Compact balanced filter with high common mode suppression using hybrid microstrip and slotline spoof surface plasmon polaritons

Hybrid folded microstrip and slotline (HFMS) spoof surface plasmon polaritons (SSPPs) are developed to design a balanced bandpass filter (BPF). The proposed HFMS SSPPs can lower the upper cut-off frequency for size reduction of nearly 65%. Microstrip-to-slotline transition structure is adopted for feeding structure. Under differential mode (DM) operation, a band-pass response is formed by the high-pass microstrip-toslotline transition structure and low-pass SSPP structure. Under common mode (CM) operation, high CM suppression is achieved due to intrinsic CM rejection ability of microstrip-to-slotline transition structure. Finally, a balanced BPF with compact size and high CM suppression is fabricated, and measured.