Band-stop Filter

The bandstop filters (BSF) are widely used to suppress the spurious signals of the High-Power transmitters and the spurious passband of the non-linear power amplifier sand the bandpass filters.The conventional micro-strip BSFs consist of the capacitively coupled quarter-wave short-circuited transmission line resonators and quarter-wave convertors. This kind of structures are large in size and cannot meet the needs of miniaturized filters. However, the waveguide BSFs, usually using half-wave resonators and three quarter-wave convertors to prevent the margin-field effect of the coupling apertures, often have large sizes. The BSFs are required of high selectivity to suppress the noises and interference of the close passbands.An coaxial line bandstop filter with six octave spurious stopband is proposed. The theory of the BSF, its design methods, and the results will all be present. The dissertation will be given in the following way:1. Introduction of the theory and structure topology of the bandstop filters, especially the narrow band BSFs.2. Structure introduction and field analysis of the coaxial line and its application in bandstop filter design.3. Sample design of an coaxial line bandstop filter using short-circuited shunt stubs.