There are more than 100 books on Circuit Analysis, Network Synthesis,
Ana- log and Digital Filters and Signal Processing written at the
undergraduate and graduate level and a few more written as Reference and
Handbooks. When and if they discuss the design of analog and digital
filters, they treat mainly the approximation of the magnitude response
of the filters and very little of their phase or group delay response.
There is hardly any discussion of designing fil- ters that
simultaneously approximate the magnitude and group delay response of the
filters. Thus most of the books routinely discuss Butterworth, Chebyshev
and sometimes the Cauer or elliptic function response of the lowpass
prototype filters, followed by the transformations to design highpass,
bandpass and band- stop filters-all of them approximating their
magnitude response only. Due to the rapid progress from analog to
digital communication and data transmission that has taken place in
recent years, there is a greater need for designing filters that
approximate both the magnitude and group delay requirements. So also is
the need to design 2-dimensional digital filters, particularly those
used in image processing, that approximate prescribed magnitude as well
as constant group delay responses. A lot of research work has been
published in professional jour- nals on the design of these filters in
the last 10-15 years.