Design of Dual-Band Bandpass Filter With Narrow-Bandwidth and Wide-Bandwidth Responses

  • 藍 祥文

Student thesis: Doctoral Thesis

Abstract

The dissertation is divided into four sections comprising: (a) design of tri-band bandpass filter (BPF) by using asymmetric stub-loaded resonators (ASLR); (b) design of low-pass filter (LPF) with ultra broad stopband characteristic; (c) design of compact ultra-wideband (UWB) BPF; (d) design of dual-band BPF with narrow-bandwidth and wide-bandwidth responses Firstly introductions about the operation of wireless communication system and relative protocol are proposed in this research Moreover the feature of filters in the wireless communication system and the basic transmission line theory are discussed Secondly a tri-band BPF constructed by ASLRs is proposed This ASLR is constructed by tapping a stub-loaded on the other uniform microstrip line By properly tuning the electrical length ratios of the ASLRs (? and γ) the spurious modes of ASLR are controlled easily to form a tri-band response In addition a resonant chart of ASLR is provided to find the frequency of each spurious mode accurately Thirdly a LPF constructed by rectangular stub loaded resonator and open-circuited stubs is proposed The rectangular stub loaded resonator consists of a parallel coupled line and a rectangular stub patch and it creates multiple transmission zeros at higher frequency side to form a low-pass response It is noted that the cutoff frequency of rectangular resonators is dominated by the electrical length ratio and impedance ratio Fourthly two UWB BPFs basically constructed by rectangular stub loaded resonator are fabricated and proposed The resonant modes of one UWB BPF are excited by adopting parallel coupled line and rectangular stub loaded resonator additionally multiple transmission zeros created by rectangular stub loaded resonator are used to eliminate interference at the higher frequency side And the resonant modes of the other UWB BPF are excited by using the mode-exciting technology By properly tuning the electrical length ratio of the stub and parallel coupled-lines a controllable resonant mode is excited and two transmission zeros are created in accordance with the results of imaginary-admittance analysis Finally a dual-band BPF constructed by stepped-impedance ring loaded resonator (SIRLR) and rectangular stub loaded resonator (RSLR) is fabricated and proposed Based on even- and odd-mode analysis the properties of SIRLR is analyzed and predicted Herein three parameters (two electrical length ratios and one impedance ratio) are defined and used to control the resonant modes of SIRLR Moreover Three transmission zeros created by RSLR are located near the passband edge to improve the band selectivity and achieve a sharp cutoff skirt The fabricated dual-band BPF exhibits good performance including a narrow passband at 2 4 GHz a wide passband from 3 GHz to 5GHz low insertion loss high passband selectivity and broad stopband region The designed dual-band bandpass filter are fabricated and measured and the measured results match the theoretical prediction
Date of Award2017 Jan 6
Original languageEnglish
SupervisorShoou-Jinn Chang (Supervisor)

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