Analysis of Reflection Coefficient in a WR90 Rectangular Waveguide with Dielectric Plug and Teflon-Filled Section

A WR90 rectangular waveguide operating in the TE10 mode has dimensions a = 2.29 cm, b = 1.02 cm. An air-filled section of the waveguide meets a Teflon-filled section as shown below. The Teflon has a relative permittivity of εr = 2.2. The loss tangent of the Teflon may be ignored in this problem.

A dielectric "plug" with a relative permittivity of εrp is inserted one-half of a guided wavelength in the air region (λg0) away from the boundary between the air-filled waveguide and the Teflon-filled waveguide, as shown below. The length of the dielectric plug Lp is one-fourth of a guided wavelength in the plug region. The plug acts as a quarter-wave transformer to allow for a perfect match to be seen by the air-filled waveguide to the left, carrying the incident wave.

Let relative permittivity εrp = 1.43 and length Lp = 0.75 cm, obtain the reflection coefficient from 8 GHz to 12 GHz with center frequency at 10 GHz.

Constructed HFSS Structure

Simulated Plot

Observation:

The lowest S31 is at 8.7, 10.9 GHz

The Highest s31 is at 8, 9.5 GHz