Using a Simple and Effective Method to Design Microstrip-Line Single-Band and Dual-Band Bandpass Filters with Frequency Adjustable Characteristic

Abstract

In this study, a novel compact and effective method was developed to design the single-band and dual-band bandpass filters with frequency adjustable characteristics. The designed filters were comprised of two uniform microstrip lines but with one shorter pairs of open-loop ring resonators (OLLRs) or one longer pairs of OLLRs to be placed between two microstrip lines. The shorter OLLRs had shorter current path and then had higher resonant frequency, they were designed for a single-band filter. The longer OLLRs had longer current path and then had lower resonant frequency, they were designed for a dual-band filter during the 0–8 GHz. A pairs of shunt quarter wavelength open stubs were also added to eliminate the unwanted harmonic frequencies and transmit the desired passbands. Finally, we would design a 5.3 GHz single-band filter and a 3.4/6.6 GHz dual-band filter to prove that the proposed theorem was a compact method and it could be used to design the microwave filters with the number and the frequency of passband adjustable characteristics.