Generalized Resolution in Radar Systems

A generalized theory of radar resolution has been developed to facilitate understanding of the fundamental resolution limitations of radar systems. Previous work by Woodward and Elspas to determine limitations on radar resolution led to the concept of an ambiguity function which is a quantitative measure of radar resolution in range and range rate. This theory has been extended to include simultaneous resolution in range, range rate, azimuth and elevation and led to the derivation of a four-dimensional ambiguity function. Resolution constants derived from the ambiguity function show clearly the trade-offs between system parameters and resolution. A new concept, "angular dispersion and compression," has been evolved from the theoretical development. An angular compression system, analogous to a pulse compression system, employs a pseudo-randomly dispersed pattern which is compressed in angle at the receiver with a correlation technique, to produce the effect of a narrow beam without having a physically narrow beam. The signal bandwidth's effect on the pattern of an antenna and on its angular resolution has been found to be slight, except for very large bandwidths. It has been concluded that trade-offs between signal complexity and antenna complexity have no practical advantage. Because of the presence of noise, radar measurement of target parameters is essentially equivalent to statistical estimation. Woodward and Elspas have shown that the range, range-rate ambiguity function is the natural quantity to use in making a maximum likelihood estimate of range and range rate. The technique of maximum likelihood estimation has been extended to angular measurement.