Tunable Three-Pole Diplexer with High Selectivity and Isolation

This paper presents a tunable three-pole diplexer, and is based on two different three-pole filters. The first filter has two transmission zeroes at the upper side and one transmission zero at the lower side. The second filter exhibits two transmission zeroes at the lower side and one transmission zero at upper side. Due to the asymmetric high rejection level of the two three-pole filters, the tunable diplexer exhibits high selectivity, high suppression and high isolation. The circuit is theoretically analyzed and experimentally demonstrated. Comparisons between measured and simulated results are used to verify the proposed ideas.