Intrusion detection apparatus

Abstract

An intrusion detector and method of operating the detector is disclosed. The detector comprises a means including an antenna for transmitting spaced pulses of radiation energy of a given frequency throughout a region to be protected. Means are also provided for receiving the radiation energy reflected from the protected region. The reflected radiation energy is received between adjacent spaced transmitted pulses in the form of an AC analog signal at the given frequency, the peaks and valleys of which signal vary in amplitude with time. Means are also provided for allocating a portion of the time occurring between transmitted pulses into a plurality of time segments, each of which segments is long enough to correspond to a plurality of cycles of the analog signal. The detector further includes: means for integrating the plural cycles in each of the time segments to arrive at an integral value for each of the time segments; means for converting the integral values into corresponding digital values; means for storing the digital values in memory; means for comparing the stored digital values obtained from the reflected energy from the first transmitted pulse with the corresponding digital values obtained from the reflected energy of an adjacent second transmitted pulse; means for storing the absolute differences obtained between corresponding integral values for each of the time segments; and, means responsive to predetermined changes in the absolute differences for a predetermined number of time segments for initiating an intrusion signal in the apparatus.