Dislocation of Lattice Points for Impedance Matching of a Photonic Bandgap Cavity Resonator

A photonic bandgap (PBG) cavity resonator encompassing a metamaterial with a sparsely populated array of metallic rods has been arrived at for potential application in future generations of particle accelerators. The star-shape array was evolved from a two-dimensional triangle lattice with certain lattice points vacant. Optimized for the TM 01 – like mode with the electric field concentrated at the center while the higher-order modes (HOMs) are constrained from the center, the cavity is excited by a standard rectangular waveguide. Input matching is accomplished by fine tuning in the positions of selected metal rods in the two outer layers. The cavity-waveguide assembly was fabricated with copper and cold tested for resonance characteristics. A return loss of over 20 dB at the designed resonance frequency of 11.41 GHz was measured. A bead pull experiment was performed to confirm the uniformity of the field along the axis of the cavity resonator.