Large area motion sensor using pseudo-random coding technique

A system for detecting a moving intruder entering within a predetermined area of coverage, comprising:

• a pair of substantially omni-directional antennas, one for transmitting and the other for receiving, one of said antennas being located at one of the two foci of an ellipse generally defining the boundary of said predetermined area of coverage and the other antenna being located at the other of said foci;
• first means for energizing said transmitting antenna with a pseudo-random coded, bi-phase modulated RF carrier;
• second means responsive to said receiving antenna for receiving signals including direct radiation from said transmitting antenna and delayed signals corresponding to reflections from objects illuminated by said transmitting antenna;
• third means within said second means for autocorrelating said delayed received signals against said direct radiation received signal to produce an autocorrelation output signal having a maximum value when said coded signals reflected from said illuminated objects arrive at said receiving antenna at substantially the same time as the coded signals received by said direct radiation, said autocorrelation output signal decreasing toward zero amplitude as a function of increasing reflected signal delay as the differential delay between said direct and reflected signals at said receiving antenna approaches one bit duration of said code, thereby to produce a response cut-off perimeter which is along the perimeter of said ellipse substantially bounding said predetermined area.
• and a Doppler filter responsive to the output of said third means for passing Doppler signals representative of the velocity of corresponding moving objects within said predetermined area.