The Synthesis of Narrow-Band Crystal Band-Elimination Filters

A new design theory is developed for the insertionloss synthesis of narrow-band crystal band-elimination filters. The theory is based on the narrow-band approximation and consequent pseudoreactance theory originally suggested by Baum and extensively used for narrow-band bandpass filter design. The structure used is a tandem connection of bridged- sections, able to accomodate arbitrary crystal capacitance ratios and, through the use of a transformer, arbitrary crystal inductances. An additional free parameter can be used to reduce the spread of element values. An example illustrates the excellent agreement between approximate theory and exact final analysis.