Backscattering Protection in a Fully Metallic PTD-Symmetric Bifilar Edge Line (BEL)

This communication presents an experimental validation of a backscattering-protected bifilar edge line (BEL) constructed entirely by metallic materials. This waveguide relies on the principle of parity (P) time-reversal (T) duality (D) symmetry. In the ideal case, parity time-reversal duality (PTD)-symmetric structures have been theoretically demonstrated to be robust against backscattering for a certain class of discontinuities, namely, those still respecting the PTD symmetry. The waveguide analyzed here is constituted by a parallel plate waveguide (PPW) in which each of the two walls comprises two parts: a perfect electric conductor (PEC) and a perfect magnetic conductor (PMC) joint by an edge. On the two opposite walls, the faced boundary conditions (BCs) exhibit a dual nature. The PMC is emulated by metallic short pillars (square cross-sectional pins). Two distinct pillar geometries are investigated for implementing the PMC. In the first case, the pillars of the top and bottom walls are aligned with each other along the propagation direction, whereas, in the second case, the pillars on the top-right wall are strategically shifted to control the dispersion of the mode supported by the structure. Numerical and experimental results are shown, demonstrating the ability to confine the electromagnetic (EM) field in the proximity of the BEL over a large bandwidth, while maintaining the backscattering protection in the 22-26.5-GHz band.