Pat.#5134408:		Detection of radar signals with large radar signatures
INVENTORS:		Harmuth; Henning F., Potomac, MD
ASSIGNEES:		Geophysical Survey Systems, Inc., North Salem, NH
ISSUED:		Jul. 28, 1992
FILED:		Jan. 30, 1991
ABSTRACT: Method and apparatus for generating and receiving carrier-free radar pulses that can be detected even though they are heavily distorted by a target and have additive noise superimposed on them, or are in an environment of unwanted signals. The method is especially applicable to signals that are based on pulses with a duration of 1 nanosecond (ns) or less. The radar signature of typical targets from such signals is very large, which makes it hard to selectively receive return signals unless they are marked. Fine structure marking is not effective for such short duration pulses. A method for organizing the signal with coarse structure marking is describedthat allows the radar receiver to discriminate heavily distorted wanted signals from unwanted signals and noise without requiring large peak power at the transmitter. The disclosed method involves placing positive-going and negative-going pulses together in a pattern of contiguous pulses to form a character. Generating one or more time-delayed replicas of the character and summed selected ones together to form a signal with coarse structure marking. The delay time of each replica may vary and some replicas may have their polarity reversed before summing, but all are based on pulses that are short enough to imply that most return pulses would not be recognized by a receiver. However, the coarse structure of this invention marks the signal for selective reception. It renders the characters within it recognizable, and thereby enables the transmission of pulses without a fine structure marking which might otherwise be absorbed by the atmosphere.