When designing filters with highpass or bandpass characteristics, it is often convenient...

When designing filters with highpass or bandpass characteristics, it is often convenient first to design a lowpass filter with the desired passband and stopband specifications and then to transform this prototype filter to the desired highpass or bandpass filter. Such transformations are called lowpass-to-highpass or highpass-to-lowpass transformations. Designing filters in this manner is convenient because it requires us only to formulate out filter design algorithms for the class of filters with lowpass chararteristics. As one example of such a procedure, consider a discrete-time