Resonant frequencies of post–wall waveguide cavities

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A new method is presented for predicting the resonant frequencies of post–wall rectangular waveguide cavities, in which the narrow walls of the guide are composed of rows of vias. By interpreting the fields inside the guide as a superposition of plane waves, the surface impedance of a row of wires, when illuminated by a plane wave, is used to model the narrow walls of the waveguide. The derivation leads to equivalent rectangular waveguide dimensions that are then used to calculate the resonant frequencies of the cavity. Theoretical results are compared with the observed TE10m resonant frequencies of several post–wall waveguide cavities fabricated in low temperature cofired ceramic (LTCC). The results confirm that the method improves the resonant frequency prediction when the pitch of the vias is at least ten times greater than their radius.