A method for processing signals of a secondary radar system and a secondary radar system

Abstract

The present invention belongs to the technical field of secondary radars, and discloses a signal processing method and a secondary radar system for a secondary radar system. At the signal transmitting end, the BPSK interrogation signal is subjected to initial phase modulation and amplitude modulation, and the modulated BPSK interrogation signal is sent to the signal receiving end through frequency control array technology; at the signal receiving end, a local code matching model is established, the local code is matched by using the local code matching model, the matched local code is subjected to correlation detection with the baseband signal, and the final result is output. While retaining the basic functions of the secondary radar, the problems of energy loss and system detection failure caused by waveform destruction when the frequency control array technology is introduced into the secondary radar are solved, so that the finally obtained secondary radar system based on the frequency diversity array has the characteristics of a frequency control array, thereby improving the information security of the secondary radar.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary radar, and more particularly, to a signal processing method for a secondary radar system and a secondary radar system. Background Art

[0002] In 2006, at the IEEE International Radar Conference, Antonik first proposed the concept of Frequency Diverse Array (FDA). The FDA adds a very small frequency offset (the added frequency offset is much smaller than the carrier frequency) to each transmitting element according to a specific rule, making the radar beam pointing have two-dimensional correlation characteristics (range and angle). Currently, the research on the FDA in China has just started, and the application directions based on the FDA are the focus of domestic and foreign researchers.

[0003] Secondary surveillance radar has developed rapidly since the 1960s and has been introduced into the air traffic control field. It has now become a conventional means of global air traffic control and is widely used in military and civilian fields. With the increasingly rich application requirements, it is necessary to continuously expand the functions of secondary surveillance radar and improve its performance. Therefore, domestic and foreign researchers are actively seeking new systems and technologies to be applied to secondary radar in order to obtain performance improvements and breakthroughs.

[0004] In view of this, the present application is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a method that combines secondary radar technology with FDA technology, while retaining the basic functions of secondary radar, solves the problems of energy loss and system detection failure caused by waveform destruction when introducing FDA technology into secondary radar, and makes the finally obtained secondary radar system based on frequency diversity array have FDA characteristics, thereby improving the information security of secondary radar.

[0006] The present invention is achieved through the following technical solutions:

[0007] On the one hand, the present invention provides a signal processing method for a secondary radar system, including the following steps: at the signal transmitting end, perform initial phase modulation and amplitude modulation on the BPSK interrogation signal, and send the modulated BPSK interrogation signal to the signal receiving end through FDA technology; at the signal receiving end, establish a local code matching model, use the local code matching model to match the local code, perform correlation detection on the matched local code and the baseband signal, and output the final result.

[0008] Further, before performing initial phase modulation and amplitude modulation on the BPSK interrogation signal, the following steps are included: perform BPSK modulation on the signal to be transmitted to obtain multiple BPSK interrogation signals.

[0009] Further, after the BPSK interrogation signal is subjected to initial phase modulation and amplitude modulation, the following steps are included: up-converting the BPSK interrogation signal that has been subjected to initial phase modulation and amplitude modulation.

[0010] Further, the modulated BPSK interrogation signal is sent to the signal receiving end through the frequency control array technology, specifically: an array antenna is used to send the up-converted BPSK interrogation signal to the signal receiving end through the frequency control array technology.

[0011] Further, the initial phase modulation of the BPSK interrogation signal includes the following steps: using simulation technology to simulate the carrier signal synthesized by the frequency control array technology; obtaining the variation law of the signal-to-noise ratio of the carrier signal over time; presetting a time period, and selecting the signal initial phase at the maximum value of the carrier signal within the preset time period; performing initial phase modulation on the BPSK interrogation signal according to the signal initial phase.

[0012] Further, before establishing the local code matching model, the following steps are included: down-converting the received BPSK interrogation signal to obtain a baseband signal.

[0013] Further, the matching of the local code using the local code matching model is specifically: substituting the local code generated by the signal receiving end and the prior parameters of the frequency control array into the local code matching model to obtain the matched local code.

[0014] Further, the expression of the local code matching model is: m' bpsk = m bpsk Φ; where m' bpsk represents the matched local code, m bpsk represents the local code generated by the signal receiving end, and Φ represents the sinc function that affects the matching between the local code generated by the signal receiving end and the BPSK interrogation signal received by the signal receiving end.

[0015] On the other hand, the present invention provides a secondary radar system, including a signal transmitting end and a signal receiving end; the signal transmitting end includes multiple signal processing branches, and each signal processing branch includes: a primary phase modulation module for performing primary phase modulation on a BPSK interrogation signal; an amplitude modulation module for performing amplitude modulation on the BPSK interrogation signal; a signal transmitting module for transmitting the modulated BPSK interrogation signal to the signal receiving end through frequency control array technology; the signal receiving end includes: a model construction module for establishing a local code matching model; a local code matching module for matching the local code using the local code matching model; a pulse interval and number detector for performing correlation detection on the matched local code and the baseband signal and outputting a final result; the primary phase modulation module includes: a carrier signal simulation unit for simulating a carrier signal synthesized by frequency control array technology using simulation technology; a calculation unit for calculating the variation law of the signal-to-noise ratio of the carrier signal over time; a primary phase selection unit for selecting the signal primary phase at the maximum value of the carrier signal within a preset time period; a primary phase modulation unit for performing primary phase modulation on the BPSK interrogation signal according to the signal primary phase; the expression of the local code matching model is: m' bpsk = m bpsk Φ; where m' bpsk represents the matched local code, m bpsk represents the local code generated by the signal receiving end, and Φ represents the sinc function that affects the matching between the local code generated by the signal receiving end and the BPSK interrogation signal received by the signal receiving end.

[0016] Further, the signal transmitting end further includes a BPSK modulation module, the BPSK module is connected to the multiple signal processing branches, and the BPSK module is used for performing BPSK modulation on the signal to be transmitted to obtain multiple BPSK interrogation signals; each signal processing branch further includes an up-conversion module, the input end of the up-conversion module is connected to the output end of the amplitude modulation module, and the up-conversion module is used for performing up-conversion on the BPSK interrogation signal that has undergone primary phase modulation and amplitude modulation; the signal receiving end further includes a signal receiving module and a down-conversion module, the signal receiving module is used for receiving the BPSK interrogation signals sent by the multiple signal processing branches, and the down-conversion module is used for performing down-conversion on the received BPSK interrogation signals to obtain baseband signals.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: On the one hand, at the transmitting end of the secondary radar system, simulation technology is used to simulate the carrier signal synthesized by the frequency control array, find the highest energy point of the carrier signal, determine the initial phase position of the transmitted signal, and use the determined initial phase position to continuously modulate different initial phase positions of the continuous carrier signal in the early stage, so that the transmitted beam has the characteristics of the frequency control array (making the transmitted beam a beam with coupled direction and distance), thereby ensuring that the energy loss of the finally obtained transmitted signal is minimized; On the other hand, at the receiving end of the secondary radar system, a local code matching preprocessing algorithm is proposed. The traditional local code and the preprocessing algorithm are used for operation to obtain the finally matched local code, making the information of the secondary radar system more secure and not easily captured and decoded by other receiving systems, improving the detection performance and stability of the secondary radar system. Overall, the present invention combines the frequency control array technology with the secondary radar technology, and by processing the signal to be transmitted and the local code at the receiving end and the transmitting end respectively, solves the problems of energy loss and system detection failure caused by waveform damage when introducing the frequency control array technology into the secondary radar, and ensures the feasibility of the secondary radar system based on the frequency control array technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 Schematic diagram of the signal processing method flow of the secondary radar system provided in Embodiment 1 of the present invention;

[0020] Figure 2 Schematic diagram of the structure of the secondary radar system provided in Embodiment 1 of the present invention

[0021] Figure 3 Schematic diagram of the method for determining the initial phase of the carrier modulation of the secondary radar system provided in Embodiment 1 of the present invention;

[0022] Figure 4 Schematic diagram of the signal-to-noise ratio varying with time and the position of the selected initial phase provided in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the embodiments and the drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not used to limit the present invention.

[0024] Embodiment 1

[0025] A signal processing method for a secondary radar system provided in this embodiment combines secondary radar technology with frequency control array technology. The purpose is to retain the basic functions of the secondary radar while solving the problems of energy loss and system detection failure caused by waveform destruction when introducing the frequency control array technology into the secondary radar, so that the finally obtained secondary radar system based on the frequency diversity array has the characteristics of a frequency control array, thereby improving the information security of the secondary radar. The implementation process of this method is as Figure 1 shown, and specifically includes the following steps:

[0026] Step 1: At the signal transmitting end, perform BPSK modulation on the signal to be transmitted to obtain multiple BPSK interrogation signals. As Figure 2 shown, the signal to be transmitted (such as 0110...) becomes a BPSK interrogation signal in the form of -1, 1, 1,... after BPSK modulation. The BPSK interrogation signal is split to obtain multiple BPSK interrogation signals.

[0027] Step 2: For each BPSK interrogation signal, perform initial phase modulation and amplitude modulation to ensure that the energy loss of the final transmitted signal is minimized.

[0028] Specifically, for the initial phase modulation, it is necessary to use simulation technology in advance to determine the lowest point of energy loss of the transmitted signal synthesized by the frequency control array, so as to determine the initial phase, which can minimize the energy loss of the signal transmitted by this system. The specific simulation method is as Figure 3 shown: The transmitted signal is continuously transmitted over time t. Within 7.2 us at each selected time point, the transmitted waveform is not a conventional single-frequency signal, but is replaced by the BPSK interrogation signal of the modulated secondary radar. Calculate the change of the signal-to-noise ratio of the transmitted waveform over time through formulas, and select the signal initial phase at the maximum value within a selected period of time as the carrier modulation initial phase of the system, as Figure 4 the selected position in is the position of the red vertical line. This can minimize the signal energy loss to the greatest extent. Summarize the above initial phase modulation method into the implementation steps as:

[0029] Step 2.1: Use simulation technology to simulate the carrier signal synthesized by the frequency control array technology.

[0030] Step 2.2: Obtain the variation law of the signal-to-noise ratio of the carrier signal over time.

[0031] Step 2.3: Preset a time period, and select the signal initial phase at the maximum value of the carrier signal within the preset time period.

[0032] Step 2.4: Perform initial phase modulation on the BPSK interrogation signal according to the signal initial phase.

[0033] Step 3: For each path of the bpsk interrogation signal that has undergone initial phase modulation and amplitude modulation, perform upconversion on it.

[0034] Step 4: For each path of the upconverted bpsk interrogation signal, use an array antenna to send the upconverted bpsk interrogation signal to the signal receiving end through frequency control array technology. The carrier of each antenna differs by a frequency offset Δf in sequence, that is, the frequency control array will use linear frequency offset.

[0035] Step 5: At the signal receiving end, receive the bpsk interrogation signal through the array antenna.

[0036] Step 6: For the received bpsk interrogation signal, use the traditional downconversion method to perform downconversion using the carrier frequency fc to obtain the baseband signal.

[0037] Step 7: To solve the problem of system detection failure caused by waveform destruction, establish a local code matching algorithm. Use the local code matching algorithm to match the local code, perform correlation detection on the matched local code and the baseband signal, and output the final result, thereby solving the problems of energy loss and system detection failure caused by waveform destruction when introducing the frequency control array technology into secondary radar.

[0038] Since this embodiment uses a frequency control array to transmit interrogation signals at the signal transmitting end, if the dpsk interrogation signal is not processed at the signal receiving end and the traditional detection algorithm is used, there will be a problem of signal distortion, and the demodulation recognition probability will be greatly reduced and unstable. Therefore, this embodiment proposes a local code matching algorithm, which can greatly improve the signal detection success probability under prior conditions. The main derivation process of this method is described as follows.

[0039] The expression of the received signal at the receiver is: In formula (1), y n (t) represents the signal waveform received by the receiver after being transmitted through space by each transmitting antenna element (the transmitting end is an array antenna with the number of antennas being n), A represents the signal amplitude, s p (t) represents pulse modulation, s bpsk (t) represents bpsk modulation, f n (t - τ n ) represents the delay of the signal in space transmission. Expanding formula (1) can obtain: (2), in formula (2), f c represents the carrier frequency, R represents the spatial transmission distance of the transmitted signal, c represents the speed of light, d represents the distance between the elements of the array antenna of the transmitter, and sinθ represents the angle between the transmitted signal and the antenna. As shown in formula (2), the main reason affecting the detection and recognition performance is that an influence term of a sinc function is added at the signal level, that is Finally, it results in the mismatch between the local code and the received signal. Therefore, in order to eliminate this influence, it is necessary to perform matching processing on the local code. So finally, the local code at the receiving end needs to use the formula m' bpsk = m bpsk Φ(4) to process the local code, that is, substitute the local code generated by the signal receiving end and the prior parameters of the frequency control array into the local code matching model to obtain the matched local code. In formula (4), m' bpsk represents the matched local code, m bpsk represents the local code generated by the signal receiving end, and Φ represents the sinc function that affects the matching between the local code generated by the signal receiving end and the bpsk interrogation signal received by the signal receiving end.

[0040] In summary, a signal processing method for a secondary radar system provided in this embodiment, on the one hand, at the transmitting end of the secondary radar system, simulation technology is used to simulate the carrier signal synthesized by the frequency control array, find the highest energy point of the carrier signal, determine the initial phase position of the transmitted signal, and use the determined initial phase position to continuously modulate different initial phase positions of the continuous carrier signal in the early stage, so that the transmitted beam has the characteristics of the frequency control array (making the transmitted beam a beam with coupled direction and distance), thereby ensuring that the energy loss of the finally obtained transmitted signal is minimized; on the other hand, at the receiving end of the secondary radar system, a local code matching preprocessing algorithm is proposed, and the traditional local code and the preprocessing algorithm are used for operation to obtain the finally matched local code, making the information of the secondary radar system more secure and not easily captured and decoded by other receiving systems, and improving the detection performance and stability of the secondary radar system. Overall, the present invention combines the frequency control array technology with the secondary radar technology, and solves the problems of energy loss and system detection failure caused by waveform damage when introducing the frequency control array technology into the secondary radar by processing the signal to be transmitted and the local code at the receiving end and the transmitting end respectively, ensuring the feasibility of the secondary radar system based on the frequency control array technology.

[0041] Embodiment 2

[0042] Corresponding to Embodiment 1, this embodiment provides a secondary radar system, including a signal transmitting end and a signal receiving end.

[0043] Among them, the signal transmitting end includes a bpsk modulation module and multiple signal processing branches. The bpsk module is connected to the multiple signal processing branches, and the bpsk module is used to perform bpsk modulation on the signal to be transmitted to obtain multiple bpsk interrogation signals; each signal processing branch includes:

[0044] An initial phase modulation module, which is used to perform initial phase modulation on the bpsk interrogation signal.

[0045] An amplitude modulation module for amplitude modulating the BPSK interrogation signal; a signal transmitting module for transmitting the modulated BPSK interrogation signal to the signal receiving end through the frequency control array technology.

[0046] An up-conversion module, the input end of the up-conversion module is connected to the output end of the amplitude modulation module, and the up-conversion module is used for up-converting the BPSK interrogation signal that has undergone initial phase modulation and amplitude modulation.

[0047] In addition, the signal receiving end includes:

[0048] A signal receiving module for receiving the BPSK interrogation signals sent by multiple signal processing branches.

[0049] A down-conversion module for down-converting the received BPSK interrogation signal to obtain a baseband signal.

[0050] A model construction module for establishing a local code matching model, and the expression of the local code matching model is: m' bpsk = m bpsk Φ; where m' bpsk represents the matched local code, m bpsk represents the local code generated by the signal receiving end, and Φ represents the sinc function that affects the matching between the local code generated by the signal receiving end and the BPSK interrogation signal received by the signal receiving end.

[0051] A local code matching module for matching the local code using the local code matching model; a pulse interval and number detector for performing correlation detection on the matched local code and the baseband signal and outputting the final result. Among them, the initial phase modulation module includes: a carrier signal simulation unit for simulating the carrier signal synthesized by the frequency control array technology using simulation technology; a calculation unit for calculating the variation law of the signal-to-noise ratio of the carrier signal over time; an initial phase selection unit for selecting the signal initial phase at the maximum value of the carrier signal within a preset time period; an initial phase modulation unit for performing initial phase modulation on the BPSK interrogation signal according to the signal initial phase.

[0052] The specific embodiments described above have further detailed the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A signal processing method for a secondary radar system, characterized in that, it includes the following steps: At the signal transmitting end, perform initial phase modulation and amplitude modulation on the BPSK interrogation signal, and send the modulated BPSK interrogation signal to the signal receiving end through the frequency control array technology; At the signal receiving end, establish a local code matching model, substitute the local code generated by the signal receiving end and the prior parameters of the frequency control array into the local code matching model to obtain the matched local code, and perform correlation detection on the matched local code and the baseband signal to output the final result; wherein, The expression of the local code matching model is: m' bpsk = m bpsk Φ; where m' bpsk represents the local code after matching, m bpsk represents the local code generated by the signal receiving end, and Φ represents the sinc function that affects the matching between the local code generated by the signal receiving end and the bpsk interrogation signal received by the signal receiving end.

2. The signal processing method for a secondary radar system according to claim 1, characterized in that, Before performing initial phase modulation and amplitude modulation on the BPSK interrogation signal, it includes the following steps: perform BPSK modulation on the signal to be transmitted to obtain multiple BPSK interrogation signals.

3. The signal processing method for a secondary radar system according to claim 2, characterized in that, After performing initial phase modulation and amplitude modulation on the BPSK interrogation signal, it includes the following steps: perform up-conversion on the BPSK interrogation signal after initial phase modulation and amplitude modulation.

4. The signal processing method for a secondary radar system according to claim 3, characterized in that, The step of sending the modulated BPSK interrogation signal to the signal receiving end through the frequency control array technology is specifically: using an array antenna to send the up-converted BPSK interrogation signal to the signal receiving end through the frequency control array technology.

5. The signal processing method for a secondary radar system according to any one of claims 1-4, characterized in that, The initial phase modulation of the BPSK interrogation signal includes the following steps: Use simulation technology to simulate the carrier signal synthesized by the frequency control array technology; Obtain the variation law of the signal-to-noise ratio of the carrier signal with time; Preset a time period, and select the signal initial phase at the maximum value of the carrier signal within the preset time period; Perform initial phase modulation on the BPSK interrogation signal according to the signal initial phase.

6. The signal processing method for a secondary radar system according to claim 1, characterized in that, Before establishing the local code matching model, it includes the following steps: perform down-conversion on the received BPSK interrogation signal to obtain the baseband signal.

7. A secondary radar system, characterized in that, it includes a signal transmitting end and a signal receiving end; The signal transmitting end includes multiple signal processing branches, and each signal processing branch includes: an initial phase modulation module for performing initial phase modulation on the BPSK interrogation signal; an amplitude modulation module for performing amplitude modulation on the BPSK interrogation signal; a signal transmitting module for sending the modulated BPSK interrogation signal to the signal receiving end through the frequency control array technology; The signal receiving end includes: a model construction module for establishing a local code matching model; a local code matching module for substituting the local code generated by the signal receiving end and the prior parameters of the frequency control array into the local code matching model to obtain the matched local code; a pulse interval and number detector for performing correlation detection on the matched local code and the baseband signal to output the final result; The initial phase modulation module includes: a carrier signal simulation unit for simulating a carrier signal synthesized by a frequency control array technology using simulation techniques; a calculation unit for calculating the variation law of the signal-to-noise ratio of the carrier signal over time; an initial phase selection unit for selecting the signal initial phase at the maximum value of the carrier signal within a preset time period; and an initial phase modulation unit for performing initial phase modulation on the bpsk interrogation signal according to the signal initial phase. The expression of the local code matching model is: m' bpsk = m bpsk Φ; where m’ bpsk represents the local code after matching, m bpsk represents the local code generated by the signal receiving end, and Φ represents the sinc function that affects the matching between the local code generated by the signal receiving end and the bpsk interrogation signal received by the signal receiving end.

8. A secondary radar system according to claim 7, wherein, the signal transmitting end further includes a bpsk modulation module, the bpsk modulation module is connected to the plurality of signal processing branches, and the bpsk modulation module is configured to perform bpsk modulation on the signal to be transmitted to obtain a plurality of bpsk interrogation signals; each signal processing branch further includes an up-conversion module, the input end of the up-conversion module is connected to the output end of the amplitude modulation module, and the up-conversion module is configured to perform up-conversion on the bpsk interrogation signal that has undergone initial phase modulation and amplitude modulation; the signal receiving end further includes a signal receiving module and a down-conversion module, the signal receiving module is configured to receive the bpsk interrogation signals sent by the plurality of signal processing branches, and the down-conversion module is configured to perform down-conversion on the received bpsk interrogation signals to obtain baseband signals.

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