A Compact Planar Dual-Band Bandpass Filter With Coupled-Line Structure

In this paper, we propose the design of compact wideband dual-band bandpass filters utilizing coupled line structures. To achieve precise design, we employ the even and odd mode analysis method to analyze the behavior of the proposed coupled-line structure. Through this analysis, we can investigate multiple reflection zeros (RZs) and transmission zeros (TZs) in detail. By adjusting the coupling impedance and electrical lengths, we have the flexibility to control the filtering characteristics, such as bandwidth and TZs, of the filters. To validate the effectiveness of our analysis method, we simulate a simple planar filter using microstrip technologies. The simulated results are in good agreement with the theoretical study, demonstrating the accuracy and reliability of our proposed analysis method.