Effective medium characterization of partially-filled rectangular waveguides

A single-mode waveguide, partially filled with dielectric materials, is an important case of a metamaterial. Here, we report an effective medium characterization of partially-filled waveguides by using the image dipole method and obtain an explicit expression for the effective permittivity. We also confirm experimentally that an electromagnetic wave propagating through a partially-filled waveguides has the same reflection and transmission characteristics as a wave propagating through a medium possessing an effective permittivity. In particular, we apply our method to the quarterwave anti-reflection structure and show that our method is suitable for designing wave-filter devices inside a rectangular waveguide.