Experimental verification of frozen mode phenomenon in printed magnetic photonic crystals

Spectral non-reciprocity, previously proposed and recently demonstrated in volumetric anisotropic crystals, is experimentally demonstrated using a simple printed transmission line set-up. Specifically, wave propagation in otherwise volumetric magnetic photonic crystals is emulated via a pair of partially coupled microstrip transmission lines printed on a ferromagnetic substrate. Directional asymmetry of wave propagation within the 1D periodic medium is validated by computing the K-ω diagram from measured S-parameters. Measurements are carried out using 8- and 9-unit-cell structures to suppress undesired finite size effects. For the first time, spectral non-reciprocity and the frozen mode behavior is clearly observed in the measured data. Additionally, the unidirectionality of the transmission medium is verified by the observed contrast between the forward and backward transmittances (75%) on the 9-unit-cell structure.