Study on slot irises for tunable filters using TE011 mode

Tunable filters using the TE₀₁₁ mode have slot irises for coupling between cavities. Unless the slot iris is appropriately designed, the coupling value of the iris varies as an operating frequency changes and the filter performance deteriorates as a result. In this reported work, it was found that the frequency-dependent coupling characteristic of the slot iris can be minimised by locating the iris appropriately. Why the coupling of a slot iris changes when the operating frequency is tuned is explained and how to find the optimum location of the slot iris for minimum variation of the coupling value is presented. The proposed theory is verified by full-wave EM simulations and experiments with a Ka-band two-pole filter.