In-plane transmission measurements of microwave TIs were performed in a parallel plate waveguide using a Keysight E5071C network analyzer with antennas from Fairview Microwave (SKU: SC3792). The sample is surrounded by radiofrequency absorbing foam and placed between two aluminum plates. The antennas are fixed to the top aluminum plate and spaced 35.8 cm apart along the long axis of the waveguide so that both antennas reside inside the photonic crystal (Figure ). Supporting Information (Figure ) Geometry, band structure, and simulated and experimental transmission plots for the trivial (compressed) honeycomb lattice. (Figure ) Additional examples of simulated corner geometries for the bent waveguide. (Table ) List of slicing parameters used in FFF. (Figure ) Illustration of the procedure used to determine the degree of deviation of each corner geometries from the original bent structure. (Figure ) Corner robustness analysis for a taller omega waveguide. (Figure ) Simulation of forward and backward propagation through a Z-shaped topological waveguide to verify reciprocity. (Figure ) Photographs of the parallel plate waveguide apparatus.