Compact UHF bandpass filter with the subwavelength metamaterial ZORs and transmission zeros for enhanced channel selectivity

In this paper, a microstrip bandpass filter for a UHF 900 MHz Band is remarkably miniaturized and its performance is enhanced using the metamaterial(MTM) Zeroth Order Resonator(ZOR) characteristics. Firstly, we propose each of the resonators for a bandpass filter is implemented by a one-cell ZOR, and the coupling between neighboring different ZORs is controlled to meet the primary goal on the bandpass filtering in the form of a sequential coupling mechanism. Secondly, this MTM ZOR filter is suggested to have transmission zeros due to source-load coupling to improve the isolation from the other wireless communication bands. It is revealed that the first and second proposed filters are less than 1/6 of the conventional filters in terms of size, and they present the smaller insertion loss and return loss in the passband and the higher isolation in the stopband due to the transmission zeros, which checked by the simulation and measurement. Besides, the MTM properties are verified with the dispersion diagram and the no-phase variation electric field distribution over the ZOR by the 3D EM simulation.