The perfectly matched layer as lateral boundary in finite-difference transmission-line analysis

Using a perfectly matched layer (PML) as lateral boundary in waveguide analysis introduces artificial modes and other unexpected effects. This paper presents results of a finite-difference frequency-domain approach and an analytical investigation of the PML's capability to simulate the lateral open space, including an accuracy estimation. A criterion how to detect the desired modes out of the mode spectrum is also given. The findings are verified for a coplanar waveguide radiating into the substrate.