This article aims to design of microstrip resonators in order to reduce size of microstrip bandpass filters in wireless communication systems. Characterized by both theoritical investigation and full-wave simulation, the proposed bandpass filters are designed consist of dual-band bandpass filters and quadruple mode bandpass filters with miniaturized size. The proposed filter is found to have benefits such that the even-mode resonant frequencies can be flexibly controlled while the odd-mode resonant frequency is reserved for the fundamental frequency. Since the structure of resonators is realized using common via holes, the difficulty and complexity of the fabrication process can be shortened. In order to achieve compact size, the total number of resonators is reduced so that the implemented resonators only occupy a small area.
