Phase locked detector

DETAILED DESCRIPTION OF THE INVENTION An intrusion detection system showing the preferred embodiment of the present invention is illustrated in FIG.
1.
A voltage controlled oscillator modulator 12 provides a continuous wave modulation signal to a carrier oscillator 10.
The output of the carrier oscillator 10 is provided to the transmit antenna 14 which radiates the signal into the intended zone to be protected.
The output of the voltage controlled oscillator modulator 12 is also applied to a digital counter 28 and to a phase comparator 22.
A receive antenna 18 senses energy reflected from an object 16 in the field of the transmitted signal.
The receive antenna 18 conveys the reflected energy to a detector 20 which provides a demodulated signal to a phase comparator 22.
The phase difference between the output of the voltage controlled oscillator modulator 12 and the output of the detector 20 is measured and a control voltage signal is passed through a low pass filter 24 to the input of the voltage controlled oscillator modulator 12 and to the input of an analog sensor 26.
Referring to FIG.
1, the carrier oscillator 10 generates an electromagnetic signal which typically may be in the "X" or "Ku" frequency bands.
This microwave signal is modulated by the output of the voltage controlled modulator 12 and is then provided to the transmit antenna 14 which directs the energy into the zone of interest which is to be protected.
Physical objects located within the zone of interest, such as object 16, will reflect a part of the electromagnetic energy back to the receive antenna 18.
The receive antenna 18 applies the reflected energy to a detector 20 which demodulates the reflected signal and conveys the demodulated signal to an input of the phase comparator 22.
Also input to the phase comparator 22 is the output signal of the voltage controlled oscillator modulator 12.
The phase comparator 22 determines the phase difference between the transmitted signal and the received signal and generates a control voltage that varies therewith