Compact dual-band bandpass filters using dual-mode resonators

To reduce the size of microstrip dual-band bandpass filters (DBBPFs) by keeping excellent performance, a novel DBBPF configuration is proposed. The novel DBBPFs include two dual-mode resonators based on square loop structure that are located one within the other to remove extra circuit area. The square open-loop stubs connected at the end of feed tines are employed to suppress harmonics. The two DBBPFs with real axis and imaginary aids transmission zeros are designed, fabricated and measured.