Distance measuring device and method based on semi-digital frequency modulation continuous wave constant beat system

Abstract

The invention discloses a distance measuring device and method based on a semi-digital frequency modulation continuous wave constant beat system. The distance measuring device and method mainly solve the problems that an existing distance measuring device cannot solve the problems of low integration level, poor data credibility, low precision, high cost and poor consistency at the same time. The device comprises an antenna, a microwave module, a power supply module, a servo module and a processing module. Wherein the antenna is connected with the microwave module through a radio frequency cable so as to realize transmitting and receiving of radio frequency signals; the microwave module is connected with the servo module and the processing module to realize sampling, processing and transmission of signals; the power supply module supplies power to the microwave module, the servo module and the processing module. When the device measures the distance of the aircraft relative to the ground or the water surface, the distance can be reported to a flight control system in real time, and safety guarantee is provided for flight of the aircraft. The method is high in distance measurement precision, high in reliability, stable in technical performance, low in distance measurement cost, good in product consistency, capable of reliably detecting the distance and capable of being used for height measurement of flight of aircrafts and missiles.

Description

Technical Field

[0001] The present invention belongs to the technical field of ranging, and particularly relates to a ranging device and method, which can be used to measure the height from an aerospace vehicle or a missile to the ground or water surface during flight. Background Art

[0002] The ranging method is a method for various aerospace vehicles and missiles to accurately obtain the actual height of the vehicle from the ground or water surface through an on-board electronic altimeter under various climatic conditions. It is mainly realized through three working systems: pulse system, frequency-modulated continuous wave system, and pseudo-code continuous wave altimetry system. The ranging method of the frequency-modulated continuous wave system can also be realized by two working systems: constant period system and constant beat system, where:

[0003] The existing mathematical model for calculating the height H of an aircraft carrier in the ranging method of the frequency-modulated continuous wave constant beat system is: H = f b ·C·T / (2F), where F is the modulation frequency deviation, C = 3×10 8 m / s, f b is the beat signal frequency, and T is the modulation time. There are two ways to realize ranging:

[0004] One is to be realized based on an analog circuit. This method is technically mature and has a low cost. The altimetry function is mainly realized through an analog circuit, and only the height calculation is realized through a microcontroller chip. Therefore, the integration level is low; the analog circuit is sensitive to power conduction interference, has limited anti-radio frequency interference ability, and the data credibility is poor; the calculated beat frequency is 25KHz, while the actual beat frequency is generated by an analog frequency discriminator, with a large error.

[0005] The other is to be realized based on a digital circuit. In this method, the measurement errors of the beat frequency and the modulation time are very small, and the altimetry function is mainly realized through an integrated chip. Compared with the analog method, the ranging integration level and accuracy of this method are both improved. However, since its accuracy mainly depends on the indicators of digital components, and the current technical performance of digital components is unstable and the consistency is poor, it is difficult to mass-produce and the cost is high. Summary of the Invention

[0006] The purpose of the present invention is to provide a ranging device and method based on a semi-digital frequency-modulated continuous wave constant beat system to solve the deficiencies of ranging based on analog circuits and digital circuits, and at the same time improve the ranging accuracy, credibility, and technical performance stability, reduce the ranging cost, and improve the consistency of the product.

[0007] The technical idea for realizing the purpose of the present invention is: by combining analog components and digital circuits to give play to their respective advantages, that is, using an FPGA to control the AD to collect and process the beat signal to realize the beat frequency f bFor measurement and calculation, an FPGA is used to control the DA to output an analog voltage. This voltage generates a sawtooth wave through an analog circuit, and controls the analog components to realize the transmission and reception of ranging signals.

[0008] According to the above idea, the technical solution of the present invention is as follows:

[0009] 1. A semi-digital frequency-modulated continuous wave ranging device, including antenna 1, microwave module 2, power supply module 3, servo module 4 and processing module 5, characterized in that:

[0010] The servo module 4 includes a sawtooth wave generator unit 41 and a sawtooth wave square wave unit 42. The sawtooth wave generator unit 41 is connected to the microwave module 2, and the sawtooth wave square wave unit 42 is connected to the processing module 5, which are respectively used to generate a sawtooth wave and a square wave;

[0011] The processing module 5 includes an FPGA unit 51, an A / D unit 52, a D / A1 unit 53, a D / A2 unit 54, an interface unit 55 and a storage unit 56;

[0012] The FPGA unit 51 is connected to the sawtooth wave square wave unit 42 for timing control;

[0013] The A / D unit 52 is respectively connected to the D / A1 unit 53 and the microwave module 2 for signal amplification, filtering and sampling;

[0014] The D / A2 unit 54 is connected to the sawtooth wave generator unit 41 for controlling the modulation time of the sawtooth wave;

[0015] The interface unit 55 is connected to the outside for communication;

[0016] The storage unit 56 is connected to the FPGA unit 51 for reading and writing parameters.

[0017] Furthermore, the microwave module 2 includes a voltage-controlled oscillator unit 21, a power amplifier unit 22, a mixer unit 23, a low-noise amplifier unit 24, a transmit port 25 and a receive port 26;

[0018] The voltage-controlled oscillator unit 21 is connected to the sawtooth wave generator unit 41 for generating a linearly frequency-modulated signal. This signal passes through the power amplifier unit 22 and is connected to the transmit port 25 and is connected to the transmit antenna 11 through a radio frequency cable to complete the transmission of the radio frequency signal;

[0019] The receive port 26 is respectively connected to the receive antenna 12 and the low-noise amplifier unit 24. The receive port 26 sends the echo signal received by the receive antenna 12 into the low-noise amplifier unit 24 for amplification and then enters the mixer unit 23 for mixing to output an intermediate frequency beat signal to the A / D unit 52.

[0020] Furthermore, the FPGA unit 51 includes a control sampling module 511, a distance automatic gain module 512, a control sawtooth wave module 513, a beat signal processing module 514, a parameter processing module 515, and a communication module 516;

[0021] The control sampling module 511 is used to control the A / D unit 52 to output sampling data, read and save it;

[0022] The beat signal processing module 514 is used to process the sampling data saved by the control sampling module 511, obtain the current beat frequency, and calculate the distance;

[0023] The control sawtooth wave module 513 is used to calculate the data for adjusting the output voltage of the D / A2 unit 54 according to the beat frequency, and this voltage controls the sawtooth wave generator unit 41 to generate a sawtooth wave;

[0024] The distance automatic gain module 512 is used to calculate the distance automatic gain parameter according to the data obtained by the control sawtooth wave module 513 to control the output value of the D / A1 unit 53, and use it to adjust the amplification factor of the signal in the A / D unit 52;

[0025] The parameter processing module 515 reads and writes the distance automatic gain parameter and temperature parameter in the storage unit 56;

[0026] The communication module 516 is connected to the interface unit 55 to realize communication with the outside world.

[0027] 2. A ranging method using the above semi-digital frequency-modulated continuous wave system ranging device for a constant beat system is carried out through different functional modules of the FPGA unit 51, and is characterized by including:

[0028] The control sawtooth wave module 513 generates a sawtooth wave with a modulation time of T by controlling the sawtooth wave generator unit 41, and this sawtooth wave outputs a beat signal through the microwave module 2;

[0029] The control sampling module 511 controls the amplification, filtering and sampling of the beat signal to obtain the sampled beat signal AD_DATA;

[0030] The control sampling module 511 samples the square wave of the sawtooth wave square wave unit 42 to obtain the modulation time T;

[0031] The beat signal processing module 514 performs signal processing on the sampled data for the main channel and the auxiliary channel to obtain the frequency value fb_a of the auxiliary channel and the frequency value fb_m of the main channel;

[0032] The distance automatic gain module 512 and the parameter processing module 515 utilize temperature coefficient compensation to modulate the change of the frequency deviation F at ambient temperature, and use the distance automatic gain parameter to control the output value of the D / A1 unit 53 to control the signal amplification amount;

[0033] The beat signal processing module 514 compares the frequency value fb_a of the auxiliary channel with the frequency value fb_m of the main channel to obtain the final beat frequency fb value, and calculates the distance of the carrier from the ground or water surface: H = fb·C·T / (2F), where F is the modulation frequency deviation, C = 3×108 m / s is the speed of light, and T is the modulation time;

[0034] The communication module 516 reports the distance information H to the flight control system.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] First, since the device of the present invention adopts a combination of analog components and digital circuits, it integrates the advantages of high integration of digital circuits, high maturity of analog component technology, stable product performance, and low cost. The device of the present invention can be more easily engineered to achieve ranging.

[0037] Second, since the device of the present invention is provided with an FPGA unit and uses it to sample the square wave of the sawtooth wave square wave unit and process the beat signal of the A / D unit respectively, the actual quantized modulation time T and beat frequency f can be obtained b , ensuring the stability of the modulation frequency deviation F, reducing the height measurement error, and improving the ranging accuracy.

[0038] Third, since the device of the present invention connects the FPGA unit with the control digital-to-analog conversion D / A1 unit, it can control the signal amplification amount of the analog-to-digital A / D unit, that is, adjust the sensitivity of the ranging device, so that the ranging device no longer depends on hardware adjustment, ensuring the consistency of the sensitivity of the ranging device.

[0039] Fourth, since the present invention uses the beat signal processing module in the FPGA unit to achieve tracking frequency discrimination, that is, searches for the beat signal frequency through the auxiliary channel, and simultaneously tracks the beat frequency with the auxiliary channel and the main channel, it can prevent tracking the wrong frequency, improving the data credibility and anti-interference ability; BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic structural diagram of the ranging device of the semi-digital frequency modulation continuous wave system of the present invention;

[0041] Figure 2 is a general flow chart for implementing the ranging method based on the semi-digital frequency modulation continuous wave constant beat system of the present invention;

[0042] Figure 3 isFigure 2 Timing design diagram for medium-range measurement. Specific implementation manners

[0043] The implementation of the present invention will be further described in detail with reference to the accompanying drawings as follows:

[0044] Referring to Figure 1 , the semi-digital frequency-modulated continuous-wave ranging device of the present invention includes an antenna 1, a microwave module 2, a power supply module 3, a servo module 4, and a processing module 5. The microwave module 2 is respectively connected to the antenna 1, the servo module 4, and the processing module 5 to realize the transceiver of radio frequency signals, the generation of linearly frequency-modulated signals, and the transmission of beat signals; the processing module 5 is connected to the servo module 4 to generate sawtooth waves with different modulation times; the power supply module 3 is respectively connected to the microwave module 2, the servo module 4, and the processing module 5 to provide power for them. The antenna 1 includes a transmitting antenna 11 and a receiving antenna 12. The microwave module 2 includes a voltage-controlled oscillator 21, a power amplifier 22, a mixer 23, a low-noise amplifier 24, a transmitting port 25, and a receiving port 26. The servo module 4 includes a sawtooth wave generator unit 41 and a sawtooth wave square wave unit 42. The processing module 5 includes an FPGA unit 51, an A / D unit 52, a D / A1 unit 53, a D / A2 unit 54, an interface unit 55, and a storage unit 56. The FPGA unit 51 includes a control sampling module 511, a distance automatic gain module 512, a control sawtooth wave module 513, a beat signal processing module 514, a parameter processing module 515, and a communication module 516. Among them:

[0045] The transmitting antenna 11 is connected to the output end of the transmitting port 25 through a radio frequency cable to realize the transmission of radio frequency signals. The receiving antenna 12 is connected to the input end of the receiving port 26 through a radio frequency cable to realize the reception of echo signals;

[0046] The input end of the voltage-controlled oscillator 21 is connected to the first output end of the sawtooth wave generator unit 41. The sawtooth wave signal output by the sawtooth wave generator unit 41 controls the voltage-controlled oscillator 21 to generate a linearly frequency-modulated signal;

[0047] The input end of the power amplifier 22 is connected to the first output end of the voltage-controlled oscillator 21 to amplify most of the energy of the linearly frequency-modulated signal. The output end of the power amplifier 22 is connected to the input end of the transmitting port 25;

[0048] The input end of the low-noise amplifier 24 is connected to the output end of the receiving port 26 to amplify the received echo signal;

[0049] The first input terminal of the mixer 23 is connected to the second output terminal of the voltage-controlled oscillator 21. The second input terminal of the mixer 23 is connected to the output terminal of the low-noise amplifier 24. A small part of the energy of the chirp signal is used as the local oscillator signal to be coupled with the echo signal passing through the low-noise amplifier 24 to generate a beat signal;

[0050] The input terminal of the sawtooth wave generator unit 41 is connected to the output terminal of the D / A2 unit 54, and is used to generate a sawtooth wave;

[0051] The input terminal of the sawtooth wave and square wave unit 42 is connected to the second output terminal of the sawtooth wave generator unit 41. The output terminal of the sawtooth wave and square wave unit 42 is connected to the second input terminal of the control sampling module 511, and is used for timing control and obtaining the width T of the sawtooth wave;

[0052] The first input terminal of the control sampling module 511 is connected to the output terminal of the A / D unit 52. The first output terminal of the control sampling module 511 is connected to the input terminal of the A / D unit 52, and is used to control the signal acquisition of the A / D unit 52;

[0053] The first input terminal of the A / D unit 52 is connected to the output terminal of the mixer 23, and is used for signal amplification, filtering and sampling;

[0054] The output terminal of the D / A1 unit 53 is connected to the second input terminal of the A / D unit 52, and is used to control the signal amplification amount of the A / D unit 52;

[0055] The first output terminal of the control sawtooth wave module 513 is connected to the input terminal of the D / A2 unit 54, and is used to control the modulation time of the sawtooth wave;

[0056] The second output terminal of the control sawtooth wave module 513 is connected to the third input terminal of the beat signal processing module 514, and is used to transmit the data for controlling the sawtooth wave modulation time;

[0057] The output terminal of the distance automatic gain module 512 is connected to the input terminal of the D / A1 unit 53, and is used to control the output value of the D / A1 unit 53;

[0058] The first input terminal of the interface unit 55 is connected to the first output terminal of the communication module 516. The first output terminal of the interface unit 55 is connected to the first input terminal of the communication module 516. The second input terminal of the interface unit 55 is connected to the external output terminal. The second output terminal of the interface unit 55 is connected to the external input terminal, and is used for communication;

[0059] The input terminal of the storage unit 56 is connected to the first output terminal of the parameter processing module 515. The output terminal of the storage unit 56 is connected to the first input terminal of the parameter processing module 515, and is used for parameter reading and writing;

[0060] The second output terminal of the control sampling module 511 is connected to the first input terminal of the beat signal processing module 514 for processing the beat signal;

[0061] The first output terminal of the beat signal processing module 514 is connected to the input terminal of the control sawtooth wave module 513 for calculating the data of the output voltage. The second output terminal of the beat signal processing module 514 is connected to the first input terminal of the distance automatic gain module 512 for calculating the distance automatic gain parameter. The third output terminal of the beat signal is connected to the second input terminal of the communication module 516 for reporting the distance information;

[0062] The second output port of the parameter processing module 515 is connected to the second input terminal of the distance automatic gain module 512 for processing the distance automatic gain parameter. The third output port of the parameter processing module 515 is connected to the second input terminal of the beat signal processing module 514 for transmitting the modulation frequency deviation;

[0063] The second output terminal of the communication module 516 is connected to the third input terminal of the parameter processing module 515 for processing the parameters;

[0064] Refer to Figure 2 , the ranging method of the present invention based on the semi-digital frequency modulation continuous wave constant beat system is carried out based on the above semi-digital digital frequency modulation continuous wave ranging device, and its implementation steps are as follows:

[0065] Step 1, the control sawtooth wave module 513 generates a sawtooth wave with a modulation time of T through the control sawtooth wave generator unit 41.

[0066] 1.1) The control sawtooth wave module 513 outputs the data D of the control sawtooth wave modulation time T. This data D is output as an analog voltage through a D / A converter, and this voltage generates a sawtooth wave with a modulation time of T and a sawtooth wave rest period of 600 us through the sawtooth wave generator unit 41;

[0067] 1.2) The generated sawtooth wave and sawtooth wave rest period are input to the comparator circuit of the sawtooth wave square wave unit 42 for rectification to obtain a square wave. Among them, the rectified sawtooth wave outputs as the low level of the square wave, and the rectified sawtooth wave rest period outputs as the high level of the square wave; Set the adjustment step D0 = D / 16;

[0068] 1.3) Set the timing of beat signal sampling and processing:

[0069] Refer to Figure 3 , the timing design of this example is divided into three stages, namely sampling signal valid, signal processing enable, and automatic gain control enable. That is, the sampling signal is valid when the square wave is at a low level, the signal processing is enabled in the first 500 us when the square wave is at a high level, and the distance automatic gain control is enabled in the last 100 us;

[0070] 1.4) When the signal processing is enabled, obtain the final beat frequency f b , and set the adjustment variable Dt = D;

[0071] 1.5) According to the final beat frequency f b , adjust the data D in the following way:

[0072] If f b = 0; then execute 1.6);

[0073] Otherwise, execute 1.7);

[0074] 1.6) Output the corresponding data D in sequence according to the sawtooth wave with modulation times T of 100 us, 300 us, 900 us, 2.7 ms, 8.1 ms, 24 ms, and 72 ms, and set the adjustment step D0 = Dt / 16;

[0075] 1.7) Calculate the data D according to the beat frequency f b :

[0076] If the final beat frequency f b = 25 KHz, keep D and D0 unchanged;

[0077] If f b > 25 KHz, then the data D = Dt - (f b - 25000) / 25000 * D0;

[0078] If f b < 25 KHz, then the data D = Dt + (25000 - f b ) / 25000 * D0;

[0079] 1.8) Repeat steps 1.4) to 1.7) to obtain a sawtooth wave with a modulation time of T, and output the beat signal f b0 .

[0080] Step 2, amplify and sample the beat signal f b0 to obtain the sampled beat signal AD_DATA.

[0081] The beat signal f b0， represents the frequency difference obtained by coupling the transmitted chirp signal and the received chirp signal. This difference is proportional to the modulation frequency deviation F, and the ratio is equal to the time t of the electromagnetic wave signal propagating in space divided by the modulation time T of the sawtooth wave, that is, f b0 / F = t / T. It is a variable for subsequent calculation of the distance between the carrier and the ground or water surface. Therefore, it is necessary to sample the beat signal f b0 . The specific implementation includes the following:

[0082] 2.1) When the distance automatic gain control is enabled, according to the data D in steps 1.6) and 1.7), the distance automatic gain parameter is set through the distance automatic gain module 512. This parameter generates an analog voltage through a D / A converter, and the analog voltage controls the amplifier circuit to obtain the amplified and filtered beat signal f b1 ;

[0083] 2.2) When the sampling signal is valid, sample the beat signal f b1 That is, control the sampling module 511 to set the sampling rate Fs, sampling conversion signal, and sampling clock of the AD sampling module. After the sampling conversion signal is completed, read the sampled data to complete the sampling of the beat signal f b1 The sampling is obtained, and the sampled data AD_DATA is obtained and saved.

[0084] Step 3: Sample the square wave to obtain the modulation time T.

[0085] Transmit the square wave generated in step 1 to the control sampling module 511;

[0086] The control sampling module 511 uses a 50MHz clock to collect the square wave. At the moment when the square wave changes from high level to low level, start counting the rising edge of the 50MHz clock. At the moment when the square wave changes from low level to high level, stop counting. When the square wave is at low level, obtain the total number SN of the rising edges of the 50MHz clock. The modulation time is obtained as follows:

[0087] T = SN * 0.02, with the unit of us.

[0088] Step 4: Perform signal processing on the sampled data AD_DATA for the main channel and the auxiliary channel to obtain the frequency value fb_a of the auxiliary channel and the frequency value fb_m of the main channel.

[0089] 4.1) Auxiliary channel processing:

[0090] 4.1.1) Set the passband range of the filter to 20KHz - 120KHz, and the order of the filter to 203. Perform a band-pass filter on the sampled data AD_DATA through the beat signal processing module 514 to obtain the filtered data FIR_A;

[0091] 4.1.2) Perform an FFT transform of FFTN points on the filtered data FIR_A to obtain the FFT-transformed data FFT_A = {FFT_Aq[x] + FFT_Ai[x] * i, x = 0,..., FFTN - 1}, where FFT_A is a set of imaginary numbers, FFT_Aq[x] represents the real part of the data, and FFT_Ai[x] represents the imaginary part;

[0092] 4.1.3) Calculate the modulus value ACQ_A and the noise threshold value NIO_A for the transformed data FFT_A:

[0093] ACQ_A = {(FFT_Aq[x] 2 + FFT_Ai[x] 2 ) 1 / 2 , x = 0, …, FFTN - 1},

[0094] NIO_A = (∑ACQ_A) / FFTN * 4 + K, where K is an empirical value in engineering;

[0095] 4.1.4) Obtain the denoised spectrum PRE_A based on the modulus value ACQ_A and the noise threshold value NIO_A:

[0096] PRE_A = {ACQ_A[x] - NIO_A, x = 0, …, FFTN - 1};

[0097] 4.1.5) Locate the position x_maxa corresponding to the maximum value in the PRE_A array, and calculate the frequency value fb_a of the auxiliary channel:

[0098] fb_a = x_maxa * Fs / FFTN, where Fs is the sampling rate set in step 2;

[0099] 4.2) Main channel processing:

[0100] 4.2.1) Set the passband range of the filter to 22.5KHz to 27.5KHz, the order of the filter to 203, and perform secondary band-pass filtering on the sampled data AD_DATA through the beat signal processing module 514 to obtain the filtered data FIR_M;

[0101] 4.2.2) Perform FFT transformation of FFTN points on the filtered data FIR_M to obtain the data FFT_M after FFT transformation = {FFT_Mq[x] + FFT_Mi[x] * i, x = 0, …, FFTN - 1}, where FFT_M is a set of imaginary numbers, FFT_Mq[x] represents the real part of the data, and FFT_Mi[x] represents the imaginary part;

[0102] 4.2.3) Calculate the modulus value ACQ_M and the noise threshold value NIO_M for the transformed data FFT_M:

[0103] ACQ_M = {(FFT_Mq[x] 2 + FFT_Mi[x] 2 ) 1 / 2 , x = 0, …, FFTN - 1},

[0104] NIO_M = (∑ACQ_M) / FFTN * 4 + K, where K is an engineering experience value;

[0105] 4.2.4) Calculate the denoised spectrum PRE_M based on the modulus value ACQ_M and the noise threshold value NIO_M:

[0106] PRE_M = {ACQ_M[x] - NIO_M, x = 0, …, FFTN - 1},

[0107] 4.2.5) Locate the position x_maxm corresponding to the maximum value in the PRE_M array, and calculate the frequency value fb_m of the main channel:

[0108] fb_m = x_maxm * Fs / FFTN

[0109] where Fs is the sampling rate set in step 2.

[0110] Step 5, use the temperature parameter to compensate for the change of the modulation frequency deviation F at the ambient temperature, and use the distance automatic gain parameter to adjust the sensitivity of the altimeter.

[0111] The temperature parameter and the distance automatic gain parameter are both two types of parameters pre - stored in the memory unit 56.

[0112] The specific implementation of this step includes the following:

[0113] 5.1) Use the temperature parameter to compensate for the change of the modulation frequency deviation F at the ambient temperature:

[0114] 5.1.1) The parameter processing module 515 obtains the temperature parameters in the memory unit 56, including the low - temperature parameter TCoe1, the normal - temperature parameter TCoe2, and the high - temperature parameter TCoe3, and obtains the current ambient temperature Temper and the modulation frequency deviation F0 at the current temperature;

[0115] 5.1.2) Define different temperature coefficients, that is, the low - temperature coefficient refers to the coefficient when the temperature is less than - 45°C, the normal - temperature coefficient refers to the coefficient when the temperature is between 19°C and 28°C, and the high - temperature coefficient refers to the coefficient when the temperature is greater than 78°C. When the temperature is between - 45°C and 19°C, the temperature coefficient linearly changes between TCoe1 and TCoe2 as the temperature changes. When the temperature is between 28°C and 78°C, the temperature coefficient linearly changes between TCoe2 and TCoe3 as the temperature changes;

[0116] 5.1.3) According to the temperature parameters TCoe1, TCoe2, TCoe3 and the current ambient temperature Temper, calculate the temperature parameter TCoe at the current working temperature:

[0117] If Temper ≤ - 45°C, then TCoe = TCoe1;

[0118] If -45°C < Temper ≤ 19°C, then TCoe = TCoe1 + (TCoe2 - TCoe1) * (Temper + 45) / 64;

[0119] If 19°C < Temper ≤ 28°C, then TCoe = TCoe2;

[0120] If 28°C < Temper ≤ 78°C, then TCoe = TCoe2 + (TCoe3 - TCoe2) * (Temper - 28) / 50;

[0121] If Temper > 78°C, then TCoe = TCoe3;

[0122] 5.1.4) Repeat 5.1.1) to 5.1.3) to continuously compensate for the change in the modulation frequency offset due to the change in the ambient temperature, so that the modulation frequency offset F is maintained at a specific value, that is, F = F0 * Tcoe;

[0123] 5.2) Use the distance automatic gain parameter to adjust the sensitivity of the altimeter.

[0124] 5.2.1) When the distance automatic gain control is enabled, the parameter processing module 515 obtains the distance automatic gain parameters GVAD1, GVAD2, GVAD3 in the memory unit 56 and the data D1, D2, D3 corresponding to these three parameters for controlling the sawtooth wave modulation time to be T1, T2, and T3 respectively;

[0125] 5.2.2) The distance automatic gain module 512 calculates the distance gain control parameter GVAD corresponding to the sawtooth wave with the modulation time T according to the data D of the control sawtooth wave modulation time T in step 1 and the parameters obtained in 5.1.1):

[0126] If D ≥ D1, then GVAD = GVAD1;

[0127] If D2 ≤ D < D1, then GVAD = GVAD1 + (GVAD2 - GVAD1) * (D1 - D) / (D1 - D2);

[0128] If D3 ≤ D < D2, then GVAD = GVAD2 + (GVAD3 - GVAD2) * (D2 - D) / (D2 - D3);

[0129] If D ≤ D3, then GVAD = GVAD3;

[0130] 5.2.3) Repeat step 5.2.1) and step 5.2.2) to make the signal amplification factor corresponding to the sawtooth wave with the modulation time T meet the sensitivity requirement by setting the distance gain control parameter GVAD.

[0131] Step 6, calculate the beat frequency f b value, and calculate the distance of the carrier aircraft relative to the ground or water surface.

[0132] 6.1) The beat signal processing module 514 calculates the beat frequency f according to the frequency value fb_a of the auxiliary channel and the frequency value fb_m of the main channel in step 4 b :

[0133] If 22.5KHz ≤ fb_a ≤ 27.5KHz and 22.5KHz ≤ fb_m ≤ 27.5KHz, then the final beat frequency f b = fb_m;

[0134] If 20KHz ≤ fb_a < 22.5KHz or 27.5KHz < fb_a ≤ 120KHz, then the final beat frequency f b = fb_a;

[0135] If fb_a < 20KHz or fb_a > 120KHz, then the final beat frequency f b = 0;

[0136] 6.2) According to the variables F, T, and f obtained in step 5, step 3, and step 6.1 b , calculate the distance of the carrier aircraft relative to the ground or water surface: H = f b ·C·T / (2F), where C = 3×10 8 m / s.

[0137] Step 7, report the distance information H to the flight control system.

[0138] The communication module 516 packs the distance information H calculated in step 6 according to the protocol defined by the flight control system and reports it to the flight control system.

[0139] The above description is only a specific example of the present invention and does not constitute any limitation to the present invention. Obviously, for professionals in the field, after understanding the content and principle of the present invention, various modifications and changes in form and details may be made without departing from the principle and structure of the present invention. However, these corrections and changes based on the idea of the present invention are still within the scope of protection of the claims of the present invention.

[0140] It should be noted that the step numbers in the specification and claims of the present invention are only for clear description of the embodiments of the present invention for easy understanding, and their sequence numbers are not limited.

Claims

1. A semi-digital frequency-modulated continuous wave ranging device, comprising an antenna (1), a microwave module (2), a power supply module (3), a servo module (4) and a processing module (5), characterized in that: The servo module (4) includes a sawtooth wave generator unit (41) and a sawtooth wave square wave unit (42). The sawtooth wave generator unit (41) is connected to the microwave module (2), and the sawtooth wave square wave unit (42) is connected to the processing module (5), which are respectively used to generate a sawtooth wave and a square wave; The processing module (5) includes an FPGA unit (51), an A / D unit (52), a D / A1 unit (53), a D / A2 unit (54), an interface unit (55) and a storage unit (56); The FPGA unit (51) is connected to the sawtooth wave square wave unit (42) for timing control; The A / D unit (52) is respectively connected to the D / A1 unit (53) and the microwave module (2) for signal amplification, filtering and sampling; The D / A2 unit (54) is connected to the sawtooth wave generator unit (41) for controlling the modulation time of the sawtooth wave; The interface unit (55) is connected to the outside for communication; The storage unit (56) is connected to the FPGA unit (51) for reading and writing parameters.

2. The device according to claim 1, wherein The antenna (1) includes a transmitting antenna (11) and a receiving antenna (12), which are respectively connected to the ports of the microwave module (2) through RF cables to realize the transmission and reception of RF signals.

3. The ranging device according to claim 1, characterized in that, The microwave module (2) includes a voltage-controlled oscillator unit (21), a power amplifier unit (22), a mixer unit (23), a low-noise amplification unit (24), a transmitting port (25) and a receiving port (26); The voltage-controlled oscillator unit (21) is connected to the sawtooth wave generator unit (41) for generating a linearly frequency-modulated signal. This signal passes through the power amplifier unit (22) and is connected to the transmitting port (25) and then connected to the transmitting antenna (11) through an RF cable to complete the transmission of the RF signal; The receiving port (26) is respectively connected to the receiving antenna (12) and the low-noise amplification unit (24). The receiving port (26) sends the echo signal received by the receiving antenna (12) into the low-noise amplification unit (24) for amplification and then into the mixer unit (23) for mixing to output an intermediate frequency beat signal to the A / D unit (52).

4. The device according to claim 1, characterized in that, The power supply module (3) is respectively connected to the microwave module (2), the servo module (4) and the processing module (5) for supplying power to them.

5. The device according to claim 1, characterized in that, The FPGA unit (51) includes a control sampling module (511), a distance automatic gain module (512), a control sawtooth wave module (513), a beat signal processing module (514), a parameter processing module (515) and a communication module (516); The control sampling module (511) is used to control the A / D unit (52) to output sampling data, read and save it; The beat signal processing module (514) is used to process the sampling data saved by the control sampling module (511) to obtain the current beat frequency and calculate the distance; The control sawtooth wave module (513) is used to calculate data for adjusting the output voltage of the D / A2 unit (54) according to the beat frequency, and this voltage controls the sawtooth wave generator unit (41) to generate a sawtooth wave; The distance automatic gain module (512) is used to calculate the distance automatic gain parameter according to the data obtained by the control sawtooth wave module (513) to control the output value of the D / A1 unit (53), and uses it to adjust the amplification factor of the signal in the A / D unit (52); The parameter processing module (515) is used to read and write the distance automatic gain parameter and temperature parameter in the storage unit (56); The communication module (516) is connected to the interface unit (55) to realize communication with the outside world.

6. A method for measuring distance in a constant-beat system using the system of claim 1, which is performed by different functional modules of an FPGA unit (51), characterized in that: Including: The control sawtooth wave module (513) generates a sawtooth wave with a modulation time of T through the sawtooth wave generator unit (41), and this sawtooth wave outputs a beat signal through the microwave module (2); The control sampling module (511) controls the amplification, filtering and sampling of the beat signal to obtain the sampled beat signal AD_DATA; The control sampling module (511) samples the square wave of the sawtooth wave square wave unit (42) to obtain the modulation time T; The beat signal processing module (514) performs signal processing on the sampled data for the main channel and the auxiliary channel to obtain the frequency value fb_a of the auxiliary channel and the frequency value fb_m of the main channel; The distance automatic gain module (512) and the parameter processing module (515) utilize the temperature coefficient to compensate for the change of the modulation frequency deviation F at the ambient temperature, and use the distance automatic gain parameter to control the output value of the D / A1 unit (53) to control the signal amplification factor; The beat signal processing module (514) compares the frequency value fb_a of the auxiliary channel with the frequency value fb_m of the main channel to obtain the final beat frequency f b value, and calculates the distance of the carrier aircraft from the ground or water surface: H = f b ·C·T / (2F), where F is the modulation frequency deviation, C = 3×10 8 m / s is the speed of light, and T is the modulation time; The communication module (516) reports the distance information H to the flight control system.

7. The method according to claim 6, wherein The control sawtooth wave module (513) generates a sawtooth wave with a modulation time of T through the sawtooth wave generator unit (41), and its implementation includes the following: 7a) The control sawtooth wave module (513) converts its output data D into an analog voltage output corresponding to the sawtooth wave with a modulation time of T through the D / A2 unit (54); 7b) According to the final beat frequency f b Iteratively adjust the output data D of the control sawtooth wave module (513): If f b = 0, then execute 7c); Otherwise, execute 7d); 7c) The distance search sequentially outputs the corresponding data D according to the sawtooth waves with a modulation time of T of 100 us, 300 us, 900 us, 2.7 ms, 8.1 ms, 24 ms and 72 ms; 7d) Determine data D based on f b in relation to 25 KHz: If f b = 25 KHz, then the data D that controls the sawtooth modulation time T remains unchanged; If f b > 25 KHz, the data D that controls the sawtooth wave modulation time T becomes smaller; If f b < 25 KHz, then the data D that controls the sawtooth wave modulation time T increases.

8. The method according to claim 6, wherein The beat signal processing module (514) performs signal processing on the sampled data for the main channel and the auxiliary channel to obtain the frequency value fb_a of the auxiliary channel and the frequency value fb_m of the main channel, and its implementation includes the following: 8a) Auxiliary channel processing: 8a1) Perform band-pass filtering on the sampled data AD_DATA with a passband range of 20 KHz to 120 KHz to obtain the filtered data FIR_A, and perform FFT transformation on the filtered data FIR_A to obtain the FFT-transformed data FFT_A; 8a2) Perform modulus value calculation and noise statistics on the transformed data FFT_A to obtain the modulus value ACQ_A and the noise threshold value NIO_A respectively, and then calculate the frequency value fb_a of the auxiliary channel from the value PRE_A obtained by subtracting the noise threshold value NIO_A from the modulus value ACQ_A; 8b) Main channel processing: 8b1) Perform band-pass filtering on the sampled data AD_DATA with a passband range of 22.5KHz to 27.5KHz to obtain the filtered data FIR_M, and perform FFT transformation on the filtered data FIR_M to obtain the FFT-transformed data FFT_M; 8b2) Perform modulus calculation and noise statistics on the transformed data FFT_M to obtain the modulus ACQ_M and the noise threshold value NIO_M respectively; Then calculate the frequency value fb_m of the auxiliary channel from the value PRE_M obtained by subtracting the noise threshold value NIO_M from the modulus ACQ_M.

9. The method according to claim 6, wherein The distance automatic gain module (512) and the parameter processing module (515) utilize temperature coefficient compensation to modulate the change of the frequency deviation F at the ambient temperature, and use the distance automatic gain parameter to control the output value of the D / A1 unit (53) to control the signal amplification amount. Its implementation includes the following: 9a) Utilize temperature coefficient compensation to modulate the change of the frequency deviation F at the ambient temperature: 9a1) Obtain the temperature parameters in the parameter processing module (515), including the low-temperature parameter TCoe1, the normal-temperature parameter TCoe2, and the high-temperature parameter TCoe3; obtain the current ambient temperature Temper and the modulation frequency deviation F0 at the current temperature; 9a2) Calculate the current compensation parameter TCoe according to the current ambient temperature Temper and the temperature parameters TCoe1, TCoe2, and TCoe3: If Temper ≤ -45°C, then TCoe = TCoe1; If -45°C < Temper ≤ 19°C, then TCoe = TCoe1 + (TCoe2 - TCoe1) * (Temper + 45) / 64; If 19°C < Temper ≤ 35°C, then TCoe = TCoe2; If 35°C < Temper ≤ 67°C, then TCoe = TCoe2 + (TCoe3 - TCoe2) * (Temper - 35) / 32; If Temper > 67°C, then TCoe = TCoe3; 9a3) Repeat 9a1) and 9a2) to continuously compensate for the change of the modulation frequency deviation caused by the change of the ambient temperature, so that the modulation frequency deviation F is maintained at a specific value, that is, F = F0 * Tcoe; 9b) Use the distance automatic gain parameter to control the output value of the D / A1 unit (53): 9b1) Obtain the distance gain control parameters GVAD1, GVAD2, GVAD3 in the parameter processing module (515) and the data D1 corresponding to the control sawtooth wave modulation time T1, the data D2 corresponding to T2, and the data D3 corresponding to T3 of these three parameters; 9b2) The distance automatic gain module (512) calculates the distance gain control parameter GVAD corresponding to the modulation time T according to the data D of the control sawtooth wave modulation time T: If D ≥ D1, then GVAD = GVAD1; If D2 ≤ D < D1, then GVAD = GVAD1 + (GVAD2 - GVAD1) * (D1 - D) / (D1 - D2); If D3 ≤ D < D2, then GVAD = GVAD2 + (GVAD3 - GVAD2) * (D2 - D) / (D2 - D3); If D ≤ D3, then GVAD = GVAD3; 9b3) Repeat 9b1) and 9b2) such that the signal amplification factor corresponding to the sawtooth wave with a modulation time of T meets the sensitivity requirements.

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