Frequency transformations for the simple 2-port wave digital filter adaptor chain

The hardware implementation of wave digital filters, based on cascaded unit element reference filters, has recently been discussed. The filters considered were lowpass filters and bandstop filters with a centre frequency of one quarter of the sampling frequency. In the paper, it is shown that highpass filters and bandpass filters with a similar restriction on the centre frequency can be designed by applying standard frequency transformations to the lowpass prototype. It is also shown how this centre frequency restriction may be lifted, leading to general bandpass and bandstop realisations. The necessary modifications to the hardware implementation are also presented. Examples are given comparing the noise performance of lowpass and highpass structures.