Satellite-borne SAR radar receiver gain distribution method
By adjusting the gain allocation of the spaceborne SAR receiver using the '60:30:0 gain allocation method, the problem of insufficient dynamic range in the receiver design was solved, and the system input dynamic range was expanded and the gain allocation relationship was clarified.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- AEROSPACE INFORMATION RES INST CAS
- Filing Date
- 2026-03-04
- Publication Date
- 2026-05-15
AI Technical Summary
Spaceborne SAR receivers may not meet the system input dynamic range requirement of ≥60dB during the design phase, and the receiver gain allocation relationship is unclear and lacks a clear theoretical explanation.
By adopting the '60:30:0 gain allocation method', the gain allocation of the pre-stage and post-stage digitally controlled attenuators is adjusted to ensure that the relationship between the receiver input signal power and the 1dB compression point of each stage amplifier meets the requirements, thereby expanding the receiver's dynamic range.
To ensure that the receiver input dynamic range meets the requirement of ≥60dB, the linkage between receiver input P-1, output P-1 and MGC is clarified, thereby improving the system's input dynamic range.
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Figure CN122043385A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of spaceborne synthetic aperture radar (SAR) receiver technology, specifically relating to a method for gain allocation in a spaceborne SAR radar receiver. Background Technology
[0002] Spaceborne synthetic aperture radar (SAR) comprises an antenna subsystem and an electronic equipment subsystem. The signal is generated by the electronic equipment subsystem, such as... Figure 1 As shown, the electronic equipment subsystem includes a DAC, transmitter, ADC, and receiver. It radiates to a designated area via the antenna subsystem, receives and collects echoes from ground objects, and obtains raw radar data. The SAR system input dynamic range is an important indicator used to measure the radar system's ability to receive echoes of different amplitudes. The calculation formula is the difference between the system input P⁻¹ and the system sensitivity. Typically, this indicator is required to be ≥60dB, meaning the radar system can linearly amplify echo signals with power differences of at least 60dB.
[0003] As the final link in the system's receiving link, the receiver in the electronic equipment subsystem must have the function of receiving gain adjustment to ensure that echo signals of different power levels are neither prematurely compressed nor insufficiently amplified. The receiver consists of numerous radio frequency and microwave components, such as low-noise amplifiers, mixers, filters, microwave switches, power dividers, isolators, and digitally controlled attenuators. Receiver gain adjustment methods generally include Manual Gain Control (MGC), Automatic Gain Control (AGC), and Sensitivity-Time Control (STC). SAR typically chooses MGC as the means of receiver gain adjustment to preserve the differences in echo amplitude between different targets. In a single imaging mission, MGC is a fixed value, meaning the receiver gain remains stable. In different imaging missions, MGC changes with factors such as target scattering characteristics and slant range. Actual receiver circuits rely on digitally controlled attenuator chips to achieve gain adjustment; the most common type currently uses an attenuation step of 0.5dB, 6-bit control code, and a maximum digitally controlled attenuation of 31.5dB.
[0004] In addition, receiver performance metrics such as maximum gain, sensitivity, input P-1, and output P-1 are all related to MGC. For ease of explanation, the receiver link is simplified as follows: Figure 2As shown, several amplifiers are arranged with MGC1 (pre-stage digitally controlled attenuator) and MGC2 (post-stage digitally controlled attenuator) as the boundaries. These include a first-stage low-noise amplifier (LNA), intermediate stage amplifiers AMP1, 2, and 3, and a final-stage amplifier AMP4. The term "fixed insertion loss" may refer to components such as mixers, microwave switches, fixed attenuators, filters, and power dividers, depending on the application. The MGC control strategy of the spaceborne SAR receiver is as follows: first, MGC2 begins attenuation until full scale, then MGC1 begins attenuation until full scale. The post-stage digitally controlled attenuator's initial activation maximizes the delay in receiver noise figure degradation, ensuring sensitivity.
[0005] Finally, the essential difference between different receiver link designs can be abstracted into gain allocation before MGC1, between MGC1 and MGC2, and after MGC2. Reasonable allocation is the key to ensuring that the input dynamic range of the SAR system meets the usual requirement of ≥60dB.
[0006] The main technical shortcomings in the current design of spaceborne SAR receivers are as follows:
[0007] 1. In practice, spaceborne SAR receivers may meet the requirements for all their functions and performance indicators, but the system input dynamic range may not meet the requirements after being integrated into a radar system. There is currently no clear solution to this problem.
[0008] 2. The relationship between the input P-1, output P-1 and MGC of the spaceborne SAR receiver is unclear and lacks a clear theoretical explanation.
[0009] The problem this invention aims to solve is to provide a method in the design phase of a spaceborne SAR receiver link that clearly defines the linkage between the receiver input P-1, output P-1, and MGC, ensuring that the system input dynamic range meets the typical requirement of ≥60dB after the receiver is connected to the radar system. Summary of the Invention
[0010] To address the above technical problems, this invention proposes a method for gain allocation in a spaceborne SAR radar receiver. The specific technical solution is as follows:
[0011] A method for gain allocation in a spaceborne SAR radar receiver, the spaceborne SAR radar receiver link comprising: a pre-stage digitally controlled attenuator MGC1 and a post-stage digitally controlled attenuator MGC2, a first-stage amplifier located before the pre-stage digitally controlled attenuator MGC1, an intermediate-stage amplifier between the pre-stage digitally controlled attenuator MGC1 and the post-stage digitally controlled attenuator MGC2, and a final-stage amplifier located after the post-stage digitally controlled attenuator MGC2, characterized in that the method comprises the following steps:
[0012] Step 1: Based on the receiver's total gain and noise figure requirements, form a preliminary gain allocation before the pre-stage digitally controlled attenuator MGC1, between the pre-stage digitally controlled attenuator MGC1 and the post-stage digitally controlled attenuator MGC2, and after the post-stage digitally controlled attenuator MGC2;
[0013] Step 2: Gradually increase the power of the receiver input signal until the final stage amplifier reaches the compression state. At this time, the output signal power of the final stage amplifier is 0dB different from the 1dB compression point of its own device.
[0014] Step 3: Adjust the gain before the pre-stage digitally controlled attenuator MGC1 until the output signal power of the first-stage low-noise amplifier differs from the 1dB compression point of its own device by at least 60dB.
[0015] Step 4: Adjust the gain between the pre-stage digitally controlled attenuator MGC1 and the post-stage digitally controlled attenuator MGC2 until the output signal power of the last stage amplifier before MGC2 differs from the 1dB compression point of its own device by at least 30dB.
[0016] Step 5: Review all receiver parameters. If there are any changes in the link, repeat steps 2 to 4 until the parameters are met.
[0017] The technical advantages of this application are as follows:
[0018] 1. An effective method for gain allocation of spaceborne SAR receivers is proposed, which can ensure that the receiver's own input dynamic range reaches the maximum to meet the input dynamic range requirements of the radar system.
[0019] 2. The linkage between receiver input P-1, output P-1 and MGC is clearly described through the step-by-step analysis of the "60:30:0 gain allocation method". Attached Figure Description
[0020] Figure 1 SAR system block diagram;
[0021] Figure 2 Simplified block diagram of the receiver link;
[0022] Figure 3 Preliminary gain distribution diagram of a certain type of receiver;
[0023] Figure 4 Gain distribution diagram adjusted according to method 2. Detailed Implementation
[0024] 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. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.
[0025] This invention proposes a method for gain allocation in a spaceborne SAR radar receiver, termed the "60:30:0 gain allocation method." Figure 2 The simplified receiver link diagram shown considers the following scenario:
[0026] 1. When both MGC1 and MGC2 are set to 0dB, meaning the two-stage digitally controlled attenuators are not attenuating, as the receiver input signal power gradually increases, the final stage amplifier AMP4 will inevitably reach the compression point first. If the intermediate stage amplifiers reach the compression point first, it indicates that the selection of the intermediate stage amplifiers is inappropriate. This state yields the receiver output P-1.
[0027] 2. When the final stage amplifier reaches its compression point and the input signal power increases further, MGC2 needs to begin attenuation to avoid saturation of the final stage amplifier. In this state, the amplifier before MGC2, namely AMP2, will gradually approach its compression point.
[0028] 3. When MGC2 is at full capacity (31.5dB attenuation) and AMP2 has not reached its compression point, if the input signal power continues to increase, then MGC1 needs to start attenuating to avoid AMP2 saturation. In this state, the amplifier before MGC1, i.e., the LNA, will gradually approach its compression point.
[0029] 4. When both MGC2 and MGC1 are fully charged, the input signal power increases to the compression point of the first-stage LNA. At this point, the receiver link can no longer linearly amplify the input power. This state yields receiver input P-1.
[0030] The above describes the relationship between the MGC attenuation of a spaceborne SAR receiver and the input signal power. Based on this, the present invention proposes a "60:30:0 gain allocation method" in the receiver link design stage, summarized as follows:
[0031] Step 1: Based on the requirements of various indicators such as the receiver's total gain and noise figure, form a preliminary gain allocation before MGC1, between MGC1 and MGC2, and after MGC2;
[0032] Step 2: Gradually increase the power of the receiver input signal until the final stage amplifier just reaches the compression state. At this time, the output signal power of the final stage amplifier is 0dB different from the 1dB compression point of its own device.
[0033] Step 3: Adjust the selection of the primary LNA until the output signal power of the device differs from the 1dB compression point of its own output by at least 60dB;
[0034] Step 4: Adjust the gain between MGC1 and MGC2 until the output signal power of the last stage amplifier before MGC2 differs from the 1dB compression point of its own device by at least 30dB;
[0035] Step 5: Review all receiver parameters. If there are any changes in the link, repeat steps 2-4.
[0036] Using this method, it can be ensured that after the receiver is installed in the system, the system input dynamic range meets the usual requirement of ≥60dB.
[0037] (ii) Examples and demonstrations
[0038] According to the requirements of a certain type of receiver, complete step 1 to form a preliminary gain allocation as follows: Figure 3 As shown in the figure, the insertion loss, gain, noise figure, and 1dB compression point of each device are displayed in the figure, with a total gain of 78.5dB.
[0039] Step 2 is completed in the form of a list below. The second row of the table shows that the final stage amplifier (AMP5) has reached the compression state. At this time, the output signal power of the final stage amplifier is 0dB different from the 1dB compression point of its own device.
[0040] Table 1 Output power of each stage amplifier in the receiver
[0041]
[0042] Some additional analysis is needed here. Line 3 indicates that the last amplifier stage before MGC2, AMP3, is compressed before MGC2 reaches its full potential. If the MGC control strategy of the spaceborne SAR receiver is followed, MGC2 will continue to increase, causing the output power of AMP5 to gradually decrease and become unsustainable at 18dBm. This will lead to a deterioration in the receiver's output P-1 performance. If, in order to prevent further degradation of the receiver's output P-1 performance, the MGC control strategy is adjusted so that MGC2 reaches 23dB and stops increasing, then MGC1 is started instead, the results will be as shown in Table 2.
[0043] Table 2 Output power of receiver amplifiers after MGC control strategy change
[0044]
[0045] As can be seen from Table 2, although the output power of AMP5 can be maintained at 18dBm, the range of input signal power is narrowed, that is, the dynamic range of the receiver input is reduced. If this type of receiver is placed in the system, the dynamic range of the SAR system input will not meet the requirements.
[0046] Returning to step 3, the output power of the primary LNA, -48.5dBm, differs from the 1dB compression point of its own device, 15dBm, by 63.5dB > 60dB, indicating that the primary LNA was correctly selected.
[0047] Continuing with step 4, the output power of the last stage amplifier (AMP3) before MGC2 is -10dBm, which is 23dB < 30dB different from the output compression point of 1dB of its own device, 13dBm. Therefore, it is necessary to adjust the gain between MGC1 and MGC2.
[0048] Adjustment methods include, but are not limited to:
[0049] 1. Move AMP3 to a position after MGC2, but re-evaluate the changes in receiver performance in all aspects.
[0050] 2. Increase the fixed attenuation between MGC1 and MGC2. At the same time, in order to maintain the total link gain, the fixed attenuation after MGC2 needs to be reduced, but attention should be paid to the slight deterioration of the receiver noise figure.
[0051] The receiver gain is now redistributed using method 2, such as... Figure 4 As shown.
[0052] Table 3. Power of each amplifier stage in the receiver after adjustment according to method 2.
[0053]
[0054] After adjustment, the receiver's total gain of 78.5dB and output P-1 of 18dBm remained unchanged, while the receiver input P-1 improved from -13dBm in Table 2 to -4.5dBm in Table 3, an increase of 8.5dB. The noise figure was almost identical before and after adjustment, resulting in consistent receiver sensitivity. Consequently, the adjusted receiver input dynamic range increased by 8.5dB. Connecting it to a radar system ensures that the system input dynamic range meets the typical requirement of ≥60dB.
[0055] Finally, complete step 5 and verify that all receiver parameters are correct. Steps 2-4 will not be repeated.
[0056] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.
[0057] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.
[0058] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.
[0059] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.
[0060] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.
[0061] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A method for gain allocation in a spaceborne SAR radar receiver, wherein the spaceborne SAR radar receiver link includes: The method comprises a pre-stage digitally controlled attenuator MGC1 and a post-stage digitally controlled attenuator MGC2, as well as a first-stage amplifier before the pre-stage digitally controlled attenuator MGC1, an intermediate-stage amplifier between the pre-stage digitally controlled attenuator MGC1 and the post-stage digitally controlled attenuator MGC2, and a final-stage amplifier after the post-stage digitally controlled attenuator MGC2, characterized in that the method includes the following steps: Step 1: Based on the receiver's total gain and noise figure requirements, form a preliminary gain allocation before the pre-stage digitally controlled attenuator MGC1, between the pre-stage digitally controlled attenuator MGC1 and the post-stage digitally controlled attenuator MGC2, and after the post-stage digitally controlled attenuator MGC2; Step 2: Gradually increase the power of the receiver input signal until the final stage amplifier reaches the compression state. At this time, the output signal power of the final stage amplifier is 0dB different from the 1dB compression point of its own device. Step 3: Adjust the gain before the pre-stage digitally controlled attenuator MGC1 until the output signal power of the first-stage low-noise amplifier differs from the 1dB compression point of its own device by at least 60dB. Step 4: Adjust the gain between the pre-stage digitally controlled attenuator MGC1 and the post-stage digitally controlled attenuator MGC2 until the output signal power of the last stage amplifier before MGC2 differs from the 1dB compression point of its own device by at least 30dB. Step 5: Review all receiver parameters. If there are any changes in the link, repeat steps 2 to 4 until the parameters are met.
2. The method for gain allocation of a spaceborne SAR radar receiver according to claim 1, characterized in that, In step 3, the output signal power of the primary amplifier differs from the 1dB compression point of its own device by at least 60dB, preferably greater than or equal to 63dB.
3. The method for gain allocation of a spaceborne SAR radar receiver according to claim 1, characterized in that, In step 4, the output signal power of the last stage amplifier before the subsequent digitally controlled attenuator MGC2 differs from the 1dB compression point of its own device by at least 30dB, preferably greater than or equal to 31.5dB.
4. The method for gain allocation of a spaceborne SAR radar receiver according to claim 1, characterized in that, In step 4, the ways to adjust the gain between MGC1 and MGC2 include: moving the last stage amplifier before MGC2 to after MGC2, or increasing the fixed attenuation between MGC1 and MGC2 while reducing the fixed attenuation after MGC2 to maintain the total link gain unchanged.
5. The method for gain allocation of a spaceborne SAR radar receiver according to claim 1, characterized in that, In step 5, the receiver's various specifications are checked, including verifying whether the receiver's total gain, output P-1, noise figure, and sensitivity meet the design requirements.
6. The method for gain allocation of a spaceborne SAR radar receiver according to claim 1, characterized in that, MGC1 and MGC2 are digitally controlled attenuators with an attenuation step of 0.5dB, a control code of 6 bits, and a maximum digitally controlled attenuation of 31.5dB.
7. The method for gain allocation of a spaceborne SAR radar receiver according to claim 1, characterized in that, In step 5, the system input dynamic range is made to reach the requirement of ≥60dB after the receiver is put into the radar system.
8. The method for gain allocation of a spaceborne SAR radar receiver according to claim 1, characterized in that, The primary amplifier uses a low-noise amplifier (LNA); the intermediate amplifier consists of three amplifiers.
9. A method for gain allocation of a spaceborne SAR radar receiver according to claim 8, characterized in that, The spaceborne SAR radar receiver also includes fixed insertion loss at the front end of the first stage amplifier, fixed insertion loss between the two intermediate stage amplifiers, and fixed insertion loss at the rear end of the final stage amplifier.
10. A method for gain allocation of a spaceborne SAR radar receiver according to claim 9, characterized in that, Fixed insertion loss includes one or more of the following: mixer, microwave switch, fixed attenuator, filter, and power divider.