Microwave measurements of the photonic bandgap in a two-dimensional   photonic crystal slab
  We have measured the photonic bandgap in the transmission of microwaves through a two-dimensional photonic crystal slab. The structure was constructed by cementing acrylic rods in a hexagonal closed-packed array to form rectangular stacks. We find a bandgap centered at approximately 11 GHz, whose depth, width and center frequency vary with the number of layers in the slab, angle of incidence and microwave polarization. 
J. M. Hickmann, D. Solli, C. F. McCormick, R. Plambeck, and R. Y.   Chiao (Dept. of Physics, UC Berkeley)