Design of high selectivity tri-band bandpass filter based on triple transversal transmission path.

By utilizing transversal signal interference concepts, a tri-band bandpass filter with a triple transmission path is proposed in this paper. Triple transversal transmission paths are respectively constructed with the employ of parallel coupled stub loaded resonator, microstrip gap coupled line and parallel coupled shorted stub loaded resonator. Based on the triple transversal transmission path, nine transmission poles (TPs) are excited; therefore, triple independently controllable wideband passbands are realized. Due to the transversal cancellation between transmission paths with the virtual short mechanism of each transmission path, seven transmission zeros (TZs) can be excited and managed. Therefore tri-wideband characteristics with high selectivity and high band-to-band isolation can be obtained by properly adjusting the TPs and TZs. To further demonstrate the proposed design methodology, a prototype tri-wideband bandpass filter operating at 1.93/3.52/5.11 GHz with fractional bandwidth of 11.8 %, 19.8 % and 22.8 % for LTE, WiMAX, Wi-Fi and 5G applications is synthesised. The presented tri-wideband bandpass filter is designed, manufactured and measured. The measured results agree well with theoretical predictions, which exhibit superior performance such as sharp shirts, high band-to-band isolation compact size and ideal out-of-band suppression. [ABSTRACT FROM AUTHOR]