A spurious signal suppression method

Abstract

A clutter suppression method uses the local oscillator frequency hopping characteristics of high repetition rate stepping frequency signals, sets the receiver bandwidth and local oscillator frequency hopping interval that meet the conditions, and combines the receiver gating filter to effectively suppress the clutter outside the target echo distance range. Without additional hardware and operation processing, it is convenient to realize, beneficial to subsequent signal processing requirements, improves the visibility level under clutter, enhances the target detection ability, and has good engineering application value.

Description

Technical Field

[0001] This invention relates to a clutter suppression method based on frequency gating of a high repetition rate step frequency signal. Background Technology

[0002] Radar seekers, especially active seekers, are a crucial component of guidance systems. Their primary task is to acquire information such as target range, velocity, and angle. Most radar seekers are affected by various natural objects when detecting different targets, such as terrain features, sea surfaces, clouds, rain, and man-made chaff. The interference caused by the electromagnetic waves reflected back from these objects is collectively referred to as passive clutter interference. Since the intensity of clutter signals generally far exceeds that of the target signal, and the clutter spectrum is often close to that of the target, coupled with limitations imposed by the radar seeker's equipment parameters, these factors significantly increase the difficulty of signal processing for radar seekers.

[0003] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art. Summary of the Invention

[0004] The purpose of this invention is to provide a clutter suppression method that effectively suppresses clutter outside the target echo range without requiring additional hardware or computational processing.

[0005] To achieve the above objectives, this invention provides a clutter suppression method, wherein the receiver bandwidth B is set to satisfy the condition: B = 2(K t -K n )Δf;

[0006] Among them, K t K is the range ambiguity number of the target echo. t =floor(R) t / R mu ), K n K is the range ambiguity number corresponding to the lower limit of the target echo range. n =floor((R t -ΔR) / R mu ), floor indicates rounding down, R t This refers to the target echo distance, with the echo distance ranging from R. t -ΔR~R t +ΔR,R mu It is the maximum unambiguous distance, R mu =c / 2f r c represents the speed of light, f r Δf is the pulse repetition frequency of the system, and Δf is the local oscillator frequency hopping interval.

[0007] The local oscillator frequency hopping interval Δf is set to 1 / 4 to 1 / 2 of the signal bandwidth.

[0008] This invention utilizes the local oscillator frequency hopping characteristics of high repetition rate step-frequency signals. By setting a receiver bandwidth and local oscillator frequency hopping interval that meet the conditions, combined with a receiver gating filter, it effectively suppresses clutter outside the target echo range. No additional hardware or computational processing is required, making it convenient to implement. It is beneficial for subsequent signal processing needs, improves visibility under clutter conditions, enhances target detection capabilities, and has good engineering application value. Attached Figure Description

[0009] Figure 1 This is a flowchart of a clutter suppression method provided by an embodiment of the present invention.

[0010] Figure 2 and Figure 3 This is a comparison diagram of embodiments of the present invention under different clutter and echo distance differences.

[0011] Figure 4 This is a schematic diagram showing the timing relationship between the local oscillator frequency and the starting frequency of the main oscillator. Detailed Implementation

[0012] The following is based on Figures 1-4 The preferred embodiments of the present invention will be described in detail below.

[0013] Suppressing clutter and detecting echo signals under clutter interference is a crucial challenge for radar seekers. This invention proposes a clutter suppression method based on frequency gating of a high-repetition-rate step-frequency signal, utilizing the local oscillator frequency hopping characteristics of the high-repetition-rate step-frequency signal to achieve clutter suppression.

[0014] like Figure 1 As shown, this invention provides a clutter suppression method based on high repetition rate step frequency signal frequency gating, comprising the following steps:

[0015] Step S1: Set the target echo distance as R t The distance range of the echo is R. t -ΔR~R t +ΔR, where ΔR refers to the range of distance for echo reception and target detection centered on the target echo distance. Clutter outside this range will be suppressed from entering the receiving channel. The specific value of ΔR can be set according to requirements. For example, under conditions with good clutter, such as sea state 1, ΔR can be appropriately increased; under conditions with severe clutter, such as ground conditions, ΔR should be appropriately decreased. The reference master oscillator frequency is set to f0, and the frequency difference between the local oscillator and the master oscillator is the receiving intermediate frequency f. I Proceed to step S2;

[0016] Step S2: Based on the system's pulse repetition frequency f r The maximum unambiguous distance R is calculated. mu :

[0017] R mu =c / 2f r

[0018] Where c represents the speed of light, proceed to step S3;

[0019] Step S3: Combine the target echo distance R t and the maximum unambiguous distance R mu The range ambiguity number K of the target echo is calculated. t :

[0020] K t =floor(R) t / R mu )

[0021] Where floor indicates rounding down, proceed to step S4;

[0022] Step S4, combined with the lower limit R of the echo distance range t -ΔR and the maximum unambiguous distance R mu The distance fuzzy number K corresponding to the lower limit of the distance range is calculated. n :

[0023] K n =floor((R t -ΔR) / R mu )

[0024] Where floor indicates rounding down, proceed to step S5;

[0025] Step S5: Combine distance ambiguity number K t And the frequency hopping interval Δf of the main oscillator is used to calculate the starting frequency f of the main oscillator. s That is, both the transmitted signal frequency and the echo signal frequency are f. s :

[0026] f s =f0+K t Δf

[0027] Proceed to step S6;

[0028] Step S6: Combine distance ambiguity number K t K n And the local oscillator frequency hopping interval Δf, the local oscillator frequency corresponding to the arrival of the echo is calculated to be f. t f n :

[0029] f t =f0+K t Δf-f I

[0030] f n =f0+K n Δf-f I

[0031] Proceed to step S7;

[0032] Step S7, combine the echo frequency f s and its corresponding local oscillator frequency f t f n The frequency difference Δf after mixing the two frequencies was calculated. t , Δf n :

[0033] Δf t =f s -f t =f I

[0034] It can be seen that the target echo, after being mixed with the local oscillator, is equal to the receiving intermediate frequency, and the target echo will be placed in the center of the gating filter;

[0035] Δf n =f s -f n =(K t -K n )Δf+f I

[0036] It can be seen that the receiver bandwidth is equal to twice the frequency difference corresponding to the lower limit of the echo distance range;

[0037] Proceed to step S8;

[0038] Step S8: Set the receiver bandwidth B and the local oscillator frequency hopping interval Δf, satisfying B = 2(Δf) / 2. n -f I ) = 2(K t -K n ) Δf condition, proceed to step S9;

[0039] According to the processing requirements of the step frequency signal, the local oscillator frequency hopping interval Δf is generally set to 1 / 4 to 1 / 2 of the signal bandwidth. Assuming the signal bandwidth is 4MHz, the setting range of the frequency hopping interval is 1MHz to 2MHz.

[0040] Step S9: Since the target echo and the local oscillator are mixed to equal the receiving intermediate frequency, the target echo will be placed in the center of the gating filter. The receiver bandwidth is equal to twice the frequency difference corresponding to the lower limit of the echo distance range, that is, it covers the upper and lower limits of the echo distance range. Clutter outside this range will be suppressed by the receiver's gating filter because the mixing frequency difference exceeds the receiver bandwidth, thereby realizing clutter suppression based on the frequency gating of the high repetition rate step frequency signal.

[0041] Example

[0042] Conditions: The target echo distance is set to 5000m through the target simulation source, and the echo distance range is 4000m to 6000m.

[0043] To apply the above conditions, perform the following steps:

[0044] Step S1: Set the target simulation source and set the echo distance R. t =5000m, clutter distance is 6200m, the reference master frequency is set to f0, and the frequency difference between the local oscillator and the master oscillator is the receiving intermediate frequency f. I =125MHz, proceed to step S2;

[0045] Step S2: Set the pulse repetition frequency f r =750kHz, and the maximum unambiguous distance R is calculated from this. mu :

[0046] R mu =c / 2f r =200m

[0047] Proceed to step S3;

[0048] Step S3: Combine the target echo distance R t and the maximum unambiguous distance R mu The range ambiguity number K of the target echo is calculated. t :

[0049] K t =floor(R) t / R mu ) = 25

[0050] Proceed to step S4;

[0051] Step S4, combined with the lower limit R of the echo distance range t -ΔR and the maximum unambiguous distance R mu The distance fuzzy number K corresponding to the lower limit of the distance range is calculated. n :

[0052] K n =floor((R t -ΔR) / R mu ) = 20

[0053] Proceed to step S5;

[0054] Step S5: Combine distance ambiguity number K t And the frequency hopping interval Δf of the main oscillator is used to calculate the starting frequency f of the main oscillator. s That is, both the transmitted signal frequency and the echo signal frequency are f. s :

[0055] f s =f0+K t Δf

[0056] Proceed to step S6;

[0057] Step S6, as follows Figure 4 As shown, combined with the distance ambiguity number K t K n And the local oscillator frequency hopping interval Δf, the local oscillator frequency corresponding to the arrival of the echo is calculated to be f. t f n :

[0058] f t =f0+K t Δf-f I

[0059] f n =f0+K n Δf-f I

[0060] Proceed to step S7;

[0061] Step S7, combine the echo frequency f s and its corresponding local oscillator frequency f t f n The frequency difference Δf after mixing the two frequencies was calculated. t , Δf n :

[0062] Δf t =f s -f t =f I

[0063] Δf n =f s -f n =(K t -K n )Δf+f I =5Δf+f I

[0064] Proceed to step S8;

[0065] Step S8: According to B = 2(Δf) n -f I =10Δf, set the local oscillator frequency hopping interval Δf = 1MHz, the receiver bandwidth B = 10MHz, that is, the receiver selection range is 120MHz~130MHz, and proceed to step S9;

[0066] Step S9: Since the target echo, after mixing with the local oscillator, equals the received intermediate frequency, the target echo will be placed in the center of the gating filter. At this time, the distance ambiguity number K corresponding to the clutter distance is... n =31, the frequency difference between the clutter frequency and the local oscillator mixing frequency is:

[0067] Δf n = (25-31)Δf+f I =119MHz

[0068] If the signal exceeds the receiver's gating range, it will be suppressed by the receiver's gating filter, thus achieving clutter suppression based on high-repetition-rate step-frequency signal frequency gating. Observe the receiver output; the specific effect is as follows. Figure 2 As shown.

[0069] Adjust the target simulation source, set the clutter distance to 5800m, and observe the receiver output. At this point, both the echo and clutter can be observed simultaneously. This is because the distance ambiguity number corresponding to the clutter is 29, and the clutter frequency differs from the local oscillator mixing frequency by:

[0070] Δf n = (25-29)Δf+f I =121MHz

[0071] Within the receiver's gating range, clutter will not be suppressed by the receiver's gating filter; the specific effect is as follows: Figure 3 As shown.

[0072] The present invention has the following advantages:

[0073] By utilizing the local oscillator frequency hopping characteristic of high repetition rate step frequency signals, effective clutter suppression can be achieved with only a receiver gating filter, without the need for additional hardware and computational costs, making it convenient to implement.

[0074] Formulas for configuring receiver parameters based on echo distance range are given, which can be adjusted in real time as needed in practical applications;

[0075] After the receiver gating filter, it provides better clutter energy suppression, which is beneficial to subsequent signal processing requirements, improves visibility under clutter, and enhances target detection capabilities.

[0076] It should be noted that, in the embodiments of the present invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the embodiments. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0077] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0078] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A clutter suppression method, characterized in that, The receiver bandwidth B is set to satisfy the condition: B = 2(K t -K n ) Δf; Among them, K t K is the range ambiguity number of the target echo. t =floor(R t / R mu ), K n K is the range ambiguity number corresponding to the lower limit of the target echo range. n =floor((R t -ΔR) / R mu ), floor indicates rounding down, R t This refers to the target echo distance, with the echo distance ranging from R. t -ΔR ~ R t +ΔR, where ΔR is the range for echo reception and target detection centered on the target echo distance. Clutter outside this range will be suppressed from entering the receiving channel. mu It is the maximum unambiguous distance, R mu =c / 2f r c represents the speed of light, f r Δf is the pulse repetition frequency of the system, and Δf is the local oscillator frequency hopping interval.

2. The clutter suppression method as described in claim 1, characterized in that, The local oscillator frequency hopping interval Δf is set to 1 / 4 to 1 / 2 of the signal bandwidth.

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