Novel resonators with a applying binomial coefficients admittance values to design multifrequency bands of microstrip filters

This work presents the superiority of designing microstrip line multifrequency band filters with a single input and a single output. Utilizing the S-parameter of a two-port network and the ABCD matrix parameters for the analysis of short-circuited and open-circuited resonators with various combinations of series and shunt sequences, multifrequency band resonators are proposed based on the stepped-impedance resonator (SIR) structure. With the idea of the impedance ratio of the resonators, the center frequency of the two passband is determined. Using transmission line connections of suitable characteristic impedances and the resonators by the binomial coefficient admittance values, the dual-band effect is obtained. Binomial coefficient admittances of resonators are chosen for higher order dual-band filter design and simulation. From the experimental results, the bandwidth is 500 MHz to the least extent, the insertion loss is less than 1dB within the passband, and more than 50 dB attenuation is permitted within 1.4 GHz from the center frequencies of the two passband. The method can be applied to any other multifrequency bands, then 5.2 GHz and 2.4 GHz filter was designed as example.