Dual-Band Absorptive Bandpass Filters Using a Dual-Behavior Matching Section

This study introduces a dual-band absorptive bandpass filter that employs a dual-behavior matching section. The proposed design utilizes a filter methodology based on a low-pass filter prototype, enabling the development of higher-order distributed dual-band absorptive bandpass filters with the control of two center frequencies and bandwidths. The proposed filter requires fewer resonators than the existing dual-band absorptive filters owing to the dual-band matching section design based on an image parameter method. The proposed configuration is implemented to design and fabricate two filter prototypes with center frequencies of 1.3 GHz and 1.6 GHz on a substrate characterized by a relative permittivity ε<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 3.42 and a thickness <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> = 30 mil. The first filter (two-pole configuration) demonstrated a measured return loss exceeding 11.3 dB at 0.8–2.2 GHz, and the second filter with three-pole exhibited a measured return loss exceeding 10.2 dB at 0.8–2.2 GHz. These dual-band absorptive bandpass filters are suitable for application in cognitive radio and carrier aggregation systems.