Recursive filter implemented as a matched clutter filter

DETAILED DESCRIPTION This invention provides apparatus and method for the implementation of a recursive filter and more particularly for the implementation of a matched clutter filter.
The general purpose of the invention is to provide new and improved recursive filters.
Utilizing the system of the present invention the desired output of a recursive filter may be obtained efficiently and economically in real time.
A particular objective of the present invention is to provide high speed apparatus for the measurement of the impulse response h and its associated transfer function H and coherence function .
gamma.
.
sup.
2 of a pair of signals y and x, or, alternatively, for the measurement of the impulse coherence .
GAMMA.
and its associated coherence function .
gamma.
.
sup.
2 and transfer function H of a pair of signals y and x.
Briefly, the present invention provides an efficient and economic recursive filter for use in real time.
The system is based on the use of the convolution integral or fast convolution and may be implemented as a serial, cascade, parallel, or array processor.
The design is conventional up to a point, the important and distinguishing feature being the selection of non-recurring means for processing of poles.
While the design of a conventional recursive filter requires a recurring and therefore complex architecture the system of the present invention uses the simple means of a read-only memory (ROM) or programmable read-only memory (PROM) and in this manner significantly reducing the software and/or hardware required.
Typically, in one embodiment which uses the fast convolution the filter transfer function H.
sub.
r is obtained at the output of a divider in the form of a ROM or PROM and is multiplied with the frequency spectrum S.
sub.
y in a multiplier to obtain the transfer function H after which the impulse response h is obtained using an inverse Fourier analyzer.
In another embodiment using the convolution integral the filter impulse response h.
sub.
r is first obtained from the transfer function H