Dual-system height measurement system and method in radio altimeter

Abstract

The invention provides a dual-system height measurement system and method in a radio altimeter. The dual-system height measurement system comprises a transmitting signal source module, a radio frequency controller, a frequency mixer, a coupler, a power amplifier, a transmitting feeder line, a transmitting antenna, a receiving antenna, a receiving feeder line, an fb signal amplifier, an analog-digital conversion module and an FPGA. According to the method, a pulse counting height calculation method in a traditional frequency modulation continuous wave radio altimeter is changed, FFT operation is performed on beat signals, digital filtering is performed through the FPGA, and the influence of in-band noise on height calculation is effectively reduced; the frequency measurement accuracy of the fb signal is improved by combining with a pulse counting method, the height can be calculated more accurately for a complex surface environment altimeter, and better environmental adaptability is achieved; the beat frequency calculation accuracy can be ensured under the condition that the signal to noise ratio of the signal is low, and the system is simple and easy to implement.

Description

Technical Field

[0001] The present invention belongs to the field of radar navigation technology, and in particular relates to a dual-system altitude measurement system and method in a radio altimeter. Background Art

[0002] A radio altimeter is a commonly used altitude-finding radar. It uses the Earth's surface as a reflector and the principle of electromagnetic wave propagation delay to measure the relative altitude (distance) between an aircraft and a target surface. Radio altimeters with a maximum range of less than 1500m typically use a frequency-modulated continuous wave (FMCW) system.

[0003] An FM continuous wave (FCM) radio altimeter typically consists of a radio frequency transceiver, a transmitting antenna, a receiving antenna, a transmitting cable, and a receiving cable. The FM radio altimeter transmitter is an FM continuous wave (CW) modulator, with a phase-locked loop (PLL) generating the CW FM signal. Modulation can be triangular, sawtooth, or sine. The first two are linear frequency modulation (LFM), while the latter is nonlinear.

[0004] Most of the energy of the transmitter's output signal is transmitted to the transmitting antenna through the transmitting cable and transmitted to the ground. The remaining part is coupled out through the coupler to obtain a small amount of energy (also called direct signal) and transmitted to the mixer as the local oscillator signal. Except for the signal amplitude, the other properties of the direct signal are exactly the same as those of the transmitted signal.

[0005] The primary function of an altimeter is to measure relative altitude from the ground. To calculate altitude, the altimeter requires the accurate frequency of the beat signal. The beat signal generated by the mixer passes through a shaping filter circuit to produce a square wave signal. Accurately counting the pulses of the square wave signal yields the beat signal frequency. However, using only pulse counting is significantly affected by noise, which is influenced by the overall noise coefficient of the circuit. When an aircraft carries a radio altimeter for altitude measurement, and the surface environment is complex, such as forests, farmlands, deserts, water surfaces, and buildings, and the echo signal amplitude is weak, the noise passing through the shaping circuit can easily cause abnormal pulse counts. This can cause the altimeter's measured altitude data to fluctuate wildly, making it impossible to accurately obtain effective altitude information.

[0006] In the existing technology, some methods increase the use of analog filters in the shaping filter circuit, but this method will increase the volume, weight and cost of the circuit, and the noise in the beat signal band cannot be filtered well using analog filters; some methods obtain the beat frequency by measuring the frequency accumulation within multiple cycles, but this method will be affected by the interference signal of the phase mutation point during triangular wave modulation or sawtooth wave modulation, and the measurement accuracy error is large, thereby reducing the low-altitude height measurement accuracy; some methods perform time domain-frequency domain conversion (FFT) on the beat signal, and the FPGA obtains the spectrum of the intermediate frequency signal and extracts the frequency with the strongest signal energy to obtain the signal frequency.

[0007] The patent document "Radio altimeter with pre-biased local oscillator" (CN119247348A) discloses a transmitting signal source module, a pre-biased local oscillator module, a radio frequency control module, a mixer module and a calculation circuit module, which effectively reduces the minimum height measurement range of the frequency-modulated continuous wave altimeter, shortens or cancels the original radio frequency feeder, reduces the link loss and improves the transmission power, but still essentially only uses the pulse counting method, and the fluctuation is great in a complex environment, and the robustness is low.

[0008] Therefore, there is a need for a dual-system height measurement method which can ensure the accuracy of beat frequency calculation in a low signal-to-noise ratio condition while maintaining the basic height measurement function of the altimeter, and reduce the influence of noise on height calculation SUMMARY

[0009] In view of the defects in the prior art, the purpose of the present application is to provide a dual-system height measurement method and system in a radio altimeter.

[0010] The dual-system height measurement system in a radio altimeter provided by the present application comprises a transmitting signal source module, a mixer, a coupler, a power amplifier, a transmitting antenna, a receiving antenna, a beat signal amplifier, an analog-to-digital conversion module and an FPGA.

[0011] The transmitting signal source module is connected with the power amplifier, and the power amplifier is connected with the coupler and the transmitting antenna respectively;

[0012] The coupler and the receiving antenna are connected with the mixer respectively, and the mixer is connected with the beat signal amplifier;

[0013] The beat signal amplifier is connected with the analog-to-digital conversion module, and the analog-to-digital conversion module is connected with the FPGA.

[0014] Preferably, the transmitting signal source module comprises a phase-locked loop.

[0015] The local oscillator signal transmitted by the phase-locked loop controlled by the FPGA is transmitted by the transmitting antenna through the power amplifier and the transmitting feeder.

[0016] The mixer mixes the direct signal transmitted by the power amplifier with the ground echo signal received by the receiving antenna through the receiving feeder, and outputs a beat signal.

[0017] The beat signal amplifier receives the beat signal, and inputs the FPGA through the analog-to-digital conversion module for signal processing.

[0018] Preferably, an ARM core is further included.

[0019] The analog-digital conversion module transmits the high-precision sampled intermediate frequency signal of the beat signal to the FPGA.

[0020] The ARM core synchronously generates a radio frequency modulation synchronization signal and transmits the radio frequency modulation synchronization signal to the FPGA.

[0021] The FPGA generates a sampling period signal T m2 , and the sampling period of the sampling period signal avoids the rising edge or the falling edge of the direct signal.

[0022] The sampling period signal and the intermediate frequency signal are subjected to AND operation, and the high value is calculated by combining the FFT spectrum measurement method and the pulse counting method through a digital low-pass filter.

[0023] Preferably, the FPGA generates a local sampling period signal F m2 , the sampling frequency is K times the frequency of the local oscillator signal, and the sampling period T m2 is 1 / K of the period T M of the local oscillator signal.

[0024] A counter of the FPGA calculates the number X of beat signal pulses in a counting period T m2 , and another counter calculates the number Y of sampling period signal pulses between the first beat signal and the last beat signal, and the beat signal frequency f b .

[0025]

[0026] The calculation formula of the height table height is:

[0027]

[0028] Wherein, ΔF represents the frequency offset;

[0029] C represents the speed of light;

[0030] H represents the aircraft height;

[0031] T s represents the modulation period.

[0032] Preferably, the beat signal frequency f b is subjected to FIR filter simulation to obtain filter parameters, and the intermediate frequency signal spectrum is obtained after FFT operation, the frequency with the largest amplitude is extracted as the real beat frequency, and the real height H2 is calculated.

[0033] A certain height dispersion ΔH is set, if H2 falls within the interval of H1±ΔH, the height table takes the aircraft height H1 as the final output height, and if H2 does not fall within the interval of H1±ΔH for three times in succession, the height table takes (H1+H2) / 2 as the final output height.

[0034] The application provides a dual-mode height measuring method in a radio altimeter.

[0035] Step one, the local oscillator signal transmitted by the phase-locked loop controlled by the FPGA is transmitted by the transmitting antenna through the power amplifier and the transmitting feeder;

[0036] Step two, the direct signal transmitted by the power amplifier and the ground echo signal received by the receiving antenna through the receiving feeder are mixed by the frequency mixer through the coupler, and the beat signal is outputted;

[0037] Step two, the beat signal amplifier receives the beat signal, and the intermediate frequency signal of the beat signal is sampled with high precision by the analog-digital conversion module and inputted into the FPGA, and the ARM core synchronously generates the radio frequency modulation synchronization signal and transmits the signal to the FPGA for signal processing.

[0038] Preferably, the FPGA generates a sampling period signal T m2 , and the sampling period of the sampling period signal avoids the rising edge or the falling edge of the direct signal;

[0039] The sampling period signal and the intermediate frequency signal are subjected to AND operation, and the height value is calculated by combining the FFT spectrum measurement method and the pulse counting method through the digital low-pass filter.

[0040] The FPGA generates a local sampling period signal F m2 , the sampling frequency is K times of the frequency of the local oscillator signal, and the sampling period T m2 is 1 / K of the period T M of the local oscillator signal.

[0041] A counter of the FPGA calculates the number X of the beat signal pulses in a counting period T m2 , and another counter calculates the number Y of the sampling period signal pulses between the first beat signal and the last beat signal, and the frequency f b of the beat signal is:

[0042]

[0043] The calculation formula of the height of the altimeter is:

[0044]

[0045] wherein ΔF represents the frequency modulation deviation;

[0046] c represents the speed of light;

[0047] H represents the height of the aircraft;

[0048] T s represents the modulation period.

[0049] Preferably, the beat signal frequency f b The FIR filter simulation is carried out to obtain filter parameters, the intermediate frequency signal spectrum is obtained after FFT operation, the frequency with the largest amplitude is extracted as the real beat frequency, and the real height H2 is calculated.

[0050] A certain height dispersion ΔH is set, if H2 falls in the interval of H1±ΔH, the height table takes the aircraft height H1 as the final output height, and if H2 does not fall in the interval of H1±ΔH for three times in succession, the height table takes (H1+H2) / 2 as the final output height.

[0051] The computer readable storage medium storing the computer program is provided according to the application, and the computer program is executed by the processor to realize the steps of the dual-system height measuring method in the radio altimeter.

[0052] The electronic device is provided according to the application, and the electronic device comprises a memory, a processor and a computer program stored in the memory and capable of running on the processor, and the computer program is executed by the processor to realize the steps of the dual-system height measuring method in the radio altimeter.

[0053] Compared with the prior art, the application has the following beneficial effects:

[0054] 1. The application changes the method of calculating height by pulse counting in the traditional frequency-modulated continuous wave radio altimeter, can ensure the accuracy of beat frequency calculation under the condition of low signal-to-noise ratio, and is simple and easy to realize.

[0055] 2. The application effectively reduces the influence of in-band noise on height calculation by performing FFT operation on the beat signal and digital filtering by FPGA, and improves the signal-to-noise ratio of the system.

[0056] 3. The application improves the frequency measurement accuracy of f b The signal by combining the pulse counting method, the radio altimeter can more accurately calculate the height in a complex terrain environment, obtain height data with higher robustness, and has better environmental adaptability. BRIEF DESCRIPTION OF DRAWINGS

[0057] Other features, objects and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings:

[0058] Figure 1 It is a schematic diagram of a dual-system height measuring system in a radio altimeter.

[0059] Figure 2 It is a schematic diagram of ADC part engineering implementation.

[0060] Figure 3 Schematic diagram of a dual-band measurement system based on the HMC703LP4E fractional frequency synthesizer.

[0061] Figure 4 This is a schematic diagram of the pulse counting method block diagram of the dual-system altimeter.

[0062] Figure 5 This is a schematic diagram of the FFT block diagram of the dual-system altimeter.

[0063] Figure 6 f b Schematic diagram of the signal modulation domain measurement block diagram.

[0064] Figure 7 Schematic diagram of transmitted signal and echo signal. DETAILED DESCRIPTION

[0065] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0066] According to the dual-system altitude measurement system in the radio altimeter provided by the present invention, the method of calculating altitude by pulse counting in the traditional frequency-modulated continuous wave radio altimeter is changed. By performing FFT (Fast Fourier Transform) operation on the beat signal and performing digital filtering through FPGA (Field Programmable Gate Array), the signal-to-noise ratio of the system is improved. By combining with the pulse counting method, the f b The frequency measurement accuracy of the signal can be improved, thereby more accurately calculating the altitude in complex surface environments and improving the performance and environmental adaptability of the altimeter.

[0067] by Figure 1 For example, including:

[0068] Transmitting signal source module: includes a phase-locked loop, which is used to generate the transmitter's frequency-modulated continuous wave signal and transmit the local oscillator signal.

[0069] Mixer: Mixes the local oscillator signal with the received ground echo signal to generate a beat signal.

[0070] Power amplifier: amplifies the RF signal from the transmitting signal source.

[0071] Transmitter feeder: used to connect the power amplifier and the transmitting antenna.

[0072] Transmitting antenna: transmits the amplified FM continuous wave signal.

[0073] Receiving antenna: Receives ground echo signals.

[0074] Receive feeder: connects the receiving antenna and mixer.

[0075] Beat signal amplifier: amplifies the beat signal generated by the mixer.

[0076] Analog-to-digital conversion module (ADC): Figure 2 For example, the high-precision ADC module samples the intermediate frequency signal of the beat signal, performs analog-to-digital conversion on the beat analog signal and transmits it to the FPGA for processing.

[0077] FPGA: RF control, controls the transmitting signal source module; receives the beat signal after ADC sampling and counts the pulses of the square wave signal, and combines FFT with the pulse counting method to calculate the current height value.

[0078] The triangle wave RF modulation signal, also known as the local oscillator signal, is generated by the FPGA. The ARM core also generates a RF modulation synchronization signal to the FPGA. After receiving the synchronization signal, the FPGA generates a sampling period signal T m2 ,This sampling period avoids the rising edge or falling edge of the square wave, thereby avoiding the turning point of the triangle wave modulation and avoiding the interference caused by the turning point noise.

[0079] Specifically, the FPGA controls the phase-locked loop to generate a triangle wave RF modulation signal. Figure 7 For example, when the transmitter sends a signal with a frequency of F, it reflects off the ground and returns to the altimeter after a time of T = 2H / c. The frequency modulated continuous wave signal in the aircraft, that is, the RF modulation synchronization signal, continues to sweep the frequency at a speed of △F / Tm. At this time, its frequency is F+2(H / c)×(ΔF / T m ), the mixed signal f obtained by the mixer b =(2H / c)×(ΔF / Tm).

[0080] After sorting, we get:

[0081]

[0082] This formula is the basic height measurement formula of FM radio altimeter.

[0083] Since the speed of light c is a constant, we can see that the height H is T m 、f b and △F. Therefore, as long as two of the three parameters are determined, the measured height H must be linearly or inversely proportional to the third parameter. The formula can also be transformed as follows:

[0084]

[0085] Where ΔF represents the difference between the maximum and minimum frequencies of the FM signal, which is called the FM frequency deviation.

[0086] τ represents the delay time caused by the radio wave from the transmitting antenna to the ground and then reflected back to the receiving antenna, τ = 2H / c (c is the speed of light, H is the altitude of the aircraft);

[0087] f b Represents the beat signal, which is the difference between the transmitted signal frequency (direct signal frequency) and the echo signal frequency at a certain moment;

[0088] T m Indicates the sweep time required for the frequency of the FM signal to go from the minimum frequency to the maximum frequency.

[0089] by Figure 6 For example, the sampling period signal and the intermediate frequency beat signal amplified by the low-frequency amplifier circuit are “ANDed” to remove the glitch signal at the turning point. The signal then passes through a digital low-pass filter inside the FPGA to remove the interference of high-frequency glitches before entering the counting process.

[0090] The local pulse is introduced into the counter method, and the local frequency generated by FPGA is recorded as F m2 , its frequency is K times the frequency of the triangle wave, and its corresponding period is T m2 is the triangle wave period T M The radio altimeter is more accurate in measuring altitude by combining two altitude calculation methods (pulse counting method and FFT spectrum measurement method) and adopting certain strategies for altitude calculation.

[0091] A counter in FPGA calculates the m2 The beat signal pulse number X in the same time, another counter counts the local pulse number Y between the first beat signal pulse to the last beat signal pulse. Through the above operation, the beat signal frequency f b The calculation formula is:

[0092]

[0093] The altimeter altitude calculation formula then becomes:

[0094]

[0095] Among them, T s Indicates the modulation period.

[0096] When the signal-to-noise ratio decreases, the in-band noise will affect the accuracy of the pulse counting method. The square wave signal obtained by the pulse counting method is simulated by FIR filter using Matlab tools to obtain the filter parameters. The filter parameters are substituted into the FPGA. At this time, the beat signal is sampled by A / D and then passed through the FIR filter to obtain 16-bit sampled data. After the FFT operation, the intermediate frequency signal spectrum is obtained. At this time, there are real beat signal frequencies and in-band noise frequencies in the intermediate frequency band. The beat signal frequency f is extracted. b Substitute it in to get the height H.

[0097] In more preferred examples, when a highly moving aircraft requires an altimeter to provide altitude information for flight guidance, inaccurate altitude data may cause the aircraft to miss its target due to the extremely complex surface environment and the aircraft's rapid vertical ascent or descent. Figure 3 For example, the HMC703LP4E fractional frequency synthesizer is based on a high-performance PLL platform that delivers the industry's best phase noise and spurious performance, enabling higher-order modulation schemes while minimizing the blocking effects of high-performance radios.

[0098] The HMC703LP4E also offers features such as frequency sweep and modulation, external triggering, double buffering, precise frequency control, and phase modulation. The precise frequency mode of the 24-bit fractional modulator generates fractional frequencies with zero frequency error and extremely low channel spurious signals. The HMC703LP4E can automatically program parameters such as the start and end frequencies of the triangle wave modulation signal, as well as the modulation rate. It also initiates rising and falling edges under the control of the TRIG signal. Based on these features, the corresponding start and end frequencies, as well as the modulation rate, are programmed into the transmitter via the FPGA. The AD7656, a monolithic integrated circuit fabricated using CMOS technology, is a 6-channel, 16-bit successive approximation capacitor-based A / D converter. It primarily consists of control logic, SAR registers, input and output controls, a reference, a clock, a D / A converter, and a comparator.

[0099] by Figure 5 For example, the internal register is reset on the valid edge of the logic input pulse, the successive approximation logic drives the sampling switch to work, the analog input signal is sampled in the charge redistribution D / A, the conversion clock is started, the corresponding binary code is obtained through successive approximation, the conversion is completed and the end signal is output, and the data is controlled to be output in 8 / 16-bit bus mode or serial mode according to the input control signal.

[0100] by Figure 4 For example, a counter inside the FPGA measures the M f within b The number of pulses N, while another counter counts the first f bThe pulse signal to the last f b The number of local pulses between the pulse signals M, the height is calculated and recorded as H1.

[0101] At the same time, the beat signal is amplified and then input into the ADC for analog-digital conversion, and the converted data is sent to the FPGA for FFT transformation to convert the time domain information into frequency domain information. The FPGA performs FIR filtering to perform spectrum analysis on the frequency in the height table frequency band, extracts the frequency with the largest amplitude as the real beat frequency, and calculates the height, which is recorded as H2.

[0102] The H1 height obtained in a triangular wave period window is used as a reference to set a certain height dispersion ΔH. If H2 falls within the interval of H1±ΔH, the height table will use the height H1 obtained by the pulse counting method as the final output height. If H2 does not fall within the interval of H1±ΔH for three consecutive times, the height table finally outputs the height (H1+H2) / 2. When the height suddenly changes, the height obtained by the FFT method and the normal height obtained in the previous period are averaged to obtain smoother height data, so that the height calculation of the height table is more accurate in the case of large in-band noise.

[0103] According to the dual-system height measuring method of the radio altimeter provided by the application, the method comprises the following steps:

[0104] Step 1: The local oscillator signal transmitted by the phase-locked loop controlled by the FPGA passes through the power amplifier and is transmitted by the transmitting antenna through the transmitting feeder;

[0105] Step 2: The mixer mixes the direct signal transmitted by the power amplifier and the ground echo signal received by the receiving antenna through the receiving feeder through the coupler and outputs the beat signal;

[0106] Step 2: The beat signal amplifier receives the beat signal, samples the intermediate frequency signal of the beat signal with high precision through the analog-digital conversion module, and inputs the FPGA, and the ARM core synchronously generates a radio frequency modulation synchronization signal and transmits it to the FPGA for signal processing.

[0107] In more preferred examples, the FPGA generates a sampling period signal T m2 , and the sampling period of the sampling period signal avoids the rising edge or falling edge of the direct signal;

[0108] The sampling period signal and the intermediate frequency signal are ANDed, and the FFT spectrum measurement method and the pulse counting method are combined to calculate the height value through the digital low-pass filter.

[0109] The FPGA generates a local sampling period signal F m2 , and the sampling frequency is K times the frequency of the local oscillator signal, and the sampling period T m2 is the period T of the local oscillator signal.M 1 / K.

[0110] A counter in FPGA calculates the m2 The number of beat signal pulses X in the sampling period is calculated by another counter, and the number of sampling period signal pulses Y between the first beat signal and the last beat signal is calculated by another counter. The beat signal frequency f b :

[0111]

[0112] The altimeter altitude is calculated as:

[0113]

[0114] Wherein, ΔF represents the FM frequency deviation;

[0115] c represents the speed of light;

[0116] H represents the aircraft altitude;

[0117] T s Indicates the modulation period.

[0118] In more preferred embodiments, the beat signal frequency f b Perform FIR filter simulation to obtain filter parameters, perform FFT operation to obtain the intermediate frequency signal spectrum, extract the frequency with the largest amplitude as the true beat frequency, and calculate the true height H2.

[0119] Set a certain altitude dispersion to ΔH. If H2 falls within the range of H1±ΔH, the altimeter will use the aircraft altitude H1 as the final output altitude. If H2 does not fall within the range of H1±ΔH for three consecutive times, the altimeter will use (H1+H2) / 2 as the final output altitude.

[0120] According to a computer-readable storage medium storing a computer program provided by the present invention, when the computer program is executed by a processor, the steps of the dual-system altitude measurement method in the radio altimeter are implemented.

[0121] An electronic device provided according to the present invention includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is executed by the processor, the steps of the dual-system altitude measurement method in the radio altimeter are implemented.

[0122] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other at will without conflict.

Claims

1. A dual-system altitude measurement system in a radio altimeter, characterized in that: include: Transmitting signal source module, mixer, coupler, power amplifier, transmitting antenna, receiving antenna, beat signal amplifier, analog-to-digital conversion module and FPGA; The transmitting signal source module is connected to the power amplifier, and the power amplifier is connected to the coupler and the transmitting antenna respectively; The coupler and the receiving antenna are respectively connected to the mixer, and the mixer is connected to the beat signal amplifier; The beat signal amplifier is connected to the analog-to-digital conversion module, and the analog-to-digital conversion module is connected to the FPGA.

2. The dual-system altitude measurement system in the radio altimeter according to claim 1, characterized in that: The transmission signal source module includes a phase-locked loop; The local oscillator signal transmitted by the phase-locked loop controlled by the FPGA is transmitted by the transmitting antenna through the power amplifier and the transmitting feeder; The mixer mixes the direct signal of the local oscillator signal transmitted by the power amplifier with the ground echo signal received by the receiving antenna via the receiving feeder through the coupler, and outputs a beat signal; The beat signal amplifier receives the beat signal and inputs the signal into the FPGA through the analog-to-digital conversion module for signal processing.

3. The dual-system altitude measurement system in the radio altimeter according to claim 2, characterized in that: Also includes ARM core; The analog-to-digital conversion module samples the intermediate frequency signal of the beat signal with high precision and transmits it to the FPGA; The ARM core synchronously generates a radio frequency modulated synchronization signal and transmits it to the FPGA; The FPGA generates a sampling period signal T m2 , the sampling period of the sampling period signal avoids the rising edge or falling edge of the direct signal; The sampling period signal and the intermediate frequency signal are operated and passed through a digital low-pass filter. The height value is calculated by combining the FFT spectrum measurement method with the pulse counting method.

4. The dual-system altitude measurement system in the radio altimeter according to claim 2, characterized in that: The FPGA generates a local sampling period signal F m2 , the sampling frequency is K times the local oscillator signal frequency, and the sampling period is T m2 is the local oscillator signal period T M 1 / K; A counter in FPGA calculates the m2 The number of beat signal pulses X in the sampling period is calculated by another counter, and the number of sampling period signal pulses Y between the first beat signal and the last beat signal is calculated by another counter. The beat signal frequency f b : The altimeter altitude is calculated as: Wherein, ΔF represents the FM frequency deviation; c represents the speed of light; H represents the aircraft altitude; T s Indicates the modulation period.

5. The dual-system altitude measurement system in the radio altimeter according to claim 4, characterized in that: For the beat signal frequency f b Perform FIR filter simulation to obtain filter parameters, perform FFT operation to obtain the intermediate frequency signal spectrum, extract the frequency with the largest amplitude as the true beat frequency, and calculate the true height H2; Set a certain altitude dispersion to ΔH. If H2 falls within the range of H1±ΔH, the altimeter will use the aircraft altitude H1 as the final output altitude. If H2 does not fall within the range of H1±ΔH for three consecutive times, the altimeter will use (H1+H2) / 2 as the final output altitude.

6. A dual-system altitude measurement method in a radio altimeter, comprising: include: Step 1: The local oscillator signal transmitted by the FPGA-controlled phase-locked loop is transmitted through the power amplifier and the transmitting feeder by the transmitting antenna; Step 2: The mixer mixes the direct signal of the local oscillator signal transmitted by the power amplifier with the ground echo signal received by the receiving antenna via the receiving feeder through the coupler, and outputs a beat signal; Step 2: The beat signal amplifier receives the beat signal, samples the intermediate frequency signal of the beat signal with high precision through the analog-to-digital conversion module and inputs it into the FPGA. The ARM core synchronously generates a radio frequency modulated synchronization signal and transmits it to the FPGA for signal processing.

7. The dual-system altitude measurement method in a radio altimeter according to claim 6, characterized in that: The FPGA generates a sampling period signal T m2 , the sampling period of the sampling period signal avoids the rising edge or falling edge of the direct signal; The sampling period signal and the intermediate frequency signal are operated and passed through a digital low-pass filter, and the height value is calculated by combining the FFT spectrum measurement method with the pulse counting method; The FPGA generates a local sampling period signal F m2 , the sampling frequency is K times the local oscillator signal frequency, and the sampling period is T m2 is the local oscillator signal period T M 1 / K; A counter in FPGA calculates the m2 The number of beat signal pulses X in the sampling period is calculated by another counter, and the number of sampling period signal pulses Y between the first beat signal and the last beat signal is calculated by another counter. The beat signal frequency f b : The altimeter altitude is calculated as: Wherein, ΔF represents the FM frequency deviation; c represents the speed of light; H represents the aircraft altitude; T s Indicates the modulation period.

8. The dual-system altitude measurement method in a radio altimeter according to claim 7, characterized in that: For the beat signal frequency f b Perform FIR filter simulation to obtain filter parameters, perform FFT operation to obtain the intermediate frequency signal spectrum, extract the frequency with the largest amplitude as the true beat frequency, and calculate the true height H2; Set a certain altitude dispersion to ΔH. If H2 falls within the range of H1±ΔH, the altimeter will use the aircraft altitude H1 as the final output altitude. If H2 does not fall within the range of H1±ΔH for three consecutive times, the altimeter will use (H1+H2) / 2 as the final output altitude.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the dual-system altitude measurement method in the radio altimeter according to any one of claims 5 to 8 are implemented.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the computer program is executed by a processor, the steps of the dual-system altitude measurement method in the radio altimeter according to any one of claims 5 to 8 are implemented.

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