Investigation Of Miniaturized Bandpass Filter And Multi-function Filtering Circuits

With the development of wireless communication, miniaturized terminal equipments with more compatible communication protocols and less power consumption are highly required. Thus, the circuits need to be designed with compact size. Therefore, high selectivity, compact size and easy to fabricate become the fundamental requirements of bandpass filters, which are the important parts in communication systems. Meanwhile, multi-band and tunable bandpass filters have also obtained much attention since they can replace multiple bandpass filters, resulting in compact size. Recently, some researchers focus on dual-function circuits, such as filtering power dividers and filtering power amplifiers since they can reduce the size and loss. This paper presents some circuits which focus on novel compact bandpass filters and multi-function filtering circuits. The main work can be summarized as follows in three parts:1. Three bandpass filters based on single stub-loaded resonator are reported. The first one is the millimetre-wave bandpass filter, which is based on the open stub centre-loaded open-ended microstrip line resonators. Meanwhile, discriminating coupling is employed. The second one is a tri-band bandpas filter, which is based on short stub centre-loaded open-ended microstrip line resonators. The last one is a dual-band bandpass filter with tunable lower passband and fixed upper passband, which is based on varactor centre-loaded short-ended microstrip line resonators. All the circuits are firstly analyzed in theory and then simulated by software. Good agreement between the simulation and measurement results validates the proposed methods. These works have been published in Micorwave and Optical Technology Letters and International Wireless Syposium.2. A serial of multi-band bandpass filters based on multi-stub-loaded resonators are presented. We proposed several multi-stub-loaded resonators, according to the even- and odd-mode analysis, they are found with multiple controllable modes. Therefore, they can be conveniently used to design multi-band bandpass filters. These circuits consist of a dual-band bandpass filter with controllable frequencies and bandwidths which is based on a quad-mode resonator, a tri-band bandpass filter with controllable frequencies and bandwidths which is based on six-mode resonator and a tri-band bandpass filter based on an eight-mode resonator which covers the 5G Wi Fi band. These works have been published in IEEE Transactions on Microwave Theory and Techniques,IEEE Microwave and Wireless Component Letters.3. Several filtering power dividers and power amplifiers are proposed. The filtering power dividers consist of a single-band case which is based on lumped elements, a tunable one with constant absolute bandwidth which is based on coupled resonators and a dual-band one which is based on dual-mode resonators. Among the three designs, the former two cases are firstly reported according to the author’s knowledge. In the filtering power amplifier, the bandpass filter is used as an impedance transformer to be implanted into the output impedance matching network. Thus, the power amplifier exhibits high efficiency with bandpass response. These works have been published in IEEE Microwave and Wireless Component Letters.