A fiber optic delay line radar active calibrator

Abstract

The application discloses an optical fiber delay line radar active calibrator, which adopts a digital control attenuation module to manually control the gain of a signal and compensate the flatness and the gain under different temperatures, and adopts a power monitoring module to connect a receiving front-end circuit and a power amplifier module, so that the power of input / output signals can be monitored in real time during use and maintenance. The application can accurately simulate the target RCS, and through temperature compensation and flatness compensation, the accurate and effective calibration of the target RCS measurement under the environment of temperature change and working frequency change can be realized.

Description

Technical Field

[0001] This invention relates to the field of radar detection technology, and in particular to an active calibrator for fiber optic delay line radar. Background Technology

[0002] Measurement radar generally requires calibration before use. Calibrators are categorized into passive and active calibrators. Passive calibrators, including metal conducting spheres, metal plates, and dihedral reflectors, require sophisticated manufacturing and design, need to be erected for field testing, and are subject to environmental requirements. Furthermore, the radar cross-section (RCS) of a passive calibrator is proportional to the physical dimensions of a standard calibrator and is relatively fixed, making it impossible to simulate a specified RCS range. Active calibrators generate an RCS simulation effect by receiving, delaying, amplifying, and retransmitting the measurement radar signal. This method allows for setting the simulated RCS size and has wide applications, but it is more difficult to design and requires the calibrator to have stability within a certain temperature range. Current technology cannot meet the calibration requirements of measurement radar under varying temperature environments.

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

[0004] The purpose of this invention is to provide an active calibrator for fiber optic delay line radar, which can accurately simulate the target RCS and achieve accurate and effective calibration of target RCS measurement under temperature and operating frequency variations through temperature compensation and flatness compensation.

[0005] To achieve the above objectives, the present invention provides an active calibrator for fiber optic delay line radar, comprising an antenna feed system and microwave components.

[0006] The antenna system includes a receiving antenna and a transmitting antenna;

[0007] The microwave component includes a receiving front-end circuit, a digitally controlled attenuation module, a delay module, a power amplifier module, and a power monitoring module.

[0008] The microwave components are installed inside the calibrator chassis, the antenna feed system is installed outside the calibrator chassis, and the calibrator chassis is installed on a two-dimensional manual turntable;

[0009] The receiving antenna is used to receive radar signals emitted by the measurement radar; the receiving front-end circuit is connected to the receiving antenna and is used to filter out interference outside the operating frequency band and amplify the signal; the numerically controlled attenuation module is connected to the receiving front-end circuit and is used to manually control the signal gain and compensate for flatness and gain at different temperatures; the delay module is connected to the numerically controlled attenuation module and is used to generate a fixed delay to avoid the radar's near-range blind zone; the power amplifier module is connected to the delay module and is used to amplify the signal; the power monitoring module is connected to the receiving front-end circuit and the power amplifier module and is used to monitor the power of the input / output signals in real time during use and maintenance; the transmitting antenna radiates the amplified and delayed radar signal to the outside; the alignment of the antenna in the antenna feed system with the measurement radar antenna is achieved by adjusting the azimuth and elevation angles of the two-dimensional manual turntable.

[0010] The equivalent RCS parameter of the active scaler is:

[0011]

[0012] In the formula, λ is the radar operating wavelength, G is the microwave component gain, and G t For the transmit antenna gain, G r This represents the receiving antenna gain.

[0013] The attenuation step of the numerically controlled attenuation module is less than or equal to 0.25dB, and the dynamic range is 0 to 23dB.

[0014] The dynamic range Δ of the numerically controlled attenuation module is:

[0015] Δ=Δ0+Δ1

[0016] In the formula, Δ0 is the fluctuation range of the microwave component at the operating frequency f and operating temperature T, which is used to realize the automatic adjustment of temperature and flatness, and Δ1 is used for manual adjustment of gain.

[0017] The fluctuation range Δ0 is:

[0018] Δ0=G max -G min

[0019] In the formula, G max G represents the maximum gain of the microwave component. min G represents the minimum gain of the microwave component. min It is a fixed value.

[0020] Maximum gain G of microwave components max for:

[0021] G max =F(f,T)

[0022] In the formula, the frequency f in the function F(f,T) is determined by the radar operating frequency, and the temperature T is determined by the temperature detector inside the microwave component.

[0023] The microwave component is placed in a high and low temperature test chamber, and its temperature is set to -20℃. The operating frequency of the microwave component is set in 0.1 GHz increments. The gain of the microwave component at various frequency points under the condition of -20℃ can be measured, which is the flatness of the microwave component under the same temperature condition. The temperature of the high and low temperature test chamber is increased in 5℃ increments. The above operation is repeated to measure the gain at different frequency points from -20℃ to +50℃. The function F(f,T) is obtained by function fitting.

[0024] The present invention has the following advantages:

[0025] 1. A temperature compensation mode is adopted, which can maintain the stability of system gain in the range of -20℃ to +50℃;

[0026] 2. It adopts a flatness compensation mode and has frequency adaptability, which can maintain the consistency of system gain at different operating frequencies;

[0027] 3. The attenuation step of the CNC attenuation module used does not exceed 0.25dB, and the dynamic range is 0~23dB, with good accuracy and a large RCS simulation range;

[0028] 4. A power monitoring module was designed to monitor the input and output power in real time, which is convenient for use and subsequent maintenance. Attached Figure Description

[0029] Figure 1 This invention provides a structural block diagram of an active calibrator for fiber optic delay line radar.

[0030] Figure 2 The front panel of the active calibrator provided by the present invention.

[0031] Figure 3 A table showing the gain-temperature / frequency function relationship of the microwave component in the active calibrator provided by this invention.

[0032] Figure 4 The structural block diagram of the power monitoring module of the active calibrator provided by the present invention. Detailed Implementation

[0033] The following is based on Figures 1-4 The preferred embodiments of the present invention will be described in detail below.

[0034] like Figure 1As shown, this invention provides an active calibrator for fiber optic delay line radar, comprising an antenna feed system and a microwave assembly. The antenna feed system includes a receiving antenna 1 and a transmitting antenna 9. The microwave assembly includes a receiving front-end circuit 2, a digitally controlled attenuation module 3, a delay module 4, a power amplifier module 5, a power monitoring module 6, a temperature compensation module 7, and a flatness compensation module 8. The microwave assembly is installed inside a calibrator housing 10, while the antenna feed system is installed outside the calibrator housing 10. The calibrator housing 10 is mounted on a two-dimensional manual turntable 11 using fasteners. The receiving antenna 1 receives radar signals emitted by the measurement radar and outputs the received signals to the microwave assembly. The microwave assembly is used to filter, amplify, delay, monitor, and compensate the power of the signals. The signal output by the microwave assembly is radiated externally through the transmitting antenna 9. The two-dimensional turntable 11 is used to align the calibrator's transmitting and receiving antennas with the measurement radar antenna.

[0035] The antenna feeder system must ensure that there is sufficient isolation between the receiving antenna 1 and the transmitting antenna 9, and ensure that the system isolation is greater than the system gain to avoid self-oscillation.

[0036] The receiving antenna 1 is used to receive radar signals emitted by the measuring radar; the receiving front-end circuit 2 is connected to the receiving antenna 1, and the receiving front-end circuit 2 includes a filter and a low-noise amplifier, which are used to filter out interference outside the operating frequency band and amplify the signal, respectively; the numerically controlled attenuation module 3 is connected to the receiving front-end circuit 2, part of which is used for manual gain control of the signal, and part of which is used for flatness and gain compensation at different temperatures; the delay module 4 is connected to the numerically controlled attenuation module 3, and the delay module 4 uses an optical fiber delay line to generate a fixed delay of 6.68us to avoid the radar's near-range blind zone; the power amplifier module 5 is connected to the delay module 4 and is used to amplify the signal; the power monitoring module 6 is connected to the receiving front-end circuit 2 and the power amplifier module 5, and is used to monitor the power of the input / output signals in real time during use and maintenance; the transmitting antenna 9 radiates the amplified and delayed radar signal to the outside; the calibrator antenna and the measuring radar antenna can be aligned by adjusting the azimuth and elevation angles of the two-dimensional manual turntable 11.

[0037] The measurement principle of the active calibrator provided by this invention is as follows:

[0038] The calibration source is located at a certain distance from the measuring radar. It receives the radar signal and then forwards it back to the radar after delay, amplification, or modulation. When the parameters such as the gain of the transmitting and receiving antennas and the gain of the amplifier are constant, the calibration source is equivalent to a standard radar target with a fixed radar cross section (RCS) parameter. Its equivalent radar cross section parameter can be obtained by tracing back to the standard object and used as the true value for calibration of the measuring radar to complete the calibration.

[0039] The radar cross section can be expressed as:

[0040]

[0041] In the formula, P r P represents the target echo power received by the radar. t For radar transmission power, G t G is the gain of the transmitting antenna in the target direction. r Let L be the gain of the receiving antenna in the direction of the target, λ be the radar wavelength, σ be the radar cross section of the target, and L be the gain of the receiving antenna in the direction of the target. t R is the transmit feeder branch loss, R is the distance from the transmit antenna to the target, and L is the transmit antenna distance. m For atmospheric transmission loss between the launch system and the target, L r To receive feeder branch losses, L P This refers to polarization loss.

[0042] The equivalent RCS parameter of the calibration source can be expressed as:

[0043]

[0044] In the formula, σ0 is the equivalent RCS parameter of the calibration source, and G t0 To calibrate the source transmit antenna gain, G r0 To calibrate the source receive antenna gain, G E0 To calibrate the source amplifier gain, λ is the radar wavelength being calibrated. To calibrate source loss, P t0 To calibrate the source's transmit power, P r0 To calibrate the source's received power.

[0045] It can be seen that the equivalent RCS parameter value of the calibration source is only related to parameters such as the receiving antenna gain, transmitting antenna gain, amplifier gain, and operating wavelength. When the location of the calibration source is fixed and its amplification factor is constant, its equivalent radar cross section parameter is a constant value. As long as the ratio of the input power to the output power of the calibration source remains constant, its equivalent RCS parameter can be kept constant. It is not necessary to calibrate all the internal parameters of the calibration source separately; only the input and output power needs to be calibrated to complete the traceability of the calibration source.

[0046] The equivalent RCS parameter of the active scaler is determined by the following formula:

[0047]

[0048] In the formula, λ is the radar operating wavelength, G is the microwave component gain, and G t For the calibrator transmit antenna gain, G r This is the gain of the scaler's receiving antenna.

[0049] The principle of flatness and temperature compensation of the active calibrator provided by this invention is as follows:

[0050] Since the gain G of the microwave component is related to the operating frequency f and the operating temperature T, with the operating frequency f ranging from 8 GHz to 12 GHz and the temperature T ranging from -20℃ to +50℃, the functional relationship between the gain G, the operating frequency f, and the operating temperature T is as follows:

[0051] G=F(f,T) (4)

[0052] Place the microwave assembly in a high and low temperature test chamber, set its temperature to -20℃, and adjust the front panel (e.g., Figure 2 Using the frequency setting knob (as shown), the operating frequency of the microwave component is set in 0.1 GHz increments. The gain of the microwave component at various frequencies under -20℃ conditions can be measured, which represents the flatness of the microwave component at the same temperature. The temperature of the high and low temperature test chamber is increased in 5℃ increments, and the above operation is repeated to measure the gain at different frequencies from -20℃ to +50℃. These gain values ​​are then entered into the system. Figure 3 In the table shown.

[0053] Since the experimentally measured data are discrete values, the function F(f,T) in formula (4) can be obtained by function fitting.

[0054] With the minimum gain G min The gain of the microwave component is given by the formula below. Any excess gain can be attenuated by the numerically controlled attenuation module 3.

[0055] A = F(f,T) - G min (5)

[0056] In formula (5), G min The frequency f in the function F(f,T) is a fixed value, determined by the radar operating frequency and set by the frequency knob on the front panel. The temperature T is determined by the temperature detector inside the microwave component. When the temperature changes, the numerically controlled attenuation module 3 can automatically adjust the attenuation amount, ensuring the consistency of system gain at different operating frequencies and the stability of system gain at different temperatures.

[0057] Based on the maximum gain G max and minimum value G min The fluctuation range Δ0 of the microwave component at the operating frequency f and operating temperature T can be calculated, which is the range of attenuation A, as shown in the following formula:

[0058] Δ0=G max -G min (6)

[0059] The adjustment accuracy and analog range of the active calibrator provided by this invention are designed as follows:

[0060] The numerically controlled attenuation module 3 uses a 7-bit numerically controlled attenuator with a minimum step of 0.25dB and a maximum step of 16dB, totaling a dynamic range of 31.5dB. Distributing this dynamic range Δ, we have:

[0061] Δ=Δ0+Δ1 (7)

[0062] In formula (7), Δ0 is used to achieve automatic adjustment of temperature and flatness, and Δ1 is used for manual adjustment of gain. Figure 2 The rocker switch on the front panel changes the system gain attenuation, and the gain of the microwave components can be determined by the difference in the readings of the "Input / Output Power Monitoring" digital display. In actual measurements, the maximum value of Δ0 is 8.5dB, therefore the maximum value of Δ1 is 23dB, ensuring a system adjustment accuracy of 0.25dB and an analog range of 23dB.

[0063] The power monitoring design of the active calibrator provided by this invention is as follows:

[0064] The power detection module 6 in the microwave assembly monitors the radio frequency input / output signals, such as... Figure 4 As shown, the radio frequency signal is split into two paths after entering the power divider. One path enters the radio frequency link (low-noise amplifier or transmitting antenna), and the other path enters the detector. The voltage signal output by the detector is converted into a digital signal by the A / D conversion module. This signal is displayed through a digital tube to indicate and monitor the power of the input / output signal.

[0065] In practical applications, before using an active calibrator for calibration, the active calibrator itself needs to be calibrated using a microwave anechoic chamber. Specifically, the gain-frequency curves of the calibrator's transmitting and receiving antennas are measured using a standard gain horn antenna, and the gain-frequency curves of the cable-microwave assembly are also measured. From these two sets of curves, the overall gain-frequency curve of the calibrator can be determined. Based on the RCS to be simulated and the operating frequency, the system gain of the calibrator can be deduced. Subtracting the gain of the transmitting and receiving antennas from the system gain yields the gain G of the microwave assembly. By setting a rocker switch and observing the power monitoring digital display, the gain of the microwave assembly can be set.

[0066] The present invention has the following advantages:

[0067] 1. A temperature compensation mode is adopted, which can maintain the stability of system gain in the range of -20℃ to +50℃;

[0068] 2. It adopts a flatness compensation mode and has frequency adaptability, which can maintain the consistency of system gain at different operating frequencies;

[0069] 3. The attenuation step of the CNC attenuation module used does not exceed 0.25dB, and the dynamic range is 0~23dB, with good accuracy and a large RCS simulation range;

[0070] 4. A power monitoring module was designed to monitor the input and output power in real time, which is convenient for use and subsequent maintenance.

[0071] It should be noted that, in the embodiments of the present invention, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the embodiments. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0072] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0073] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. An active calibrator for fiber optic delay line radar, characterized in that, Includes antenna feed system and microwave components; The antenna system includes a receiving antenna and a transmitting antenna; The microwave component includes a receiving front-end circuit, a digitally controlled attenuation module, a delay module, a power amplifier module, and a power monitoring module. The microwave components are installed inside the calibrator chassis, the antenna feed system is installed outside the calibrator chassis, and the calibrator chassis is installed on a two-dimensional manual turntable; The receiving antenna is used to receive radar signals emitted by the measurement radar; the receiving front-end circuit is connected to the receiving antenna and is used to filter out interference outside the operating frequency band and amplify the signal; the numerically controlled attenuation module is connected to the receiving front-end circuit and is used to manually control the signal gain and compensate for flatness and gain at different temperatures; the delay module is connected to the numerically controlled attenuation module and is used to generate a fixed delay to avoid the radar's near-range blind zone; the power amplifier module is connected to the delay module and is used to amplify the signal; the power monitoring module is connected to the receiving front-end circuit and the power amplifier module and is used to monitor the power of the input / output signals in real time during use and maintenance; the transmitting antenna radiates the amplified and delayed radar signal outwards; the alignment of the antenna in the antenna feed system with the measurement radar antenna is achieved by adjusting the azimuth and elevation angles of the two-dimensional manual turntable. The dynamic range of the numerically controlled attenuation module for: In the formula, For microwave components at the operating frequency f The fluctuation range at operating temperature T is used to achieve automatic adjustment of temperature and flatness. Manual adjustment of gain; Fluctuation range for: In the formula, This represents the maximum gain of the microwave component. This represents the minimum gain of the microwave component. It is a fixed value; Maximum gain of microwave components for: In the formula, the function frequency in f The temperature T is determined by the radar operating frequency and by the temperature detector inside the microwave component. The microwave component was placed in a high and low temperature test chamber, with the temperature set to -20℃. The operating frequency of the microwave component was set in 0.1 GHz increments. The gain of the microwave component at various frequency points under -20℃ conditions could be measured, which represents the flatness of the microwave component under the same temperature conditions. The temperature of the high and low temperature test chamber was increased in 5℃ increments, and the above operation was repeated to measure the gain at different frequency points from -20℃ to +50℃. The function was then obtained through function fitting. .

2. The fiber optic delay line radar active calibrator as described in claim 1, characterized in that, The equivalent RCS parameter of the active scaler is: In the formula, G is the radar operating wavelength, and G is the microwave component gain. For the transmit antenna gain, This represents the receiving antenna gain.

3. The fiber optic delay line radar active calibrator as described in claim 2, characterized in that, The attenuation step of the numerically controlled attenuation module is less than or equal to 0.25dB, and the dynamic range is 0~23dB.

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