Broadband and Dual-Band Bandpass Filter Using Spoof Surface Plasmon Polaritons and Microstrip Coupled-Line Structure

A broadband bandpass filters (BPF) are designed by using spoof surface plasmon polaritons (SSPPs) and microstrip coupled-line (MCL) structure in this paper. The passband frequency response is realized by the lowpass property of SSPPs and highpass property of MCL structure. To obtain enough coupling strength for wideeband frequency response, interdigital structure and defected ground structure are adopted. Moreover, the general horizontal feeding lines are folded to vertical direction for circuit miniaturization. The designed broadband BPF finally achieves a frequency range of 0.9 GHz to 3.9 GHz. Additionally, by introducing the U-shaped slotline resonant rings on the bottom layer of the designed broadband filter, a transmission zero within the passband is produced and such that a compact dual-band BPF is then designed. The simulated results show that two designed BPFs exhibit steep edge characteristics and compact circuit size, which proves the feasibility of the proposed structure and design method.