Compact dual-mode loop resonators for microwave triplexer applications

In this paper, we study meandered topologies of a dual-mode loop resonator for microwave multiplexer applications. Compact channel filter structures that characterize controllable transmission zeros locating simultaneously at the lower stopband or upper stopband are, for the first time, investigated for such a kind of resonators and based on this, a microstrip triplexer is proposed. The studied triplexer uses one of the filter structures to realize the middle channel, and the rest structure to realize the upper and lower channels. The center frequencies of the three channels are 1.8 GHz, 2.0 GHz and 2.2 GHz, and the 3-dB fractional bandwidths are 3.6%, 3.6% and 4.1%, respectively. The developed triplexer features high channel-isolations of over 40 dB as a result of the controllable transmission zeros of the channel filters.