The inductive iris double discontinuity

Abstract

The reflection coefficient of a double discontinuity consisting of two closely spaced inductive irises in a rectangular waveguide is found. Standard transmission line techniques are no longer valid when the irises lie close together. Instead, the solution must include effects of interaction of the higher order modes excited by each iris. A variational expression for the reflection coefficient including the effects of the higher order modes is derived in terms of integrals of the induced current on one of the irises. The solution shows how more higher order mode terms become significant in determining the reflection coefficient as the iris spacing decreases. A numerical example is presented using only a few of the higher order mode factors. The results follow measured values of the reflection coefficient with spacings as close as 1/32 of a waveguide wavelength. More terms in the solution are required for closer spacings. The numerical example correctly predicts the spacing (3/16 of a waveguide wavelength) at which the higher order mode interaction becomes significant and the transmission line solution deteriorates.