Doppler radar speed sensor.

摘要

A Doppler radar speed sensor for a land vehicle comprises a radar transmitter/receiver circuit (1) coupled to an aerial system (2). R.F. energy from a source (3) is transmitted by the aerial system in forward (9) and backward (10) directions and energy reflected from these directions is mixed with a sample of the transmitted energy in a mixer arrangement (8) to yield a pair of Doppler frequency components representative of the vehicle speed. In order to ensure that these components always have mutually different frequencies, and thereby avoid the necessity of constructing the mixer arrangement as a pair of quadrature-related mixers, the forward and backward directions make different angles ( theta + DELTA theta and theta - DELTA theta respectively) with the direction of travel (15). <IMAGE>