CRLH-TL Bandpass Filter with Controllable Attenuation Poles by Applying Tap-Coupling Technique

A resonator and a bandpass filter (BPF) with controllable attenuation pole by applying tap-coupling to a com-posite right/left-handed (CRLH) transmission line that achieves a negative order resonant frequency is proposed. The unique negative order resonant frequency of the CRLH line allows for circuit miniaturization. By using tap-coupling, attenuation pole can be realized, and sharp skirt characteristics are obtained. The control of the attenuation poles of these resonators using a circuit simulator is discussed. In addition, a bandpass filter using the proposed resonators is designed and simulated. As a result, it is confirmed that the proposed method enables the size reduction of resonator compared with conventional type in the BPF and attenuation poles are generated at desired frequency. The proposed BPF is also validated by the fabrication in the microstrip line and measurement.