Negative phase velocity 6 Parallel-plate waveguide Photonic band gap 6 Bragg condition 4 Fabry-Perot condition 4 Multilayer 4 Alternating layers 2 Antennas 2 Band gaps 2 Circular waveguides 2 Coaxial waveguides 2 Cross-sectional shape 2 Cut-off 2 Dielectric materials 2 Dielectric waveguides 2 Dielectric-magnetic material 2 Electromagnetic waves 2 Energy gap 2 Gap map 2 Magnetic materials 2 Multilayers 2 Optical devices 2 Optical waveguides 2 PBG structure 2 Parallel plate waveguide 2 Parallel plates 2 Perfectly conducting walls 2 Phase velocity 2 Photonic band-gap structures 2 Photonic bandgap materials 2