Surface wave resonances supported on a square array of square metallic pillars

A family of transverse-magnetic surface waves is shown to be supported at microwave frequencies by a square array of subwavelength square cross-section metal pillars on a conducting ground plane. These surface waves are experimentally characterised with a collimated microwave beam apparatus that utilises a pair of two-dimensional parabolic mirrors positioned on the sample surface. The dispersion of the modes, each associated with a quantisation of the electromagnetic field in the depth of the slits, is fully characterised and compared with the predictions of finite element modelling.