High-orbit SAR (Synthetic Aperture Radar) receiving front end design method

Abstract

According to the high-orbit SAR receiving front-end design method, a feed source participating in beam forming is in a working state, and other feed sources not participating in beam forming are in a low-noise amplifier shutdown state, so that a relatively low noise coefficient of a system is realized, and the detection capability of weak and small targets is improved. According to the method, the influence of a receiving front end amplitude limiter, a low noise amplifier, a phase shift attenuator, a combiner and the like on system receiving noise is considered, the design problem of the high-orbit SAR low noise coefficient receiving front end is solved, and the sensitivity of a receiving system is improved.

Description

Technical Field

[0001] The present application relates to the field of synthetic aperture radar, and in particular, to a method for designing a high-orbit SAR receiving front end. Background Art

[0002] SAR receiver design is an important part of radar system design, and the performance of the receiver greatly affects the overall performance of the radar system. The lower the noise coefficient of the receiver, the higher the signal-to-noise ratio that the SAR can obtain, and the more obvious the imaging and detection effect of weak targets. For high-orbit SAR, the antenna adopts a reflector antenna system based on multiple feeds. Due to the requirements of the system working mode, its beam needs to be switched among multiple feeds. Different beam designs and feed participation methods affect the overall noise coefficient of the system. Due to the long range of high-orbit SAR, the transmission power of the overall radar system is extremely precious. The sensitivity of the radar system receiving system plays an important role in the detection of weak targets, especially the noise coefficient of the receiver determines the system receiving sensitivity of the entire radar to a certain extent. In the receiving beam forming of high-orbit SAR, not only the number of feed sources participating should be considered, but also the channel amplification gain of different feed sources needs to be adjusted and weighted in order to form an antenna pattern with low side lobes. In the prior art, when designing the receiving end, the high-orbit SAR adopts a method based on phased array multi-beam feed switching. If the traditional beam combiner direct synthesis method is adopted, it will introduce a lot of noise, causing the system's noise coefficient index to deteriorate, thereby affecting the radar system's signal-to-noise ratio and other performance indicators. Summary of the invention

[0003] In order to overcome at least one deficiency in the prior art, the present application provides a high-orbit SAR receiving front-end design method.

[0004] In a first aspect, a high-orbit SAR receiving front-end design method is provided, comprising:

[0005] Calculate the number of beams at the high-orbit SAR receiver;

[0006] According to the antenna beam gain and antenna sidelobe level, determine the number and position of feed sources participating in the reception of each beam forming;

[0007] For each beam, the low noise amplifier is switched on and off to enable the corresponding feed participating in the reception of the beam to be turned on, and other feeds not participating in the reception to be turned off.

[0008] The radar echo signal passes through each participating feed source, is synthesized in the combiner, and then enters the back-end receiver.

[0009] In one embodiment, calculating the number of beams of a high-orbit SAR receiving end includes:

[0010] Determine the number of survey strips M in the elevation direction of the high-orbit SAR, then the number of beams at the high-orbit SAR receiving end is M.

[0011] In one embodiment, determining the number and position of feed sources participating in receiving for each beam forming according to the antenna beam gain and the antenna sidelobe level includes:

[0012] The number and position of the feed sources participating in the beamforming reception are taken as optimization variables, and the antenna beam gain and antenna sidelobe level are taken as optimization targets to construct the optimization function:

[0013] min F(X)=u(G(X)-G j )+w(I(X)-I j )

[0014] X=[N j ,X1]

[0015] Among them, F(X) is the function value, X is the optimization variable, and N j is the number of feed sources participating in the j-th beamforming reception, X1 is the position of each feed source participating in the j-th beamforming reception, G(X) is the antenna beam gain when the optimization variable is X, G j is the antenna beam gain requirement of the jth beam, I(X) is the antenna sidelobe level when the optimization variable is X, and I j is the required value of the antenna sidelobe level of the jth beam, and u and w are weight coefficients;

[0016] Solve the optimization function to obtain the number and position of feed sources participating in beamforming reception.

[0017] In one embodiment, the feed source includes a feed antenna, a circulator, a limiter, a low noise amplifier, an attenuator, and a phase shifter.

[0018] Compared with the prior art, the present application has the following beneficial effects: In the high-orbit SAR receiving front-end design method of the present application, the feeds participating in beamforming are in working state, and other feeds not participating in beamforming are in the low-noise amplifier shutdown state, thus achieving a lower noise coefficient of the system and improving the detection capability of weak targets. The method takes into account the influence of the receiving front-end limiter, low-noise amplifier, phase shift attenuator, combiner, etc. on the system receiving noise, solves the design problem of the high-orbit SAR low-noise coefficient receiving front-end, and improves the sensitivity of the receiving system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present application may be better understood by referring to the following description given in conjunction with the accompanying drawings, which together with the following detailed description are included in this specification and form a part of this specification. In the drawings:

[0020] Figure 1 A flowchart of a high-orbit SAR receiving front-end design method according to an embodiment of the present application is shown;

[0021] Figure 2 A schematic diagram of the feed system is shown. DETAILED DESCRIPTION

[0022] The exemplary embodiments of the present application will be described below in conjunction with the accompanying drawings. For the sake of clarity and conciseness, not all features of the actual embodiments are described in the specification. However, it should be understood that many implementation-specific decisions can be made in the process of developing any such actual embodiments in order to achieve the specific goals of the developer, and these decisions may vary from embodiment to embodiment.

[0023] It is also necessary to explain here that, in order to avoid obscuring the present application due to unnecessary details, only the device structure closely related to the scheme according to the present application is shown in the drawings, while other details that are not closely related to the present application are omitted.

[0024] It should be understood that the present application is not limited to the described implementation forms due to the following description with reference to the accompanying drawings. In this article, where feasible, the embodiments can be combined with each other, features between different embodiments can be replaced or borrowed, and one or more features can be omitted in one embodiment.

[0025] The present invention provides a method for designing a high-orbit SAR receiving front end. Figure 1 A flowchart of a method for designing a high-orbit SAR receiving front end according to an embodiment of the present application is shown. Figure 1 , methods include:

[0026] Step S1, calculating the number of beams at the high-orbit SAR receiving end.

[0027] Here, according to the requirement of receiving beams in the elevation direction of the high-orbit SAR, the required number of beams is calculated. Assuming that the high-orbit SAR needs M survey strips in the elevation direction, the required number of beams is M.

[0028] Step S2, determining the number and positions of feed sources participating in reception for each beam forming according to the antenna beam gain and the antenna sidelobe level.

[0029] Assume that the number of feeds participating in beam 1 is N 1 , the number of feed sources participating in beam 2 is N 2 , the number of feed sources participating in beam j is N j The number and position of the participating feed sources mainly depend on the requirements of beam forming on antenna beam gain, antenna sidelobe level, etc.

[0030] Specifically, the number and position of the feed sources participating in the beamforming reception are taken as optimization variables, and the antenna beam gain and antenna sidelobe level are taken as optimization targets to construct the optimization function:

[0031] minF(X)=u(G(X)-G j )+w(I(X)-I j )

[0032] X=[N j ,X1]

[0033] Among them, F(X) is the function value, X is the optimization variable, and N j is the number of feed sources participating in the j-th beamforming reception, X1 is the position of each feed source participating in the j-th beamforming reception, G(X) is the antenna beam gain when the optimization variable is X, G j is the antenna beam gain requirement of the jth beam, I(X) is the antenna sidelobe level when the optimization variable is X, and I j is the required value of the antenna sidelobe level of the jth beam, and u and w are weight coefficients;

[0034] An optimization algorithm is used to solve the optimization function to obtain the number and position of feed sources participating in beamforming reception. Here, the optimization algorithm can adopt a method in the prior art, such as a genetic algorithm.

[0035] Here, the initial value of the number of feed sources is N j0 It can be determined using the following formula:

[0036]

[0037] Among them, G 0 is the secondary radiation gain after the single feed source illuminates the reflector.

[0038] Step S3, for each beam, the on / off of the low noise amplifier is selected so that the feed source participating in the reception corresponding to the beam is in the on state, and other feed sources not participating in the reception are in the off state.

[0039] Step S4: After the radar echo signal passes through each of the feed sources participating in the reception, it is synthesized in the combiner and then enters the back-end receiver.

[0040] Figure 2 A schematic diagram of the feed system is shown. Figure 2 , each feed includes a feed antenna, a circulator, a limiter, a low noise amplifier, an attenuator and a phase shifter. In order to facilitate calculation, the receiving front-end system of the high-orbit SAR can be simplified into a multi-port network model. At this time, the noise coefficient NF′ of the branch is:

[0041]

[0042] Among them, N fA is the noise coefficient of the low noise amplifier in the branch, L1 is the loss of the circulator, L2 is the loss of the limiter, L3 is the loss of the attenuator and phase shifter, and G is the branch amplifier gain.

[0043] Since the antenna side lobe needs to be suppressed during antenna reception, the gain of different branches can be adjusted through the phase shift attenuator. At this time, if the low noise amplifier of other feed sources is not turned off, the noise at the receiving end includes the noise of other beams (feed sources), which will cause the overall noise factor of the receiving end to increase. Assuming that the branch amplification gain G and the branch noise factor NF' are consistent, the overall noise factor NF of the receiving end can be obtained after combining:

[0044] NF=N[1+T e / T 0 +(L-1) / G]

[0045] =N[NF 1 +(L-1) / G]

[0046] Where N is the number of branches, T 0 is the ambient temperature, T e is the equivalent noise temperature of the active channel, and L is the loss of the combiner. Here, T e =T 0 (NF′-1).

[0047] If only one branch is working and the other branches are in shutdown state, the noise factor of the network becomes:

[0048] NF=NF 1 +(L-1) / G

[0049] Among them, NF 1 is the noise factor of the working branch.

[0050] It can be seen that after shutting down other branches, the noise factor is reduced by (N-1)·NF 1 times.

[0051] In order to verify the effectiveness of the method in this application, the following parameters are selected for simulation verification. Assuming G = 30dB, NF 1 =3dB, the loss of the combiner is L=2dB, there are 4 branches in total. If one working branch is turned on and the three non-working branches are turned off, the noise factor of the entire link is NF=3.0067dB. If one working branch is turned on to pass the signal and the other branches are also turned on to receive noise, the noise factor of the entire link is: NF=12.0268dB.

[0052] In summary, this application has the following technical effects:

[0053] In the high-orbit SAR receiving front-end design method of the present application, the feeds participating in beamforming are in working state, and other feeds not participating in beamforming are in the low-noise amplifier shutdown state, thus achieving a lower noise coefficient of the system and improving the detection capability of weak targets. The method takes into account the influence of the receiving front-end limiter, low-noise amplifier, phase shift attenuator, combiner, etc. on the system receiving noise, solves the design problem of the high-orbit SAR low-noise coefficient receiving front-end, and improves the sensitivity of the receiving system.

[0054] The above are only various implementations of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A high-orbit SAR receiving front-end design method, characterized in that: include: Calculate the number of beams at the high-orbit SAR receiver; According to the antenna beam gain and antenna sidelobe level, determine the number and position of feed sources participating in the reception of each beam forming; For each beam, the switching of the low noise amplifier is performed so that the feed source participating in the reception corresponding to the beam is in the on state, and other feed sources not participating in the reception are in the off state; The radar echo signal passes through each participating feed source, is synthesized in the combiner, and then enters the back-end receiver.

2. The method according to claim 1, characterized in that in, Calculate the number of beams at the high-orbit SAR receiver, including: Determine the number of survey strips M in the elevation direction of the high-orbit SAR, then the number of beams at the high-orbit SAR receiving end is M.

3. The method according to claim 1, characterized in that in, According to the antenna beam gain and antenna sidelobe level, determine the number and position of feed sources participating in the reception of each beam forming, including: The number and position of the feed sources participating in the beamforming reception are taken as optimization variables, and the antenna beam gain and antenna sidelobe level are taken as optimization targets to construct the optimization function: min F(X)=u(G(X)-G j )+w(I(X)-I j ) X=[N j ,X1] Among them, F(X) is the function value, X is the optimization variable, and N j is the number of feed sources participating in the reception of the jth beamforming, X1 is the position of each feed source participating in the reception of the jth beamforming, G(X) is the antenna beam gain when the optimization variable is X, G, is the required value of the antenna beam gain of the jth beam, I(X) is the antenna sidelobe level when the optimization variable is X, I j is the required value of the antenna sidelobe level of the jth beam, and u and w are weight coefficients; The optimization function is solved to obtain the number and positions of feed sources participating in beamforming reception.

4. The method according to claim 1, characterized in that in, The feed source comprises a feed antenna, a circulator, a limiter, a low noise amplifier, an attenuator and a phase shifter.

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