Off-axis diffraction by perfectly conducting capacitive grids: Modal formulation and verification

We consider the diffraction of plane electromagnetic waves incident at an arbitrary angle on a capacitive grid of perfectly conducting cylinders of arbitrary length. We comment on the formulation of modes within the grid region, concentrating on the case of transverse magnetic polarization, for which the generalization from on-axis to off-axis modes is not straightforward. We solve the diffraction problem by a mode-matching method, and give analytic expressions for the inner products between plane waves and modes, and normalization factors for modes. We give numerical results of the diffraction formulation, and comment on tests for its accuracy.