초록 ▼

Range-dependent sensitivity of an RF doppler radar apparatus is reduced to prevent false alarms when small objects move in close proximity to the apparatus\antenna. The sensitivity is reduced by periodically FM-modulating the transmitted RF signal at a frequency corresponding to a wavelength which i

Range-dependent sensitivity of an RF doppler radar apparatus is reduced to prevent false alarms when small objects move in close proximity to the apparatus\antenna. The sensitivity is reduced by periodically FM-modulating the transmitted RF signal at a frequency corresponding to a wavelength which is at least four times the operating range of the apparatus. The reflection of the transmitted signal is mixed with the transmitted signal to produce a difference frequency signal which is sampled at instants of maximum amplitude.

대표청구항 ▼

A doppler radar apparatus for surveillance of an area lying within a predetermined operating range, comprising: (a) a transmitter for producing a radio frequency signal at an output thereof; (b) a modulator coupled to the transmitter for momentarily modulating said radio frequency signal during succ

A doppler radar apparatus for surveillance of an area lying within a predetermined operating range, comprising: (a) a transmitter for producing a radio frequency signal at an output thereof; (b) a modulator coupled to the transmitter for momentarily modulating said radio frequency signal during succesive periods of duration T at a predetermined modulation frequency, said modulation frequency corresponding to a wavelength which is at least four times the operating range of the apparatus; (c) a transmit antenna coupled to the transmitter for transmitting the modulated radio frequency signal across the area; (d) a receive antenna for receiving a reflection of the transmitted signal from an object within the area; (e) mixer means coupled to said transmitter output and to said receive antenna for mixing the transmitted and received signals and for producing a difference frequency signal representing the range of said object, said mixer means comprising: (1) a power divider for coupling the transmitter output to first and second outputs thereof; (2) a 90°coupler having an input coupled to the receive antenna and having first and second outputs for providing 90°phase-shifted replicas of the received signal; (3) a first balanced mixer coupled to the first output of each of the power divider and the 90°coupler for mixing the transmitted signal and one of the replicas of the received signal, and for producing at an output thereof a first difference frequency signal; (4) a second balanced mixer coupled to the second output of each of the power divider and the 90°coupler for mixing the transmitted signal and the other one of the replicas of the received signal, and for producing at an output thereof a second difference frequency signal; and (5) a 90°phase shifter coupled to the output of the first balanced mixer for producing at an output of the phase shifter a 90°phase-shifted replica of the first difference signal; and (f) an evaluation device, coupled to the outputs of the 90°phase shifter and the second balance mixer, for sampling the difference frequency signal during each period at a predetermined instant when the difference frequency signal amplitude is a maximum.