Broadband receiving circuit applied to X-band synthetic aperture radar

Abstract

The invention provides a broadband receiving circuit applied to an X-band synthetic aperture radar. The broadband receiving circuit comprises an orthogonal demodulation circuit, a broadband radio frequency amplification circuit and an equalization circuit. The quadrature demodulation circuit demodulates the X-waveband linear frequency modulation signal with the bandwidth of B to a baseband in a zero intermediate frequency manner through a quadrature demodulator, and outputs an I / Q baseband signal with the frequency of DC-B / 2; the broadband radio frequency amplification circuit adopts alternating current coupling, a broadband radio frequency amplifier is used for performing signal gain processing on an I / Q baseband signal, and the amplified I / Q baseband signal is transmitted to the equalization circuit; an amplitude equalizer is arranged in the equalization circuit, the amplitude equalizer is used for correcting the amplitude distortion of the I / Q baseband signal, and the I / Q baseband signal after amplitude equalization is input to an analog-to-digital converter for sampling. According to the analog-to-digital conversion circuit, the sampling clock frequency requirement of the analog-to-digital conversion circuit can be reduced, the maximum bandwidth of a signal which can be processed by a receiving link is improved, the problem of direct-current bias of an analog quadrature demodulator is solved, signal distortion is reduced, and GHz-level broadband signal high-gain amplification is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of synthetic aperture radar, and in particular relates to a broadband receiving circuit applied to an X-band synthetic aperture radar. Background Art

[0002] Synthetic Aperture Radar (SAR) is an active remote sensing technology that can use electromagnetic waves emitted and received by the radar to acquire images of ground objects. The range resolution of the radar is determined by the radar signal bandwidth. The larger the bandwidth, the higher the radar resolution. Specifically, the receiving link is an important part of the synthetic aperture radar. Its function is to amplify and down-convert the echo signal for analog-to-digital conversion sampling. Therefore, the bandwidth of the receiving link will determine the bandwidth of the entire synthetic aperture radar.

[0003] Zero IF reception is a commonly used receiving method for broadband radar. It down-converts the RF signal to zero IF and then directly samples the IF signal. As the signal bandwidth increases, the analog-to-digital converter requires a higher sampling clock frequency. At the same time, the baseband circuit of traditional zero IF reception is DC amplification, which requires the use of an operational amplifier. However, the operational amplifier is limited by the gain-bandwidth product and it is difficult to achieve high-gain amplification of broadband signals. In addition, the zero IF receiving circuit also has problems such as DC bias and signal distortion. Summary of the invention

[0004] The present invention aims to provide a broadband receiving circuit for X-band synthetic aperture radar to solve the technical problems that conventional broadband radar receiving links cannot improve the signal bandwidth that can be processed by the receiving links, avoid DC bias, and reduce signal distortion under the prior art.

[0005] To solve the above problems, the technical solution of the present invention is: a broadband receiving circuit applied to X-band synthetic aperture radar, comprising: an orthogonal demodulation circuit, a broadband radio frequency amplification circuit and an equalization circuit;

[0006] The orthogonal demodulation circuit is provided with an orthogonal demodulator, and the orthogonal demodulator is used to orthogonally demodulate the linear frequency modulation signal received by the radar into an I / Q baseband signal at zero intermediate frequency, and the I / Q baseband signal is transmitted to the broadband radio frequency amplification circuit respectively;

[0007] The broadband RF amplification circuit comprises a first broadband RF amplification circuit and a second broadband RF amplification circuit, the first broadband RF amplification circuit and the second broadband RF amplification circuit are respectively applied to the in-phase channel and the quadrature channel of the baseband signal, and a broadband RF amplifier is respectively provided in the first broadband RF amplification circuit and the second broadband RF amplification circuit, and the broadband RF amplifier is used to perform signal gain processing on the I / Q baseband signal, and the amplified I / Q baseband signal is transmitted to the equalization circuit;

[0008] The equalizing circuit includes a first equalizing circuit and a second equalizing circuit, the first equalizing circuit and the second equalizing circuit are respectively applied to the in-phase channel and the quadrature channel of the baseband signal, and an amplitude equalizer is respectively provided in the first equalizing circuit and the second equalizing circuit, the amplitude equalizer is used to correct the amplitude distortion of the I / Q baseband signal, and the I / Q baseband signal after amplitude equalization is input to the analog-to-digital processor for sampling.

[0009] Preferably, the frequency band of the linear frequency modulation signal received by the radar is X-band, the bandwidth B of the linear frequency modulation signal can reach GHz level, and the frequency of the I / Q baseband signal obtained after orthogonal demodulation processing is DC~B / 2.

[0010] Preferably, the orthogonal demodulation circuit is also provided with a local oscillator signal link, which is used to receive the RF carrier signal input by the radar, and output the RF carrier signal to the orthogonal demodulator after amplifying and processing the RF carrier signal. During the orthogonal demodulation process of the orthogonal demodulator, the RF carrier signal is mixed with the linear frequency modulation signal as a local oscillator signal.

[0011] Preferably, a first fixed attenuator is respectively provided in the transmission link of the linear frequency modulation signal and the transmission link of the radio frequency carrier signal, and the first fixed attenuator is used to reduce the signal amplitude and improve the signal-to-noise ratio. In the orthogonal demodulation circuit, the linear frequency modulation signal and the radio frequency carrier signal are transmitted to the orthogonal demodulator after passing through the first fixed attenuator.

[0012] Preferably, the first broadband RF amplifier circuit and the second broadband RF amplifier circuit are respectively provided with an AC coupling circuit, and the AC coupling circuit is used to remove the DC component in the I / Q baseband signal. In the broadband RF amplifier circuit, after the I / Q baseband signal with a frequency of DC to B / 2 is first subjected to AC coupling processing, the frequency range of the I / Q baseband signal becomes kHz to B / 2.

[0013] Preferably, the first broadband RF amplifier circuit and the second broadband RF amplifier circuit are respectively provided with a low-pass filter, and the low-pass filter is used to filter out non-essential frequency components in the I / Q baseband signal. In the broadband RF amplifier circuit, the I / Q baseband signal with a frequency of kHz~B / 2 is filtered by the low-pass filter and then transmitted to the broadband RF amplifier.

[0014] Preferably, the low-pass filter is constructed using LC lumped parameter elements, and the passband range is DC to B / 2.

[0015] Preferably, the first equalizing circuit and the second equalizing circuit are respectively provided with a second fixed attenuator, and the second fixed attenuator is used to limit the signal amplitude. In the equalizing circuit, the I / Q baseband signal passes through the amplitude equalizer and is transmitted to the second fixed attenuator.

[0016] Preferably, in the external circuit of the broadband RF amplifier circuit, the broadband RF amplifier input end is connected in parallel with a first capacitor and a second capacitor, the broadband RF amplifier output end is connected to the first branch and the second branch, the first branch is connected in parallel with a fifth capacitor and a sixth capacitor, the end of the second branch is connected to the power supply end, and the second branch is connected in series with a first resistor and a first inductor; a third capacitor and a fourth capacitor are also provided, the third capacitor and the fourth capacitor are arranged in parallel, and the first ends of the third capacitor and the fourth capacitor are connected between the first resistor and the power supply end, and the second ends of the third capacitor and the fourth capacitor are grounded.

[0017] Preferably, the input end of the amplitude equalizer configuration circuit is connected in parallel with a seventh capacitor and a second resistor, the output end is connected in parallel with a second inductor and a third resistor, the seventh capacitor is connected in series with the second inductor, and the second resistor is connected in series with the third resistor; a fourth resistor is also provided, the first end of the fourth resistor is connected between the second resistor and the third resistor, the second end of the fourth resistor is connected in parallel with the third inductor and the eighth capacitor and then grounded.

[0018] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0019] (1) The present invention provides a broadband receiving circuit for X-band synthetic aperture radar, which is provided with an orthogonal demodulation circuit and adopts an analog orthogonal demodulation scheme to reduce the baseband signal bandwidth from B, which is the bandwidth of the radar echo signal, to B / 2. Compared with the traditional digital sampling and demodulation scheme, the sampling clock frequency of the back-end ADC can be effectively reduced, thereby increasing the maximum bandwidth of the signal that can be processed by the receiving link.

[0020] (2) The present invention provides a broadband receiving circuit for use in an X-band synthetic aperture radar, which is provided with a broadband radio frequency amplification circuit. The broadband radio frequency amplifier is used to amplify a baseband signal with a frequency of kHz to B / 2, so that a broadband signal at the GHz level can obtain a larger gain. Compared with a traditional operational amplifier, the circuit overcomes the limitation of the gain-bandwidth product and reduces the design cost. At the same time, due to the use of AC coupling processing, the DC bias problem of the analog orthogonal demodulator is solved.

[0021] (3) The present invention provides a broadband receiving circuit for X-band synthetic aperture radar, which is provided with an equalizing circuit. The amplitude flatness of the baseband signal is improved by using an amplitude equalizer, and the amplitude inconsistency problem between I / Q baseband signals caused by analog orthogonal demodulation is optimized, thereby effectively reducing signal distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic structural diagram of a broadband receiving circuit for use in an X-band synthetic aperture radar provided by the present invention;

[0023] Figure 2 A schematic structural diagram of an external circuit of a broadband radio frequency amplifier circuit provided by the present invention;

[0024] Figure 3 A schematic diagram of a gain characteristic curve of a broadband radio frequency amplifier provided by the present invention;

[0025] Figure 4 A schematic diagram of the structure of an amplitude equalizer circuit provided by the present invention;

[0026] Figure 5 A schematic diagram of an amplitude-frequency characteristic curve of an amplitude equalizer provided by the present invention. DETAILED DESCRIPTION

[0027] The following is a further detailed description of a broadband receiving circuit for X-band synthetic aperture radar proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and claims.

[0028] See also Figure 1 This embodiment provides a broadband receiving circuit applied to an X-band synthetic aperture radar to improve the performance of the X-band synthetic aperture radar for echo signal processing. Specifically, the broadband receiving circuit includes an orthogonal demodulation circuit, a broadband radio frequency amplification circuit and an equalization circuit arranged in sequence.

[0029] The orthogonal demodulation circuit is provided with an orthogonal demodulator, two groups of first fixed attenuators and an amplifier, wherein one group of first fixed attenuators is directly connected to the input end of the orthogonal demodulator to form a linear frequency modulation signal link, which is used to receive and transmit the linear frequency modulation signal received by the radar, and the other group of first fixed attenuators is connected to the input end of the orthogonal demodulator after the amplifier to form a local oscillator signal link, which is used to receive and transmit the radio frequency carrier signal. The frequency band of the linear frequency modulation signal used in the X-band synthetic aperture radar described in the present invention is the X-band. In this embodiment, a linear frequency modulation signal with a center frequency of 9.6 GHz and a bandwidth of 2.4 GHz (i.e., a frequency range of 8.4 GHz to 10.8 GHz) is selected as an example for description.

[0030] Specifically, the linear frequency modulation signal with a frequency of 9.6±1.2GHz received by the radar first passes through the first fixed attenuator, which is used to reduce the amplitude of the signal, helps to protect the subsequent circuit from damage by high-power signals, and can improve the signal-to-noise ratio. Then, the linear frequency modulation signal is transmitted to the orthogonal demodulator. Similarly, the RF carrier signal with a frequency of 9.6GHz input to the radar first passes through the first fixed attenuator, and then passes through the amplifier. The amplifier is used to limit the amplitude of the signal to the required level. Subsequently, the RF carrier signal is transmitted to the orthogonal demodulator, and the RF carrier signal is used as the local oscillator signal. The orthogonal demodulator can use two local oscillator signals with a phase difference of 90 degrees to mix with the input RF signal respectively. For RF and LO signals with the same center frequency, a baseband signal will be obtained after mixing. Since the bandwidth of the input signal is 2.4GHz, the frequency range of the demodulated signal will be 0Hz (DC) to 1.2GHz, that is, the output signal is an I / Q baseband signal with a frequency range of DC to 1.2GHz, and the output end of the orthogonal demodulator includes an in-phase (I) channel and a quadrature (Q) channel. The I / Q baseband signal will be output to the corresponding in-phase channel and quadrature channel respectively.

[0031] The broadband RF amplifier circuit includes a first broadband RF amplifier circuit and a second broadband RF amplifier circuit, which correspond to the in-phase channel and the quadrature channel of the I / Q baseband signal respectively. A broadband RF amplifier, an AC coupling circuit and a low-pass filter are respectively provided in the first broadband RF amplifier circuit and the second broadband RF amplifier circuit.

[0032] Specifically, the I / Q baseband signal with a frequency of DC to 1.2GHz first passes through an AC coupling circuit. The AC coupling circuit can be composed of capacitor components to remove the DC component in the I / Q baseband signal while keeping the AC component of the I / Q baseband signal unchanged. After the first AC coupling process, the frequency range of the I / Q baseband signal becomes kHz to 1.2GHz. Then, the I / Q baseband signal passes through a low-pass filter, which is used to filter out high-frequency noise and other unnecessary frequency components above the required bandwidth, thereby reducing noise interference. Finally, the I / Q baseband signal is input to a broadband RF amplifier, which is used to amplify the signal so that the I / Q baseband signal obtains a higher gain. Preferably, the amplified I / Q baseband signal can pass through another AC coupling circuit again, and after AC coupling, further remove the possible DC offset while keeping the AC component of the signal unchanged.

[0033] Similarly, the equalization circuit includes a first equalization circuit and a second equalization circuit, which correspond to the in-phase channel and the quadrature channel of the I / Q baseband signal respectively. The first equalization circuit and the second equalization circuit are respectively provided with an amplitude equalizer and a second fixed attenuator.

[0034] Specifically, the I / Q baseband signal first passes through the amplitude equalizer, which is used to adjust the amplitude response of the signal to eliminate the amplitude imbalance caused by analog orthogonal demodulation and the uneven amplitude-frequency response of the broadband signal in the baseband link. Then, the I / Q baseband signal passes through the second fixed attenuator, which is used to limit the signal amplitude to prevent the subsequent analog-to-digital converter from overloading. Finally, the attenuated I / Q baseband signal is input into the analog-to-digital converter for back-end digital sampling processing.

[0035] In summary, this embodiment provides a broadband receiving circuit for X-band synthetic aperture radar, which is provided with an orthogonal demodulation circuit and adopts an analog orthogonal demodulation scheme to reduce the baseband signal bandwidth from 2.4GHz of the radar echo signal bandwidth to 1.2GHz. Compared with the traditional digital sampling and demodulation scheme, it can effectively reduce the sampling clock frequency of the back-end ADC, thereby increasing the maximum bandwidth of the signal that can be processed by the receiving link. At the same time, a broadband RF amplification circuit is provided, and a broadband RF amplifier is used to amplify the baseband signal with a frequency of kHz to 1.2GHz, so that the GHz-level broadband signal obtains a large gain. Compared with the traditional operational amplifier, it overcomes the limitation of the gain-bandwidth product and reduces the design cost. At the same time, due to the use of AC coupling processing, the DC bias problem of the analog orthogonal demodulator is solved. In addition, an equalization circuit is also provided, which uses an amplitude equalizer to improve the amplitude flatness of the baseband signal, and optimizes the amplitude inconsistency problem between the I / Q baseband signals caused by analog orthogonal demodulation, effectively reducing signal distortion.

[0036] Preferably, in one embodiment, the low-pass filter in the broadband RF amplifier circuit is made of LC lumped parameter elements, and the structure is a 7th-order Butterworth filter with a passband range of DC to 1.2 GHz. The 7th-order Butterworth filter has a higher slope and can attenuate signals outside the passband more quickly, that is, it is used to ensure that only signals with frequencies of kHz to 1.2 GHz can pass through, and to quickly and accurately filter out higher frequency noise or other unnecessary signal components.

[0037] See also Figure 2 Preferably, in one embodiment, the broadband RF amplifier is an MMIC amplifier. In the external circuit of the broadband RF amplifier circuit, the broadband RF amplifier input end is connected in parallel with a first capacitor and a second capacitor to form an AC coupling circuit to achieve input coupling, which is used to remove the DC component and only allow the AC signal to pass. The output end of the broadband RF amplifier is connected to the first branch and the second branch, and the first branch is connected in parallel with a fifth capacitor and a sixth capacitor to form another AC coupling circuit to achieve output coupling, further remove the DC offset that may be generated, and keep the AC component of the signal unchanged. The end of the second branch is connected to the power supply end, and the power supply provides a stable bias voltage for the amplifier. The second branch has a first resistor and a first inductor connected in series. The first resistor is used to provide a suitable bias voltage to the amplifier to ensure its stable operation. The first inductor is used for choking to prevent the instantaneous large current of the power supply from burning the amplifier. The external circuit of the broadband RF amplifier circuit is also provided with a third capacitor and a fourth capacitor. The third capacitor is arranged in parallel with the fourth capacitor, and the first end of the third capacitor and the fourth capacitor is connected between the first resistor and the power supply end. The second end of the third capacitor and the fourth capacitor is grounded. The third capacitor and the fourth capacitor are used together to filter out high-frequency noise and stray signals. The grounding ends of the broadband RF amplifier are grounded respectively.

[0038] Specifically, in this embodiment, the first capacitor is 1000pF, the second capacitor is 1uF, the third capacitor is 2.2uF, the fourth capacitor is 1000pF, the fifth capacitor is 1000pF, the sixth capacitor is 1uF, the first resistor is 100Ω, and the first inductor is 680nH.

[0039] See also Figure 3 In this embodiment, the signal gain characteristic curve of the broadband RF amplifier is shown in the figure. It has the characteristics of high gain in a wide frequency band. The gain is greater than 15dB in the DC~3GHz band, which proves that it can provide sufficient amplification capability in a wider frequency range. The gain fluctuation is about 1.5dB in the kHz~1.2GHz range.

[0040] See also Figure 4Preferably, in one embodiment, the input end of the amplitude equalizer configuration circuit is connected in parallel with the seventh capacitor and the second resistor, the output end is connected in parallel with the second inductor and the third resistor, and the seventh capacitor is connected in series with the second inductor, and the second resistor is connected in series with the third resistor, wherein the seventh capacitor is used to adjust the amplitude of the low-frequency signal, the second inductor is used to provide impedance matching and filtering, and the second resistor is used to provide input impedance. A fourth resistor is also provided in the amplitude equalizer configuration circuit, the first end of the fourth resistor is connected between the second resistor and the third resistor, the second end of the fourth resistor is connected in parallel with the third inductor and the eighth capacitor and then grounded, wherein the third resistor and the fourth resistor cooperate to form a voltage divider network, the third inductor and the eighth capacitor are respectively used to provide impedance, improve the signal amplitude flatness, and make the signal gain at different frequencies more uniform.

[0041] Specifically, in this embodiment, the seventh capacitor is selected as 4.3pF, the eighth capacitor is selected as 1.6pF, the second inductor is selected as 1nH, the third inductor is selected as 1nH, the second resistor is selected as 9.1Ω, the third resistor is selected as 15Ω, and the fourth resistor is selected as 43Ω.

[0042] See also Figure 5 In this embodiment, the amplitude-frequency characteristic curve of the amplitude equalizer obtained by simulation is shown in the figure. The insertion loss is -6.478dB at 1MHz and -4.852dB at 1.2GHz, achieving an equalization amount of 1.6dB in the frequency domain from kHz to 1.2GHz, compensating for the uneven gain of the broadband RF amplifier, thereby reducing signal distortion.

[0043] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they still fall within the protection scope of the present invention.

Claims

1. A broadband receiving circuit for X-band synthetic aperture radar. It is characterized in that include: Orthogonal demodulation circuit, broadband RF amplifier circuit and equalization circuit; The orthogonal demodulation circuit is provided with an orthogonal demodulator, and the orthogonal demodulator is used to orthogonally demodulate the linear frequency modulation signal received by the radar into an I / Q baseband signal at zero intermediate frequency, and the I / Q baseband signal is transmitted to the broadband radio frequency amplification circuit respectively; The broadband RF amplification circuit comprises a first broadband RF amplification circuit and a second broadband RF amplification circuit, the first broadband RF amplification circuit and the second broadband RF amplification circuit are respectively applied to the in-phase channel and the quadrature channel of the baseband signal, and a broadband RF amplifier is respectively provided in the first broadband RF amplification circuit and the second broadband RF amplification circuit, and the broadband RF amplifier is used to perform signal gain processing on the I / Q baseband signal, and the amplified I / Q baseband signal is transmitted to the equalization circuit; The equalizing circuit includes a first equalizing circuit and a second equalizing circuit, the first equalizing circuit and the second equalizing circuit are respectively applied to the in-phase channel and the quadrature channel of the baseband signal, and an amplitude equalizer is respectively provided in the first equalizing circuit and the second equalizing circuit, and the amplitude equalizer is used to correct the amplitude distortion of the I / Q baseband signal. The I / Q baseband signal after amplitude equalization is input to the analog-to-digital converter for sampling.

2. The broadband receiving circuit for X-band synthetic aperture radar according to claim 1, It is characterized in that The frequency band of the linear frequency modulation signal received by the radar is the X band, the bandwidth B of the linear frequency modulation signal can reach the GHz level, and the frequency of the I / Q baseband signal obtained after orthogonal demodulation processing is DC~B / 2.

3. The broadband receiving circuit for X-band synthetic aperture radar according to claim 1, It is characterized in that The orthogonal demodulation circuit is also provided with a local oscillator signal link, which is used to receive the radio frequency carrier signal input by the radar, and output the radio frequency carrier signal to the orthogonal demodulator after amplifying and processing the radio frequency carrier signal. During the orthogonal demodulation process of the orthogonal demodulator, the radio frequency carrier signal is mixed with the linear frequency modulation signal as a local oscillator signal.

4. The broadband receiving circuit for X-band synthetic aperture radar according to claim 3, It is characterized in that A first fixed attenuator is also provided in the transmission link of the linear frequency modulation signal and the transmission link of the radio frequency carrier signal, respectively. The first fixed attenuator is used to reduce the signal amplitude and improve the signal-to-noise ratio. In the orthogonal demodulation circuit, the linear frequency modulation signal and the radio frequency carrier signal are transmitted to the orthogonal demodulator after passing through the first fixed attenuator.

5. The broadband receiving circuit for X-band synthetic aperture radar according to claim 1, It is characterized in that The first broadband RF amplifier circuit and the second broadband RF amplifier circuit are respectively provided with an AC coupling circuit, and the AC coupling circuit is used to remove the DC component in the I / Q baseband signal. In the broadband RF amplifier circuit, after the I / Q baseband signal with a frequency of DC to B / 2 is first subjected to AC coupling processing, the frequency range of the I / Q baseband signal becomes kHz to B / 2.

6. The broadband receiving circuit for X-band synthetic aperture radar according to claim 5, It is characterized in that The first broadband RF amplifier circuit and the second broadband RF amplifier circuit are respectively provided with a low-pass filter, and the low-pass filter is used to filter out non-essential frequency components in the I / Q baseband signal. In the broadband RF amplifier circuit, the I / Q baseband signal with a frequency of kHz~B / 2 is filtered by the low-pass filter and then transmitted to the broadband RF amplifier.

7. The broadband receiving circuit for X-band synthetic aperture radar according to claim 6, It is characterized in that The low-pass filter is constructed by using LC lumped parameter elements, and the passband range is DC to B / 2.

8. The broadband receiving circuit for X-band synthetic aperture radar according to claim 1, It is characterized in that The first equalizing circuit and the second equalizing circuit are respectively provided with a second fixed attenuator, and the second fixed attenuator is used to limit the signal amplitude. In the equalizing circuit, the I / Q baseband signal passes through the amplitude equalizer and is transmitted to the second fixed attenuator.

9. The broadband receiving circuit for X-band synthetic aperture radar according to claim 1, It is characterized in that In the external circuit of the broadband RF amplifier circuit, the broadband RF amplifier input end is connected in parallel with a first capacitor and a second capacitor, the broadband RF amplifier output end is connected to the first branch and the second branch, the first branch is connected in parallel with a fifth capacitor and a sixth capacitor, the end of the second branch is connected to the power supply end, and the second branch is connected in series with a first resistor and a first inductor; a third capacitor and a fourth capacitor are also provided, the third capacitor and the fourth capacitor are arranged in parallel, and the first ends of the third capacitor and the fourth capacitor are connected between the first resistor and the power supply end, and the second ends of the third capacitor and the fourth capacitor are grounded.

10. The broadband receiving circuit for X-band synthetic aperture radar according to claim 1, It is characterized in that The input end of the amplitude equalizer configuration circuit is connected in parallel with a seventh capacitor and a second resistor, and the output end is connected in parallel with a second inductor and a third resistor, and the seventh capacitor is connected in series with the second inductor, and the second resistor is connected in series with the third resistor; a fourth resistor is also provided, a first end of the fourth resistor is connected between the second resistor and the third resistor, and a second end of the fourth resistor is connected in parallel with the third inductor and the eighth capacitor and then grounded.

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