ANALYTICAL SOLUTION AND FREQUENCY EXTRACTION OF IRIS PROBLEMS IN WAVE-GUIDE BY SEPARATION OF VARIABLES

The field nearby a thin iris discontinuity can be found in an exact ma nner by solving the wave equation in an appropriate coordinate system, To this end, it is necessary to select a coordinate system that fits the iris boundary, As an example, capacitive and inductive irises in r ectangularwaveguides have been solved by considering the Helmholtz equ ation in the elliptic-cylinder coordinate system, The presence of the waveguide environment is then enforced either by using the aperture fi eld solution in a variational expression of the equivalent shunt susce ptance or by taking images. The advantage of the new solution is that a single term solution, apart from being very accurate and numerically efficient, also contains the correct frequency dependence; thus provi ding results over the entire band, Moreover, wide-band equivalent circ uits with frequency independent elements of the Foster's canonical for m descend directly from the field analysis.