Amtech Technology Corp.

David A Eckhardt

Jeremy A Landt

Alfred R Koelle

Briefly, the range limiting system of the invention is capable of differentiating desired received signals having an amplitude above a predetermined threshold level and at least one other recognizable predetermined characteristic, from other received signals below that predetermined threshold amplitude. The system has a means for combining the received signal, which is of unknown amplitude which may be above or below the predetermined threshold amplitude, with a known signal of the predetermined threshold amplitude having at least one other predetermined characteristic which is distinguishable from the other recognizable characteristic of the received signal. The output of the combining means passes to a signal processing means which produces an output signal whose other recognizable characteristic is determined by the received signal only when the received signal is above the predetermined threshold amplitude, and by the known signal when the received signal is below the predetermined threshold amplitude. The presence or absence of the desired signal is determined on the basis of analysis of the other predetermined characteristic of the output signal of the signal processing means.

Range limiting system

The invention provides a system for discriminating between modulated backscattered signals based upon transmission-to-reception time delay. The system employs a carrier, phase-modulated with a modulating signal, having characteristics which provide unity output when correlated with itself with zero time shift and a substantially lower output level when correlated with itself with a significant time shift. The system works with a backscatter-modulator located a finite distance from the transmitter for receiving and modulating the backscatter of the carrier. A receiver/detector receives and detects the modulated backscattered phase-modulated signal, the detector being phase-sensitive and having as a reference signal the transmitted phase-modulating carrier signal, and having as an input signal the phase modulated backscattered carrier. The detector provides an output signal whose averaged amplitude is substantially dependent upon the degree of phase correlation between the phase of the modulation returned input signal and the reference signal. Finally, the output signal from the detector is selectively processed only when its averaged amplitude is above a threshold level. In a preferred embodiment, the transmitted signal is a spread spectrum signal.

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Albuquerque, NM, United States of America

David A Eckhardt