A radar device precisely detects a target in short time intervals by detecting a true peak frequency with high accuracy via a calculation which does not require a large amount of computation. A discrete frequency spectrum of a beat signal multiplied by a window function is determined, and values of signal strength at two discrete frequencies which are, respectively, higher and lower than a peak frequency of the discrete frequency spectrum of the beat signal and which are adjacent to the peak frequency. The frequency difference between the discrete peak frequency of the beat signal and the peak frequency of the window function is then determined from the ratio between the values of signal strength at those two discrete frequencies adjacent to the peak frequency. Thus, the true peak frequency of the beat signal is determined with a high frequency resolution.
A frequency modulation radar apparatus for vehicle use can suppress the influence of noise to avoid incorrect estimation due to noise thereby to provide a beat frequency with high accuracy and at high speed without increasing the frequency resolution of the beat frequency that causes an increase in an observation time. The apparatus includes a frequency correction section that calculates a corrected frequency (f.sub.n+.delta.) by adding an amount of frequency correction (.delta.) to the frequency (f.sub.n) of a peak signal, and a CPU that calculates a distance or a relative speed to a target object based on the corrected frequency (f.sub.n+.delta.). In an FFT calculation section, the frequency (f.sub.t) of the true peak signal is calculated based on the characteristic of a window function, and if the frequency (f.sub.t) thus calculated is determined as an incorrect estimation, the frequency of the true peak signal is further corrected.
