A new multiple-frequency millimeter diplexer using microstrip periodic-stub

In this paper, we introduce a three-port microstrip multi-frequency diplexer which can be used in phased-array transceiver system (PATS) and local multipoint distribution service (LMDS) that employ band-stop filters with open-circuited stubs for band selection and separation. The diplexer is designed to take 39.8, 42.4, 44.8 and 47.4 GHz into port 1 and to separate 39.8 and 44.8 GHz to port 2 and 42.4 and 47.4 GHz to port 3 with minimal dispersion. The insertion loss for each frequency varies from 0.4 to 1.2 dB and the return loss is better than 17.5 dB. The isolation between channels at the four frequencies is greater than 30 dB. Each passband created between adjacent stopbands has a bandwidth over 1.2 GHz. The microstrip diplexer is designed using periodic stubs that collectively have the advantages of low insertion loss, high isolation and rejection, wide-band performance on each channel, and easy fabrication. This type of diplexer has many applications in multi-frequency transceivers for millimeter communication systems.