Chebyshev Filter Based On Dual-band Generalized Load The Branch Line Split Ring Cut

In recent years, dual-band WLAN(wireless local area network)becomes quite popular due to the need of wireless communications, dual-band filters become key components in the front of these communication systems. Meanwhile, with the growing congestion and interference of communication channel, high selectivity filters are needed. The generalized Chebyshev filters are able to accomplish these specifications by introducing the prescribed transmission and/or equalization zeros. This thesis is mainly devoted to design dual-passband cross coupled filters with generalized Chebyshev functions.Firstly, using synthesis theory of generalized Chebyshev filtering functions to design cross coupled structure filter is discussed in this dissertation. And a brief calculating method of external circuit quality factors is proposed. Based on this, a high selection performance generalized Chebyshev filter is designed.Then, open-loop resonators loaded by shunt open stubs are proposed to design dual-band bandpass filters. The second passband of the dual-band filter is obtained by tuning higher resonant modes can be controlled by the stub length and position of the open-loop resonator. The connection between the open position of loop and the ratio of the coupling coefficient at two resonant frequencies is built by simulations. Subsequently, a brief calculating method of external circuit quality factors at two passband and a theory of dual-band impedance-matching are proposed for realizing in practical microwave circuits.Finally, two generalized Chebyshev dual-passband filters are designed using four-cavity topology structure with two symmetric transmission zeros. The simulation and test results show that the stopband rejection characteristic of the dual-passband is well. Thus the feasibility and practicability of the methods are verified. Using generalized Chebyshev filter function and stub-loaded open-loop structure to realize dual-passband filter can effectively improve the selection performance, and the dual-passband filter resonant frequency can be flexibility controlled.