Abstract: An apparatus (10) and method for detecting an intrusion into a predetermined area. The apparatus (10) includes a transmitter (28) and a receiver (30). The receiver (30) generates an output signal indicative of reflected return signals received. The apparatus (10) also includes a controller (38). The controller (38) receives the output signal from the receiver (30) and determines a peak value of the output signal during a first time window. The first time window continues no longer than a first maximum duration when the peak value of the output signal during the first maximum duration is at least a predetermined value. The first time window continues no longer than a second maximum duration when the peak value of the output signal during the first maximum duration is less than the predetermined value.

Abstract: A patch antenna is formed of one or more flat disc-shaped radiators disposed parallel to and spaced apart from a common ground-plane element. At each radiator, there is a feed assembly of two feeds positioned to one side of a center of the radiator in space quadrature and excited in phase quadrature for generating circularly polarized radiation from the radiator. Each of the feeds, in a preferred embodiment of the invention, is formed as a post extending through an aperture in the ground-plane element partway to the radiator for capacitive coupling with the radiator. At each radiator, a reactance element on the form of a capacitive block extends from the ground-plane element partway to the radiator at a location diametrically opposite the feed assembly.