Doppler effect vehicle speed measuring equipment - has numerically controlled oscillator for sum and difference frequencies from processed Janus aerial system

摘要

Mounted on a vehicle, a microwave unit has a transmitter for directing radiation from an aerial at an angle to the ground and a receiver intercepts the reflected signal. The difference frequency between the two signals is processed by a circuit with a control stage adjusting the frequency of a numerically controlled oscillator to obtain a signal containing the sum and difference frequencies after passing through high and low pass filters having partly overlapping frequencies. From the control stage with an overrunning return, the vehicle speed is obtained. Two signal processing stages for upper and lower speed measurements are included, also two evaluating stages for signals from a Janus aerial arrangement. ADVANTAGE - Accuracy at high and low speeds and sudden speed changes.