Research On Wideband Bandpass Filter

Along with the rapid development of multimedia technology, wireless communication technology has been developed from sole transmission of original text, voice to high-rate transmission of video and even larger files. Traditional narrowband communication technologies are unable to meet requirement of high speed, large data transmission, so there is an urgent motivation to develop wide-band communication technologies.Since the Federal Communications Committee(FCC) authorized the unlicensed use of the ultra-wideband(UWB) frequency spectrum for indoor and hand-held wireless communications in 2002, UWB technology immediately became one of research hotspots in the field of wireless communications. As one of the essential components in UWB communication system, UWB filter plays a significant role in deciding the overall performance of the system. Unfortunately, there exist so many wireless narrowband applications whose signal will interfere with UWB communication.Thus, UWB filters with multiple notched bands are proposed to eliminate those narrowband interferances. In this thesis, some UWB filters with single and dual notch bands are proposed and discussed. The main work is presented as follows:1. Compact microstrip ultra-wideband(UWB) bandpass filters with multiple superposable notched bands are discussed. By cascading n T-Shaped structures to a three coupled-line section, UWB bandpass frequency response with n notched bands can be obtained. The analysis shows that these notched bands are superposable and can be relatively independently adjusted in wide frequency range. Two UWB filters with notched bands are designed, fabricated and measured. The measured results show that two filters are featured by good performance and compact size.2. A novel compact UWB filter with narrow notched band is presented by directly cascading a pair of shorted stubs to parallel cross-coupling lines. The frequency positions of the notched bands can be shifted from 4.2 GHz to 9.2 GHz by tuning the dimension of the shorted stubs. The measured results show that the filter has the merits of low insertion losse, sharp rejection and flat group delay. The bandwidth of the notched band is about 100 MHz, and the performance in and out of the passband is good. Moreover, the filter exhibits the advantages of simple topology and compact size.3. A UWB filter with good rectangular coefficient is presented. It consistes of two ring resanators which could produce a transmission zero in low and upper stopband, respectively. The transmission zeros help to improve the rectangular coefficient to 1.066. In addition, the filter also has excellent out-band performance.