Dispersion of spoof surface plasmons in open-ended metallic hole arrays

Using phase sensitive microwave frequency measurements, we obtain the dispersion of spoof surface plasmon waves on a highly conducting sheet perforated with a two-dimensional array of subwavelength holes, and compare our results to an explicit analytical dispersion relation obtained by the modal matching method. We observe splitting into symmetric and antisymmetric surface modes, a behavior analogous to that of surface plasmons in thin metallic films at optical frequencies. We show that spoof surface modes play an important role in both near and far field transmissions. Specifically, we show that superfocussing effects which are present for surface plasmons in metallic films are absent for hole arrays (i.e., no amplification of near fields is possible for spoof surface plasmons). While many of the apparent properties of spoof surface plasmons resemble those of surface plasmons in thin metallic films, the analogy is therefore incomplete in the high frequency limit.