Wide-band low-loss high-isolation microstrip periodic-stub diplexer for multiple-frequency applications

This paper introduces a three-port microstrip multifrequency diplexer used in a phased-array transceiver system that employs band-stop filters with op en-circuited stubs for band selection and separation. The diplexer is desig ned to take 10, 12, 19, and 21 GHz into port I and to separate 10 and 19 GH z to port 2 and 12 and 21 GHz to port 3 with minimal dispersion. The insert ion loss for each frequency varies from 0.4 to 3.4 dB and the return loss i s better than 10 dB. The isolation between channels at the four frequencies is greater than 50 dB. Each passband created between adjacent stopbands ha s a bandwidth over 1 GHz. The microstrip diplexer is designed using periodi c stubs that collectively have the advantages of low insertion loss, high i solation and rejection, wide-band performance on each channel, and easy fab rication. This type of diplexer has many applications in multifrequency tra nsceivers for communication systems.