Researches On The Applications Of Transmission Zeros In Planar Microstrip Filters

Microwave filters are essential components in wireless communication system. Asthe further development of modern communication system, such as the applications ofGPS, Wi-Fi, WLAN, Bluetooth, WiMax and etc, the demands of microwave filters withgood performance are urgent. In this thesis, the structural compactness, passbandselectivity and out-band suppression of microstrip filters are discussed and analyzed.The main contents are:1. The background and significance of this thesis are investigated. The currentresearches and development trends are introduced briefly. Then, based on the existedwork, the research contents of this thesis are proposed.2. The basic theories of microwave filter, including the design method oftraditional lowpass prototype filters, frequency and element transformations fromlowpass prototypes to actual filters, the application of conventers in filter design and thecoupling characteristics of resonators, are introduced respectively, which will be thefoundations of the following researches.3. Design of single-band bandpass filter based on stepped-impedance resonators.First, the characteristics of stepped-impedance resonators (SIR) and anti-parallelcoupled lines (APCL) are analyzed respectively. Then, a single-band bandpass filterbased on SIR and APCL is designed. And its frequency responses with differentstructures are discussed.4. Design of single-band bandpass filter based on source-load cross coupling.First, a traditional single-band bandpass filter with source-load cross coupling isdesigned and the causations of transmission zeros are analyzed. Then, based on theabove discussion, single-band bandpass filter with stub-loaded source-load crosscoupling is proposed. Its advantages are demonstrated by two filters structure withpassbands located at different frequencies.5. Design of dual-band bandpass filter based on source-load cross coupling. First,based on the single-band filter designed before, dual-band bandpass filter withsingle-stub-loaded source-load cross coupling is proposed. Its transmission characteristics are discussed. And its advantages and shortages are summarized. Then,dual-band bandpass filter with double-stub-loaded source-load cross coupling isproposed. The last kind of filter has better in/out-band performances while keepingcompact size.