Compact diplexer with edge-coupled and nonbianisotropic split-ring resonators

A microstrip sixth-order compact diplexer formed by split-ring resonators is presented. As a compact multiplexer, it consists entirely of a set of resonators coupled between them and with the ports, with no additional junction structure. The central element, shared by both channels and connected to the diplexer common port, is a conventional edge-coupled SRR (EC-SRR) that shows dual band behaviour with a central transmission zero. Each first order band corresponds to one band of the diplexer. An increase up to third order and the isolation between channels are provided by two single-band nonbianisotropic SRRs (NB-SRR), one for each channel. A prototype synthesis is presented with good agreement between measurements, electromagnetic simulations and circuit models.