A single FM/CW radar antenna and accompanying electronics are positioned within a space that is to be guarded. A moving object within the space under surveillance produces a doppler frequency shift in the echo return signal which return signal is, in turn, analyzed for signal content. Through FM and range gating the return signal analysis is selectively adjustable for moving target size and range such that moving targets of below minimum size and/or beyond maximum range are not detected as hostile objects while moving targets of or above minimum size and/or at or within maximum range are detected as hostile objects. Range gating is selectively adjustable to produce an alarm signal by selected size hostile objects within a predetermined range of detection, e.g., of 300 feet, such as a man crawling through the radar beam at a range of 300 feet within an enclosed fenced-in area while not producing an alarm signal by relatively large non-hostile objects without the range of detection, such as a large truck moving through the radar beam at a range of 330 feet outside the enclosing fence or by relatively small non-hostile objects within the range of detection, such as a guard dog moving through the radar beam at a range of 270 feet inside the enclosing fence.

FM/CW surveillance radar system with range gating

A fail-safe sensor system to provide a positive indication of the proper operation of a sensor system by accounting for the return signals from an active zone and a monitor zone beyond. Search signals, provided by a transducer operating in the transmit mode, are transmitted within an active zone within which objects to be detected are expected to be located. Unreturned search signals are permitted to travel beyond the active zone into a monitor zone beyond and objects in such monitor zone cause return signals which are also employed. A counter feed from a free running clock source is permitted to run up a count whose predetermined limit represents the estimated maximum time period during which a sensor system should operate without contacting an object. Return signals, whether from objects in the active zone or the monitor zone, reset the counter back to zero. The absence of a return signal permits the counter to exceed its predetermined limit and produce an output signal which can be directed to control circuitry, an alarm or logic circuitry to determine if the system is operative.

Fail-safe sensor system

For use in an intrusion alarm system, an on-line test circuit operative for the continuous supervision of system operation without affecting normal operation thereof. The transmitted signal is frequently modulated at a low rate to produce a detectable change in reflected energy sensed by sub-Doppler processing circuitry and operative to produce a failure indication in the absence of such sub-Doppler signal.

On-line test circuit for intrusion alarm systems

In an active system a transmitter transducer and a receiver transducer are both secured to an object such as a glass panel the intrusion through which is to be monitored. The transmitter transducer establishes a relatively low frequency signal in the panel and a supervisory branch which couples from the receiver transducer monitors the presence of this supervisory signal. A second branch which also couples from the receiver transducer is for monitoring intrusion and comprises digital circuitry including a pair of monostable multivibrators and a counter which counts pulses from one of the monostable multivibrations during a time interval determined by the other monostable multivibrator to discriminate between panel breakage and panel rapping, for example. The tampering with voltage lines is also detected and a special holder is employed for fastening the transducers to the panel.

Intrusion detection apparatus

Microwave apparatus for detecting the movement of a moving object comprising a Gunn oscillator device having input terminals that are capable of receiving a potential difference which serves to produce a bias current in the device, said potential difference being subject to variations, the device being responsive to a constant potential difference and operative to radiate microwave energy at a first frequency, and further responding to Doppler shifted energy reflected from the moving object and producing a variation in the bias current, an operational amplifier responsive to the potential difference and a reference signal for developing a first signal when the potential difference exceeds the reference signal and a second signal when it is less, a series-pass transistor connected to a source of DC potential and the operational amplifier and being switchable between a conducting and a non-conducting state in response to the first and second signals and serving to maintain the potential difference at a constant value, and a resistive element connected between an output of the transistor and the Gunn oscillator for sensing the variation in the bias current and developing an output signal representative of the movement of the moving object.

Microwave motion-detection apparatus employing a gunn oscillator in a self-detecting mode

The illustrated detection apparatus includes a radio frequency transmitter and a receiver having an amplifier which has a constant gain portion and a following roll-off above the highest motion Doppler frequency signal to be detected. The transmitter is a Clapp oscillator. A free running multi-vibrator is coupled into a voltage regulator of the bias supply of the Clapp oscillator to superimpose a supervisory signal which falls within the roll-off portion.

B. Korta Lawrence

Papers

Intrusion detection apparatus having supervisory control means