Ultra-wideband Microstrip Bandpass Filter In Wireless Communication Research And Design

Ultra-wideband (UWB) technology shows a promising application prospect in high-resolution radar, high data-rate communication, power-efficient RF tracking and positioning systems. As one of the essential components in UWB wireless communication systems, UWB filters play an important part in deciding overall performances of the systems.This dissertation mainly focuses on the design and implementation of UWB bandpass filters. Firstly, developing trends of the UWB bandpass filters is summarized and several typical realization approaches are discussed. Then, with the concept of multi-mode resonator (i.e., one of the fundamental approaches), two type of UWB bandpass filters structures are explored. One is based on a novel CRLH-TL resonator and the other is on basis of the net-type resonator. The primary work of this dissertion can be generalized as follows:1. A novel periodic CRLH-TL structure is proposed and its dispersion characteristic is investigated by using Bloch-Floquet theorem. Then, a multi-mode resonator is constructed with the proposed CRLH-TL structure, its seven-mode resonances behaviors is theoretically verified. This CRLH-TL resonator is further applied to the design of UWB bandpass filters. Simulation and experiment results show that the filters designed have two transmission zeros (TZs) at upper stopband, which is in accordance with theoretical analysis. As a result of these two TZs,40dB stopband rejection level of the filters can be extended up to16GHz. Meanwhile, the filters also have excellent in-band performance.2. A net-type multi-mode resonator is discussed. Allocations of its tri-mode resonances are studied through even-and odd-mode analysis. TZs generation mechanism of the BCMC stub structure is investigated, which can be used to improve frequency selectivity property of the UWB bandpass filters. An extended L-shaped coupling line structure is utilized in the design of UWB bandpass filters, together with the net-type resonator and BCMC stub structure. At the same time, the shunt capacitive stubs and the ground patterned structures are adopted to improve impedance matching property of the UWB bandpass filters. Measured results indicate that for the fabricated filters,20dB suppression levels have been achieved around18.6GHz and19.5GHz due to the L-shaped feeding lines and TZs introduced by the BCMC stub structure, respectively. Consequently, the stopband rejection characteristic is greatly enhanced and which results in a wide stopband.