The Analytical Approach to the Full-Band Matching of Wave-Guide Discontinuities Applied to Capacitive Irises and Steps

It is current practice to match a given discontinuity in waveguide by means of an identical one (matching element) placed a quarter-wavelength away from the first. For accessible discontinuities, a superior technique consists in placing two matching elements symmetrically with respect to the (symmetric) discontinuity, so that they are seen as its dual. Usually a discontinuity behaves as a nonresonant element, for instance a lumped capacitance. Then its dual is also "lumped" and must be placed at the location of the discontinuity, with hardly ary length of waveguide interposed. Due to interaction via higher-order modes, a two-port representation of the individual discontinuities no longer holds. Therefore application of the new matching technique requires accurate, wideband, finite multiport equivalent circuits of the discontinuities. As an example, it is shown numerically and experimentally how an iris with original reflection coefficient of 40% can be matched over the whole waveguide band with a residual reflection ¿2%.