Extension of Spectral Domain Approach to Unilateral Finlines with Finite Metallisation Thickness and Substrate Supporting Grooves

An extension of the spectral domain approach to characterising the effects of both finite metallisation thickness and substrate supporting groove in unilateral finlines is described. The formulation regards the equivalent magnetic current sheets at the apertures of the groove and on either side of the slot as the source quantities to be determined, which leads to a computationally efficient matrix equation for the propagation constant and the characteristic impedance. A new procedure for deriving the spectral Green's function relating the magnetic fields to the magnetic current sheet at the groove aperture is proposed, where the conventional spectral domain immittance approach is not valid. The results are provided to show how the behaviour of unilateral finlines are affected by the metallisation thickness and substrate supporting groove.