Microwave/seismic security system

摘要

Method and apparatus is disclosed for detecting a security threat in a zone. A transmitter within the zone directs a first microwave signal of frequency f0 to a reflector. The reflector doubles the frequency to 2f0 and reradiates it to a receiver. The receiver correlates the reflected signal (phase and/or amplitude) with the transmitted signal and provides spectral data to a digital signal processor. A seismic sensor within the security zone also provides seismic spectral data to the digital signal processor whenever seismic disturbances are detected within the zone. The digital signal processor compares the spectral data with predetermined stored spectral data. Whenever both the reflector signal and the seismic signal spectra indicate a security threat within the zone, an alarm signal is output. Loss of reflector output plus adverse seismic spectral data may also trigger an alarm. The dual-sensor configuration reduces false alarms and circumvention of the detection system.