Single ground plane interdigital band-pass filter apparatus and method

Abstract

A method of fabrication and apparatus are disclosed for realizing a high-frequency non-transverse electromagnetic (non-TEM) mode interdigital band-pass filter. The filter has interdigital microstrip resonators R.sub.i separated a constant distance H from a ground plane by a propagation medium. The method of fabrication allows the W.sub.i /H.sub.i and S.sub.i,i+1 /H.sub.i dimensions of the filter to be obtained. The method starts by determining the self and mutual admittance values Y.sub.i,i and Y.sub.i,i+1, respectively, of each resonator R.sub.i. An estimate for W.sub.i /H.sub.i for each resonator can be made, if desired, using a single microstrip approach. The W.sub.i /H.sub.i estimates are used to obtain the S.sub.i,i+1 /H.sub.i value for each adjacent pair of resonators R.sub.i,R.sub.i+1. The S.sub.i,i+1 /H.sub.i values are used to obtain the values for Y.sub.f and/or Y.sub.fe for each resonator R.sub.i. The values for Y.sub.f and/or Y.sub.fe are used to calculate the value for Y.sub.pp for each resonator R.sub.i. Each Y.sub.pp value is used to obtain a value for W.sub.i /H.sub.i. The method of fabrication is convergent and can be iterated to obtain convergent values for S.sub.i,i+1 /H.sub.i and W.sub.i /H.sub.i so that a filter can be produced having the desired electrical passband response.