Abstract: An outdoor microwave transceiver area intrusion detection system includes circuitry for both amplitude and frequency modulation of the microwave carrier signal pulses, which are transmitted at approximately a 50% duty cycle pulses, from a radar antenna to a target. The return signal is mixed with a portion of the transmitted signal to produce first and second doppler frequency signals which are amplified and sampled during a narrow gating pulse. The two resulting sampled doppler frequency signals are alternately switched, in synchronization with the amplitude and frequency modulation signals, into first and second sample/hold circuits to reconstruct the first and second doppler frequency signals. The reconstructed signals are coupled to a differential amplifier to obtain a "range signal" which is proportional to the phase difference between the first and second doppler signals.

Abstract: An intrusion detection system includes a transmitter coupled to one end of a coaxial cable, a plurality of antennas spaced along and loosely coupled to the cable, and a receiver circuit coupled to the opposite end of the cable, the antennas being aimed at a protected region. The transmitter transmits microwave energy along the cable. A portion of the energy is transmitted by each antenna into the protected region and is reflected by a moving intruder or target back to one of the antennas. The receiver circuit imposes a low frequency square wave signal on the center conductor of the cable. A diode is attached across the two radiating elements of each antenna. The square wave on the center conductor forward biases the diode and thereby shorts each antenna for half of each low frequency cycle, resulting in chopping of the received signals from each antenna.

Abstract: An optimum coupling unit for joining adjacent sections of coaxial cable and a coupled radiating antenna includes different diameters of the dielectric material, different diameters of central conductor and different values of the dielectric constant material in order to provide impedance matching at any section of the coupler including the coupled antenna to the impedance of the coaxial cable. The coupling unit is combined with the antenna as an integral unit. The antenna may be a dipole whose elements are coupled to the coupling unit through a parallel plate transmission line. Impedance matches are maintained at each coupling point.

Abstract: An intrusion detection system includes a transmitter of wave energy at one end of a transmission line or coaxial cable, for example, and a receiver connected directly to the transmission line or a cable at the other end together with a series or discrete antennas uniformly spaced along the transmission line and relatively loosely coupled thereto. The coupling between the antennas and the transmission line or coaxial cable is determined to be of an optimum value and in such a system the sensitivity to an intrusion is the same along the length of the coaxial cable or transmission line for the same distance from the transmission line.