Dual-band second order microstrip filter using dual-mode perturbed meander loop resonators

A dual-band dual-mode filter with second order response in each band is presented for application in near-adjacent channel communications systems. Utilizing large perturbations in a meander resonant structure the resonant frequencies of orthogonal field modes are split allowing for a linear coupling arrangement. The filter´s passbands are centered at 2.35 GHz and 2.57 GHz with fractional bandwidths of 3.5% and 3%. A method for developing the filter from an unperturbed second order filter and EM optimization is presented. The measured filter shows good performance in both in-band matching and stopband rejection between the bands of operation.