A combined transmitting-receiving isolation method for inhibiting self-excitation of a satellite navigation purification repeating signal

Abstract

The application discloses a kind of joint transmission isolation methods for inhibiting satellite navigation purification retransmission signal self-excitation, receiving antenna array uses anti-interference processing isolation, and space domain filtering is carried out to purification retransmission signal;Transmitting antenna is inhibited by optimizing antenna pattern to back lobe radiation, and directional isolation is carried out;Photoelectric conversion equipment is introduced on the propagation path between receiving antenna array and transmitting antenna, and radio frequency signal is converted into optical signal for long-distance space isolation.The method disclosed in the application, by the systematic transmission and reception isolation design of transmitting end, space propagation link and receiving end, using the cooperation of hardware and algorithm, high isolation degree that traditional method cannot be realized can be obtained under limited physical constraint.

Description

Technical Field

[0001] This invention belongs to the field of satellite navigation, and specifically relates to a joint transmission and reception isolation method for suppressing self-excitation of satellite navigation purification and forwarding signals. Background Technology

[0002] Satellite navigation retransmission technology does not require analysis of the received real signal. It simply adds delays and other operations according to mission instructions before radiating the retransmission signal to the target, altering the target receiver's observations and causing incorrect navigation and positioning results. This technology has become a key research focus for relevant research institutions both domestically and internationally. The core advantage of retransmission lies in the high consistency between the retransmission signal and the real satellite signal in terms of pseudocode, carrier phase, and message structure. This provides strong feasibility and stealth, effectively inducing target receivers equipped with anti-interference algorithms. Therefore, retransmission technology requires the system to obtain a clean reference signal through the receiving antenna array to maintain accurate synchronization. However, when the system transmits high-power retransmission signals to distant targets, they are easily leaked into its own receiving antenna array, forming a self-feedback loop. This severely pollutes the reference signal, destroys signal coherence, and leads to reduced or even failed retransmission performance. Therefore, achieving strict transmit-receive isolation is a necessary prerequisite for ensuring normal system operation and avoiding self-oscillation; its design directly determines the feasibility and actual performance of the retransmission technology.

[0003] Currently, common technical approaches to achieving transmit / receive isolation include spatial isolation, frequency isolation, time isolation, directional isolation, and digital processing isolation. Spatial isolation, by increasing the physical distance between transmitting and receiving antennas and utilizing path loss, is a simple and direct method, serving as a fundamental isolation technique. However, this method is limited by the system platform, and relying solely on distance sometimes fails to achieve the required isolation for transmitting high-power purified and relayed signals. Frequency isolation involves operating the transmitting and receiving signals in different frequency bands and suppressing leakage through filters, achieving high-frequency out-of-band suppression. However, because the relayed signal shares the same frequency as the actual navigation signal, it is unsuitable for satellite navigation countermeasures. Time isolation controls the transmission and reception in a time-division multiplexing manner to avoid simultaneous operation, theoretically preventing instantaneous coupling. However, in practice, time-division multiplexing leads to signal interruptions, disrupting the continuity and coherence of the navigation signal and failing to achieve high-precision purified and relayed effects. Polarization isolation involves using different polarizations for the transmitting and receiving antennas, providing an additional 20-30 dB of isolation. However, this method is limited by the purity of the antenna polarization, and the use of unconventional polarization in the relay signal introduces additional losses and reduces signal power when entering the target receiving antenna array. Directional isolation utilizes the directivity of directional antennas to make the transmitting and receiving main lobes face away from each other, naturally suppressing back radiation through the antenna pattern. However, due to engineering limitations, the antenna back lobe gain is not infinitely low, and signal leakage still exists. Digital processing isolation uses techniques such as adaptive nulling and beamforming at the receiver to create nulls in the direction of interference. However, this method is almost ineffective for feedback signals originating from the same source, as the other real signals completely overlap in the spatial, time, and frequency domains, making it difficult for the algorithm to distinguish them. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the self-excitation problem in satellite navigation purification and forwarding signals. It provides a joint transmission and reception isolation method to suppress self-excitation in satellite navigation purification and forwarding signals. Based on the idea of ​​"transmission suppression-optical isolation-reception cancellation", a systematic transmission and reception isolation design is carried out from the transmitter, space propagation link and receiver. The three are organically combined to jointly ensure the signal purity and coherence of the purification and forwarding system.

[0005] The present invention adopts the following technical solution:

[0006] An improved method for joint transmission and reception isolation to suppress self-excitation of satellite navigation purified relay signals is as follows: the receiving antenna array adopts anti-interference processing isolation and performs spatial filtering on the purified relay signal; the transmitting antenna suppresses back lobe radiation by optimizing the antenna pattern and performs directional isolation; and a photoelectric conversion device is introduced in the propagation path between the receiving antenna array and the transmitting antenna to convert the radio frequency signal into an optical signal for long-distance spatial isolation.

[0007] Furthermore, the receiving antenna array employs anti-interference processing to achieve digital processing isolation. Based on the real-time desired signal direction and the magnitude of the noise signal, the total signal output is minimized while ensuring the signal-to-noise ratio of the desired signal direction, and the corresponding adaptive weighting coefficients are calculated.

[0008] Furthermore, the steps for anti-interference isolation of the receiving antenna array are as follows:

[0009] Step 11: Establish the receiving antenna array signal model and calculate the sample covariance matrix:

[0010] Let the complex signal vector received by the receiving antenna array at time k be... for:

[0011]

[0012] In the above formula, It is the desired signal vector from the direction of the satellite, and its steering vector is , It is a relay signal vector originating from the direction of leakage from the transmitting antenna. It is the background noise vector;

[0013] Calculate the sample covariance matrix using K snapshots. :

[0014]

[0015] In the above formula, H represents the conjugate transpose of the original matrix;

[0016] Step 12: Construct an estimate of the covariance matrix of the forwarded signal plus noise. :

[0017]

[0018] In the above formula, E[⋅] represents the expected value. Indicates the noise variance. Represents the identity matrix;

[0019] Step 13: Solve for the maximum signal-to-interference-plus-noise ratio (MSIR) weight vector based on the maximum MSIR criterion. :

[0020]

[0021] In the above formula, These are the weighting coefficients, and Solve using Cholesky decomposition And perform normalization processing;

[0022] Step 14, Real-time anti-interference processing:

[0023] Will Used to receive data streams and adjust anti-interference output :

[0024]

[0025] Step 15, Tracking and Updates:

[0026] Determine whether to update the interactive window and ephemeris. If updating the interactive window is required, update the snapshot data K and return to step 11. If updating the ephemeris is required, update the guide vector. Then return to step 11.

[0027] Furthermore, a genetic algorithm is used as the optimization algorithm to optimize the target radiation pattern of the transmitting antenna, with constraints including the back lobe level, the 3dB beamwidth, and the maximum gain of the main lobe.

[0028] Furthermore, the steps for employing directional isolation for the transmitting antenna are as follows:

[0029] Step 21, confirm the array configuration and pattern formula:

[0030] Define the transmitting antenna as a planar array with m elements, and the element positions are as follows: Located on the z=0 plane, the array element amplitude is Phase vector to be optimized ;

[0031] Based on the transmitting antenna array structure, the array factor of the transmitting antenna is calculated as follows:

[0032]

[0033] In the above formula, k is the wave number. λ is the wavelength of the transmitted signal. Indicates azimuth. Indicates the pitch angle;

[0034] The power radiation pattern is represented as follows:

[0035]

[0036] Step 22, optimize the objective function:

[0037] The back lobe gain of the main target antenna is expressed as:

[0038]

[0039] In the above formula, The dorsal lobule region;

[0040] The main lobe gain of the constrained target antenna is expressed as:

[0041]

[0042] In the above formula, Main lobe region;

[0043] The constrained target beamwidth is defined as:

[0044]

[0045] In the above formula, for Planar beamwidth, for Planar beamwidth;

[0046] The fitness function is solved using a primary objective plus constraint form, with back lobe minimization as the primary objective and main lobe gain and beamwidth as constraints.

[0047]

[0048] In the above formula, The target value for main lobe gain. The target value for beamwidth. , , These are the weighting coefficients;

[0049] Step 23: Use a genetic algorithm to find the optimal solution:

[0050] Using phase as an individual, a group of individuals is randomly generated, and the fitness value of each individual is calculated. Individuals with good fitness values ​​are selected to generate the next generation. New individuals are generated through crossover operations. The generated offspring will partially or completely replace the parents and enter the next round of iteration. The previous steps are repeated until the fitness is lower than the set threshold.

[0051] Step 24: The phase values ​​obtained by solving the genetic optimization algorithm are used to simulate the radiation pattern, gradually approximating the index requirements until the optimal radiation pattern is obtained.

[0052] Furthermore, a method for achieving spatial isolation between the receiving antenna array and the transmitting antenna using photoelectric conversion is as follows:

[0053] The receiving antenna array and the transmitting optoelectronic conversion device are placed on the receiving vehicle platform, and the receiving optoelectronic conversion device and the transmitting antenna are placed on the transmitting vehicle platform.

[0054] The signal received by the receiving antenna array is transmitted to the transmitting optoelectronic conversion device. The transmitting optoelectronic conversion device is connected to the receiving optoelectronic conversion device through optical fiber cables. The signal received by the receiving optoelectronic conversion device is transmitted to the transmitting antenna.

[0055] The isolation distance D between the receiving vehicle platform and the transmitting vehicle platform is:

[0056]

[0057] In the above formula, This represents the actual output power of the power amplifier. To improve the power of the relay signal when it reaches the receiving antenna array, Where F is the maximum back lobe gain of the transmitting antenna, and F is the signal frequency.

[0058] The receiving vehicle platform and the transmitting vehicle platform are deployed according to the isolation distance, and the receiving antenna array must be located in the back lobe area of ​​the transmitting antenna.

[0059] The beneficial effects of this invention are:

[0060] The method disclosed in this invention, through systematic transmission and reception isolation design of the transmitter, space propagation link, and receiver, and by utilizing the synergy of hardware and algorithms, can achieve a high degree of isolation (up to 120dB or more) that is unattainable by traditional methods under limited physical constraints. This "fixed + adaptive" hybrid architecture can provide stable basic isolation and dynamically compensate for the isolation fluctuations caused by environmental multipath and platform motion, thereby maintaining reliable self-excitation suppression capability in complex environments. At the same time, this multi-level redundancy design also significantly improves the robustness and fault tolerance of the purification forwarding system, providing a key engineering foundation for the implementation of purification forwarding.

[0061] The method disclosed in this invention can improve the transmit-receive isolation of the satellite navigation purification and relay system to over 120dB, ensuring the high purity of the local reference signal and laying a key technical foundation for generating highly realistic and coherent purified and relay signals. Attached Figure Description

[0062] Figure 1 This is a flowchart illustrating the process of using anti-interference isolation for the receiving antenna array;

[0063] Figure 2 This is the signal flow diagram of the purification and forwarding system;

[0064] Figure 3 This is a simulated radiation pattern of the receiving antenna array after anti-interference processing;

[0065] Figure 4 This is the radiation pattern (1.2GHz) of the transmitting antenna with back lobe suppression measures.

[0066] Figure 5 This is the radiation pattern (1.2 GHz) of the transmitting antenna without back lobe suppression measures.

[0067] Figure 6 This is a diagram of a test scenario for spatial isolation of the propagation path. Detailed Implementation

[0068] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0069] Example 1: Due to inherent theoretical or engineering bottlenecks in any single isolation method, it is impossible to meet the stringent isolation requirements (typically >120dB) of the purified relay signal. This example discloses a joint transceiver isolation method to suppress self-excitation of satellite navigation purified relay signals. Taking a vehicle-mounted platform as an example, the receiving antenna array employs anti-interference processing isolation to perform spatial filtering on the purified relay signal; the transmitting antenna suppresses back lobe radiation by optimizing the antenna pattern, achieving directional isolation; and an optoelectronic conversion device is introduced along the propagation path between the receiving antenna array and the transmitting antenna to convert the radio frequency signal into an optical signal for long-distance spatial isolation.

[0070] The receiving antenna array employs anti-interference processing to achieve digital processing isolation. Based on the real-time desired signal direction and the magnitude of the noise signal, it minimizes the total signal output while ensuring the signal-to-noise ratio of the desired signal direction, and calculates the corresponding adaptive weighting coefficients.

[0071] like Figure 1 As shown, the steps for anti-interference isolation of the receiving antenna array are as follows:

[0072] Step 11: Establish the receiving antenna array signal model and calculate the sample covariance matrix:

[0073] Let the complex signal vector received by the receiving antenna array at time k be... for:

[0074]

[0075] In the above formula, It is the desired signal vector from the direction of the satellite, and its steering vector is It is related to the structure of the receiving antenna array elements and the directional gain of the elements. It is a relay signal vector originating from the direction of leakage from the transmitting antenna. It is the background noise vector;

[0076] Calculate the sample covariance matrix using K snapshots. :

[0077]

[0078] In the above formula, H represents the conjugate transpose of the original matrix;

[0079] Step 12: Construct an estimate of the covariance matrix of the forwarded signal plus noise. :

[0080] Since the ground level of satellite navigation signals is generally around -128dBm, its power is usually less than the purified relay signal transmitted by the system, that is:

[0081]

[0082] Therefore, use As an estimate of the covariance matrix of the forwarded signal plus noise:

[0083]

[0084] In the above formula, E[⋅] represents the expected value. Indicates the noise variance. Represents the identity matrix;

[0085] Step 13: Solve for the maximum signal-to-interference-plus-noise ratio (MSIR) weight vector based on the maximum MSIR criterion. (Optimal weight):

[0086] According to the maximum signal-to-interference-plus-noise ratio criterion, in the steering vector Given that the exact weighting coefficients are known, The optimal closed-form solution is:

[0087]

[0088] To avoid direct inversion, the weights are calculated... Transform into solving Solve using Cholesky decomposition And perform normalization:

[0089]

[0090] Step 14, Real-time anti-interference processing:

[0091] Will Used to receive data streams and adjust anti-interference output :

[0092]

[0093] Step 15, Tracking and Updates:

[0094] Determine whether to update the interactive window and ephemeris. If updating the interactive window is required, update the snapshot data K and return to step 11. If updating the ephemeris is required, update the guide vector. Then return to step 11.

[0095] Interactive window update: Discard old snapshot data, add new snapshot data, return to step 11 to recalculate the sample covariance matrix to track changes in the surrounding environment;

[0096] Steering Vector Update: Whenever there is a significant movement of the system platform or satellite orientation, the steering vector of the desired signal needs to be recalculated based on the new position and ephemeris information. Return to step 11 to recalculate.

[0097] Steps 11-15 will adapt the weight vector Constrained within the noise subspace, the steering weights of the desired signal are modified. Output signal. In this process, the relay signal component from the direction of the transmitting antenna is significantly suppressed, forming a null in that direction. During the calculation, the weights change as the direction of the relay signal changes, thus enabling real-time processing.

[0098] To optimize the target radiation pattern of a transmitting antenna, the shape of the beam pattern is adjusted to maximize the beam gain and minimize the back lobe gain in the target direction. In antenna arrays, this type of beamforming problem typically involves optimizing the array's weights or phase distribution to form a specific beam pattern. Genetic algorithms can effectively optimize these parameters by searching for optimal values ​​in the weight space. Therefore, this invention employs a genetic algorithm as the optimization algorithm to optimize the target radiation pattern of the transmitting antenna, with constraints including back lobe level, 3dB beamwidth, and maximum main lobe gain.

[0099] The steps for directional isolation of the transmitting antenna are as follows:

[0100] Step 21, confirm the array configuration and pattern formula:

[0101] Define the transmitting antenna as a planar array with m elements, and the element positions are as follows: Located on the z=0 plane, the array element amplitude is Phase vector to be optimized ;

[0102] Based on the transmitting antenna array structure, the array factor of the transmitting antenna is calculated as follows:

[0103]

[0104] In the above formula, k is the wave number. λ is the wavelength of the transmitted signal. Indicates azimuth. Indicates the pitch angle;

[0105] The power radiation pattern is represented as follows:

[0106]

[0107] Step 22, optimize the objective function:

[0108] The back lobe gain of the main target antenna is expressed as:

[0109]

[0110] In the above formula, The dorsal lobule region. , .

[0111] The main lobe gain of the constrained target antenna is expressed as:

[0112]

[0113] In the above formula, Main lobe region;

[0114] The constrained target beamwidth is defined as:

[0115]

[0116] In the above formula, for Planar beamwidth, for Planar beamwidth;

[0117] The fitness function is solved using a primary objective plus constraint form, with back lobe minimization as the primary objective and main lobe gain and beamwidth as constraints.

[0118]

[0119] In the above formula, The target value for main lobe gain. The target value for beamwidth. , , This is the weighting coefficient; set the base value according to the design requirements.

[0120] Step 23: Use a genetic algorithm to find the optimal solution:

[0121] Using phase as an individual, a set of individuals (solution) is randomly generated:

[0122]

[0123] Calculate the fitness value of each individual, select individuals with better fitness values ​​to generate the next generation, and generate new individuals through crossover operations (single-point or multi-point crossover).

[0124] Crossover simulates the process of biological inheritance, producing offspring by exchanging a portion of genes from parent individuals. Random mutations are applied to individual genes to increase population diversity and avoid getting trapped in local optima.

[0125] The generated offspring will partially or completely replace the parent generation, entering the next iteration, repeating the previous steps, until after K consecutive generations, the fitness no longer significantly improves and falls below a set threshold, i.e.:

[0126]

[0127] In the above formula, Value 10 -4 ~10 -6 .

[0128] Step 24: The phase values ​​obtained by solving the problem using the genetic optimization algorithm in the HFSS simulation software are used to simulate the radiation pattern, gradually approximating the target requirements until the optimal radiation pattern is obtained.

[0129] The method of achieving spatial isolation between the receiving antenna array and the transmitting antenna using photoelectric conversion is as follows:

[0130] The system places the receiving antenna array, purification and transponder exciter, and photoelectric conversion equipment (transmitter) on the receiving vehicle platform, and places the photoelectric conversion equipment (receiver), power amplifier, and transmitting antenna on the transmitting vehicle platform.

[0131] The receiving antenna array receives satellite navigation signals and performs reception, filtering, noise reduction, separation, and calibration processes using phased array beamforming technology according to control commands to separate satellite signals. The separated single-satellite signals are then transmitted to the purification and transponder exciter in the form of optical signals.

[0132] The purification and retransmission exciter receives the separated individual satellite signals and extracts information from each signal. Based on the mission intent and target state, the purification and retransmission exciter issues control commands and performs mathematical simulation calculations such as multi-channel retransmission delay and frequency. Based on the calculation results, it adjusts parameters such as delay, frequency, and Doppler of the individual satellite signals to generate false navigation signals. After up-conversion processing, these signals are transmitted as electrical signals to the photoelectric conversion device (transmitter).

[0133] The photoelectric conversion equipment (transmitter) receives, purifies, and transmits the signal. Through power amplification and photoelectric conversion, it converts the transmitted signal into optical form and transmits it to the photoelectric conversion equipment (receiver). The optical signal is transmitted by connecting the photoelectric conversion equipment of the two vehicles using fiber optic cables.

[0134] The transmit / receive isolation distance between the receiving vehicle and the transmitting vehicle is calculated and determined based on parameters such as the output power of the power amplifier, the maximum gain of the back lobe of the transmitting antenna, and the anti-interference limit of the receiving antenna array.

[0135] The formula for calculating the transmission and reception isolation distance between the receiving vehicle and the transmitting vehicle is:

[0136]

[0137] In the above formula, This represents the actual output power (dBm) of the power amplifier. This represents the maximum back lobe gain of the transmitting antenna. To improve the power of the relay signal reaching the receiving antenna array, the required signal power is specified here to ensure that the relay signal emitted by the transmitter does not affect the normal reception of satellite navigation signals by the receiving antenna array of the receiver vehicle. This mainly includes the following situations:

[0138] Scenario 1:

[0139] The saturation power of the receiving antenna array is crucial. When the transmitted signal power is too strong, the low-noise amplifier (LNA) and analog-to-digital converter (ADC) of the receiving antenna array will enter the nonlinear region or directly saturate. At this point, the signal is severely clipped and distorted, and the useful signal is completely overwhelmed, making interference suppression impossible. Therefore, it is necessary to meet the following requirements: .

[0140] The receiving antenna array can handle the minimum power.

[0141] For the anti-interference module of the receiving antenna array to function properly, it needs to identify its characteristics based on the energy of the relayed signal. The higher the signal energy entering each channel, the more pronounced its spatial characteristics. When the signal is weak, the spatial characteristics are not obvious, which leads to a poor match between the calculated signal spatial characteristics and the actual spatial characteristics, resulting in a poor anti-interference (cancellation) effect. To ensure effective anti-interference, it is necessary to ensure that the relayed signal can be distinguished from the receiver's noise floor.

[0142] The receiver noise floor is defined as the noise power level intercepted in the passband of the receiver at a temperature of 290K (i.e., 17℃). Its calculation formula is as follows:

[0143]

[0144] In the above formula, PN represents the noise floor, measured in dBm; K is the Boltzmann constant, typically K = 1.38 * 10^- ... -23 (J / K); T represents temperature, generally T=290K (i.e., room temperature 17℃); B represents signal bandwidth. The maximum bandwidth of GPS / BDS signal is 32.736MHz. Considering redundancy, the bandwidth is taken as B=33*10 6 (Hz).

[0145] The receiver noise floor can be calculated as follows:

[0146]

[0147] Therefore, considering that the receiver noise floor is -100dBm, it is recommended that the minimum arrival power of the relay signal be -90dBm, which is at least 10dB higher than the receiver noise floor. The relay signal should be about 1.5 bits higher than the noise floor in the digital domain. This will ensure that the training results of the relay signal characteristics are different from the noise and that the anti-interference is effective.

[0148] Scenario 2:

[0149] When the arriving power of the relay signal is lower than the receiver noise floor when it reaches the receiving antenna array, that is... At this point, although the receiving antenna array cannot perform anti-interference processing on the purified and relayed signal, the relayed signal is already below the receiver's noise floor, so it will not have a significant impact on the normal operation of the receiving antenna array. In this case, digital processing isolation at the receiving end is not required; the directional isolation at the transmitting end and the spatial isolation of the propagation path are sufficient to meet the isolation requirements for purification and relay.

[0150] This is the path loss for radio wave propagation, and its value is related to factors such as isolation distance, signal frequency, and environmental information related to radio wave propagation.

[0151]

[0152] In the above formula, F is the signal frequency (MHz) and D is the isolation distance (km).

[0153] The transmit / receive isolation distance D can be calculated using the above formula:

[0154]

[0155] Calculate the isolation distance D based on the different power levels reached, and determine the length of the fiber optic cable based on the isolation distance.

[0156] The vehicle-mounted platform is deployed according to the calculated transmit / receive isolation distance, and the receiving antenna array must be located in the back lobe region of the transmitting antenna. Fiber optic cables are connected, and the photoelectric conversion equipment (receiving end) receives the optical signal transmitted through the fiber optic cable. After photoelectric conversion, the purified and forwarded signal is transmitted to the power amplifier in the form of an electrical signal. After amplification, the high-power purified and forwarded signal is radiated outward through the transmitting antenna.

[0157] The method of this invention implements a systematic transmit-receive isolation design for the transmitter, space propagation link, and receiver, ensuring that the system can achieve the high degree of isolation required for purification and forwarding under limited physical constraints.

[0158] like Figure 2As shown, the purification and retransmission system places the receiving antenna array, purification and retransmission exciter, and photoelectric conversion device (transmitter) on the receiving vehicle platform, and places the photoelectric conversion device (receiver), power amplifier, and transmitting antenna on the transmitting vehicle platform.

[0159] (1) Digital processing isolation at the receiving end:

[0160] The receiving antenna array structure adopts a spherical cap + cylindrical form, with a total of 552 antenna elements, enabling narrow-beam, high-gain directional reception and extraction of satellite navigation signals. The three-dimensional Cartesian coordinates of each array element in the global coordinate system are determined based on the antenna structure. The element pattern function of each array element is obtained based on electromagnetic simulation data. That is, the k-th array element in the direction The gain value.

[0161] In the HFSS software, the desired signal direction is set to an elevation angle of 20 degrees and an azimuth angle of 0 degrees. The purified relay signal direction is set to an elevation angle of 20 degrees and an azimuth angle of 90 degrees. The desired signal steering vector is then calculated. Based on the anti-interference processing steps, the simulation radiation pattern of the receiving antenna array after anti-interference processing can be obtained, as shown below. Figure 3 As shown in the figure. The red line is the anti-interference main polarization pattern, the blue line is the anti-interference cross-polarization pattern, and the green line is the composite pattern. It can be clearly seen that at an azimuth angle of 0 degrees, the desired signal direction has a maximum gain of 26dB, and at an azimuth angle of 90 degrees, there is a significant null of -72dB in this direction, which can effectively suppress the purified relay signal in this direction.

[0162] (2) Transmitter directional isolation:

[0163] The transmitting antenna is a planar array antenna with two rows of elements arranged alternately, four elements per row, for a total of eight elements. The spacing between elements in the same row is 9mm. Based on practical engineering requirements, the transmitting antenna has a 3dB beamwidth > 30°, a maximum main lobe gain > 10dB, and a back lobe range of 180° ± 60°. Under these constraints, minimizing the back lobe gain is the criterion for solving the fitness function:

[0164]

[0165] The optimal phase value under the condition of minimizing back lobe gain is solved using a genetic algorithm according to the fitness function, and the antenna radiation pattern after back lobe suppression is obtained by simulation based on the phase value (taking 1.2 GHz frequency as an example). Figure 4 As shown.

[0166] Compare it with the antenna pattern of an antenna without back lobe suppression measures (e.g.) Figure 5As shown in the comparison, it can be seen that the maximum back lobe gain of the antenna without suppression measures is -10dB, while the back lobe gain of the antenna with suppression measures is -16dB, with a suppression effect of 6dB. The smaller the back lobe range, the more obvious the antenna back lobe gain suppression effect.

[0167] (3) Spatial isolation of transmission paths:

[0168] Taking the B3 signal (frequency 1268.52MHz) as an example, actual engineering requirements dictate that the maximum power of the purified relay signal output from the power amplifier should be 30dBm, and the maximum back lobe gain of the transmitting antenna should be -16dB. According to the receiving antenna array design, when the anti-interference function is enabled, the saturation power is -70dBm, and the minimum power that the anti-interference function can handle is -100dBm. Based on the formula for calculating the transmit / receive isolation distance, we can obtain:

[0169] ①When At that time, the transmit / receive isolation distance can be calculated as follows:

[0170]

[0171] ②When At that time, the transmit / receive isolation distance can be calculated as follows:

[0172]

[0173] Considering the ease of engineering implementation, it is recommended that the transmission and reception isolation distance between the receiving vehicle platform and the transmitting vehicle platform be set to 0.31km~3.02km. Fiber optic cables should be laid according to the calculated isolation distance, with 500-meter sections per reel. Equipping 1~4 reels is sufficient to ensure the high isolation requirements of the purification and relay system in different scenarios.

[0174] In actual testing, such as Figure 6 As shown, the distance between the receiving vehicle and the transmitting vehicle is 339m. The power amplifier outputs a 30dBm B3 band purified relay signal (frequency 1268.52MHz). The anti-interference function of the receiving antenna array is enabled, and the receiving antenna is positioned within 180°±20° of the back lobe of the transmitting antenna. After the transmitting antenna outputs a signal, the receiving antenna array receives navigation signals normally, the built-in receiver can locate normally, and the purified relay signal can be transmitted normally. The test receiver can receive the purified signal and locate the wrong position. Disabling the anti-interference function of the receiving antenna array significantly reduces the satellite carrier-to-noise ratio received by the receiving antenna array, and may even result in the inability to locate. The output of the purified relay signal is also affected. Using a transmitting antenna without back lobe suppression can also lead to abnormal satellite reception by the receiving antenna array and the inability of the purified relay signal to deceive the test receiver.

[0175] In summary, the method of this invention employs anti-interference processing for the receiving antenna array and directional isolation for the transmitting antenna. The receiving and transmitting antennas are arranged according to the calculated isolation distance. Through combination optimization, the high isolation requirement (above 120dB) for purification and forwarding can be met. The multi-level redundancy mechanism improves the robustness of the purification and forwarding system in complex electromagnetic environments, providing an engineering foundation for the realization of high-fidelity and high-coherence purification and forwarding signals.

Claims

1. A joint transmit / receive isolation method for suppressing self-excitation of satellite navigation purification and relay signals, characterized in that: The receiving antenna array employs anti-interference isolation and performs spatial filtering on the purified relay signal; the transmitting antenna suppresses back lobe radiation by optimizing the antenna pattern, thus achieving directional isolation; and an optoelectronic conversion device is introduced along the propagation path between the receiving antenna array and the transmitting antenna to convert the radio frequency signal into an optical signal for long-distance spatial isolation.

2. The joint transmit / receive isolation method for suppressing self-excitation of satellite navigation purification and forwarding signals according to claim 1, characterized in that: The receiving antenna array employs anti-interference processing to achieve digital processing isolation. Based on the real-time desired signal direction and the magnitude of the noise signal, it minimizes the total signal output while ensuring the signal-to-noise ratio of the desired signal direction, and calculates the corresponding adaptive weighting coefficients.

3. The joint transmit / receive isolation method for suppressing self-excitation of satellite navigation purification and forwarding signals according to claim 1, characterized in that, The steps for anti-interference isolation of the receiving antenna array are as follows: Step 11: Establish the receiving antenna array signal model and calculate the sample covariance matrix: Let the complex signal vector received by the receiving antenna array at time k be... for: In the above formula, It is the desired signal vector from the direction of the satellite, and its steering vector is , It is a relay signal vector originating from the direction of leakage from the transmitting antenna. It is the background noise vector; Calculate the sample covariance matrix using K snapshots. : In the above formula, H represents the conjugate transpose of the original matrix; Step 12: Construct an estimate of the covariance matrix of the forwarded signal plus noise. : In the above formula, E[⋅] represents the expected value. Indicates the noise variance. Represents the identity matrix; Step 13: Solve for the maximum signal-to-interference-plus-noise ratio (MSIR) weight vector based on the maximum MSIR criterion. : In the above formula, These are the weighting coefficients, and Solve using Cholesky decomposition And perform normalization processing; Step 14, Real-time anti-interference processing: Will Used to receive data streams and adjust anti-interference output : Step 15, Tracking and Updates: Determine whether to update the interactive window and ephemeris. If updating the interactive window is required, update the snapshot data K and return to step 11. If updating the ephemeris is required, update the guide vector. Then return to step 11.

4. The joint transmit / receive isolation method for suppressing self-excitation of satellite navigation purification and forwarding signals according to claim 1, characterized in that: A genetic algorithm is used as the optimization algorithm to optimize the target radiation pattern of the transmitting antenna. The constraints are the back lobe level, the 3dB beamwidth, and the maximum gain of the main lobe.

5. The joint transmit / receive isolation method for suppressing self-excitation of satellite navigation purification and forwarding signals according to claim 1, characterized in that, The steps for directional isolation of the transmitting antenna are as follows: Step 21, confirm the array configuration and pattern formula: Define the transmitting antenna as a planar array with m elements, and the element positions are as follows: Located on the z=0 plane, the array element amplitude is Phase vector to be optimized ; Based on the transmitting antenna array structure, the array factor of the transmitting antenna is calculated as follows: In the above formula, k is the wave number. λ is the wavelength of the transmitted signal. Indicates azimuth. Indicates the pitch angle; The power radiation pattern is represented as follows: Step 22, optimize the objective function: The back lobe gain of the main target antenna is expressed as: In the above formula, The dorsal lobule region; The main lobe gain of the constrained target antenna is expressed as: In the above formula, Main lobe region; The constrained target beamwidth is defined as: In the above formula, for Planar beamwidth, for Planar beamwidth; The fitness function is solved using a primary objective plus constraint form, with back lobe minimization as the primary objective and main lobe gain and beamwidth as constraints. In the above formula, The target value for main lobe gain. The target value for beamwidth. , , These are the weighting coefficients; Step 23: Use a genetic algorithm to find the optimal solution: Using phase as an individual, a group of individuals is randomly generated, and the fitness value of each individual is calculated. Individuals with good fitness values ​​are selected to generate the next generation. New individuals are generated through crossover operations. The generated offspring will partially or completely replace the parents and enter the next round of iteration. The previous steps are repeated until the fitness is lower than the set threshold. Step 24: The phase values ​​obtained by solving the genetic optimization algorithm are used to simulate the radiation pattern, gradually approximating the index requirements until the optimal radiation pattern is obtained.

6. The joint transmit / receive isolation method for suppressing self-excitation of satellite navigation purification and forwarding signals according to claim 1, characterized in that, The method of achieving spatial isolation between the receiving antenna array and the transmitting antenna using photoelectric conversion is as follows: The receiving antenna array and the transmitting optoelectronic conversion device are placed on the receiving vehicle platform, and the receiving optoelectronic conversion device and the transmitting antenna are placed on the transmitting vehicle platform. The signal received by the receiving antenna array is transmitted to the transmitting optoelectronic conversion device. The transmitting optoelectronic conversion device is connected to the receiving optoelectronic conversion device through optical fiber cables. The signal received by the receiving optoelectronic conversion device is transmitted to the transmitting antenna. The isolation distance D between the receiving vehicle platform and the transmitting vehicle platform is: In the above formula, This represents the actual output power of the power amplifier. To improve the power of the relay signal when it reaches the receiving antenna array, Where F is the maximum back lobe gain of the transmitting antenna, and F is the signal frequency. The receiving vehicle platform and the transmitting vehicle platform are deployed according to the isolation distance, and the receiving antenna array must be located in the back lobe area of ​​the transmitting antenna.

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