Narrow bandpass filter using symmetrical Left-Handed transmission line Zeroth-Order Resonators

A bandpass filter using symmetrical Left-Handed (LH) transmission line (TL) Zeroth-Order Resonators (ZOR) is proposed. The symmetrical LH TL is first characterized by the dispersion characteristics of the unit cell and its left handedness is verified by the transmission characteristics of 15 cells cascaded LH TL. A symmetrical LH TL open circuited on both sides, acting as a ZOR with shunt resonance, is used as a resonating element in the microstrip end coupled resonator bandpass filter. The open circuited ZOR is characterized by susceptance slope parameter, and bandpass filter is designed using microstrip series gaps as the admittance inverters. Size independent resonance property of the ZOR combined with homogeneity condition of the LH TL unit cell is utilized in the size reduction of bandpass filter. The full wave simulated transmission characteristics of the designed bandpass filter are experimentally verified. They show that size of the filter is greatly reduced (approximately 64%) when compared to a conventional half wavelength coupled bandpass filter.