Multiple ranging devices and methods within a frequency sweep cycle

Abstract

This invention discloses a ranging device and method for multiple range measurements within a single frequency sweep cycle. It primarily addresses the problems of long frequency sweep cycles and slow altitude update rates in existing technologies for aircraft operating at high altitudes. The device comprises a transceiver antenna, a transceiver unit, an A / D unit, and a signal processing unit. The signal processing unit includes a timing control module, an AD sampling module, a data analysis and control module, and an altitude calculation module. The signal processing unit generates a frequency sweep cycle command and sends it to the transmitting unit. The transmitting unit generates a linear frequency modulated signal using a DDS device and transmits it through the transmitting antenna. The signal reflected from the target ground enters the receiving unit via a receiving antenna, is mixed, sampled by the A / D unit, and the target distance is determined through data analysis. This invention enables multiple sampling and signal processing within a single frequency sweep cycle, allowing for timely updates of the target distance. This improves the altitude tracking capability and altitude update speed of the ranging device under complex terrain conditions and can be used for measuring flight altitude in aircraft.

Description

Technical Field

[0001] This invention belongs to the field of ranging technology, and specifically relates to a multiple ranging device that can be used for measuring flight altitude or radar ranging in aircraft. Background Technology

[0002] Distance measuring devices are used to measure the distance between a user and a target, and are typically used by various vehicles or aircraft to measure the required distance.

[0003] Radio altimeters are essential electronic ranging devices on various aerospace vehicles, capable of measuring the vehicle's altitude relative to the ground in real time. There are three main operating modes for radio altimeters: pulse mode, frequency-modulated continuous wave (FM) mode, and pseudo-code continuous wave altimeter mode. Each mode operates through a capture and tracking process. Traditional FM altimeters generate a sawtooth wave modulated linear frequency modulated signal, adjusting the slope of the sawtooth wave to maintain a constant beat signal between the echo and the transmitted wave. During this process, the altitude of the vehicle above the ground is calculated by measuring the period of the sawtooth wave: h = fb / F*T*c / 2, where T is the sawtooth wave period (sweep period), the beat frequency fb = 25kHz (constantly maintained), the sweep bandwidth F = 100MHz, and c is the speed of light. Therefore, h = 37500*T.

[0004] Because altitude calculation requires a sawtooth wave period parameter, altitude updates must wait for one sawtooth wave cycle. For example, at an altitude of 1000m, the sawtooth wave period is approximately 27ms; at 10000m, the period reaches 270ms. The altitude calculation program is triggered by the sawtooth wave scan start or stop pulse, meaning that in this case, generating an altitude value takes 270ms, which fails to meet the altitude update rate requirements. Based on the altimeter principle, the sweep bandwidth can be reduced, but this would decrease spectral efficiency; alternatively, the constant beat frequency could be increased, but multi-frequency control would increase the complexity of the control system.

[0005] To address or improve the problem of height measurement using linear frequency modulated altimeters, patent CN202111083383 discloses "A height measurement method and system based on linear frequency modulated continuous wave system", and patent CN201210166779 discloses "A digital processing method for linear frequency modulated continuous wave radar altimeter". Both inventions describe the height measurement algorithm, but neither describes the number of samplings and height calculations within the modulation period.

[0006] For traditional frequency-modulated continuous wave altimeters, one sawtooth wave scan cycle equals one altimeter cycle; the same applies to earlier digital frequency-modulated continuous wave altimeters. At high altitudes, a sawtooth wave scan cycle is often quite long, severely impacting altimeter tracking capabilities in complex terrain conditions. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of the prior art by proposing a multiple ranging system and method within a frequency sweep cycle, thereby improving data utilization and the responsiveness of digital altimeters, avoiding the problem of slow altitude updates caused by excessively long frequency sweep cycles, and enhancing the altimeter's altitude tracking capability under complex terrain conditions.

[0008] The technical concept of this invention is as follows: Altitude is calculated by repeatedly sampling the frequency-modulated continuous wave within a sweep cycle. When the beat signal is within a controllable range of the sweep cycle, only altitude measurement is performed, and the sweep cycle is adjusted at the end of the sweep cycle. When the altitude change is significant and the beat signal is about to exceed the frequency tracking range, the sweep cycle can be adjusted immediately to bring the beat signal back into the tracking frequency range.

[0009] Based on the above approach, the present invention provides a multiple ranging device within a frequency sweep cycle, comprising a transmitting antenna, a receiving antenna, an RF transceiver assembly, an A / D unit, a signal processing unit, an interface unit, and a power supply unit, characterized in that:

[0010] The signal processing unit includes:

[0011] The AD sampling module is used to read the sampled data from the A / D unit and store it in the RAM area;

[0012] The data analysis and control module is used to analyze the sampled data and adjust the sweep frequency period;

[0013] The altitude calculation module receives the calculation results from the data analysis and control module, calculates the altitude value based on the frequency sweep period and frequency sweep bandwidth, and transmits it to the interface unit, which then transmits the altitude value to the system.

[0014] The timing control module is used to control the start and stop of the AD sampling module, data analysis and control module, and height calculation module.

[0015] The radio frequency transceiver component includes:

[0016] The transmitting unit uses a DDS chip to generate frequency-modulated continuous waves;

[0017] The receiving unit is used to receive the signal transmitted from the antenna, mix it with the frequency-modulated continuous wave to generate a beat signal, and output it to the A / D unit.

[0018] Furthermore, the timing control module controls the start and stop of the AD sampling module, data analysis and control module, and height calculation module through a busy signal:

[0019] After the height calculation module calculates the height value and transmits it to the interface unit, the busy signal is cleared to zero.

[0020] Once the AD sampling module has sampled a sufficient amount of data, the busy signal will be immediately set to 1.

[0021] When the AD sampling module has insufficient sampled data and the frequency sweep cycle has ended, the value of the busy signal is set according to different situations:

[0022] If the height calculation module fails to calculate the height value within the frequency sweep cycle and the frequency sweep cycle of the data analysis and control module is not controlled, then the busy signal is set to 1, and the height value is calculated by the height calculation module.

[0023] Otherwise, the busy signal is 0;

[0024] When the busy signal is 0, the AD sampling module samples the data and sends the sampled data to the data analysis and control module after the sampling is completed.

[0025] When the busy signal is 1, the data analysis and control module performs data analysis and calculation. When the data analysis ends and the frequency sweep cycle restarts, it sends a control command to the DDS chip in the transmitting unit to adjust the frequency sweep cycle to ensure the constant frequency of the beat signal. The timing control module controls the data analysis and control module to transmit the data analysis results to the altitude calculation module.

[0026] Furthermore, the data analysis and control module generates a frequency sweep cycle command, which controls the DDS chip in the transmitting unit to generate a frequency-modulated continuous wave and transmit it through the transmitting antenna. The signal reflected from the target ground passes through the receiving antenna and enters the receiving unit in the RF transceiver assembly for mixing. The mixed signal is output to the A / D unit for sampling and then returned to the AD sampling module. The AD sampling module transmits this signal to the data analysis and control module. The data analysis and control module transmits the data analysis results to the altitude calculation module to calculate its beat signal frequency, obtain the target distance or equipment height, and output it through the interface unit.

[0027] The signal processing unit is implemented by an FPGA and a DSP, which are connected by printed lines. The AD sampling module, data analysis and control module, and timing control module run on the FPGA. The height calculation module runs on the DSP and the FPGA. The data analysis and control module transmits the data analysis results to the height calculation module running on the DSP through the printed lines. The height calculation module completes the height value calculation on the DSP and then transmits the height value to the FPGA for output to the interface unit.

[0028] Based on the above approach, the present invention provides a method for performing multiple ranging measurements within a frequency sweep period, comprising the following steps:

[0029] 1) Initialize the equipment. After the DDS chip in the transmitting unit generates a frequency-modulated continuous wave, it is transmitted through the transmitting antenna. The signal reflected from the target ground passes through the receiving antenna and enters the receiving unit in the radio frequency transceiver assembly for mixing. The mixed signal is output to the A / D unit for sampling, and the initial value is assigned to the required number of samples.

[0030] 2) Count the sampled data;

[0031] 3) Based on the sampling count, determine whether the number of samples is sufficient:

[0032] If sufficient, proceed to data analysis and control, and execute step 7;

[0033] If not enough, proceed to step 4).

[0034] 4) Determine if this frequency sweep cycle has ended:

[0035] If not finished, return to step 2);

[0036] If it has already ended, then step 5) is required;

[0037] 5) Determine whether to issue a control command for the frequency sweep cycle:

[0038] If no instruction is issued, then data analysis and control must be entered, and step 6) must be executed.

[0039] If an instruction has been issued, the number of samples is reset to zero, and the process returns to step 2.

[0040] 6) Determine whether this frequency sweep cycle is the first time the sampling phase has begun:

[0041] If this is not the first time entering the sampling stage, the number of samples is reset to zero, and the process returns to step 2.

[0042] If this is the first time entering the sampling stage, step 7) must be performed;

[0043] 7) Perform FFT operation on the sampled data and take the modulus. By comparing these results, obtain the beat frequency. When the beat frequency is within the set range, set the control transmission flag tran_do_b = 1. When the beat frequency is not within the set range, set the control transmission flag tran_do_a = 1 and execute 8).

[0044] 8) Calculate the height value based on the sweep frequency period and beat frequency, report it to the upper-level system, clear the number of samples, and return to step 2);

[0045] 9) Control the sweep frequency cycle:

[0046] While the above steps are being performed, the data analysis and control module monitors and controls the transmission flag. When tran_do_a = 1, or tran_do_b = 1, and the frequency sweep period ends, the data analysis and control module adjusts the frequency sweep period of the DDS chip in the transmission unit to generate the frequency-modulated continuous wave, and adjusts the number of samples required within the frequency sweep period to maintain the tracking of distance data.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] First, the present invention employs all-digital technology in its signal processing unit, resulting in simple, flexible, and stable control.

[0049] Secondly, the data analysis and control module of the present invention uses FFT calculation and inputs the calculated beat frequency into the height calculation module to calculate the height value of the target relative to the ground. It has high sensitivity and is beneficial for use under complex terrain conditions.

[0050] Third, since the transmitting unit uses a DDS chip to generate frequency-modulated continuous waves, there is no need to consider the linearity of sawtooth waves. The modulation period is stable, the error is small, and the altitude value is accurate and stable, which is conducive to adapting to use under complex terrain conditions.

[0051] Fourth, within the frequency sweep cycle, this invention performs multiple samplings through the data analysis and control module in the signal processing unit, and calculates multiple height values ​​through the height calculation module. When the beat signal is within the controllable range of the frequency sweep cycle, only height calculation is performed without adjusting the frequency sweep cycle, which is adjusted at the end of the sweep cycle. When the height value changes significantly and the beat signal is about to exceed the frequency tracking range, the frequency sweep cycle is immediately adjusted to bring the beat signal back into the frequency tracking range. This method avoids the problem of slow height updates caused by an excessively long frequency sweep cycle, is beneficial for use in complex terrain conditions, and improves the utilization rate of the A / D unit's sampled data. Attached Figure Description

[0052] Figure 1 This is an overall structural block diagram of the present invention;

[0053] Figure 2 This is a structural diagram of the signal processing unit in this invention;

[0054] Figure 3 This is a flowchart illustrating multiple ranging measurements within a frequency sweep cycle in this invention.

[0055] Figure 4 This is a flowchart illustrating the process of controlling the scanning cycle according to the present invention. Detailed Implementation

[0056] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0057] Reference Figure 1 This example includes: a transmitting antenna 1, a receiving antenna 2, an RF transceiver assembly 3, an A / D unit 4, a signal processing unit 5, an interface unit 6, and a power supply unit 7. The RF transceiver assembly 3 consists of a transmitting unit 31 and a receiving unit 32. The signal processing unit 5 uses a DSP+FPGA signal processing mode. This unit generates a frequency sweep cycle command, which the transmitting unit 31 receives and generates a frequency-modulated continuous wave. After amplification, the wave is transmitted through the transmitting antenna 1. The signal reflected from the target ground passes through the receiving antenna 2 and enters the receiving unit 32 within the RF transceiver assembly. After mixing, a beat signal is output and sent to the A / D unit 4. The A / D unit 4 performs analog-to-digital conversion and sends the converted sampled data to the signal processing unit 5 for FFT and modulus calculation. The target distance or equipment height is determined by the frequency difference between the transmitted and received signals and the frequency sweep time, and then output through the interface unit 6.

[0058] Interface unit 6 receives data from signal processing unit 5 and uploads it to the system, completing communication between the device and the system. The device uses the CAN bus protocol. Interface unit 6 uses, but is not limited to, the TMS320F28235ZJZS chip from TI, which supports the CAN 2.0B protocol and has a data transmission rate of up to 1Mbps.

[0059] Power supply unit 7 converts the 28V power supplied by the system into various voltages required for device operation. Its main power module uses, but is not limited to, the DVTR2812T DC-DC power module from VPT Corporation for +5V to +12V voltage conversion. The DVTR2812T has an input voltage range of 15V to 50V and a total power output of up to 30W. Other power supply sections use, but are not limited to, the LTC3404 switching power supply chip from LINEAR Corporation and the TPS54312 switching power supply chip from TI Corporation for +3.3V to +1.2V voltage conversion, respectively. The converted +5V and +12V voltages are supplied to the RF transceiver component 3, and the +3.3V and +1.2V voltages are supplied to the A / D unit 4, signal processing unit 5, and interface unit 6 to enable their normal operation.

[0060] This example uses digital frequency-modulated continuous wave (FMCV) technology to capture and track ground echo signals to complete the altitude measurement task. Existing altimeters require a complete frequency sweep cycle for one altitude calculation cycle, which is time-consuming, especially for high altitudes.

[0061] To address the shortcomings of existing altimeters, this invention focuses on improving the structure of the signal processing unit 5. Specifically, it samples and calculates the altitude multiple times within the sweep cycle. When the beat signal is within a controllable range of the sweep cycle, only altitude measurement is performed. At the end of the sweep cycle, the sawtooth wave scanning cycle is adjusted. When the altitude change is significant and the beat signal is about to exceed the frequency tracking range, the scanning cycle can be adjusted immediately to bring the beat signal back into the tracking frequency range. This method avoids the problem of slow altitude updates during long sweep cycles and improves the utilization rate of measurement data.

[0062] Reference Figure 2 The signal processing unit 5 includes an AD sampling module 51, a data analysis and control module 52, a height calculation module 53, and a timing control module 54.

[0063] The timing control module 54 controls the start and stop of the AD sampling module 51, the data analysis and control module 52, and the height calculation module 53, i.e., generates a busy signal. This busy signal is cleared to zero after height calculation and output, and set to 1 once the number of sampled data is sufficient. If the number of sampled data is insufficient and the scan cycle has ended, its value is determined based on whether height calculation and scan cycle control were performed.

[0064] If no height calculation or scan cycle control is performed within the frequency sweep cycle, the busy signal needs to be set to 1 to perform height calculation; otherwise, the busy signal is 0, the sampled data is discarded, and no calculation is performed.

[0065] When the busy signal is 1, the AD sampling module 51 enters the data analysis and control period 52 and the height calculation module 53.

[0066] The AD sampling module 51 performs data sampling when the busy signal is 0.

[0067] The data analysis and control module 52 performs data analysis and calculation when the busy signal is 1. When the data analysis ends and the scanning cycle restarts, it sends a control command to the DDS chip in the transmitting unit 31 to adjust the scanning cycle to ensure the constant frequency of the beat signal.

[0068] The height calculation module 53 receives the calculation results from the data analysis and control module 52, and finally calculates and sends the height value.

[0069] Reference Figure 3 This example demonstrates a method for performing multiple altitude and distance measurements within a frequency sweep cycle, comprising the following steps:

[0070] Step 1, device initialization.

[0071] 1.1) After the DDS chip in the transmitting unit generates a frequency-modulated continuous wave, it is transmitted through the transmitting antenna. The signal reflected from the target ground passes through the receiving antenna and enters the receiving unit in the radio frequency transceiver assembly for mixing. The mixed signal is output to the A / D unit for sampling.

[0072] 1.2) Assign a value to the required number of samples M: M = M0, M0 ≤ 4096:

[0073] 1.3) Set the busy signal busy=0.

[0074] Step 2, sampling and counting.

[0075] When the busy signal is 0, the beat signal is sampled and counted by AD at a frequency of not less than 400kHz to meet the sampling requirements of 20kHz-125kHz when the beat signal frequency is not constantly controlled.

[0076] Step 3: Determine the number of samples.

[0077] Compare the sampling count with the required number of samples M to determine if the quantity is sufficient:

[0078] If the number of samples is greater than or equal to M, then the quantity is sufficient. Set the busy signal to 1 and proceed to step 7.

[0079] If the number of samples is less than M, then the quantity is insufficient, and step 4 is executed.

[0080] Step 4: Determine the frequency sweep period.

[0081] At the end of the frequency sweep cycle, the DDS chip in the transmitting unit sends a scan start pulse signal to the data analysis and control module. The data analysis and control module determines whether the frequency sweep cycle has ended based on whether it receives the scan start pulse signal.

[0082] If the data analysis and control module does not receive the scan start pulse signal, the frequency sweep cycle has not ended, and the process returns to step 2.

[0083] If the data analysis and control module has received the scan start pulse signal, the scan cycle has ended and step 5 will be executed.

[0084] Step 5: Confirm the issuance of the sweep frequency cycle control command.

[0085] After the data analysis and control module issues a frequency sweep control command, it will trigger the DDS to re-sweep the frequency. For this purpose, a flag JCB_num is set to 1. JCB_num is cleared to zero after the frequency sweep cycle restarts. The issuance of frequency sweep cycle control commands is determined based on the change in the JCB_num flag.

[0086] If JCB_num = 0, no sweep frequency cycle control command will be issued. The busy signal will be set to 1, and data analysis and control will be entered, and step 6 will be executed.

[0087] If JCB_num = 1, then a sweep frequency cycle control command is issued, the number of samples is cleared to zero, and the process returns to step 2.

[0088] Step 6: Confirm the initial sampling step.

[0089] Judgment based on the first entry into the sampling phase within the frequency sweep cycle:

[0090] If the data analysis and control module has been entered once or multiple times within the frequency sweep cycle, it is not the first time to enter the sampling stage. The number of samples is cleared to zero, and the process returns to step 2.

[0091] If the data analysis and control module has not been entered within the frequency sweep cycle, then it is the first time entering the sampling stage, and step 7 is executed;

[0092] Step 7, Data Analysis and Control.

[0093] 7.1) Perform FFT and modulus operations on the sampled data sequentially, and search the results from low to high frequency. The frequency of the first peak point found is the beat frequency fb.

[0094] 7.2) Calculate the sweep period Tg of the new frequency-modulated continuous wave based on the beat frequency fb:

[0095] Tg = 25kHz / fb*Tn,

[0096] Where Tn is the original sweep period T, Tn=T;

[0097] 7.3) Determine the number of samples Mc to be sampled within the new sweep cycle:

[0098] Let Mmax be the maximum number of samples required beforehand, and assign the instance the value Mmax = 4096.

[0099] Based on the new sweep period Tg and sampling period Ts = 1 / fs, where fs is the sampling frequency, calculate the number of samples required within the sweep period: Mc = Tg / Ts:

[0100] The calculated number of samples is compared with the pre-set maximum required number of samples:

[0101] If the calculated number of samples Mc is greater than the preset maximum required number of samples Mmax, then Mc = Mmax = 4096.

[0102] If the calculated number of samples is less than or equal to the preset maximum number of samples required, Mmax, then the calculated number of samples Mc is used as the number of samples required in the new sweep frequency cycle.

[0103] Its formula is expressed as follows:

[0104]

[0105] 7.4) When the beat frequency is within the set range, in this example it is set to 22K~28KHz, and the control transmission flag tran_do_b = 1 is set. When the beat frequency is not within the set range, the control transmission flag tran_do_a = 1 is set, and step 8 is executed.

[0106] Step 8, calculate the height value

[0107] 8.1) Reset the number of samples to zero, and calculate the height value h based on the sweep period and beat frequency:

[0108] h = fb / F*Tn*c / 2,

[0109] Where F is the sweep bandwidth, F = 100kHz, Tn is the original sweep period, fb is the beat frequency, and c is the speed of light, c = 3 × 10⁻⁶. 8 m / s.

[0110] 8.2) Report the altitude value to the superior system, set the busy signal value to 0, and return to step 2.

[0111] Step 9: Based on the new sweep frequency period Tg and the new required number of samples Mc calculated in Step 7, adjust the existing sweep frequency period T and the existing required number of samples M.

[0112] Reference Figure 4 The specific implementation of each step is as follows:

[0113] While steps 1 to 8 are being performed, the data analysis and control module monitors and controls the transmission flag. When tran_do_a = 1, or tran_do_b = 1, and the scan start pulse arrives, that is, the frequency sweep period has ended, the module sends a frequency sweep period control command to the DDS chip of the transmitting unit. The frequency sweep period is adjusted to the latest calculated result T = Tg, and the number of samples required for adjustment is M = Mc.

[0114] When the above conditions are not met, the sweep period T and the required number of samples M will not be adjusted.

[0115] The above description is merely an example of the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the concept of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A multiple ranging device within a frequency-sweep cycle, comprising: The application relates to a height measurement system, which comprises a transmitting antenna (1), a receiving antenna (2), a radio frequency transceiver assembly (3), an A / D unit (4), a signal processing unit (5), an interface unit (6) and a power supply unit (7), characterized in that: The signal processing unit (5) comprises: An AD sampling module (51) for reading A / D unit (4) sampling data and storing in RAM area; A data analysis and control module (52) for analyzing sampling data and adjusting the sweep frequency period; A height calculation module (53) for receiving data analysis and control module (52) calculation results, calculating height value according to sweep frequency period and sweep frequency bandwidth, and transmitting the height value to the interface unit (6) to transmit the height value to the system through the interface unit (6); A timing control module (54) for controlling the start and termination of the AD sampling module (51), the data analysis and control module (52) and the height calculation module (53); specifically, the busy signal is used for control: After the height calculation module (53) calculates the height value and transmits it to the interface unit (6), the busy signal is cleared to zero; After the AD sampling module (51) samples enough data, the busy signal is set to 1 immediately; In the case that the AD sampling module (51) samples insufficient data and the sweep frequency period ends, the value of the busy signal is set according to different conditions: If the height calculation module (53) does not calculate the height value in the sweep frequency period and the data analysis and control module (52) does not control the sweep frequency period, the busy signal is set to 1, and the height value is calculated through the height calculation module (53); Otherwise, the busy signal is 0; When the busy signal is 0, the AD sampling module (51) samples data, and after sampling is completed, the sampling data is transmitted to the data analysis and control module (52); When the busy signal is 1, the data analysis and control module (52) analyzes and calculates data, and when the data analysis ends and the sweep frequency period restarts, a control command is sent to the DDS chip in the transmitting unit (31) to adjust the sweep frequency period to ensure the constant frequency of the beat signal; the timing control module (54) controls the data analysis and control module (52) to transmit the data analysis result to the height calculation module (53). The radio frequency transceiver assembly (3) comprises: A transmitting unit (31) using a DDS chip for generating a frequency-modulated continuous wave; A receiving unit (32) for receiving signals transmitted by the receiving antenna and generating a beat signal after mixing with the frequency-modulated continuous wave and outputting the beat signal to the A / D unit (4).

2. The apparatus of claim 1, wherein, The power supply unit (7) is connected with the radio frequency transceiver assembly (3), the A / D unit (4), the signal processing unit (5) and the interface unit (6) respectively, and is used for converting 28V power supplied by the system into 5V, 12V, 3.3V, 1.2V and 1.8V to provide working voltages required by the radio frequency transceiver assembly (3), the A / D unit (4), the signal processing unit (5) and the interface unit (6).

3. The apparatus of claim 1, wherein, The data analysis and control module (52) generates a sweep cycle instruction to control the DDS chip in the transmitting unit (31) to generate a frequency-modulated continuous wave, which is then transmitted through the transmitting antenna (1). The signal reflected from the target ground passes through the receiving antenna (2) into the receiving unit (32) in the radio frequency transceiver assembly (3) for frequency mixing. The mixed signal is output to the A / D unit (4) for sampling and then returned to the AD sampling module (51). The AD sampling module (51) transmits the signal to the data analysis and control module (52), which transmits the data analysis result to the height solving module (53) to calculate the beat signal frequency, and the target distance or device height is obtained and output through the interface unit (6).

4. The apparatus of claim 1, wherein, The signal processing unit (5) is realized by FPGA and DSP, which are connected by printed lines. The AD sampling module (51), the data analysis and control module (52), and the timing control module (54) run on the FPGA. The height solving module (53) runs on the DSP and FPGA. The data analysis result is transmitted by the data analysis and control module (52) to the height solving module (53) running on the DSP. The height solving module (53) completes the height value calculation on the DSP, and then transmits the height value to the interface unit (6) through the FPGA for output.

5. A method of multiple ranging within a frequency sweep cycle, the method comprising: The method comprises the following steps: 1) initializing the device, the DDS chip in the transmitting unit generates a frequency-modulated continuous wave, which is then transmitted through the transmitting antenna. The signal reflected from the target ground passes through the receiving antenna into the receiving unit in the radio frequency transceiver assembly for frequency mixing. The mixed signal is output to the A / D unit for sampling, and the required sampling sample number is assigned an initial value; 2) counting the sampling data; 3) determining whether the sampling sample number is sufficient according to the sampling count: If sufficient, proceed to data analysis and control, and execute 7); If not sufficient, execute 4) 4) determining whether the sweep cycle is over: If not over, return to step 2); If over, execute 5); 5) determining whether to issue a control sweep cycle control instruction: If no instruction is issued, proceed to data analysis and control, and execute 6); If an instruction is issued, clear the sampling sample number, and return to step 2); 6) determining whether this is the first time to enter the sampling link: If not the first time, clear the sampling sample number, and return to step 2); If the first time, execute 7); 7) performing FFT operation on the sampling data and taking the modulus, and obtaining the beat frequency by comparing the results. When the beat frequency is within the set range, set the control transmission flag tran_do_b=1. When the beat frequency is not within the set range, set the control transmission flag tran_do_a=1, and execute 8); 8) according to the sweep cycle and the beat frequency, solving the height value and reporting to the upper system, clearing the sampling sample number, and returning to step 2); 9) controlling the sweep cycle: At the same time of the above steps, the data analysis and control module monitors the control sending flag, when tran_do_a = 1, or tran_do_b = 1, and the sweep frequency cycle ends, the data analysis and control module adjusts the DDS chip in the transmitting unit to generate the sweep frequency cycle of the frequency-modulated continuous wave, adjusts the required sampling sample number in the sweep frequency cycle, and keeps tracking of the distance data.

6. The method of claim 5, wherein, In step 9), the data analysis and control module adjusts the DDS chip in the transmitting unit to generate the sweep frequency cycle of the frequency-modulated continuous wave, which is to adjust the original sweep frequency cycle to a new sweep frequency cycle Tg, as shown below: Tg = 25 kHz / fb*Tn, Wherein, Tn is the original sweep frequency cycle, and fb is the beat frequency.

7. The method of claim 5, wherein, In step 9), the adjustment of the required sampling sample number in the sweep frequency cycle is to calculate the required sampling sample number Mc in the new sweep frequency cycle according to the sweep frequency cycle and the sampling cycle through the following formula: ， Wherein, Tg is the new sweep frequency cycle, Ts = 1 / fs is the sampling cycle, fs is the sampling frequency, and Mmax is the maximum sampling sample number Mc preset.

8. The method of claim 5, wherein, In step 8), the height value is calculated according to the frequency-modulated continuous wave radar ranging, and the height value h is calculated through the following formula: h = fb / F*Tn*c / 2, Wherein, F is the sweep bandwidth, Tn is the original sweep frequency cycle, fb is the beat frequency, and c is the light speed value.

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