Compact Triple-Band Bandpass Filter With Multiple Transmission Zeros and Large Frequency Ratio Using Sub-Matrix Analysis Method

Abstract

This letter proposes a compact triple-band bandpass filter with ten transmission zeros (TZs) and large frequency ratio, which is composed of a three-line coupled structure (TLCS) and four open-circuited stubs (OCSs). By classifying the coupled lines ports and utilizing the voltage and current constraint relationships at its ports, the Z-matrix of the input and output ports was obtained, and then the S-parameters were derived. To validate the theoretical analysis and design concept, a triple-band filter with center frequencies (CFs) of 0.86, 2.07, and 3.18 GHz was simulated, fabricated, and measured. The filter has three bandwidths (BWs) of 0.12, 1.1, and 0.13 GHz, respectively, with insertion losses (ILs) of 0.34, 0.29, and 0.36 dB. The theoretical predictions, simulated, and measured results are in good agreement.