High-isolation diplexer on triple-mode cavity filters

Abstract

This paper proposes a diplexer based on two triple-mode cavity filters. Each of filters is realized in a single rectangular waveguide cavity with the operation of triple resonant modes. These triple modes are classified as a TM mode and a pair of TE modes, which are excited by two short circuited ended along the x-, y-, z-orientations in a cavity. By simultaneously creating three transmission zeros in both the upper band of the lower channel and lower band of the higher channel, a diplexer with high isolation between two output ports is realized in addition to good suppression of upper harmonic passbands. Moreover, the whole diplexer does not inquire any screws, irises or cornercuts. Finally, a diplexer prototype operating in the 2.55/2.66 GHz bands for Long-Term Evolution (LTE) application is fabricated by using the silver plated aluminum technology for demonstration. Experimental and simulated results are presented, both validating the predicted results of the proposed diplexer.