Dual-band bandpass filter and filtering power divider with ultra-wide upper stopband using hybrid microstrip/DGS dual-resonance cells

Abstract

In this paper, two types (i.e., type-A and type-B) of hybrid microstrip/defected ground structure (DGS) cells are proposed for passive circuit implementation with ultra-wide stopband. Both cells consist of the stepped-impedance DGS and embedded folded slotline on the ground, which could obtain the dual-resonances. In type-A cell, a microstrip T-stub on the top side is introduced, which can not only allocate a strong coupling to the DGS with slotline on the bottom side, but also act as the input/output port. To finely adjust the dual-resonances of the type-B cell, a grounded microstrip patch is used. Meanwhile, such compact cells could feature an ultra-wide upper stopband, due to their own slow-wave effect. Based on the aforementioned hybrid microstrip/DGS cells, two dual-band bandpass filters (BPFs) and a dual-band filtering power divider (FPD) are proposed and fabricated. Measured and simulated results are in a fairly-close agreement. Both dual-band BPFs exhibit the ultra-wide upper stopband, which extends up to 40 GHz with a high rejection level about 30 dB. Besides, the dual-band FPD has merits of more than 18.7 dB of in-band isolation and 28 dB stopband rejection levels up to 40 GHz.