Spatial Field Distributions of Electromagnetic Waves in Coupled System of One-Dimensional Photonic Crystals

We fabricated and validated a coupled waveguide composed of striplines configured with a pair of closely aligned one-dimensional photonic crystals to develop a microwave component such as a demultiplexer with multiports. The system became opaque inside the photonic band gap region because of the absence of electromagnetic modes. Outside the photonic band gap region, the wave entered from the incident port is reflected at the coupled region despite of the geometric transmission configuration. A previous study suggested that this scattering characteristics must be interpreted as a result of coupling between two closely aligned transmission lines. In this study, we performed additional numerical analyses using the finite element method for the spatial distributions of electric fields, current, and charges to confirm the propagation patterns of modes and to elucidate the origin of the interesting transmission characteristics. We confirmed that this extraordinary propagation mechanism must be understood by the superposition effect of the photonic band structure and stripline coupling. Our findings provide the knowledge to design multiport microwave devises.