Design of compact microstrip diplexer with high selectivity

A novel design of compact microstrip diplexer, using coupled dual-mode open-loop resonators, is proposed. The main advantage in using dual-mode open-loop resonators is that a compact narrowband bandpass filter with high selective asymmetrical frequency response is easily realized. This property is explored to design diplexer for a system with two extremely close bands. A prototype diplexer operating in the 2.07/2.3 GHz band, having compact size (44 mm × 11 mm) and high isolation (>;-40 dB), is designed for demonstration.