Harmonic Suppressed Reconfigurable Dual-band, Multi-mode Ultra-wideband, and Compact High Selective Microstrip Bandpass Filters

Abstract

As an indispensable component, microwave bandpass filters play a very important role in many modern wireless systems. They are used to carry out the selection of only the wanted frequencies from RF signals with various spurious frequencies. The reconfigurable filter with multi-band has attracted much attention for both research and industry because of the increasing importance in making RF components that have multi-function with compact size. Wide or Ultra-wideband (UWB) bandpass filters are becoming more and more in demand in many wireless applications due to the high data transmission rate. This dissertation focuses on the study of microwave filters with many applications in various wireless systems. Firstly, bandpass filters using stepped impedance stubs are presented. The resonant frequencies and transmission zeros are analyzed, and harmonic suppression by novel S-shaped coupled feed lines is presented. A resonator with a dual-band characteristic is introduced, and it is analytically shown that each passband can be independently controlled by the parameters of the resonator. PIN diodes are used to introduce an electrically controlled dual-band bandpass filter. Secondly, symmetric stepped impedance resonators with asymmetric stepped impedance stubs are also presented to develop Ultra-wide band (UWB) bandpass filters with and without a notched band. The resonant frequencies and transmission zeros of the resonator are effectively located to achieve a very wide passband and a high attenuation rate in rejection bands. The interdigital coupled feed lines with rectangular slots are designed for a better passband characteristic. A notched characteristic is introduced by using modified feed lines to avoid the interferences with other existing signals. UWB bandpass filter performances in time-domain and frequency-domain are analyzed and discussed. Thirdly, UWB bandpass filters with a different configuration are developed. Similarly, the analyzed resonant frequencies are used to achieve a passband for UWB applications. A different technique is used to introduce a very narrow notched band within the passband. Time-domain analysis is made to verify the frequency-domain performance. Lastly, a very high selective wideband bandpass filter is presented using an inverted T-shaped resonator. The characteristic of the resonator is analyzed to design a bandpass filter with specified bandwidth. The short stubs are introduced to achieve a very high attenuation rate at both sides of the passband and a wide stopband characteristic. In summary, various microwave filters to meet the requirements of specific applications are studied and designed. Analysis and design methodology of the proposed microwave filters in this dissertation can be applied in many applications in wireless systems.