Research On Dual-band Bandpass Filter Based On Substrate Integrated Suspended Line (SISL)

With the dramatic development of modern wireless communication technology,the requirements of RF transceiver's performance in the electronic system for various areas are getting higher and higher.As an important band-selected device,by which the useless signals can be filtered out in RF front-end circuits.The filter determines the overall performance of the transceiver to some extent,so the design of high-performance filter is always one of the hot spots in the field of microwave millimeter-wave circuit.In a wide variety of filters,dual-band bandpass filter receives widespread attentions since two bands can be filtered simultaneously.In order to realize miniaturization,high performance and easy integration,the dual-band bandpass filters based on a novel microwave transmission line,substrate integrated suspended line(SISL),are studied in this thesis.First,the application and research significance of the dual-band bandpass filter are discussed and its development history and research status are also reviewed.Several common resonators such as defected ground structure and stepped impedance resonator are introduced,and the concept of SISL is brought in.Second,the working principle,performance indicators and general design methods of microwave filters including the equivalent-circuit analysis method and the even-odd mode analysis method are briefly discussed.The basic structure and modeling approach of SISL are introduced in detail,therefore the theory foundation for the design of SISL filter is established.Then,based on the even-odd mode analysis method,the SISL multimode resonator and the feed line are analyzed in detail,and design methods of the SISL dual-band bandpass filter are also given.The feasibility and correctness of the design methods of the SISL dual-band bandpass filter are verified by the measured results from the fabrication.Finally,based on the aboved even-odd mode analysis method,three SISL dual-band bandpass filters with different performance are designed.The first dual-band bandpass filter has a wide stopband.The capacitor loading technique is used to extend the parasitic passband to a higher frequency.Moreover,with a slot line on the feed line,transmission zeros are introduced in the high frequency,thus widen the high frequency stopband further.The second dual-band bandpass filter has a sharp skirt.The coupling between the source and the load can be realized with double-layered circuit on SISL.And in this way,multiple transmission zeros are generated around the passbands.Thus high selectivity is achieved.The third dual-band bandpass filter has good isolation.A wide band or high isolation band can be achieved by controlling the transmission zeros between the two passbands.