Balanced dual-wideband BPF utilizing quad-mode slotline resonator

Abstract In this paper, a balanced dual-wideband BPF based on a novel quad-mode slotline resonator is proposed, achieving flexible, wide differential-mode (DM) bandwidths and high intrinsic common-mode (CM) suppression. With the application of the quad-mode slotline resonator, four transmission poles (TPs) are generated, leading to the creation of two wide DM passbands. The positions of these TPs can be flexibly adjusted by controlling the length of resonator. Meanwhile, utilizing quad-mode slotline resonator avoids multiple energy conversions between the slotline and microstrip line, simplifying the design and reducing overall size. In order to achieve intrinsic CM suppression, the BPF utilizes a microstrip/slotline structure, enabling the DM circuit to be designed independently of the CM circuit model, which greatly simplified the design procedure and thereby achieving excellent CM suppression. For the purpose of demonstrating the theoretical design, a dual-band BPF operating at 1.60 GHz and 3.75 GHz with bandwidths of 1,072 MHz and 1,088 MHz is fabricated. The results show good agreement between the simulations and measurements.