Compact wide-stopband diplexer using dual mode resonators

A compact microstrip diplexer for UMTS and WCDMA systems is presented. The size of the diplexer can be reduced by using capacitance loaded square meander loop resonators. Owing to the capacitance loaded arms, the resonator has the advantages of compact size and harmonic suppression. The two degenerate-mode resonances are used to form the lower and upper channel of the diplexer, respectively, which generate two transmission zeroes so as to obtain high frequency selectivity. Simulated and measured results are presented and show good agreement.