Frequency offset error control device for distance measurement of responder

Abstract

The utility model discloses a frequency offset error control device for the distance measurement of a responder, and mainly solves the problem that the modulation frequency offset error is increased in the prior art. The system comprises a transmitting channel, a receiving channel, a frequency synthesizer source module, a ramp generator loop module and a high frequency mixing module. The frequency synthesizer source module outputs in two paths, one path is connected with the ramp generator loop module through a first power divider, a frequency divider and a second power divider, and the other path is connected with the high frequency mixing module through the first power divider, a first filter and a frequency multiplier; the slope generator loop module is connected with the high frequency mixing module through the low frequency mixer and the third filter; the high frequency mixing module mixes the signal output by the frequency multiplier and the signal output by the third filter and then inputs the mixed signal to a transmitting channel for transmission; and the receiving channel receives a transmitted signal and outputs a constant difference frequency signal for distance measurement. According to the utility model, the modulation frequency offset error of the linear frequency modulation signal can be reduced, the frequency stability of the transmitted signal can be improved, and the device can be used for distance measurement based on the linear frequency modulation continuous wave signal responder.

Description

Technical Field

[0001] The utility model belongs to the technical field of radar ranging, and in particular relates to a frequency deviation error control device, which can be used for distance measurement of a transponder to improve the ranging accuracy of the transponder. Background Art

[0002] The radar and the transponder form an interrogation and response secondary radar system. The transponder is installed on the aircraft and the radar is located on the ground. The radar periodically transmits a pulse interrogation signal to the transponder. The transponder receives the interrogation signal, judges and processes it, and replies a pulse response signal to the radar. At the same time, the transponder also has the function of an altimeter, which can detect the distance between the aircraft and the ground. It uses a linear frequency modulated continuous wave signal with a sawtooth wave waveform, a frequency modulation bandwidth of B, and a signal period of T. The voltage-controlled oscillator of the transponder generates a linear frequency modulated continuous wave transmission. The transmission signal is reflected by the target to generate an echo signal with a certain time delay, which is received by the transponder. The transponder mixes the echo signal with a replica of the transmission signal, and then performs filtering, coherent detection and sampling in sequence. Finally, a set of narrowband filters are used to perform spectrum analysis using the FFT method to extract the frequency information, namely the difference frequency f b , then according to the speed of light c, sawtooth signal period T, difference frequency f b The relationship between these four factors and the target distance R is: R = (c × T × f b )÷(2×B), calculate the target distance, and get the ranging error △R / R=△f b / f b +△T / T-△B / B. In the formula, f b The error is related to the number of FFT processing points. The larger the number of points, the higher the frequency resolution. b The error of B is controlled within 0.1%; using high-stability crystal oscillator and high-speed digital clock counting, the quantization error of T is very small, and the error of T can be controlled within 0.1%; the error of B is related to the stability of the voltage-controlled oscillator. The fluctuation of the voltage-controlled oscillator frequency causes the modulation frequency deviation error. When the operating frequency of the transponder is not higher than the C band, the error of B can be controlled within 1%. According to the above formula, the error of B is the primary factor restricting the improvement of the ranging accuracy of the transponder.

[0003] The existing modulation methods for voltage-controlled oscillators mainly include analog modulation and digital modulation, among which:

[0004] Methods of analog modulation of voltage-controlled oscillators, such as Figure 1As shown in the figure, it uses a sawtooth voltage with a linear amplitude change from low to high to modulate the output frequency of the voltage-controlled oscillator. This method not only generates a linear frequency-modulated continuous wave signal with a certain bandwidth, but also when the tuning end of the voltage-controlled oscillator is affected by the power supply ripple, it will cause the linearity of the input sawtooth voltage to deteriorate, causing the output frequency of the voltage-controlled oscillator to produce random offsets, resulting in changes in the frequency modulation bandwidth B, affecting the ranging accuracy of the transponder. The higher the frequency, the easier it is for the output frequency of the voltage-controlled oscillator to produce random offsets, resulting in an increase in the error of the frequency modulation bandwidth B. When the operating frequency of the transponder is higher than the C band, the error of the frequency modulation bandwidth B is greater than 1% in the full temperature range, reducing the ranging accuracy of the transponder.

[0005] When digital modulation is used for the voltage-controlled oscillator, the analog sawtooth voltage is converted into a digital voltage, and a digital phase-locked loop is used to control the output frequency of the voltage-controlled oscillator. The frequency increment step of the digital phase-locked loop is controlled by the digital voltage, and the frequency step and the sampling step are linearly related. When the sawtooth signal is short in period, the number of digital sampling points is small. When the fast Fourier transform FFT is used for spectrum analysis, the extracted frequency information is inaccurate due to the large frequency step and small number of points, and an offset phenomenon will occur, which causes the short-range ranging accuracy to fail to meet the use requirements. Utility Model Content

[0006] The purpose of the utility model is to address the deficiencies of the above-mentioned prior art and to propose a frequency deviation error control circuit and control method for transponder ranging, so as to achieve precise control of the modulation frequency deviation of the linear frequency modulation signal, improve the frequency stability of the linear frequency modulation signal, and thus improve the ranging accuracy of the transponder.

[0007] The technical idea of ​​the utility model is: output a point frequency signal with high frequency stability through the frequency synthesis source module; divide it into two outputs through the power divider, one of which is mixed with the low-frequency linear frequency modulation signal output by the ramp generator loop module after frequency division to generate a high-frequency linear frequency modulation signal input to the high-frequency mixing module, and the other is mixed with the high-frequency linear frequency modulation signal in the high-frequency mixing module after frequency multiplication to generate a higher-frequency linear frequency modulation signal, and transmit it to the antenna through the transmission channel for transmission. Its implementation scheme is as follows:

[0008] 1. A frequency deviation error control device for transponder ranging, comprising: a transmitting channel and a receiving channel, characterized in that: it also includes a frequency synthesis source module 1, a ramp generator loop module 2, and a high frequency mixing module 3;

[0009] The frequency synthesis source module 1 is divided into two output paths, one path is connected to the ramp generator loop module 2 through the first power divider H1, the frequency divider D1, and the second power divider H2; the other path is connected to the high frequency mixing module 3 through the first power divider H1, the first filter B1, and the frequency multiplier J;

[0010] The ramp generator loop module 2 is used as a frequency modulation source, which is connected to the high frequency mixing module 3 through the low frequency mixer F1 and the third filter B3;

[0011] The high frequency mixing module 3 mixes the signal output by the frequency multiplier J with the signal output by the third filter B3 and inputs the mixed signal to the transmitting channel 4, and transmits the mixed signal through the antenna transmitting port; the receiving channel 5 receives the transmitted signal and outputs a constant difference frequency signal for ranging.

[0012] Further, the frequency synthesis source module 1 includes: a crystal oscillator E, a second frequency divider D2, a phase detector A, a fourth filter B4, a voltage-controlled oscillator C and a third power divider H3; the output end of the crystal oscillator E is connected to the first input end of the phase detector A, the output end of the phase detector A is connected to the input end of the voltage-controlled oscillator C through the fourth filter B4, and the output end of the voltage-controlled oscillator C is divided into two outputs through the third power divider H3, that is, the first output enters the input end of the first power divider H1, and the second output is fed back to the second input end of the phase detector A through the second frequency divider D2, forming a phase-locked loop; when the phase difference between the output signal of the second frequency divider D2 and the output signal of the crystal oscillator E is constant, the phase detector A will output a constant DC voltage signal, so that the output frequency of the voltage-controlled oscillator C is locked at the point frequency of 11600MHz, and is input to the input end of the first power divider H1 through the first output end of the third power divider H3.

[0013] Furthermore, the ramp generator loop module 2 includes: a digital ramp generating device L, a fifth filter B5, and a sixth filter B6; the fifth filter B5 filters the dot frequency signal input by the second power divider H2 and transmits it to the digital ramp generator L as its reference clock. The ramp generating device L generates a 93MHz to 257MHz low-frequency digital linear frequency modulation signal under the drive of the reference clock and the control of an external sawtooth wave digital signal. The digital linear frequency modulation signal is filtered by the sixth filter B6 and then enters the input end of the low mixer F1.

[0014] Furthermore, the low frequency mixer F1 has two input terminals, one of which is connected to the output terminal of the ramp generator loop module 2, and the other is connected to the output terminal of the second filter B2, and the input terminal of the second filter B2 is connected to the second output terminal of the second power divider H2.

[0015] Furthermore, the high frequency mixing module 3 includes: a seventh filter B7, a first amplifier G1, an eighth filter B8 and a high frequency mixer F2; the seventh filter B7 filters the signal output by the frequency multiplier J and then enters the high frequency mixer F2; the first amplifier G1 performs power amplification on the signal output by the third filter B3, and then filters it through the eighth filter B8 and enters the high frequency mixer F2; the high frequency mixer F2 mixes the two incoming signals to generate a higher frequency linear frequency modulation signal of 24018MHz to 24182MHz, and transmits it to the transmitting channel 4.

[0016] Furthermore, the transmitting channel 4 includes: a ninth filter B9, a second amplifier G2, a tenth filter B10 and a coupler K; the higher frequency linear frequency modulation signal output by the high mixing module 3 is transmitted to the antenna transmitting port through the ninth filter B9, the second amplifier G2, the tenth filter B10 and the coupler K in sequence, and then is transmitted to the antenna transmitting port for transmission, and is received by the receiving channel 5.

[0017] Compared with the prior art, the utility model has the following advantages:

[0018] Firstly, the utility model uses a crystal oscillator with high frequency stability and low phase noise as a reference source, and uses a phase-locked loop technology to enable the frequency synthesis source module to generate a stable point frequency signal of 11600MHz, thereby improving frequency stability and reducing phase noise.

[0019] Secondly, the utility model adopts digital ramp generation technology and uses 725MHz point frequency signal as reference clock, which can speed up the frequency sweep speed, reduce the frequency increment step, reduce the sampling step, increase the number of sampling points, and improve the frequency stability and linearity.

[0020] Thirdly, the utility model mixes the dot frequency signal with the linear frequency modulation signal to generate a higher frequency 24018MHz~24182MHz linear frequency modulation signal, which further improves the stability of the output frequency, reduces the probability of frequency deviation of the output signal, and increases the output frequency of the signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A block diagram of the structure for generating a linear frequency modulation signal in the prior art;

[0022] Figure 2 It is a structural block diagram of the utility model;

[0023] Figure 3 It is a structural block diagram of the frequency synthesis source module in the utility model;

[0024] Figure 4 This is a structural block diagram of the ramp generator loop module in the utility model;

[0025] Figure 5 This is a structural block diagram of the high frequency mixing module in the utility model;

[0026] Figure 6 This is a structural block diagram of the transmission channel in the utility model. DETAILED DESCRIPTION

[0027] The embodiments of the present invention are described in further detail below in conjunction with the accompanying drawings.

[0028] Reference Figure 2 The transponder ranging frequency deviation error control device of this example includes: frequency synthesis source module 1, harmonic generator loop module 2, high frequency mixer module 3, transmitting channel 4, receiving channel 5, frequency multiplier J, low frequency mixer F1, frequency divider D1, two power dividers H1, H2 and three filters B1, B2, B3. Among them:

[0029] A frequency synthesis source module 1, whose output is connected to the input end of a first power divider H1, the first power divider H1 is provided with two output ends, namely, the first output end is connected to the input end of a high frequency mixer module 3 through a first filter B1 and a frequency multiplier J in sequence, and the second output end is connected to the input end of a second power divider H2 through a first frequency divider D1; the second power divider H2 is also provided with two output ends, namely, the first output end is connected to the input end of a low frequency mixer F1 through a second filter B2, and the second output end is connected to the input end of a ramp generator loop module 2;

[0030] The ramp generator loop module 2 has a sawtooth wave digital signal and a reference clock output by the second power divider H2 as inputs, and an output end thereof is connected to an input end of a low frequency mixer F1, and an output end of the low frequency mixer F1 is connected to an input end of a high frequency mixer module 3 through a third filter B3;

[0031] The output end of the high frequency mixing module 3 is connected to the antenna transmission port through the transmission channel 4, and the receiving channel 5 receives the signal transmitted by the antenna transmission port and outputs a constant difference frequency signal for ranging.

[0032] Reference Figure 3The frequency synthesis source module 1 includes a crystal oscillator E, a second frequency divider D2, a phase detector A, a fourth filter B4, a voltage-controlled oscillator C and a third power divider H3; the output end of the crystal oscillator E is connected to the first input end of the phase detector A, the output end of the phase detector A is connected to the input end of the voltage-controlled oscillator C through the fourth filter B4, and the output end of the voltage-controlled oscillator C is divided into two outputs through the third power divider H3, that is, the first output enters the input end of the first power divider H1, and the second output is fed back to the second input end of the phase detector A through the second frequency divider D2, forming a phase-locked loop; when the phase difference between the output signal of the second frequency divider D2 and the output signal of the crystal oscillator E is constant, the phase detector A will output a constant DC voltage signal, so that the output frequency of the voltage-controlled oscillator C is locked at the point frequency of 11600MHz, and is input to the input end of the first power divider H1 through the first output end of the third power divider H3.

[0033] Reference Figure 4 The ramp generator loop module 2 includes: a digital ramp generator L, a fifth filter B5, and a sixth filter B6; the fifth filter B5 filters the dot frequency signal input by the second power divider H2 and transmits it to the digital ramp generator L as its reference clock. The ramp generator L generates a 93MHz to 257MHz low-frequency digital linear frequency modulation signal under the drive of the reference clock and the control of the external sawtooth wave digital signal. The digital linear frequency modulation signal is filtered by the sixth filter B6 and then enters the input end of the low mixer F1. The digital ramp generating device L is provided with a control register L1, a frequency synthesizer L2 and a D / A converter L3. The input end of the control register L1 is connected to an external sawtooth wave digital signal through a serial port. The external sawtooth wave digital signal includes three signals: a sawtooth period SPI_CLK, a sawtooth wave amplitude SPI_DATA and a sawtooth wave enable control SPI_LE. The output end of the control register L1 is connected to the frequency synthesizer L2 and the first input end of the D / A converter L3 in sequence. The second input end of the D / A converter L3 is connected to the output end of the fifth filter B5.

[0034] Reference Figure 5 The high frequency mixing module 3 includes: a seventh filter B7, a first amplifier G1, an eighth filter B8 and a high frequency mixer F2; the seventh filter B7 filters the signal output by the frequency multiplier J and then enters the high frequency mixer F2; the first amplifier G1 amplifies the power of the signal output by the third filter B3, and then filters it through the eighth filter B8 and enters the high frequency mixer F2; the high frequency mixer F2 mixes the two incoming signals to generate a higher frequency linear frequency modulation signal of 24018MHz to 24182MHz, and transmits it to the transmitting channel 4.

[0035] Reference Figure 6The transmitting channel 4 includes: a ninth filter B9, a second amplifier G2, a tenth filter B10 and a coupler K; the higher frequency linear frequency modulation signal output by the high mixing module 3 is transmitted to the antenna transmitting port through the ninth filter B9, the second amplifier G2, the tenth filter B10 and the coupler K in sequence, and then transmitted to the receiving channel 5 for reception.

[0036] The working principle of the utility model is as follows:

[0037] First, a phase-locked loop is formed to output a stable frequency signal:

[0038] When different voltages are added to the tuning input of the voltage-controlled oscillator C, different frequencies are output. Initially, the voltage-controlled oscillator C inputs the voltage V1, and the output frequency is f1. The output signal of the voltage-controlled oscillator C is divided into two outputs through the third power divider H3. The first output enters the input of the first power divider H1, and the second output signal is frequency-divided by the second frequency divider D2, with a frequency-division coefficient of N1=116. The divided signal and the 100MHz signal output by the crystal oscillator E enter the input of the phase detector A at the same time. The phase detector A detects the phase difference between the two signals and outputs a DC voltage signal associated with the phase difference. The DC voltage signal is filtered by the fourth filter B4 and then enters the input of the voltage-controlled oscillator C to control the frequency of the output signal of the voltage-controlled oscillator C. The frequency and phase of the output signal of the voltage-controlled oscillator C are then fed back to the phase detector A through the third power divider H3 and the second frequency divider D2 to form a phase-locked loop.

[0039] When the phase difference between the 100MHz signal output by the second frequency divider D2 and the 100MHz signal output by the crystal oscillator E is constant, the phase detector A will output a DC voltage signal with a constant value, so that the output frequency of the voltage-controlled oscillator C is locked at the point frequency of 116×100MHz=11600MHz. Since the 100MHz output of the crystal oscillator E is a point frequency signal with high frequency stability and low phase noise, the output of the voltage-controlled oscillator C is also a point frequency signal with high frequency stability and low phase noise through the phase-locked loop.

[0040] Secondly, the frequency stabilization signal is output in a branch path:

[0041] The voltage-controlled oscillator C divides its stable 11600MHz frequency signal into two outputs through the first power divider H1, wherein the first output signal is filtered by the first filter B1 and then enters the frequency multiplier J, the frequency multiplier J doubles the frequency of the input 11600MHz frequency signal to obtain a 2×11600MHz=23200MHz frequency signal, and then enters the input end of the high frequency mixer F2 after being filtered by the seventh filter B7;

[0042] The second output signal is frequency-divided by the first frequency divider D1, with the frequency division coefficient being N2=16, to obtain a frequency-divided signal of 11600MHz / 16=725MHz, which is input to the second power divider H2.

[0043] Next: split the frequency-divided signal and output it in different ways:

[0044] The second power divider H2 divides the divided 725MHz frequency signal into two outputs:

[0045] The first output is filtered by the second filter B2 and then enters the input end of the low frequency mixer F1;

[0046] The second output is sent to the fifth filter B5, and after being filtered, enters the input end of the digital ramp generating device L as a reference clock signal.

[0047] Next, a stable high-frequency linear frequency modulation signal is generated:

[0048] Driven by the reference clock and controlled by the external sawtooth wave digital signal, the digital ramp generator L generates a stable low-frequency linear frequency modulation signal with a frequency of 93MHz to 257MHz and enters the input end of the low mixer F1. The minimum step frequency of the low-frequency linear frequency modulation signal is: reference clock frequency / 2 32 =0.2Hz, the minimum step time is: 4 / reference clock frequency = 5ns;

[0049] The low frequency mixer F1 mixes the input 725MHz dot frequency signal with the low frequency linear frequency modulation signal of 93MHz to 257MHz, and outputs a stable high frequency linear frequency modulation signal of 818MHz to 982MHz.

[0050] Next: The high frequency mixer F2 generates a stable higher frequency linear frequency modulation signal through mixing:

[0051] The high-frequency linear frequency modulation signal of 818MHz~982MHz is power amplified by the first amplifier G1 and filtered by the eighth filter B8 before entering the input end of the high frequency mixer F2. The high frequency mixer F2 mixes the input 23200MHz point frequency signal with the high-frequency linear frequency modulation signal of 818MHz~982MHz, and outputs a higher-frequency linear frequency modulation signal of 24018MHz~24182MHz into the transmitting channel.

[0052] Finally: a constant difference frequency signal f is generated by mixing the transmitted signal with the echo signal b , calculate the target distance R according to the difference frequency signal and the parameters of the external input system:

[0053] The higher frequency linear frequency modulation signal of 24018MHz to 24182MHz is filtered by the ninth filter B9, amplified by the second amplifier G2, filtered by the tenth filter B10 in the transmission channel 4, and then transmitted to the antenna transmission port through the coupler K for transmission;

[0054] The transmitted higher frequency linear frequency modulation signal is reflected by the target to form an echo signal and enter the receiving channel 5. At this time, the coupler K in the transmitting channel 4 mixes the coupled transmitting signal with the echo signal to generate a constant difference frequency signal f b .

[0055] According to the sawtooth wave starting voltage V1 of the external input system, the corresponding system output starting frequency is f v1 ;

[0056] According to the sawtooth wave termination voltage V2 of the external input system, the corresponding system output termination frequency is f v2 ;

[0057] According to the starting frequency f of the system output v1 , stop frequency f v2 , we get the frequency modulation bandwidth B = f v2 -f v1 ;

[0058] According to the difference frequency signal f b The distance R between the target and the transponder is calculated by using the frequency modulation bandwidth B:

[0059] R=(c×T×f b )÷(2×B)

[0060] Where c is the speed of light and T is the period of the sawtooth wave signal.

[0061] According to the distance R, guide the aircraft to land towards the target location.

Claims

1. A frequency deviation error control device for transponder ranging, comprising: Transmitting channel (4), receiving channel (5); characterized in that: it also includes a frequency synthesis source module (1), a ramp generator loop module (2), and a high frequency mixing module (3); The frequency synthesis source module (1) is divided into two output paths, one path is connected to the ramp generator loop module (2) through the first power divider H1, the frequency divider D1, and the second power divider H2; the other path is connected to the high frequency mixing module (3) through the first power divider H1, the first filter B1, and the frequency multiplier J; The ramp generator loop module (2) is used as a frequency modulation source and is connected to the high frequency mixing module (3) via a low frequency mixer F1 and a third filter B3; The high frequency mixing module (3) mixes the signal output by the frequency multiplier J with the signal output by the third filter B3 and inputs the mixed signal to the transmitting channel (4), and transmits the mixed signal through the antenna transmitting port; the receiving channel (5) receives the transmitted signal and outputs a constant difference frequency signal for distance measurement.

2. The device according to claim 1, characterized in that The frequency synthesis source module (1) comprises: a crystal oscillator E, a second frequency divider D2, a phase detector A, a fourth filter B4, a voltage-controlled oscillator C and a third power divider H3; the output end of the crystal oscillator E is connected to the first input end of the phase detector A, the output end of the phase detector A is connected to the input end of the voltage-controlled oscillator C through the fourth filter B4, the output end of the voltage-controlled oscillator C is divided into two outputs through the third power divider H3, that is, the first output enters the input end of the first power divider H1, and the second output is fed back to the second input end of the phase detector A through the second frequency divider D2, forming a phase-locked loop; when the phase difference between the output signal of the second frequency divider D2 and the output signal of the crystal oscillator E is constant, the phase detector A will output a DC voltage signal with a constant value, so that the output frequency of the voltage-controlled oscillator C is locked at a point frequency of 11600 MHz, and is input to the input end of the first power divider H1 through the first output end of the third power divider H3.

3. The device according to claim 1, characterized in that The ramp generator loop module (2) comprises: a digital ramp generator L, a fifth filter B5, and a sixth filter B6; the fifth filter B5 filters the dot frequency signal input by the second power divider H2 and transmits the filtered signal to the digital ramp generator L as its reference clock; the ramp generator L generates a 93MHz to 257MHz low-frequency digital linear frequency modulation signal under the drive of the reference clock and the control of an external sawtooth wave digital signal; the digital linear frequency modulation signal is filtered by the sixth filter B6 and then enters the input end of the low frequency mixer F1.

4. The device according to claim 3, characterized in that The low frequency mixer F1 is provided with two input ends, one of which is connected to the output end of the ramp generator loop module (2), and the other is connected to the output end of the second filter B2, and the input end of the second filter B2 is connected to the second output end of the second power divider H2.

5. The device according to claim 1, characterized in that The high frequency mixer module (3) comprises: a seventh filter B7, a first amplifier G1, an eighth filter B8 and a high frequency mixer F2; the seventh filter B7 filters the signal output by the frequency multiplier J and then enters the high frequency mixer F2; the first amplifier G1 performs power amplification on the signal output by the third filter B3, and then filters it through the eighth filter B8 and enters the high frequency mixer F2; the high frequency mixer F2 mixes the two incoming signals to generate a higher frequency linear frequency modulation signal of 24018 MHz to 24182 MHz, and transmits it to the transmission channel (4).

6. The device according to claim 1, characterized in that The transmitting channel (4) comprises: a ninth filter B9, a second amplifier G2, a tenth filter B10 and a coupler K; the higher frequency linear frequency modulation signal output by the high frequency mixing module (3) is transmitted to the antenna transmitting port through the ninth filter B9, the second amplifier G2, the tenth filter B10 and the coupler K in sequence, and then is transmitted to the receiving channel (5) for transmission.

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