TW200409933A - A digital controlled linear swept frequency mode for FMCW radar altimeter - Google Patents

Abstract

The digital controlled linear swept frequency mode of the present invention relates to FMCW radar altimeter, characterized in (1) adopts up swept frequency and down swept frequency to solve problem of mixture of distance and doppler signals; (2) in between swept intervals to add in a random generated variable time delay to overcome the interferences among different altimeters, and (3) to switch to different swept frequence bands according to different altitudes.

Description

200409933 V. Description of the invention (1) Detailed description The present invention relates to a frequency-modulated continuous wave radar altimeter (FMCW hcUr A11 i me ter), especially a frequency-modulated continuous wave radar altimeter with a digitally controlled linear frequency sweep mode. The basic technology of the traditional continuous wave radar southmeter is to transmit a linear sweep signal whose frequency changes with day to day. When the straight sweep signal is transmitted to the ground or an object, it will generate an echo, and the echo signal will have a relative time delay with the distance. After mixing with the transmitted signal, a beat frequency output is generated. After this time delay function is converted and calculated, the height distance can be obtained. Conventional continuous wave radar altimeters also use VC0 (Voltage Controlled Oscillator) technology to generate linear frequency sweep signals. In the actual environment, there are often many external factors that affect the operation and calculation of the altimeter; for example, the error caused by the angle of the altimeter and the ground during flight, the effect of multiple reflections near the altimeter, the mutual interference between different altimeters, The problem of mixed Doppler signals. If the traditional linear sweep signal is maintained at a fixed sweep bandwidth, the complexity of the circuit design is high and it is difficult to maintain the accuracy of the measurement. In addition, the linear sweep signal generated by the previous technology using VC0 technology is not accurate enough in linearity and precision. Therefore, in application, redundant circuits are often required to perform calculation correction. Digital control type of FMCW continuous wave radar altimeter of the present invention

200409933 V. Description of the invention (2) ---- Linear frequency sweep mode In order to solve the above shortcomings of the prior art radar altimeter, a direct digital synthesis DDS (Direc1: —Dtgitai

Synthesis) can be programmed to generate Chlrp SWeep (Linear Frequency Sweep) waveforms with high accuracy and linearity. One of the features of the present invention is to adopt the frequency sweeping method and frequency sweeping method, and the scan pattern randomly generated in the previous period is randomly delayed to solve the problem of mutual interference between different altimeters and the mixing of Doppler signals. . In order to simplify the distance of the DSP module circuit for calculating distance, another feature of the present invention is to maintain the difference frequency value at 2101 (112 out of '112 in the frequency range garden) by controlling the output bandwidth of the DDS. The characteristics of the wave radar height-count bit-controlled linear frequency sweep mode are described as follows: 1 · Transmitting sweep waveform U sampling / frequency sweeping and down sweeping methods to solve the phenomenon that the distance and Doppler signal are mixed with β. Week plus a randomly generated scan pattern with irregular delay to meet the interference between different two-meter meter. After the system is changed to the above two methods, the resulting waveform will be as shown in the figure below: where rl And r2 is the time delay randomly generated by the DSP, which can separate the signal interference between different altimeters. The method is described below with reference to the table (1).

200409933 V. Description of the invention (3) a. Initialization: • Mode = 0 (FS -100MHz) • Perform up-sweep (ΐ〇1) and calculate the height value. b ·, τ1, 1:11, the main tasks are as follows: • 10 2: Execute the down sweep • r 1: Random time delay • 111: Execute the up sweep within this time, also solve the problem according to (Formula 2) Pooler phenomenon, interference elimination between altimeters, object comparison, etc. are performed by DSP data processing to obtain the exact height value. c. In the process, if fb is not in the range of 3k ~ 10kHz, the following processing methods will be performed: • If fb > 1 0 Κ Η z ', then reduce the frequency sweep rate, for example, switch from m 0de 0 to Mode 1 ; If fb is still greater than ΙΟΚΗζ, continue to drop; the lowest is mode 4 (sweep rate = 6.25MHz / 0. 0 1 sec) • If fb < 3KHz, increase the sweep rate, up to m〇 (ie 〇 (sweep rate = 100MHz / 0. Olsec) d. The method of ΐ12 'r2' 作 21 is the same as the above two items b and c, and so on. 2 · The frequency sweep mode is switched so that the DSP module circuit that calculates the distance can be simplified, and Maintain the accuracy of the measurement; therefore, by controlling the output bandwidth of the DDS, the difference frequency value can be maintained within the 2 & η z intermediate frequency range. As shown by formula (1), when the altimeter is higher than the ground, the higher the distance

Page 7 200409933 V. Description of the invention (4), because the echo time is long, the width F s generated is inversely proportional to the difference frequency fb, so '', 'are large; however, because the frequency value of the frequency sweep is within a certain bandwidth . Therefore, the swept frequency bandwidth can be controlled to maintain ^ The present invention divides the sweep mode into five kinds of% I _ 檄 彳 + private ^ w sacrifice, the scan slope of the work as shown in Figure (3), the higher the distance, the The narrower the sweep frequency, the wider the bandwidth. When the altimeter is lower from the ground, the sweep frequency is wider. $ & Conversely ’The scanning frequency used when the distance from the ground is measured twice. The five types of 檄 ^ ,,, will change according to the current distance. Table (1) Sweep mode Mode Sweep range (MHz) Bandwidth

Mode 4

Mode 3 Mode 2 4250-4275 5MHz

The actual operation is as follows: If fb is in the range of 3k-10kHz, the scan frequency will be switched, and the mode is unchanged; if fb is not in 3k— • If fb> 10KHz, decrease Sweep frequency y is processed according to the following principles. Model; if f b ratio is still greater than! 0KHz, then continue to drop the m0de0 to 4250-4256. 25 4250-4262.5 25¾ 5〇MH2 mode 4 (sweep rate = 6.25MHz / 0 〇13ec; • If fb < 3KHZ 'then increase the frequency sweep rate, up to _ 0 (sweep

Page 8 200409933 V. Description of the invention (5) rate = 100 MHz / O. 01 sec) The following describes the working principle of the present invention. 1_ The relationship between the distance between the object to be measured and the sweep frequency bandwidth (fb: a beat frequency) can be obtained by the following formula: fb = (2R / cT) Fs Formula (1) where T: sweep time, c : The speed of light, Fs: sweep bandwidth, R: The distance of the object to be measured is determined by formula (1). When R is greater, fb is greater; and fb passes the intermediate frequency data. The wave is sent to the DSP module circuit to calculate the distance. Therefore, in order to maintain the same bandwidth to simplify the complexity of the design and maintain the accuracy of the measurement, the value of fb should be maintained within a certain bandwidth, so changing the Fs value is an optimal way; therefore, only with. That is an inverse relationship. 2. Solve the phenomenon of Doppler signal mixing If the vehicle of the altimeter is in a moving state, fb of formula (1) contains the data of distance and Doppler signal mixing, so if you want to analyze the exact distance, you need to scan up Frequency and down-sweep mode, as shown in formula (2). (Fb = (2R / cT) Fs = kR-fbl = kR— fd, fb2 = kR + f d —R = (f bl + f b2) / 2k, f d = (f b2-f bl) / 2

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Page 10 200409933 Schematic description of the diagram Illustrated to further understand the content of the present invention, the following will be described in detail in conjunction with the related diagram, MCW continuous wave radar height count bit controlled linear sweep mode sweep frequency waveform. Control of the month_continuous wave radar height count bit The scanning mode switching principle of the s ® in *, bay mode. Invented: CW radar height count bit, 筮 = ,,,, five scan mode slopes of frequency sweep mode. : 4a is a green diagram of the FM curve of the FMCW radar transmitted and reflected waves. f 4b is the frequency difference between the FMCW radar transmitted wave and reflected wave. Figure 5 is a system architecture diagram of the FMCW continuous wave radar height-counting-controlled linear frequency sweep mode of the present invention. Figure 1 illustrates the frequency sweep waveforms of the FMCW continuous wave radar height-count bit-controlled linear frequency sweep mode of the present invention, where t0l, t 丨 j, t21, ..., etc. represent upsweep waveforms, t02, t12, ΐ22 … Etc. indicates that the lower sweep frequency 幵 y τ Γ 2 represents a random time delay, and its sweep mode has a parallax frequency of '5 sweep modes to choose from. FIG. 2 illustrates that in a preferred embodiment of the present invention, when the frequency difference fb is greater than 10KΗζ, the frequency sweep rate can be reduced, for example, switching from Mode 0 to Mode 1 (as shown in Table 1). The frequency difference fb is still greater than 10KΗζ, then continue to reduce it

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Keep the frequency difference fb at 3 KHz _ When the frequency difference fM is captured at 3KHz, increase the sweep KHz = white and vice versa 'Switch to Mode 3 (as shown in Table 1) m, for example, since the heart 4 continues to increase its Sweep frequency d frequency difference two frequency / fb is still less than, then time. The third figure maintained at 3 KHz-0 heart is a description of the present invention. "Continuous wave ray: five sweeps of the linear sweep mode of the industrial system:-率 十 #: the mode with the largest slope., The bottom = : The slope of the upper two difference V frequency difference fb selects the scanning mode slope, which can be 'in order to simplify the complexity of the design' within a certain bandwidth and maintain the accuracy of the measurement. The relationship between the curves. Figure 4b illustrates the time-frequency relationship between the corresponding fourth & Figure 1 ^ (^ 雷 逹 出 波 ", where the solid line is the transmitted wave and the dashed line is the target reflected wave. Figure 5 is the original The invention "(^ continuous wave radar height leaf digital :: type, the frequency sweep mode system architecture diagram, the working principle is described in a preferred embodiment of the present invention as follows ..." Digital L 旒 Processor DSP 1 through a direct digital synthesizer Out the control port (digital i / 0 port), to make the direct digital combination 2 round out, for example, a frequency sweep signal between 21 · 428 ~ 24. 3MHz. The direct digital synthesizer DDS 2 outputs a frequency sweep signal, which is mixed up

200409933 The diagram briefly explains the frequency 3 and the frequency doubling 4, and then the power is amplified by the transmitting / receiving module 5 so that the radar altimeter outputs, for example, a swept frequency wave (FMCW) between 4.25 to 4.35 GHz. 3. The received RF signal and the transmitted RF signal are demodulated by a mixer (Mixer) to a difference frequency (fb 'beat frequency), and the difference frequency is proportional to the height value. 4. DSP 1 through gain control STC 6 control 璋 (digital I / O port) Control gain control ST C 6 Processes the input differential frequency signal so that its output frequency falls within the intermediate frequency IF bandwidth, for example, 2 kHz Then, the IF signal is captured by A / D and digitized. 5 · After the IF signal is digitized, it is calculated by the fast Fourier transform (F F τ) to find the frequency of the maximum power value (work of the DSP). 6 · This frequency is the frequency generated by the surface reflection signal after the above processing. It is proportional to the height, and the height value can be obtained by converting the appropriate ratio (s c a 1 e). If the frequency is not between 3 and 10KΗζ, then according to the method described in the present invention, select a suitable scanning mode and control the DDS 2 output, for example, a swept signal between 21 · 428 ~ 24, 3MHz (the operation of DSp). From the above description, it can be understood that 'the present invention adopts an up-sweep and a down-sweep mode' and adds a period of randomly generated non-time-delayed scan form during the period 'and switches different sweep frequency bandwidths according to different heights. Mutual interference between them and the problem of mixed Doppler signals. The present invention! ^ "Continuous wave radar high counting bit control linear frequency sweep mode is

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Claims (1)

200409933 6. Scope of patent application Patent scope 1 · A digitally controlled linear frequency sweep mode of FMCW continuous wave radar altimeter, which is characterized by 1) adopting frequency sweep up and frequency sweep to solve the problem of mixed distance and Doppler signals Phenomenon; 2) ^ A period of randomly generated sweeps with irregular delays = form 'is added to overcome the interference between different altimeters; 3) Switching sweep modes with different sweep bandwidths according to different degrees. Equation 2. The digitally controlled linear sweep mode of the first item in the H range of Λ is doubled when the ground distance is higher. In several modes, the lower the height of the altimeter, the more the frequency of 1 is swept; otherwise, when the altimeter Ground clearance scan frequency. The wider the bandwidth, the higher or lower the viewing distance to change the formula used. Among them, the digitally controlled linear sweep mode around the second term. There are five types of% frequency modes in a preferred embodiment. 4 · According to the application for patent 籁) fi 其中 1. Among them, different frequency sweeping frequency bands are switched: the linear sweep mode of the two systems is determined by the difference frequency of the wave. When the frequency is set, the formula is switched to — ' When the limit is still set, the sweep bandwidth is swept from the original limit: at 1 limit •, sweep = = wide mode: otherwise, the sweep bandwidth mode of the difference frequency station. See ’, the frequency bandwidth mode is switched to a comparison coffee Page 15 200409933