Compact Microstrip Dual-mode Dual-band Band-pass Filters Using Stubs Loaded Cou- Pled Line

This paper presents two novel dual-mode dual-band bandpass filters (BPFs) by using stubs loaded coupled line. The analytical equations of their transmission poles and transmission zeros are given by the classical even-/odd-mode method. Design rules for two dual-band BPFs are also given, which show the easily tuned passband frequency locations and in-band performance. As examples, two dualmode dual-band BPFs, dual-band filter A with central frequencies (CFs) at 3.5/6.8 GHz and −3 dB fractional bandwidth (FBW) of 14%/10%, while dual-band filter B with CFs at 2.4/6.8 GHz and −3 dB FBW of 43%/16% are designed, fabricated and measured. Good agreement can be observed between the simulations and measurements. These two filters exhibit simple design procedures, simple physical topology, low insertion losses, good return losses, high isolation and compact sizes.