Radio frequency signal automatic gain control method and system

Abstract

The invention discloses a radio frequency signal automatic gain control method and system, and the method comprises the steps: automatically adjusting the gain of each amplifier in a radio frequency signal system according to the gain of a to-be-tested antenna AUT, adjusting an S21 parameter measured by the to-be-tested antenna AUT to be in an optimal dynamic range interval, enabling each power amplifier to work in an optimal linear state, and enabling each power amplifier to work in an optimal linear state; the method avoids the situation that the testing efficiency is affected by manually adding attenuators before each test, improves the measurement precision, simplifies the testing process, and is suitable for RCS testing and near-far field darkroom testing radio frequency signal systems.

Description

Technical Field

[0001] The present invention relates to the fields of antenna and RCS testing, and in particular to a method and system for automatic gain control of radio frequency signals. Background Art

[0002] As attached Figure 1 As shown, the antenna is measured in a far-field microwave anechoic chamber. The working principle of the RF signal system in a near-field anechoic chamber or a compact field anechoic chamber is similar.

[0003] Due to the different gains or sidelobe magnitudes of the antenna AUT to be tested, it is necessary to manually add an attenuator to the link or replace the power amplifier with a suitable gain before testing to keep the S21 measurement value within a reasonable effective range, otherwise the measurement error will increase. However, since the gains of various types of power amplifiers in the RF signal system are fixed values, when the gain G_AUT of the antenna AUT to be tested is too large, the received power P3 will be too high, resulting in saturation of the low-noise amplifier or even burning of the low-noise amplifier. At this time, the S21 tested by the vector network analyzer VNA is no longer the value of the real link, causing an increase in the measurement error; when the gain of the antenna AUT to be tested is small or the antenna AUT to be tested is rotated so that the sidelobe is facing the mark When the antenna is aligned, if the sidelobe level is small, the signal-to-noise ratio of the received signal of the vector network analyzer VNA is too low. At this time, the S21 measured by the vector network analyzer VNA fluctuates greatly, and the poor stability of the RF signal system causes the increase of the measurement error. The difference between the maximum power P4_MAX and the minimum power P4_MIN that the entire link can receive is the dynamic range. P4_MAX is limited by the saturation power of the low-noise amplifier, and P4_MIN is limited by the background noise of the instrument. The gain of the entire link cannot be automatically adjusted according to the gain or sidelobe level of the AUT. The S21 measurement value is distorted due to the saturation of the low-noise amplifier or fluctuates greatly due to the low signal-to-noise ratio of the received signal, affecting the test accuracy of the antenna or RCS. Summary of the invention

[0004] In order to solve the technical problem that the S21 measurement value is distorted due to the saturation of the low noise amplifier or has a large fluctuation due to the low signal-to-noise ratio of the received signal, which affects the test accuracy of the antenna or RCS, the present invention proposes a method and system for automatic gain control of radio frequency signals, so that the electrical performance test level of the device under test is within the optimal dynamic range of the system, and the method is suitable for far-field, near-field and compact field measurements.

[0005] A method for automatic gain control of a radio frequency signal comprises the following steps:

[0006] S1: Turn on the automatic gain control RF signal system, and align the maximum radiation direction or maximum scattering direction of the device under test with the system feed source after it stabilizes;

[0007] S2:

[0008] When the analyzer is a vector network analyzer VNA, the vector network analyzer VNA reads the S parameter S21 value of the automatic gain control RF signal system link, and the host computer PC reads the current S21 value of the vector network analyzer VNA through the far-field serial port or Ethernet;

[0009] When the analyzer is a signal source and a power meter / spectrum analyzer, the host PC reads the signal source output power P1 and the power P4 measured by the power meter / spectrum analyzer through the far-field serial port or Ethernet, and calculates the S parameter S21 value of the automatic gain control RF signal system link:

[0010] S21 = P4 - P1;

[0011] S3: The host computer calculates the gain value ΔS that needs to be adjusted for each amplifier. The formula is:

[0012] ΔS = S21 - S21_THRESHOLD;

[0013] The S21_THRESHOLD is the S parameter of the optimal automatic gain control radio frequency signal system link;

[0014] S4: Determine the size of ΔS:

[0015] If ΔS is less than 0, the gain of the power amplifier is increased first. The host computer PC directly sends a command to the power amplifier to increase the gain of the power amplifier |ΔS|. If the gain of the power amplifier has increased to the maximum value and |ΔS| is still less than 0, the gain of the low noise amplifier is increased by controlling the output voltage of the programmable DC power supply until ΔS=0.

[0016] If ΔS>0, the gain of the power amplifier is reduced first. The host PC directly sends a command to the power amplifier to reduce the gain of the power amplifier |ΔS|. If the gain of the power amplifier has been reduced to the minimum value, |ΔS| is still>0, and the gain of the low noise amplifier is reduced by controlling the output voltage of the programmable DC power supply until ΔS=0;

[0017] If ΔS=0, it is in the optimal working range, and the gain of each gain adjustable device in the radio frequency signal system link is locked.

[0018] Further, in a method for automatic gain control of a radio frequency signal, step S2 comprises the following sub-steps:

[0019] When the analyzer is a vector network analyzer (VNA):

[0020] S21: The excitation signal of Port 1 of the vector network analyzer VNA is input into the power amplifier for amplification, and the gain is G_P;

[0021] The excitation signal transmission power is P1;

[0022] S22: The power amplifier inputs the amplified signal to the standard antenna gain, and the gain is G_ANT;

[0023] The excitation signal amplification power is P2;

[0024] S23: The signal transmitted by the standard antenna is received by the antenna under test AUT after transmission attenuation in the air of the microwave darkroom, and the gain is G_AUT;

[0025] The signal power received by the antenna under test AUT is P3;

[0026] S24: If the received signal strength of the antenna under test AUT is weak, the low noise amplifier amplifies the received signal with a gain of G_LNA;

[0027] S25: Port 2 of the vector network analyzer VNA receives the signal amplified by the low noise amplifier. Assume that the transmission loss of the signal in space is S_AIR;

[0028] The received power of Port2 of the vector network analyzer VNA is P4;

[0029] S26: Vector network analyzer VNA measures the S parameter S21 value of the link automatic gain control RF signal system link:

[0030] S21=P4-P1=G_P+G_ANT-S_AIR+G_AUT+G_LNA;

[0031] S27: During the measurement, the antenna AUT rotates with the turntable of the device under test to obtain the S21 values ​​of the AUT at different angles. After data processing, the radiation pattern of the AUT is obtained.

[0032] When the analyzer is a signal source and power meter / spectrum analyzer:

[0033] S21: The excitation signal of the signal source Port1 is input to the power amplifier for amplification, and the gain is G_P;

[0034] The excitation signal transmission power is P1;

[0035] S22: The power amplifier inputs the amplified signal to the standard antenna gain, and the gain is G_ANT;

[0036] The excitation signal amplification power is P2;

[0037] S23: The signal transmitted by the standard antenna is received by the antenna under test AUT after transmission attenuation in the air of the microwave darkroom, and the gain is G_AUT;

[0038] The signal power received by the antenna under test AUT is P3;

[0039] S24: If the received signal strength of the antenna under test AUT is weak, the low noise amplifier amplifies the received signal with a gain of G_LNA;

[0040] S25: Port 2 of the power meter / spectrum analyzer receives the signal amplified by the low noise amplifier. Assume that the transmission loss of the signal in space is S_AIR;

[0041] The receiving power of Port2 of the power meter / spectrum analyzer is P4;

[0042] S26: The host PC calculates the S parameter S21 value of the automatic gain control RF signal system link through the far-field serial port or Ethernet:

[0043] S21=P4-P1=G_P+G_ANT-S_AIR+G_AUT+G_LNA;

[0044] S27: During the measurement, the antenna AUT rotates with the turntable of the device under test to obtain the S21 values ​​of the AUT at different angles. After data processing, the radiation pattern of the AUT is obtained.

[0045] Further, in a method for automatic gain control of a radio frequency signal, step S3 comprises the following sub-steps:

[0046] If S21_THRESHOLD is the threshold value, the formula is:

[0047] S21_THRESHOLD=P4_MAX-P1-S_MARGIN;

[0048] The received power of the power amplifier and the low noise amplifier in the P4_MAX radio frequency link both working in saturation state;

[0049] The S_MARGIN is a reserved value;

[0050] If S21_THRESHOLD is within a range, the formula is:

[0051] S21_THRESHOLD=[S21_TD_DOWN, S21_TD_UP];

[0052] The S21_TD_DOWN is the lower limit value of the interval centered on S21_THRESHOLD=P4_MAX-P1-S_MARGIN, and S21_TD_UP is the upper limit value of the interval centered on S21_THRESHOLD=P4_MAX-P1-S_MARGIN.

[0053] An automatic gain control radio frequency signal system, comprising a microwave darkroom, a power amplifier, an analyzer, a host computer PC, a programmable DC power supply, a low noise amplifier, and a radio frequency cable;

[0054] The analyzer may be a vector network analyzer VNA or a signal source and a power meter / spectrum analyzer;

[0055] The microwave darkroom comprises a standard antenna and an antenna under test AUT;

[0056] When the analyzer is a vector network analyzer VNA, the output end of the vector network analyzer VNA is connected to the input end of the power amplifier through a radio frequency cable, the output end of the power amplifier is connected to the input end of the standard antenna through a radio frequency wire, the output end of the antenna to be tested AUT is connected to the input end of the low noise amplifier through a radio frequency wire, and the output end of the low noise amplifier is connected to the input end of the vector network analyzer VNA through a radio frequency wire; the host computer PC is respectively connected to the interfaces of the power amplifier and the programmable DC power supply through control lines, the programmable DC power supply is connected to the interface of the noise amplifier through the control line, and the host computer PC is connected to the interface of the vector network analyzer VNA through a serial port / network cable;

[0057] When the analyzer is a signal source and a power meter / spectrum analyzer, the output end of the signal source is connected to the input end of the power amplifier through a radio frequency cable, the output end of the power amplifier is connected to the input end of the standard antenna through a radio frequency wire, the output end of the antenna to be tested AUT is connected to the input end of the low noise amplifier through a radio frequency wire, and the output end of the low noise amplifier is connected to the input end of the power meter / spectrum analyzer through a radio frequency wire; the host computer PC is connected to the interfaces of the power amplifier and the programmable DC power supply through control lines, the programmable DC power supply is connected to the interface of the noise amplifier through control lines, and the host computer PC is connected to the interfaces of the signal source and the power meter / spectrum analyzer through serial ports / network cables.

[0058] Furthermore, an automatic gain control radio frequency signal system is provided, wherein the power amplifier is a chassis-type power amplifier, including a power amplifier module and a microprocessor, and the power amplifier gain is controlled by remote commands to output different powers.

[0059] Further, in an automatic gain control radio frequency signal system, the low noise amplifier adjusts the gain by adjusting the bias voltage, and the programmable DC power supply controls the bias voltage of the low noise amplifier;

[0060] The standard antenna is supported by an antenna bracket, and the antenna under test AUT is supported by a turntable for the device under test.

[0061] The beneficial effects of the present invention are as follows: through an automatic gain control method and system for radio frequency signals, the gains of each amplifier in the radio frequency signal system are automatically adjusted according to the gain of the antenna AUT to be tested, the S21 parameter measured by the antenna AUT to be tested is adjusted to the optimal dynamic range, each power amplifier operates in the optimal linear state, and the manual addition of a de-attenuator before each test to affect the test efficiency is avoided, the measurement accuracy is improved, and the test process is simplified. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a structural diagram of a conventional RF signal system.

[0063] Figure 2 The invention is a flow chart of a method for automatic gain control of radio frequency signals.

[0064] Figure 3 It is a structure of automatic gain control RF signal system Figure 1 .

[0065] Figure 4 It is a structure of automatic gain control RF signal system Figure 2 . DETAILED DESCRIPTION

[0066] The present invention is further described below, but the protection scope of the present invention is not limited to the following description.

[0067] As attached Figure 2 As shown, a method for automatic gain control of radio frequency signals comprises the following steps:

[0068] S1: Turn on the automatic gain control RF signal system, and align the maximum radiation direction or maximum scattering direction of the device under test with the system feed source after it stabilizes;

[0069] S2:

[0070] When the analyzer is a vector network analyzer VNA, the vector network analyzer VNA reads the S parameter S21 value of the automatic gain control RF signal system link, and the host computer PC reads the current S21 value of the vector network analyzer VNA through the far-field serial port or Ethernet;

[0071] When the analyzer is a signal source and a power meter / spectrum analyzer, the host PC reads the signal source output power P1 and the power P4 measured by the power meter / spectrum analyzer through the far-field serial port or Ethernet, and calculates the S parameter S21 value of the automatic gain control RF signal system link:

[0072] S21 = P4 - P1;

[0073] S3: The host computer calculates the gain value ΔS that needs to be adjusted for each amplifier. The formula is:

[0074] ΔS = S21 - S21_THRESHOLD;

[0075] The S21_THRESHOLD is the S parameter of the optimal automatic gain control radio frequency signal system link;

[0076] S4: Determine the size of ΔS:

[0077] If ΔS is less than 0, the gain of the power amplifier is increased first. The host computer PC directly sends a command to the power amplifier to increase the gain of the power amplifier |ΔS|. If the gain of the power amplifier has increased to the maximum value and |ΔS| is still less than 0, the gain of the low noise amplifier is increased by controlling the output voltage of the programmable DC power supply until ΔS=0.

[0078] If ΔS>0, the gain of the power amplifier is reduced first. The host PC directly sends a command to the power amplifier to reduce the gain of the power amplifier |ΔS|. If the gain of the power amplifier has been reduced to the minimum value, |ΔS| is still>0, and the gain of the low noise amplifier is reduced by controlling the output voltage of the programmable DC power supply until ΔS=0;

[0079] If ΔS=0, it is in the optimal working range, and the gain of each gain adjustable device in the radio frequency signal system link is locked.

[0080] Further, in a method for automatic gain control of a radio frequency signal, step S2 comprises the following sub-steps:

[0081] When the analyzer is a vector network analyzer (VNA):

[0082] S21: The excitation signal of Port 1 of the vector network analyzer VNA is input into the power amplifier for amplification, and the gain is G_P;

[0083] The excitation signal transmission power is P1;

[0084] S22: The power amplifier inputs the amplified signal to the standard antenna gain, and the gain is G_ANT;

[0085] The excitation signal amplification power is P2;

[0086] S23: The signal transmitted by the standard antenna is received by the antenna under test AUT after transmission attenuation in the air of the microwave darkroom, and the gain is G_AUT;

[0087] The signal power received by the antenna under test AUT is P3;

[0088] S24: If the received signal strength of the antenna under test AUT is weak, the low noise amplifier amplifies the received signal with a gain of G_LNA;

[0089] S25: Port 2 of the vector network analyzer VNA receives the signal amplified by the low noise amplifier. Assume that the transmission loss of the signal in space is S_AIR;

[0090] The received power of Port2 of the vector network analyzer VNA is P4;

[0091] S26: Vector network analyzer VNA measures the S parameter S21 value of the link automatic gain control RF signal system link:

[0092] S21=P4-P1=G_P+G_ANT-S_AIR+G_AUT+G_LNA;

[0093] S27: During the measurement, the antenna AUT rotates with the turntable of the device under test to obtain the S21 values ​​of the AUT at different angles. After data processing, the radiation pattern of the AUT is obtained.

[0094] When the analyzer is a signal source and power meter / spectrum analyzer:

[0095] S21: The excitation signal of the signal source Port1 is input to the power amplifier for amplification, and the gain is G_P;

[0096] The excitation signal transmission power is P1;

[0097] S22: The power amplifier inputs the amplified signal to the standard antenna gain, and the gain is G_ANT;

[0098] The excitation signal amplification power is P2;

[0099] S23: The signal transmitted by the standard antenna is received by the antenna under test AUT after transmission attenuation in the air of the microwave darkroom, and the gain is G_AUT;

[0100] The signal power received by the antenna under test AUT is P3;

[0101] S24: If the received signal strength of the antenna under test AUT is weak, the low noise amplifier amplifies the received signal with a gain of G_LNA;

[0102] S25: Port 2 of the power meter / spectrum analyzer receives the signal amplified by the low noise amplifier. Assume that the transmission loss of the signal in space is S_AIR;

[0103] The receiving power of Port2 of the power meter / spectrum analyzer is P4;

[0104] S26: The host PC calculates the S parameter S21 value of the automatic gain control RF signal system link through the far-field serial port or Ethernet:

[0105] S21=P4-P1=G_P+G_ANT-S_AIR+G_AUT+G_LNA;

[0106] S27: During the measurement, the antenna AUT rotates with the turntable of the device under test to obtain the S21 values ​​of the AUT at different angles. After data processing, the radiation pattern of the AUT is obtained.

[0107] Further, in a method for automatic gain control of a radio frequency signal, step S3 comprises the following sub-steps:

[0108] If S21_THRESHOLD is the threshold value, the formula is:

[0109] S21_THRESHOLD=P4_MAX-P1-S_MARGIN;

[0110] The received power of the power amplifier and the low noise amplifier in the P4_MAX radio frequency link both working in saturation state;

[0111] The S_MARGIN is a reserved value and can be set to a smaller value such as 1dB, 2dB, 3dB, etc.

[0112] If S21_THRESHOLD is within a range, the formula is:

[0113] S21_THRESHOLD=[S21_TD_DOWN, S21_TD_UP];

[0114] The S21_TD_DOWN is the lower limit value of the interval centered on S21_THRESHOLD=P4_MAX-P1-S_MARGIN, and S21_TD_UP is the upper limit value of the interval centered on S21_THRESHOLD=P4_MAX-P1-S_MARGIN.

[0115] An automatic gain control radio frequency signal system, comprising a microwave darkroom, a power amplifier, an analyzer, a host computer PC, a programmable DC power supply, a low noise amplifier, and a radio frequency cable;

[0116] The analyzer may be a vector network analyzer VNA or a signal source and a power meter / spectrum analyzer;

[0117] The microwave darkroom comprises a standard antenna and an antenna under test AUT;

[0118] As attached Figure 3As shown, when the analyzer is a vector network analyzer VNA, the output end of the vector network analyzer VNA is connected to the input end of the power amplifier through a radio frequency cable, the output end of the power amplifier is connected to the input end of the standard antenna through a radio frequency wire, the output end of the antenna to be tested AUT is connected to the input end of the low noise amplifier through a radio frequency wire, and the output end of the low noise amplifier is connected to the input end of the vector network analyzer VNA through a radio frequency wire; the host computer PC is connected to the interfaces of the power amplifier and the programmable DC power supply through control lines, the programmable DC power supply is connected to the interface of the noise amplifier through the control line, and the host computer PC is connected to the interface of the vector network analyzer VNA through a serial port / network cable;

[0119] As attached Figure 4 As shown, when the analyzer is a signal source and a power meter / spectrum analyzer, the output end of the signal source is connected to the input end of the power amplifier through a radio frequency cable, the output end of the power amplifier is connected to the input end of the standard antenna through a radio frequency wire, the output end of the antenna to be tested AUT is connected to the input end of the low noise amplifier through a radio frequency wire, and the output end of the low noise amplifier is connected to the input end of the power meter / spectrum analyzer through a radio frequency wire; the host computer PC is connected to the interfaces of the power amplifier and the programmable DC power supply through control lines, the programmable DC power supply is connected to the interface of the noise amplifier through control lines, and the host computer PC is connected to the interfaces of the signal source and the power meter / spectrum analyzer through serial ports / network cables.

[0120] Furthermore, an automatic gain control radio frequency signal system is provided, wherein the power amplifier is a chassis-type power amplifier, including a power amplifier module and a microprocessor, and the power amplifier gain is controlled by remote commands to output different powers.

[0121] Further, in an automatic gain control radio frequency signal system, the low noise amplifier adjusts the gain by adjusting the bias voltage, and the programmable DC power supply controls the bias voltage of the low noise amplifier;

[0122] The standard antenna is supported by an antenna bracket, and the antenna under test AUT is supported by a turntable for the device under test.

[0123] Specific embodiment 1 Dynamic gain of low noise amplifier

[0124] If the amplifiers in the link all have fixed gain, set S21 to a threshold value S21_THRESHOLD, the maximum value of the antenna gain G_AUT to be tested, that is, the maximum radiation direction facing the standard antenna, and the minimum value of the antenna gain G_AUT to be tested, that is, the side lobe facing the standard antenna, the corresponding value of S21 is shown in Table 1:

[0125] Table 1 Dynamic range corresponding to fixed gain

[0126]

[0127] If the automatic gain method of the present invention is adopted to automatically adjust the gain of the low noise amplifier according to the gain of the antenna AUT under test, the gain of the antenna AUT under test is increased by ΔG on the basis of Table 1. In order to achieve S21_THRESHOLD for S21 of the system, the power amplifier gain needs to be reduced. The corresponding dynamic range is shown in Table 2. Similarly, if the gain of the AUT is reduced by ΔG on the basis of Table 1, the system gain is compensated.

[0128] Table 2 Dynamic range corresponding to dynamic gain

[0129]

[0130]

[0131] It can be seen from Table 1 and Table 2 that the measurable dynamic range of the antenna AUT under test increases by 2ΔG compared with the fixed gain system.

[0132] Table 2 only adjusts the gain G_LNA of the low noise amplifier. In actual application, the power amplifier gain G_P and the transmission power P1 can also be adjusted.

[0133] This solution uses an automatic gain control method and system for radio frequency signals to automatically adjust the gain of each amplifier in the radio frequency signal system according to the gain of the antenna AUT to be tested, adjust the S21 parameter measured by the antenna AUT to the optimal dynamic range, and make each power amplifier work in the optimal linear state, so as to avoid the manual addition of attenuators before each test to affect the test efficiency, improve the measurement accuracy, and simplify the test process.

[0134] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for automatic gain control of radio frequency signals, characterized in that: The following steps are involved: S1: Turn on the automatic gain control RF signal system, and align the maximum radiation direction or maximum scattering direction of the device under test with the system feed source after it stabilizes; S2： When the analyzer is a vector network analyzer VNA, the vector network analyzer VNA reads the S parameter S21 value of the automatic gain control RF signal system link, and the host computer PC reads the current S21 value of the vector network analyzer VNA through the far-field serial port or Ethernet; When the analyzer is a signal source and a power meter / spectrum analyzer, the host PC reads the signal source output power P1 and the power P4 measured by the power meter / spectrum analyzer through the far-field serial port or Ethernet, and calculates the S parameter S21 value of the automatic gain control RF signal system link: S21 = P4 - P1; S3: The host computer calculates the gain value ΔS that needs to be adjusted for each amplifier. The formula is: ΔS = S21 - S21_THRESHOLD; The S21_THRESHOLD is the S parameter of the optimal automatic gain control radio frequency signal system link; S4: Determine the size of ΔS: If ΔS is less than 0, the gain of the power amplifier is increased first. The host computer PC directly sends a command to the power amplifier to increase the gain of the power amplifier |ΔS|. If the gain of the power amplifier has increased to the maximum value and |ΔS| is still less than 0, the gain of the low noise amplifier is increased by controlling the output voltage of the programmable DC power supply until ΔS=0. If ΔS>0, the gain of the power amplifier is reduced first. The host PC directly sends a command to the power amplifier to reduce the gain of the power amplifier |ΔS|. If the gain of the power amplifier has been reduced to the minimum value, |ΔS| is still>0, and the gain of the low noise amplifier is reduced by controlling the output voltage of the programmable DC power supply until ΔS=0; If ΔS=0, it is in the optimal working range, and the gain of each gain adjustable device in the radio frequency signal system link is locked.

2. The method for automatic gain control of radio frequency signals according to claim 1, characterized in that: The step S2 comprises the following sub-steps: When the analyzer is a vector network analyzer (VNA): S21: The excitation signal of Port 1 of the vector network analyzer VNA is input into the power amplifier for amplification, and the gain is G_P; The excitation signal transmission power is P1; S22: The power amplifier inputs the amplified signal to the standard antenna gain, and the gain is G_ANT; The excitation signal amplification power is P2; S23: The signal transmitted by the standard antenna is received by the antenna under test AUT after transmission attenuation in the air of the microwave darkroom, and the gain is G_AUT; The signal power received by the antenna under test AUT is P3; S24: If the received signal strength of the antenna under test AUT is weak, the low noise amplifier amplifies the received signal with a gain of G_LNA; S25: Port 2 of the vector network analyzer VNA receives the signal amplified by the low noise amplifier. Assume that the transmission loss of the signal in space is S_AIR; The received power of Port2 of the vector network analyzer VNA is P4; S26: Vector network analyzer VNA measures the S parameter S21 value of the link automatic gain control RF signal system link: S21=P4-P1=G_P+G_ANT-S_AIR+G_AUT+G_LNA; S27: During the measurement, the antenna AUT rotates with the turntable of the device under test to obtain the S21 values ​​of the AUT at different angles. After data processing, the radiation pattern of the AUT is obtained. When the analyzer is a signal source and power meter / spectrum analyzer: S21: The excitation signal of the signal source Port1 is input to the power amplifier for amplification, and the gain is G_P; The excitation signal transmission power is P1; S22: The power amplifier inputs the amplified signal to the standard antenna gain, and the gain is G_ANT; The excitation signal amplification power is P2; S23: The signal transmitted by the standard antenna is received by the antenna under test AUT after transmission attenuation in the air of the microwave darkroom, and the gain is G_AUT; The signal power received by the antenna under test AUT is P3; S24: If the received signal strength of the antenna under test AUT is weak, the low noise amplifier amplifies the received signal with a gain of G_LNA; S25: Port 2 of the power meter / spectrum analyzer receives the signal amplified by the low noise amplifier. Assume that the transmission loss of the signal in space is S_AIR; The receiving power of Port2 of the power meter / spectrum analyzer is P4; S26: The host PC calculates the S parameter S21 value of the automatic gain control RF signal system link through the far-field serial port or Ethernet: S21=P4-P1=G_P+G_ANT-S_AIR+G_AUT+G_LNA; S27: During the measurement, the antenna AUT rotates with the turntable of the device under test to obtain the S21 values ​​of the AUT at different angles. After data processing, the radiation pattern of the AUT is obtained.

3. The method for automatic gain control of radio frequency signals according to claim 1, characterized in that: The step S3 comprises the following sub-steps: If S21_THRESHOLD is the threshold value, the formula is: S21_THRESHOLD=P4_MAX-P1-S_MARGIN; The received power of the power amplifier and the low noise amplifier in the P4_MAX radio frequency link both working in saturation state; The S_MARGIN is a reserved value; If S21_THRESHOLD is within a range, the formula is: S21_THRESHOLD=[S21_TD_DOWN, S21_TD_UP]; The S21_TD_DOWN is the lower limit value of the interval centered on S21_THRESHOLD=P4_MAX-P1-S_MARGIN, and S21_TD_UP is the upper limit value of the interval centered on S21_THRESHOLD=P4_MAX-P1-S_MARGIN.

4. An automatic gain control radio frequency signal system, implemented based on an automatic gain control radio frequency signal method according to any one of claims 1 to 3, characterized in that: Including microwave darkroom, power amplifier, analyzer, host PC, programmable DC power supply, low noise amplifier, RF cable; The analyzer may be a vector network analyzer VNA or a signal source and a power meter / spectrum analyzer; The microwave darkroom comprises a standard antenna and an antenna under test AUT; When the analyzer is a vector network analyzer VNA, the output end of the vector network analyzer VNA is connected to the input end of the power amplifier through a radio frequency cable, the output end of the power amplifier is connected to the input end of the standard antenna through a radio frequency wire, the output end of the antenna to be tested AUT is connected to the input end of the low noise amplifier through a radio frequency wire, and the output end of the low noise amplifier is connected to the input end of the vector network analyzer VNA through a radio frequency wire; the host computer PC is respectively connected to the interfaces of the power amplifier and the programmable DC power supply through control lines, the programmable DC power supply is connected to the interface of the noise amplifier through the control line, and the host computer PC is connected to the interface of the vector network analyzer VNA through a serial port / network cable; When the analyzer is a signal source and a power meter / spectrum analyzer, the output end of the signal source is connected to the input end of the power amplifier through a radio frequency cable, the output end of the power amplifier is connected to the input end of the standard antenna through a radio frequency wire, the output end of the antenna to be tested AUT is connected to the input end of the low noise amplifier through a radio frequency wire, and the output end of the low noise amplifier is connected to the input end of the power meter / spectrum analyzer through a radio frequency wire; the host computer PC is connected to the interfaces of the power amplifier and the programmable DC power supply through control lines, the programmable DC power supply is connected to the interface of the noise amplifier through control lines, and the host computer PC is connected to the interfaces of the signal source and the power meter / spectrum analyzer through serial ports / network cables.

5. The automatic gain control radio frequency signal system according to claim 4, characterized in that: The power amplifier is a chassis-type power amplifier, including a power amplifier module and a microprocessor. The power amplifier gain is controlled by remote commands to output different powers.

6. The automatic gain control radio frequency signal system according to claim 4, characterized in that: The low noise amplifier The gain is adjusted by adjusting the bias voltage, and the programmable DC power supply controls the bias voltage of the low noise amplifier; The standard antenna is supported by an antenna bracket, and the antenna under test AUT is supported by a turntable for the device under test.

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