CN109581369B - Radar altimeter with non-uniform multi-channel constant difference beat frequency system - Google Patents
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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- G01C5/00—Measuring height; Measuring distances transverse to line of sight; Levelling between separated points; Surveyors' levels
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Abstract
The invention discloses a radar altimeter with a non-uniform multi-channel constant-difference beat frequency system, which mainly solves the problems that the radar altimeter in the prior art has low sensitivity in a low-height system and poor real-time performance in a high-height system. It includes: microwave subassembly module (1), analog-to-digital conversion module (2) and digital processing module (3), the output of microwave subassembly module (1) links to each other with the input of analog-to-digital conversion module (2), for it provides the analog beat signal, the output of analog-to-digital conversion module (2) links to each other with the input of digital processing module (3), for it provides digital signal, the output of digital processing module (3) links to each other with the input of microwave subassembly module (1), for it provides the modulation parameter of transmission signal. The invention has the characteristics of low altitude sensitivity, high altitude and high data rate, has the advantages of strong anti-interference capability, low later maintenance cost and high measurement precision, and can be used for measuring the altitude of an aircraft.
Description
Technical Field
The invention belongs to the technical field of radar signal processing, and particularly relates to a radar altimeter which can be used for measuring the height of an aircraft.
Background
Along with the development of modern aviation, radar altimeters are more and more widely applied to various aircrafts, such as helicopter fixed-height hovering, automatic driving, low-altitude missile flying and the like, and frequency modulation continuous wave radar altimeters have the advantages of no distance blind area, high precision, light weight, simple structure, low power consumption and the like; the existing radar altimeter is mainly based on two working systems of single constant beat frequency and uniform multi-channel constant beat frequency, and has the defects of poor high-height real-time performance, low height sensitivity and the like.
The radar altimeter commonly used at present is a working system based on single constant beat frequency, for example, the radar altimeter introduced in the thesis "FMCW radar altimeter digital signal processing technology research" of Master Potention of China engineering physics research institute, which is specifically realized by firstly obtaining an analog beat signal from a mixer at the front end of the radar altimeter and carrying out A/D sampling; and then, continuously adjusting the modulation time of the transmitted signal, when the obtained beat frequency falls within the range of the passband of the set narrow-band filter, effectively outputting the frequency spectrum after FFT (fast Fourier transform) by more than a threshold, and at the moment, entering a tracking state by the altimeter, and finally calculating to obtain the current height value according to the modulation parameter of the transmitted signal. The patent application of Beijing aerospace university 'a digital processing method of a linear frequency modulation continuous wave radar altimeter' (patent application CN 201210166779.5 publication No. CN 102707275B) discloses a radar altimeter of a single working system with constant beat frequency, wherein although a Chirp-Z conversion method is adopted by the altimeter to improve the height measurement precision, the method still does not solve the problems of low height sensitivity and poor high height real-time performance; the radar altimeter with the single constant beat frequency system type has poor flexibility and adaptability of the system.
The research and implementation of FMCW radar altimeter signal processing method in the thesis of Master Liao of the university of Western's electronic technology provides a radar altimeter based on a uniform channel constant beat frequency system, the radar altimeter sets 4 center frequencies as 25kHz, 50kHz, 75kHz and 100kHz respectively, the height of measurement is 0m-12000m, a channel is distributed at every 3000m in a tracking state, because the height and the set beat frequency are uniformly distributed, the number of sampling points is too small at low height, the sensitivity of the system is reduced, the threshold setting is complex, the system is easily interfered by noise, and in the measurement of the height of 9000m-12000m, because the adopted constant beat frequency is 100kHz, the modulation time of a transmitted signal is still too long, the number of sampling points is redundant, and the real-time of the system is poor; meanwhile, as the system adopts a structure of FPGA and DSP, the precision is reduced due to the data transmission and data type conversion between the FPGA and the DSP, and the hardware circuit design of the architecture is complex.
Because the method cannot simultaneously take into account the characteristics of high system sensitivity when the radar altimeter is at low altitude and good system real-time performance when the radar altimeter is at high altitude, and the device has no fault self-checking function, and has high later maintenance cost, the method adopts the radar altimeter based on the non-uniform multi-channel homodyne beat frequency system to solve the problems, and all digital signal processing processes are independently completed by the FPGA, so that the hardware design is simple.
Disclosure of Invention
The invention aims to provide a radar altimeter with a non-uniform multi-channel constant difference beat frequency system and a height measurement method aiming at the defects of the prior art, so as to improve the sensitivity of a system at a low height of less than 20m and improve the real-time performance of the system at a high height of more than 6000 m.
To achieve the above object, a radar altimeter of the present invention includes: microwave subassembly module, analog-to-digital conversion module and digital processing module, the input of analog-to-digital conversion module links to each other with microwave subassembly module output, and the output links to each other with digital processing module input, and digital processing module's output links to each other its characterized in that with microwave subassembly module input: the digital processing module includes:
the signal processing sub-module is used for calculating the altitude data of the aircraft by a signal processing method of non-uniform multi-channel homodyne beat frequency;
the self-checking sub-module is used for detecting whether the microwave assembly works normally or not and whether the microwave assembly module and the digital processing module communicate normally or not;
and the storage submodule is used for storing the cable delay height and a zero height value existing between the aircraft and the ground when the aircraft is stopped on the ground.
Furthermore, the signal processing submodule is provided with a search channel and a tracking channel;
the searching channel roughly calculates the flying height of the aircraft through multiple searching;
the tracking channel is divided into 5 sub-channels with different frequencies and used for accurately calculating altitude data on the basis of a search channel and transmitting the altitude data to an airplane display screen through an ARINC429 communication protocol;
freely switching between the search channel and the tracking channel, namely after the search channel searches height data for 5 times continuously, selecting a corresponding tracking sub-channel according to the searched height; when the tracking is lost, the tracking channel is closed and the channel is switched to a searching channel.
Further, the self-test sub-module is divided into power-on self-test, periodic self-test and ordered self-test, namely, the power-on self-test is carried out on whether the receiving channel of the microwave assembly normally works or not before the system normally works after power-on, the periodic self-test is carried out on whether the receiving channel of the microwave assembly normally works or not and on whether the modulation parameter of the transmitting signal transmitted to the microwave assembly module by the digital processing module is correct or not every 10s when the system normally works, and the ordered self-test is carried out on whether the receiving channel of the microwave assembly normally works or not and on whether the modulation parameter of the transmitting signal transmitted to the microwave assembly module by the digital processing module is correct or not when the outside sends a detection instruction to the altimeter; the results of the three self-tests are transmitted to the display screen of the airplane through the serial bus.
Furthermore, the storage submodule stores the cable delay height and the zero height value existing between the aircraft and the ground when the aircraft stops on the ground, and the zero height value is processed through I 2 The protocol C is written into the EEPROM of the storage chip so as to directly read a zero height value from the EEPROM when the altimeter is powered on for use next time, and zero height calibration does not need to be repeated.
In order to achieve the above object, the present invention provides a method for measuring height by using the radar altimeter, comprising the steps of:
1) Through the self-checking, judge whether there is the trouble:
whether the microwave assembly module normally works or not, whether normal communication is carried out between the microwave assembly module and the digital processing module or not is detected:
if the microwave component module and the communication between the microwave component module and the digital processing module are failed, executing 9);
if the microwave assembly module and the communication between the microwave assembly module and the digital processing module are not in fault, executing 2);
2) An oscillator in the microwave component module generates a transmitting signal according to the modulation parameter and transmits the transmitting signal through a transmitting antenna, the modulation time of the first height measurement period after the microwave component module is powered on is 200us, the modulation bandwidth is 150MHz, the transmitting power is 0dbm, and the modulation parameter of the height measurement period is transmitted to the microwave component module by the digital processing module.
3) A frequency mixer in the microwave component module mixes a receiving signal received by a receiving antenna with a transmitting signal to obtain an analog beat signal, and an analog-to-digital (A/D) conversion module performs A/D sampling to convert the analog beat signal into a digital beat signal;
4) Averaging all the digital beat signals to obtain an average value m of the digital beat signals, averaging the digital beat signals larger than m to obtain an average value n of the signals with the amplitude higher than the central amplitude value, and calculating the amplitude V of the digital beat signals by using n-m;
5) Selecting a corresponding filtering channel according to the current system working state to filter the digital beat signal, and performing fast Fourier transform on the filtered signal to obtain a global frequency spectrum M of the digital beat signal;
6) Judging the working state of the altimeter:
6a) Calculating a threshold value:
wherein T represents the modulation time of the transmitted signal, and K varies with the modulation time;
6b) Comparing the global spectrum M with a threshold value D:
if the frequency points larger than the threshold value D exist in the global frequency spectrum M, detecting the front edge of the frequency spectrum, and executing 6 c);
if no frequency point larger than the threshold value D exists in the global frequency spectrum M, the front edge of the frequency spectrum is not detected, and 6D) is executed;
6c) If the front edge of the frequency spectrum can be detected in 5 continuous height measurement periods, judging the system to be in a tracking state, and executing 7), otherwise, judging the system to be in a searching state, and executing 8);
6d) Judging the current working state of the system according to the working state of the system in the previous height measurement period:
judging the system to be in a searching state if the system is in the searching state in the previous height measurement period, and executing 8);
if the system is in a tracking state in the previous height measurement period and the spectrum front edge is not detected in 3 continuous height measurement periods, judging the system to be in a searching state, and executing 8), otherwise, judging the system to be in a tracking state, and executing 7);
7) Calculating the flight height of the aircraft:
the detected spectral front in the tracking state is taken into the expression,calculating the height data of the height measurement period:
wherein c represents the propagation velocity of electromagnetic waves, f represents the detected leading edge value of the frequency spectrum in the tracking state, T represents the modulation time of the transmitted signal, and B represents the modulation bandwidth of the transmitted signal;
8) Determining the modulation parameter of the next altimetry period:
8a) If the system works in the tracking state, the modulation parameters of the next height measuring period are as follows:
fixing the modulation bandwidth B at 150MHz;
determining the modulation time of the next height measurement period according to the height data h obtained from the current height measurement period in the tracking state:
wherein c represents the propagation speed of electromagnetic waves, h represents height data of the current height measurement period, B represents the modulation bandwidth of the transmitted signal, and F represents a constant beat frequency value;
determining the transmitting power P of the next height measurement period according to the height data h of the current height measurement period in the tracking state:
wherein h represents height data of the current height measurement period;
8b) If the system is operating in the search state, the modulation parameters for the next altimeter cycle are as follows:
fixing the modulation bandwidth B at 150MHz;
modulation time of next altimeter period:
wherein, T n Representing the modulation time of the current altimetry period;
emission power:
9) And (3) data output:
9a) Transmitting the working state of the altimeter obtained in the step 6) and the height data h or fault codes in the step 7) to an airplane display screen through an ARIN429 protocol for reference of a pilot;
9b) And the digital processing module transmits the modulation parameter of the transmitting signal of the next measuring period obtained in the step 8) to the microwave component module in a serial transmission mode.
Compared with the prior art, the invention has the following advantages:
firstly, the signal processing submodule of the invention calculates the height of the aircraft by adopting a signal processing method of non-uniform multi-channel homodyne beat frequency, thereby not only overcoming the defects of low sensitivity and low measurement precision of the system below 20m, but also solving the problem of poor real-time performance of the system above 6000 m.
Secondly, the self-checking module detects whether the microwave assembly works normally or not and whether the microwave assembly module and the digital processing module communicate normally or not, so that the later maintenance cost of the radar altimeter is reduced.
Thirdly, the cable delay height and the zero height value existing between the airplane and the ground when the airplane stops on the ground are stored through the storage submodule, repeated operation of zero height calibration is achieved, meanwhile, different zero height values are stored, the altimeter can work on different types of airplanes, and universality is high.
Fourthly, the digital signal processing process is independently finished through the FPGA, the circuit is simple in structure, is less influenced by severe environment, can stably work in complex environment, and is extremely high in adaptability.
Drawings
FIG. 1 is a block diagram of the overall architecture of the present invention;
FIG. 2 is a block diagram of the signal processing sub-module of the present invention;
FIG. 3 is a flowchart of the operation of the altimeter of the present invention.
The specific implementation mode is as follows:
the invention will be further explained below with reference to the drawings of the invention.
Referring to fig. 1, the radar altimeter of the present invention includes a microwave module 1, an analog-to-digital conversion module 2 and a digital processing module 3, wherein an output terminal of the microwave module 1 is connected to an input terminal of the analog-to-digital conversion module 2; the output end of the analog-to-digital conversion module 2 is connected with the input end of the digital processing module 3, and the analog-to-digital conversion module 2 converts the analog beat signal into a 14-bit digital beat signal through A/D sampling and sends the digital beat signal to the digital processing module 3; the output end of the digital processing module 3 is connected with the input end of the microwave component module 1, and provides modulation parameters of the transmitting signals for the microwave component module 1.
The microwave component 1 module mainly comprises a transmitting antenna, a receiving antenna, an oscillator and a mixer; the oscillator generates a transmitting signal and transmits the transmitting signal through the transmitting antenna, and the mixer sends an analog beat signal obtained by mixing a signal received by the receiving antenna and the transmitting signal to the analog-to-digital conversion module 2.
The digital processing module 3 comprises a signal processing submodule 31, a self-test submodule 32 and a storage submodule 33, wherein the three submodules are mutually independent and are realized by Xilinx Kintex-7 series FPGA with the model of xc7k410tiffg 900-2L. Wherein:
and the signal processing submodule 31 is used for calculating the altitude data of the aircraft through the working system of the non-uniform multi-channel constant beat frequency.
The self-checking sub-module 32 is used for detecting whether the microwave assembly works normally or not and whether the microwave assembly module and the digital processing module communicate normally or not; the method comprises the following steps of (1) carrying out power-on self-test, periodic self-test and ordered self-test, wherein the power-on self-test is used for detecting whether a receiving channel of a microwave assembly works normally or not after a system is powered on and before the system works normally; the periodic self-check is to detect whether the receiving channel of the microwave assembly works normally and whether the modulation parameter of the transmitting signal transmitted to the microwave assembly module by the digital processing module is correct every 10s when the system works normally; the ordered self-checking is to check whether the receiving channel of the microwave assembly works normally and whether the modulation parameter of the transmitting signal transmitted to the microwave assembly module by the digital processing module is correct when the outside sends a detection instruction to the altimeter; the results of the three self-tests are transmitted to the display screen of the airplane through the serial bus.
A storage submodule 33 for storing the cable delay altitude and the zero altitude value existing between the aircraft and the ground when it is stopped on the ground, and for passing the zero altitude value through I after receiving an external zero altitude calibration command 2 And the protocol C is written into the EEPROM of the storage chip so as to directly read a zero height value from the EEPROM when the altimeter is powered on for use next time, and zero height calibration is not required to be repeatedly carried out.
Referring to fig. 2, the signal processing sub-module 31 includes a search channel 311 and a tracking channel 312, the tracking channel 312 is provided with 5 sub-channels with non-uniform incremental constant beat frequencies of 10kHz, 40kHz, 70kHz, 120kHz and 180kHz, and when the aircraft is less than 20m in height, the constant beat channel frequency is set to 10kHz, so that the number of sampling points is increased, the signal-to-noise ratio is improved, and the height measurement error is reduced; when the height of the aircraft is larger than 6000m, the frequency of the constant beat channel is set to 180kHz, the modulation time is shortened, and the real-time performance of the system is improved; different channels are provided with different band-pass filters, the passband range of the filter set by the search channel 311 is 10 kHz-150 kHz, the passband range of the narrow-band filter set by the first sub-channel is 7 kHz-13 kHz and the measurement range is 0 m-20 m in 5 sub-channels of the tracking channel 312, the passband range of the narrow-band filter set by the second sub-channel is 37 kHz-43 kHz and the measurement range is 20 m-1000 m in height, the passband range of the narrow-band filter set by the third sub-channel is 67 kHz-73 kHz and the measurement range is 1000 m-3000 m in height, the passband range of the narrow-band filter set by the fourth sub-channel is 117 kHz-123 kHz, the measurement range is 3000 m-6000 m in height, the narrowband filter set by the fifth sub-channel is 177 kHz-183 kHz and the measurement range is 6000 m-10000 m in height.
Referring to fig. 3, the altimetry procedure for the altimeter of the present invention is as follows:
step 1, self-checking.
The self-checking sub-module is used for detecting whether the microwave assembly module works normally or not and whether the microwave assembly module and the digital processing module communicate normally or not.
And 2, judging whether a fault exists or not.
And (3) if the communication between the microwave assembly module and the digital processing module fails, executing the step 10, and if the communication between the microwave assembly module and the digital processing module fails, executing the step 3.
And 3, sending the modulation signal.
An oscillator in the microwave component module generates a transmitting signal according to the modulation parameter and transmits the transmitting signal through a transmitting antenna, the modulation time of the first height measurement period after the microwave component module is powered on is 200us, the modulation bandwidth is 150MHz, the transmitting power is 0dbm, and the modulation parameter of the height measurement period is transmitted to the microwave component module by the digital processing module.
Step 4, extracting digital beat signals
A mixer in the microwave component module mixes a receiving signal received by a receiving antenna with a transmitting signal to obtain an analog beat signal, and an analog-to-digital conversion module performs A/D sampling to convert the analog beat signal into a digital beat signal.
And 5, calculating the amplitude of the beat signal.
Averaging all the digital beat signals to obtain an average value m of the digital beat signals, averaging the digital beat signals larger than m to obtain an average value n of the signals with the amplitude higher than the central amplitude value, and calculating the amplitude V of the digital beat signals by using n-m;
and 6, filtering and fast Fourier transform.
(6a) Filtering a digital beat signal obtained in a first height measuring period after a system is powered on through a band-pass filter of a search channel of 10 kHz-150 kHz; and selecting a corresponding channel according to the system state by the digital beat signal received in the following altimetry period:
if the current system works in a searching state, filtering the digital beat signal of the current height measuring period by using a band-pass filter of a searching channel of 10 kHz-150 kHz;
if the current system works in a tracking state, selecting a band-pass filter of a corresponding sub-channel in a tracking channel for filtering;
(6b) And carrying out fast Fourier transform on the filtered signal to obtain a global frequency spectrum M of the beat signal.
And 7, judging the working state of the altimeter.
(7a) Calculating to obtain a threshold value according to the beat signal amplitude V obtained in the step 5
Where T represents the modulation time of the transmitted signal and K varies with the modulation time, as shown in Table 1
TABLE 1K-value Change Table
(7b) Comparing the global spectrum M with a threshold value D:
if the frequency points larger than the threshold value D exist in the global frequency spectrum M, detecting the front edge of the frequency spectrum, and executing the step (7 c);
if no frequency point larger than the threshold value D exists in the global frequency spectrum M, the front edge of the frequency spectrum is not detected, and the step (7D) is executed;
(7c) If the front edge of the frequency spectrum can be detected in 5 continuous height measurement periods, judging the system to be in a tracking state, and executing the step 8, otherwise, judging the system to be in a searching state, and executing the step 9;
(7d) Judging the current working state of the system according to the working state of the system in the previous height measurement period:
if the system is in the searching state in the previous height measuring period, judging the system to be in the searching state, and executing the step 9;
if the system is in the tracking state in the previous height measurement period and the spectrum front edge is not detected in 3 continuous height measurement periods, judging the system to be in the searching state, and executing the step 9, otherwise, judging the system to be in the tracking state, and executing the step 8;
and 8, calculating the flying height of the aircraft.
The frequency spectrum front edge detected in the tracking state is brought into the following expression, and the height data h of the current height measurement period is calculated:
where c represents the propagation velocity of the electromagnetic wave, f represents the detected spectrum leading edge value in the tracking state, T represents the modulation time of the transmission signal, and B represents the modulation bandwidth of the transmission signal.
And 9, determining the modulation parameter of the next height measurement period.
(9a) If the system works in the tracking state, the modulation parameters of the next height measuring period are as follows:
fixing the modulation bandwidth B at 150MHz;
determining the modulation time T of the next height measurement period according to the height data h obtained by the current height measurement period in the tracking state n+1 ：
Where c represents the speed of electromagnetic wave propagation, h represents the height data of the current altimetry period, B represents the modulation bandwidth of the transmitted signal, and F represents the constant beat frequency value, as shown in table 2.
TABLE 2 constant beat frequency values for different h
Determining the transmitting power P of the next height measurement period according to the height data h obtained in the current height measurement period in the tracking state:
h in the formula represents height data of the current height measuring period, and the transmitting power P is divided into three intervals of 0-1500m, 1500m-6000 m and 6000 m-10000 m according to the height data;
(9b) If the system is operating in the search state, the modulation parameters for the next altimeter cycle are as follows:
fixing the modulation bandwidth B at 150MHz;
modulation time T of next altimeter period n+1 ：
Wherein, T n Representing the modulation time of the current altimetry period;
transmission power P:
and step 10, outputting data.
(10a) And (4) transmitting the working state of the altimeter obtained in the step (7) and the final altitude data h or fault code obtained in the step (8) to an airplane display screen for reference of a pilot through an ARIN429 protocol.
(10b) And the digital processing module transmits the modulation parameter of the transmitting signal of the next height measuring period obtained in the step 9 to the microwave component module in a serial transmission mode.
The foregoing description is only an embodiment of the present invention and is not intended to limit the present invention, and it will be apparent to those skilled in the art that various modifications and variations in form and detail can be made without departing from the principle and structure of the present invention, but these modifications and variations are within the scope of the invention as defined in the appended claims.
Claims (8)
1. A method for measuring height by using a radar altimeter based on a non-uniform multi-channel homodyne beat frequency system is characterized by comprising the following steps: comprises the following steps:
1) Through the self-checking, judge whether there is the trouble:
whether the microwave assembly module normally works or not, whether normal communication is carried out between the microwave assembly module and the digital processing module or not is detected:
if the microwave component module and the communication between the microwave component module and the digital processing module are failed, executing 9);
if the microwave assembly module and the communication between the microwave assembly module and the digital processing module are not in fault, executing 2);
2) An oscillator in the microwave component module generates a transmitting signal according to the modulation parameter and transmits the transmitting signal through a transmitting antenna, the modulation time of the first height measurement period after the microwave component module is electrified is 200us, the modulation bandwidth is 150MHz, the transmitting power is 0dbm, and the modulation parameter of the height measurement period is transmitted to the microwave component module by the digital processing module;
3) A frequency mixer in the microwave component module mixes a receiving signal received by a receiving antenna with a transmitting signal to obtain an analog beat signal, and an analog-to-digital (A/D) conversion module performs A/D sampling to convert the analog beat signal into a digital beat signal;
4) Averaging all the digital beat signals to obtain an average value m of the digital beat signals, averaging the digital beat signals larger than m to obtain an average value n of the signals with the amplitude higher than the central amplitude value, and calculating the amplitude V of the digital beat signals by using n-m;
5) Selecting a corresponding filtering channel according to the current system working state to filter the digital beat signal, and performing fast Fourier transform on the filtered signal to obtain a global frequency spectrum M of the digital beat signal;
6) Judging the working state of the altimeter:
6a) Calculating a threshold value:
wherein T represents the modulation time of the transmitted signal, and K varies with the modulation time;
6b) Comparing the global spectrum M with a threshold value D:
if the global frequency spectrum M has a frequency point which is larger than the threshold value D, detecting the front edge of the frequency spectrum, and executing 6 c);
if no frequency point larger than the threshold value D exists in the global frequency spectrum M, the front edge of the frequency spectrum is not detected, and 6D) is executed;
6c) If the front edge of the frequency spectrum can be detected in 5 continuous height measurement periods, judging the system to be in a tracking state, and executing 7), otherwise, judging the system to be in a searching state, and executing 8);
6d) Judging the current working state of the system according to the working state of the system in the previous height measurement period:
judging the system to be in a searching state if the system is in the searching state in the previous height measurement period, and executing 8);
if the system is in a tracking state in the previous height measurement period and the spectrum front edge is not detected in 3 continuous height measurement periods, judging the system to be in a searching state, and executing 8), otherwise, judging the system to be in a tracking state, and executing 7);
7) Calculating the flight height of the aircraft:
and (3) bringing the detected spectrum leading edge in the tracking state into the following expression, and calculating the height data of the current height measurement period:
wherein c represents the propagation speed of electromagnetic waves, f represents the detected spectrum leading edge value in the tracking state, T represents the modulation time of the transmitted signal, and B represents the modulation bandwidth of the transmitted signal;
8) Determining the modulation parameter of the next altimeter period:
8a) If the system works in the tracking state, the modulation parameters of the next height measuring period are as follows:
fixing the modulation bandwidth B at 150MHz;
determining the modulation time of the next height measurement period according to the height data h obtained from the current height measurement period in the tracking state:
where c represents the speed of electromagnetic wave propagation and h represents the height of the current altimetry periodDegree data, B representing the modulation bandwidth of the transmitted signal, F representing the constant beat frequency value;
determining the transmitting power P of the next height measurement period according to the height data h of the current height measurement period in the tracking state:
wherein h represents height data of the current height measurement period;
8b) If the system is operating in the search state, the modulation parameters for the next altimeter cycle are as follows:
fixing the modulation bandwidth B at 150MHz;
modulation time of next altimeter cycle:
wherein, T n Representing the modulation time of the current altimetry period;
9) And (3) data output:
9a) Transmitting the working state of the altimeter obtained in the step 6) and the height data h or fault codes in the step 7) to an airplane display screen through an ARIN429 protocol for reference of a pilot;
9b) And the digital processing module transmits the modulation parameter of the transmitting signal of the next measuring period obtained in the step 8) to the microwave component module in a serial transmission mode.
2. A radar altimeter for implementing the altimetry method of claim 1, comprising: microwave subassembly module (1), analog-to-digital conversion module (2) and digital processing module (3), the input of analog-to-digital conversion module (2) links to each other with microwave subassembly module (1) output, and the output links to each other with digital processing module (3) input, and the output of digital processing module (3) links to each other its characterized in that with microwave subassembly module (1) input: the digital processing module (3) comprises:
a signal processing submodule (31) for calculating altitude data of the aircraft;
the self-test sub-module (32) is used for detecting whether the microwave assembly works normally or not and whether the microwave assembly module and the digital processing module communicate normally or not;
and a storage submodule (33) for storing the cable delay altitude and the zero altitude value existing with the ground when the aircraft is stopped on the ground.
3. The radar altimeter of claim 2, wherein: the signal processing submodule (31) is provided with a search channel (311) and a tracking channel (312);
the search channel (311) roughly calculates the flying height of the aircraft through multiple searches;
the tracking channel (312) is divided into 5 sub-channels with different frequencies and used for accurately calculating altitude data on the basis of a search channel and transmitting the altitude data to an airplane display screen through an ARINC429 communication protocol;
the searching channel (311) and the tracking channel (312) are freely switched, namely after the searching channel searches height data for 5 times continuously, a corresponding tracking sub-channel is selected according to the searched height; when the tracking is lost, the tracking channel is closed and the channel is switched to a searching channel.
4. The radar altimeter of claim 3, wherein: the 5 sub-channels of the tracking channel (312) are respectively the non-uniformly increased constant beat frequencies of 10kHz, 40kHz, 70kHz, 120kHz and 180kHz, and when the height of the aircraft is less than 20m, the constant beat channel frequency is set to 10kHz, so that the number of sampling points is increased, the signal-to-noise ratio is improved, and the height measurement error is reduced; when the height of the aircraft is larger than 6000m, the frequency of the constant beat channel is set to be 180kHz, the modulation time is shortened, and the real-time performance of the system is improved.
5. The altimeter of claim 2, wherein: the self-checking sub-module (32) is divided into power-on self-checking, periodic self-checking and ordered self-checking, namely, the power-on self-checking is carried out on whether a receiving channel of the microwave assembly normally works or not before the system normally works after power-on, the periodic self-checking is carried out on whether the receiving channel of the microwave assembly normally works or not and whether a transmitting signal modulation parameter transmitted to the microwave assembly module by the digital processing module is correct or not every 10s when the system normally works, and the ordered self-checking is carried out on whether the receiving channel of the microwave assembly normally works or not and whether the transmitting signal modulation parameter transmitted to the microwave assembly module by the digital processing module is correct or not when a detection instruction is sent to the altimeter from the outside; the results of the three self-tests are transmitted to the display screen of the airplane through the serial bus.
6. The altimeter of claim 2, wherein: the storage submodule (33) stores the cable delay height and the zero height value existing between the airplane and the ground when the airplane stops on the ground, and the zero height value is passed through I 2 And the protocol C is written into the EEPROM of the storage chip so as to directly read the zero height value from the EEPROM when the altimeter is powered on for use next time, and zero height calibration is not repeated.
7. The radar altimeter of claim 2, wherein: the microwave component module (1) comprises a transmitting antenna, a receiving antenna, an oscillator and a mixer, wherein according to modulation parameters provided by the digital processing module, the oscillator generates a linear frequency modulation signal and sends the linear frequency modulation signal as a transmitting signal through the transmitting antenna, after time delay, the receiving antenna mixes the received signal and the transmitting signal through the mixer to obtain an analog beat signal and transmits the analog beat signal to the analog-to-digital conversion module (2).
8. The altimeter of claim 2, wherein: the signal processing submodule (31), the self-checking submodule (32) and the storage submodule (33) are all realized through an FPGA.
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