Digital processing method of altimeter of linear frequency modulation continuous wave radar

Abstract

The invention discloses a digital processing method of an altimeter of a linear frequency modulation continuous wave radar, which belongs to the field of the radio altimeters. The digital processing method comprises the following steps: step 1, obtaining beating signals from an orthogonal mixer arranged at the front end of the altimeter of the radar, and carrying out A / D (analog-to-digital) sampling to obtain a digital signal sequence; step 2, performing Fourier transform on the digital signal sequence, and calculating the amplitude of a spectral line; step 3, judging according to the amplitude of the spectral line of an amplitude spectrum, and measuring the beating frequency of the digital signal sequence; step 4, refining the frequency spectrum, calculating the slope correction of saw-tooth wave, and correcting the slope of the voltage signals of the saw-tooth wave; and step 5, calculating the high value of the current altimeter according to the slope of the voltage signals of the saw-tooth wave. The FFT-CZT method adopted by the invention is insensitive to noises and can perfectly work at lower signal-to-noise ratio, but the measurement precision is reduced. Because of having no limit on the properties of the targets, the digital processing method can be applied to the measurement and the analysis of point targets or surface targets.

Description

technical field [0001] The invention relates to a digital processing method for a linear frequency modulation continuous wave radar altimeter, which belongs to the field of radio altimeters. Background technique [0002] The linear frequency modulation continuous wave radar altimeter, that is, the LFMCW radar altimeter, is a means of measuring the height through the beat signal of the echo signal and the transmitted signal. Due to its small radiation power, high measurement accuracy, relatively simple equipment, Good electronic countermeasure performance and low probability of interception have been widely used in various aircraft such as drones. The earlier LFMCW radar altimeter used the method of average frequency counting to obtain the altitude information in the beat signal. Later, in the mid-1980s, due to the application of digital technology, especially the microprocessor in the altimeter, the frequency modulation continuous wave Much progress has been made in institu...

AI Technical Summary

Problems solved by technology

Different from the previous time-domain processing method, digital signal processing technology is used to extract the height information for the obtained beat signal. The most commonly used algorithm is FFT, but because FFT is performed on the entire unit circle in the Z domain Spectrum analysis, so its frequency resolution is f s / N, where f s is the sampling frequency, and N is the effective length of the signal x(n). In order to improve the frequency resolution and achieve high measurement accuracy, it is necessary to increase the interception length of the signal x(n), but this will greatly increase the amount of calculation

At the same time, when traditional FFT is used to analyze the signal spectrum, it will be affected by aliasing effect, quantization error, leakage effect and fence effect, especially the "fence effect" of FFT. The distance spectrum obtained directly by FFT has a fixed The interval ΔR (range resolution of the radar), resulting in a ranging error of ΔR / 2, which makes the relative error of the radar altimeter measurement at low altitudes larger

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