ka-band signals into a vertically polarized signal and transmits it to the vertical polarization port of the orthomode coupler through the connecting waveguide. The orthomode coupler combines the horizontal polarization signal and the vertical polarization signal and transmits them to the horn, and realizes the radiation of K-band and Ka-band dual-linearly polarized electromagnetic waves through the horn.

[0014] In the above-mentioned stable antenna, the horn includes a mode conversion section, an optical-wall shaping section, a horn mouth section, a uniaxial slot and a choke ring; where:

[0015] The mode conversion section is a conical waveguide transformation section structure, which is used for the conversion of the main mode at the horn input port to the higher-order mode in the horn cavity to achieve the broadband matching of the horn;

[0016] The inner cavity of the optical-wall shaping section is a surface formed by rotating a spline shaping curve by 360 degrees, which realizes the high gain and high cross-polarization characteristics of the horn;

[0017] A uniaxial slot is arranged at the connection between the horn mouth section and the optical-wall shaping section, which is used to improve the equalization of the radiation beam of the horn antenna and obtain a stable phase center;

[0018] The top of the horn mouth section is turned outwards to form a flanging and an outer edge. On the flanging, a choke ring with a depth of M is arranged at a position S away from the outer edge, which is used to suppress the current on the flanging of the horn mouth surface.

[0019] In the above-mentioned stable antenna, S = λ0 / 8~λ0 / 4, M = λ0 / 8~λ0 / 2, where λ0 is the wavelength corresponding to the center frequency of the horn operation.

[0020] In the above-mentioned stable antenna, the orthogonal mode coupler includes a coupling hub, a T-type combiner, and a bent waveguide, where: The coupling hub includes four E-plane coupling rectangular waveguides; the T-type combiner and the bent waveguide combine the two pairs of opposite E-plane coupling rectangular waveguides into one waveguide, and realize the conversion to a standard waveguide through a stepped transition; the bent waveguide includes an E-plane rectangular bent waveguide and an H-plane rectangular bent waveguide, and a stepped transition is adopted at the connection of the E-plane rectangular bent waveguide and the H-plane rectangular bent waveguide.

[0021] In the above-mentioned stable antenna, the coupling hub further includes a common port circular waveguide and a stepped cylinder; wherein, the four E-plane coupling rectangular waveguides are vertically symmetrically distributed around the common port circular waveguide, and the stepped cylinder is located at the center of the common port circular waveguide; the E-plane coupling rectangular waveguide realizes the separation of horizontal linear polarization and vertical linear polarization, and the stepped cylinder realizes the signal matching of the E-plane coupling rectangular waveguide.

[0022] In the above-mentioned stable antenna, the frequency duplexer includes a T-type branch, a K-band bandpass filter, and a Ka-band high-pass filter, where:

[0023] The T-type branch is of a T-type structure, and the two side arms of the T-type structure are respectively connected to the K-band bandpass filter and the Ka-band high-pass filter; the K-band filter adopts a low-order corrugated bandpass filter structure, and the Ka-band filter adopts a cut-off waveguide type filter structure.

[0024] Further, in the above-mentioned stable antenna, the mirror design of the dual-star antenna is specifically as follows: When realizing dual-star communication, the antennas of the two satellites are twisted by 45° linear polarization to realize the physical structure mirror of the two satellites and the matching of the receiving and transmitting polarizations.

[0025] Further, in the above-mentioned stable antenna, the horn has the characteristics of high efficiency, wide bandwidth, low cross polarization, simple structure, and light weight.

[0026] Further, in the above-mentioned stable antenna, the polarization isolation of the orthogonal mode coupler is greater than 65 dB in both the K-band and the Ka-band.

[0027] Further, in the above-mentioned stable antenna, the frequency duplexer has high delay stability.

[0028] The beneficial effects of the present invention compared with the prior art are as follows:

[0029] (1) The antenna designed by the present invention has extremely high co-frequency polarization isolation, delay stability, and multipath suppression performance, and meets the requirements of the micron-level measurement accuracy of the dual-star microwave ranging system through ground tests and in-orbit verification;

[0030] (2) The present invention obtains high gain and high phase center stability by using an axially grooved light-wall shaped horn antenna. At the same time, a choke groove is arranged on the horn flange to suppress the far radiation side lobes, improving the antenna's suppression of multipath;

[0031] (3) The present invention greatly improves the polarization port isolation of the antenna through the optimized design of a four-arm symmetric coupled orthomode coupler and refined tolerance analysis;

[0032] (4) The present invention introduces a low-order corrugated band-pass filter and a cutoff waveguide filter into a T-type branch frequency duplexer, avoiding the influence of multiple resonances in traditional duplexers on the phase of the propagating electromagnetic field and improving the delay stability of the entire transmission channel.

[0033] (5) The present invention is designed and developed for the core payload KBR (K-band ranging) system of China's first gravity measurement satellite, solving the technical bottleneck of the antenna design for the micrometer-level microwave ranging system, and is of great significance for improving the ranging and velocity measurement accuracy of radar and navigation systems;

[0034] (6) The antenna designed by this invention is not only applicable to satellite payloads, but also to ground systems. At the same time, its considerations and design analysis methods for phase center stability and multipath suppression can also be extended to other antenna designs, so it has strong practicability and broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0036] Figure 1 is a block diagram of the antenna system described in the present invention;

[0037] Figure 2 is a schematic diagram of the overall structure of the antenna described in the present invention;

[0038] Figure 3 is a schematic diagram of the horn structure composition of the antenna described in the present invention;

[0039] Figure 4 is the test result of the radiation pattern of the antenna horn described in the present invention; (a) Radiation pattern in the K band; (b) Radiation pattern in the Ka band;

[0040] Figure 5It is a comparison result diagram of the influence of the axial slot on the delay stability of the horn; (a) Without axial slot in the K band; (b) Without axial slot in the Ka band; (c) With axial slot in the K band; (d) With axial slot in the Ka band;

[0041] Figure 6 It is a comparison result diagram of the influence of the choke ring on the radiation pattern of the horn;

[0042] Figure 7 It is a schematic diagram of the design and result comparison of the orthogonal mode coupler of the antenna described in the present invention; (a) Composition of the orthogonal mode coupler; (b) Structural model of the orthogonal mode coupler; (c) Port polarization isolation in the literature; (d) Polarization isolation of this design;

[0043] Figure 8 It is an innovative design schematic diagram of the antenna frequency duplexer described in the present invention; (a) Traditional T-shaped branch waveguide frequency duplexer, (b) Design of the present invention;

[0044] Figure 9 It is a schematic diagram of the mirror image design of the double-star antenna described in the present invention;

[0045] Figure 10 It is a test result curve diagram of the physical object of the antenna described in the present invention, (a) VSWR of X01G port, (b) VSWR of X02G port; (c) VSWR of X03G port, (d) VSWR of X04G port; (e) Isolation between X01G and X03G ports (f) Isolation between X02G and X04G ports; (g) Radiation pattern in the K band, (h) Radiation pattern in the Ka band. Detailed implementation manners

[0046] Next, the design method of the high-delay stability antenna applied to the inter-satellite micron-level ranging system according to the present invention will be further described in detail in conjunction with the accompanying drawings and specific embodiments. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0047] The present invention discloses a high-delay-stability antenna applied to an inter-satellite micrometer-level ranging system, comprising: a horn 1, an orthomode coupler 2, a frequency duplexer 3, and a connecting waveguide 4, wherein: the frequency duplexer 3 includes a first frequency duplexer and a second frequency duplexer; as a transmitting end or a receiving end, the mirror symmetry design of a dual-satellite antenna is adopted to achieve two-way dual-frequency communication between two satellites; the mirror symmetry design of the dual-satellite antenna is specifically as follows: when realizing communication between two satellites, the antennas of the two satellites are subjected to a 45° linear polarization twist to achieve the mirror symmetry of the physical structures of the two satellites, and the transmitting and receiving polarizations are matched. The horn has the characteristics of high efficiency, wide bandwidth, low cross polarization, simple structure, and light weight. The polarization isolation degree of the orthomode coupler is greater than 65 dB in both the K band and the Ka band. The frequency duplexer has high-delay stability. The present invention makes the antenna become the radio frequency front end of a new type of high-precision inter-satellite ranging system, and uses the mirror symmetry relationship of 45° linear polarization to achieve the consistency of the dual-satellite antenna and system layout, simplifying the design of the system and the entire satellite.

[0048] When acting as a receiving end, the horn 1 receives a linearly polarized signal and transmits the linearly polarized signal to the orthomode coupler 2; the orthomode coupler 2 separates the linearly polarized signal to obtain a horizontally polarized signal and a vertically polarized signal; the horizontally polarized signal is further separated by the first frequency duplexer to obtain horizontally polarized signals in the K band and the Ka band, and the vertically polarized signal is separated by the second frequency duplexer and the connecting waveguide 4 to obtain vertically polarized signals in the K band and the Ka band;

[0049] When acting as a transmitting end, a transmitter sends signals in the K band and the Ka band to the two frequency duplexers respectively. The first frequency duplexer synthesizes the K-band and Ka-band signals into a horizontally polarized signal and transmits it to the horizontal polarization port of the orthomode coupler 2. The second frequency duplexer synthesizes the K-band and Ka-band signals into a vertically polarized signal and transmits it to the vertical polarization port of the orthomode coupler 2 through the connecting waveguide 4. The orthomode coupler 2 combines the horizontal polarization signal and the vertical polarization signal and transmits them to the horn 1, and the horn realizes the radiation of dual-linearly polarized electromagnetic waves in the K band and the Ka band.

[0050] The horn 1 includes a mode conversion section 11, a light wall shaping section 12, a horn mouth section 15, a uniaxial groove 13, and a choke ring 14; where: The mode conversion section 11 is a conical waveguide transformation section structure, which is used for the conversion of the main mode at the horn input port to the higher-order mode in the horn cavity to achieve broadband matching of the horn; the inner cavity of the light wall shaping section 12 is a surface formed by rotating a spline shaping curve by 360 degrees to achieve high gain and high cross-polarization characteristics of the horn; a uniaxial groove 13 is arranged at the connection between the horn mouth section 15 and the light wall shaping section 12, which is used to improve the equalization of the radiation beam of the horn antenna and obtain a stable phase center; the top of the horn mouth section 15 is turned outwards to form a flange 151 and an outer edge 152. On the flange 151, a choke ring 14 with a depth of M is arranged at a position S from the outer edge 152, which is used to suppress the current on the flange 151 of the horn mouth surface. Reducing the side lobes and back lobes of the horn antenna can weaken the coupling between the horn and the front panel of the satellite body and has the effect of suppressing multipath. S = λ0 / 8 to λ0 / 4, M = λ0 / 8 to λ0 / 2, where λ0 is the wavelength corresponding to the center frequency of the horn operation.

[0051] The orthomode coupler 2 includes a coupling hub 21, a T-type combiner 22, and a bent waveguide 23, where: The coupling hub 21 includes four E-plane coupling rectangular waveguides; the T-type combiner 22 and the bent waveguide 23 combine the two relatively E-plane coupling rectangular waveguides into one waveguide and realize the conversion to a standard waveguide through a stepped transition; the bent waveguide 23 includes an E-plane rectangular bent waveguide and an H-plane rectangular bent waveguide, and a stepped transition is adopted at the connection between the E-plane rectangular bent waveguide and the H-plane rectangular bent waveguide. The coupling hub 21 also includes a common port circular waveguide and a stepped cylinder; where the four E-plane coupling rectangular waveguides are vertically symmetrically distributed around the common port circular waveguide, and the stepped cylinder is located at the center of the common port circular waveguide; the E-plane coupling rectangular waveguide realizes the separation of horizontal linear polarization and vertical linear polarization, and the stepped cylinder realizes the signal matching of the E-plane coupling rectangular waveguide. The coupling hub uses two adjacent perpendicular arms to realize the separation of two orthogonal linear polarizations. The symmetry of the opposite arms helps to improve the isolation of the two orthogonal linear polarizations in the broadband range, and its internal circular step can achieve good matching of the coupling hub in the broadband; the T-type combiner combines the two symmetric arms into one path, and the bent waveguide combines the E-plane bend and H-plane bend of the waveguide to realize the connection between the four arms of the coupling hub and the two T-type combiners, and a stepped transition is adopted at the bend to reduce the processing difficulty and achieve high processing accuracy.

[0052] The frequency duplexer 3 includes a T-shaped branch 31, a K-band bandpass filter 32, and a Ka-band high-pass filter 33, where: The T-shaped branch 31 is of a T-shaped structure, and the two side arms of the T-shaped structure are respectively connected to the K-band bandpass filter 32 and the Ka-band high-pass filter 33; The K-band filter adopts a low-order ripple type bandpass filter structure, and the Ka-band filter adopts a cut-off waveguide type filter structure. The design of the frequency duplexer is different from that of the traditional waveguide frequency duplexer, and higher delay stability is obtained on the basis of realizing the separation of K and Ka-band electromagnetic waves.

[0053] The horn adopts a shaped light-wall horn form to realize the radiation of K and Ka-band dual-line polarization electromagnetic waves, achieving high phase stability and anti-multipath suppression.

[0054] The above high-delay stability antenna applied to the inter-satellite micron-level ranging system, the orthomode coupler adopts an electromechanical integration design concept, and the influence of process chamfers and dimensional tolerances on the results is considered during simulation. More importantly, according to the polarization multiplexing antenna theory, the relationship between the polarization misalignment angle α, the polarization loss Lp, and the polarization isolation degree Sp is:

[0055] Lp = -20×log 10 (cosα)

[0056] Sp = |-20×log 10 (sinα)|

[0057] Obviously, when the polarization misalignment angle is 90°, the polarization isolation degree is the largest. In this orthomode coupler, the factors determining the polarization misalignment angle are the perpendicularity between the four rectangular waveguide arms and the coaxiality of the common port circular waveguide. Therefore, these two key points need to be controlled during processing. The test results of the polarization isolation degree of this orthomode coupler are greater than 65 dB in both the K and Ka bands, exceeding the highest value in the visible literature.

[0058] The above high-delay stability antenna applied to the inter-satellite micron-level ranging system, the orthomode coupler structure design adopts a three-layer laminated design, avoiding a closed cavity, simplifying processing and improving processing accuracy. At the same time, it is different from the thin-wall structure form of previous spaceborne feed products, avoiding processing deformation.

[0059] The above high-delay stability antenna applied to the inter-satellite micron-level ranging system, the frequency duplexer includes a T-shaped branch, a K-band bandpass filter, and a Ka-band high-pass filter. Among them, the K-band bandpass filter adopts a low-order ripple type bandpass filter structure, and the Ka-band high-pass filter adopts a cut-off waveguide type filter. The resonance effect of the internal electromagnetic field is weak, and the phase of the transmission field inside the entire duplexer is less affected by temperature changes, thus obtaining high-delay stability.

[0060] The above high-delay-stability antenna applied to the inter-satellite micrometer-range measurement system. The mirror-image design of the dual-satellite antenna proposes a dual-satellite dual-frequency ranging system with a 45° polarization arrangement of the antenna, ensuring that the layouts of the two satellites are exactly the same and enabling two-way dual-frequency simultaneous communication.

[0061] The co-frequency polarization isolation degree refers to the isolation degree between the transmitting and receiving ports of the antenna with the same frequency. A low isolation degree will cause the signal received by the antenna itself to be submerged in the noise of the transmitted signal, and the system cannot work. The delay stability of the antenna refers to the stability of the signal transmission delay between the input port of the antenna's back-end feeding network and the antenna phase center in the space environment, including the stability of the phase center position of the antenna radiator and the stability of the signal propagation delay of the antenna's back-end feeding network. Multipath refers to the multiple reflections of the antenna radiator's external environment on the antenna radiation signal, which mainly affects the phase of the transmitted signal and reduces the measurement accuracy, so it needs to be suppressed.

[0062] Embodiment

[0063] The antennas are used in pairs, and the transmitting and receiving channels of the two satellites are reciprocal. Therefore, the four radio-frequency channels of the antenna can be used as either transmit or receive, depending on the system connected to the back end. According to the antenna function and technical index requirements, in order to meet the requirement of high polarization isolation, the antenna adopts a scheme of first separating polarization and then dividing frequency, as Figure 1 shown. The antenna consists of a K / Ka dual-frequency common horn, a circular-rectangular transition, a four-arm orthomode coupler, a frequency duplexer, and the corresponding connecting waveguides. The horn antenna provides dual-frequency radiation. The four-arm orthomode coupler realizes the separation of two linear polarizations, and then the two linear polarization signals are divided by frequency through two frequency duplexers, finally realizing the dual-frequency and dual-linear polarization operation of the antenna. The antenna model is as Figure 2 shown.

[0064] The horn is designed in the form of a shaped smooth-wall + single axial slot horn. The shaped smooth-wall part of the horn is shaped by a spline curve, which has the characteristics of high efficiency, wide bandwidth, and low cross polarization, and has a simple structure and light weight. By loading an axial slot on the horn aperture, the equalization of the horn antenna beam and the cross polarization can be further improved, thereby obtaining a stable phase center. The inner cavity and aperture of the horn are as Figure 3 shown. The horn consists of a mode conversion section, a smooth-wall section, a single axial slot, a horn aperture flanging, and a choke ring. Figure 4 (a) and (b) respectively give the test results of the radiation pattern of the horn in the K band and Ka band. It can be seen that the horn has high gain and low cross polarization characteristics in the dual frequency. Figure 5 (a) to (d) give the change of the phase center of the horn with an axial slot. Figure 5 (a) and (c) show that the phase center of the smooth-wall horn without an axial slot fluctuates about 15 mm and 35 mm in the K and Ka bands respectively, while Figure 5(b) and (d) show that after the axial slots are introduced into the horn, the fluctuations of the phase center are about 10 mm and 11 mm respectively. Obviously, the introduction of the axial slots has a good effect on improving the phase center stability of the horn. Figure 6 The comparison diagrams of the radiation patterns of the horn with and without the choke ring are given. It can be seen that after the horn is equipped with the choke ring (the square loop line in the figure), compared with without the choke ring (the circular loop line in the figure), the far side lobes, especially the back lobe, are significantly suppressed.

[0065] The Orthomode Transducer (OMT) is the core component of the antenna, and its port polarization isolation directly determines the requirement for the isolation of the antenna's co-frequency ports in the mission. According to the link budget of the system, the antenna is required to provide a polarization isolation greater than 65 dB in both the K and Ka frequency bands, and this performance exceeds the highest value in the visible literature. After comparing and analyzing multiple schemes, an OMT with a four-arm symmetric coupling form is finally adopted. As Figure 7 (a) shows, the OMT form of four-arm E-plane coupling and then pairwise synthesis utilizes the symmetry of the four-arm structure to obtain two orthogonally polarized signals with extremely high polarization purity within a relatively wide frequency band. By means of combining theoretical calculation and simulation optimization, the OMT is refinedly designed. The three-layer laminated dissection processing shown in Figure 7 (b) not only makes the structure easy to achieve high-precision processing, but also weakens the influence of processing tolerances on the electrical performance indicators. Through the development of this product, key technical problems such as broadband OMT design, high-polarization isolation OMT design, and high-precision processing technology have been broken through. Figure 7 (c) gives the optimal result of the polarization isolation in the literature, and the overall magnitude is less than -60 dB. The simulated polarization isolation of the OMT is as shown in Figure 7 (d) is overall less than -78 dB.

[0066] This Orthomode Transducer adopts the mechatronic design concept, and the influence of process chamfers and dimensional tolerances on the results is considered during simulation. More importantly, according to the theory of polarization multiplexing antennas, the relationship between the polarization misalignment angle α, the polarization loss Lp, and the polarization isolation Sp is:

[0067] Lp = -20×log 10 (cosα)

[0068] Sp = |-20×log 10 (sinα)|

[0069] Obviously, when the polarization misalignment angle is 90°, the polarization isolation is the largest. In this Orthomode Transducer, the factors determining this polarization misalignment angle are the perpendicularity between the four rectangular waveguide arms and the coaxiality of the common port circular waveguide. Therefore, these two key points need to be controlled during processing.

[0070] The frequency duplexer in the KBR antenna mainly realizes the separation of the K and Ka band signal channels. According to the performance indicators and volume requirements, the T-branch waveguide frequency duplexer scheme is the most suitable. However, the commonly used T-branch waveguide frequency duplexer is composed of a T-head connecting two waveguide inductive diaphragm filters, as Figure 8 (a) shows. The multi-order inductive diaphragm filter introduces multi-order resonances, which are frequency-dependent and determined by the size of the filter. Therefore, the change in the resonance state of this type of filter in high and low temperature environments will introduce a phase change to the antenna, affecting the phase center stability of the antenna. Based on the above theoretical analysis, we innovatively designed a new type of T-branch waveguide frequency duplexer, as Figure 8 (b) shows. This duplexer uses a low-order corrugated bandpass filter to realize the transmission of K-band signals and a cutoff waveguide filter to realize the transmission of Ka-band signals. Since the resonance effect of the internal electromagnetic field of the low-order corrugated bandpass filter is weak, and the cutoff waveguide filter is similar to the waveguide and almost has no resonance, the phase of the internal transmission field is less affected by temperature changes.

[0071] To verify the above design, we took the K-band channel as an example to conduct a simulation analysis on the transmission phase stability (delay stability) of the KBR antenna (excluding the horn part) using two types of duplexers. The statistical results are shown in Table 1. It can be seen that compared with the traditional duplexer, the delay difference between the new-designed duplexer and the orthomode coupler in the 1K temperature change environment is greatly reduced, so its phase center stability is higher.

[0072] Table 1 Comparison results of delay stability analysis of orthomode coupler + frequency duplexer

[0073]

[0074]

[0075] For a binary star system, the simplest system is one where the two stars are exactly the same. However, if strict horizontal / vertical polarization is adopted, the layout of the transceiver channels at the backend cannot be exactly the same. The port of star A is connected to the transmit channel, and the corresponding port of star B must be connected to the receive channel, and vice versa. Therefore, this design cleverly utilizes the physical mirror relationship of 45° linear polarization to achieve the reciprocity of the transceiver ports, that is, as Figure 9In this case, the signal transmitted by satellite A's X01G is exactly corresponding to the receiving channel of satellite B's X02G in terms of polarization, and the signal transmitted by satellite B's X01G is exactly corresponding to the receiving channel of satellite A's X02G in terms of polarization. The same corresponding relationship also exists for other ports. Therefore, both X01G of satellite A and satellite B are connected to the K-band transmitting system, both X02G are connected to the K-band receiving system, both X03G are connected to the Ka-band transmitting system, and both X04G are connected to the Ka-band receiving system, enabling two-way communication between the two satellites. The system layouts of the two satellites are exactly the same, and mass production can be carried out.

[0076] To verify the design of the above KBR antenna, a physical object was fabricated. Figure 10 The test results of the physical product are given. From Figure 10 (a) to (d), it can be seen that the voltage standing wave ratios of the four ports of the KBR antenna are all less than 1.25; Figure 10 The isolation test results of the two orthogonally polarized ports in the K-band in (e) and (f) are less than -65 dB, and the isolation test results of the two orthogonally polarized ports in the Ka-band in (e) and (f) are less than -70 dB in the Ka-band; Figure 10 (g) and (h) are respectively the test results of the radiation patterns of the antenna in the K and Ka bands, which are consistent with the simulation. The far side lobes are all less than -20 dB, showing excellent electrical performance.

[0077] The parts not described in detail in the present invention belong to the common general knowledge of those skilled in the art.

[0078] The above are only the preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. For those skilled in the art, without creative efforts, several modifications and substitutions can be made to the present invention, and all these modifications and substitutions should be covered within the protection scope of the present invention.

Claims

1. A high time-delay stability antenna applied to an inter-satellite micrometer-level ranging system, characterized in that Comprising: a horn (1), an orthomode coupler (2), a frequency duplexer (3) and a connecting waveguide (4), wherein: the frequency duplexer (3) includes a first frequency duplexer and a second frequency duplexer; As a transmitting end or a receiving end, the mirror symmetry design of a dual-star antenna is adopted to achieve dual-star two-way dual-frequency communication; When acting as a receiving end, the horn (1) receives a linearly polarized signal and transmits the linearly polarized signal to the orthomode coupler (2); the orthomode coupler (2) separates the linearly polarized signal to obtain a horizontally polarized signal and a vertically polarized signal; the horizontally polarized signal is further separated by the first frequency duplexer to obtain K-band and Ka-band horizontally polarized signals, and the vertically polarized signal is separated by the second frequency duplexer and the connecting waveguide (4) to obtain K-band and Ka-band vertically polarized signals; When acting as a transmitting end, a transmitter sends K-band and Ka-band signals to two frequency duplexers respectively. The first frequency duplexer synthesizes the K-band and Ka-band signals into a horizontally polarized signal and transmits it to the horizontal polarization port of the orthomode coupler (2). The second frequency duplexer synthesizes the K-band and Ka-band signals into a vertically polarized signal and transmits it to the vertical polarization port of the orthomode coupler (2) through the connecting waveguide (4). The orthomode coupler (2) combines the horizontal polarization signal and the vertical polarization signal and transmits them to the horn (1), and realizes the radiation of K-band and Ka-band dual-linearly polarized electromagnetic waves through the horn.

2. The high-delay stability antenna applied to the inter-satellite micron-level ranging system according to claim 1, wherein: The horn (1) includes a mode conversion section (11), an optical wall shaping section (12), a horn mouth section (15), a uniaxial slot (13) and a choke ring (14); wherein: The mode conversion section (11) is a conical waveguide transformation section structure, which is used for the conversion of the main mode at the horn input port to the higher-order mode in the horn cavity to achieve the broadband matching of the horn; The inner cavity of the optical wall shaping section (12) is a curved surface formed by rotating a spline shaping curve by 360 degrees to achieve the high gain and high cross-polarization characteristics of the horn; A uniaxial slot (13) is arranged at the connection between the horn mouth section (15) and the optical wall shaping section (12) to improve the equalization of the radiation beam of the horn antenna and obtain a stable phase center; The top end of the horn mouth section (15) turns outwards to form a flanging (151) and an outer edge (152). On the flanging (151), a choke ring (14) with a depth of M is arranged at a position S from the outer edge (152) to suppress the current on the flanging (151) of the horn mouth surface.

3. The high-delay-stability antenna applied to the inter-satellite micron-level ranging system according to claim 2, wherein: S = λ0 / 8 to λ0 / 4, M = λ0 / 8 to λ0 / 2, where λ0 is the wavelength corresponding to the center frequency of the horn operation.

4. The high-delay stability antenna applied to the inter-satellite micron-level ranging system according to claim 1, wherein: The orthomode coupler (2) includes a coupling hub (21), a T-type synthesizer (22) and a turning waveguide (23), wherein: the coupling hub (21) includes four E-plane coupling rectangular waveguides; the T-type synthesizer (22) and the turning waveguide (23) synthesize the two pairs of opposite E-plane coupling rectangular waveguides into one waveguide and realize the conversion to a standard waveguide through a stepped transition; the turning waveguide (23) includes an E-plane rectangular turning waveguide and an H-plane rectangular turning waveguide, and a stepped transition is adopted at the connection between the E-plane rectangular turning waveguide and the H-plane rectangular turning waveguide.

5. The high-delay-stability antenna applied to the inter-satellite micrometer-level ranging system according to claim 4, wherein: The coupling hub (21) further includes a common-port circular waveguide and a stepped cylinder; wherein, four E-plane coupling rectangular waveguides are vertically symmetrically distributed around the common-port circular waveguide, and the stepped cylinder is located at the center of the common-port circular waveguide; the E-plane coupling rectangular waveguides achieve the separation of horizontal linear polarization and vertical linear polarization, and the stepped cylinder achieves the signal matching of the E-plane coupling rectangular waveguides.

6. The high-delay-stability antenna applied to the inter-satellite micrometer-level ranging system according to claim 1, wherein: The frequency duplexer (3) includes a T-branch (31), a K-band bandpass filter (32) and a Ka-band high-pass filter (33), wherein: The T-branch (31) is of a T-shaped structure, and the two side arms of the T-shaped structure are respectively connected to the K-band bandpass filter (32) and the Ka-band high-pass filter (33); the K-band filter adopts a low-order corrugated bandpass filter structure, and the Ka-band filter adopts a cut-off waveguide type filter structure.

7. The high-delay stability antenna applied to the inter-satellite micrometer-level ranging system according to claim 1, wherein: The mirror-image design of the dual-satellite antenna is specifically as follows: when realizing dual-satellite communication, the antennas of the two satellites are twisted by 45° in linear polarization to achieve the mirror image of the physical structures of the two satellites and the matching of the receiving and transmitting polarizations.

8. The high-delay-stability antenna applied to the inter-satellite micrometer-level ranging system according to claim 1, characterized in that: The horn has the characteristics of high efficiency, wide bandwidth, low cross polarization, simple structure and light weight.

9. The high-delay-stability antenna applied to the inter-satellite micron-level ranging system according to claim 1, characterized in that: The polarization isolation of the orthomode coupler is greater than 65 dB in both the K-band and the Ka-band.

10. The high-delay stability antenna applied to the inter-satellite micrometer-level ranging system according to claim 1, wherein: The frequency duplexer has high delay stability.

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