Design and Simulation of a Circular Waveguide Adapter for TEM-TE₁₁ Mode Transition

This Waveguides transport high-frequency microwave signals efficiently with no major loss in signal power. A waveguide with a circular/rectangular cross-section operates on different electromagnetic modes namely transverse electric/magnetic (TE/TM) modes, with defined cut-off frequencies. Conversely, a coaxial cable, a key component in high-frequency device operations, carries the signal only via TEM mode. Thus, a suitable waveguide adapter (also known as a mode-converter) is often essential in a microwave system to minimize signal loss. Here, we present the modelling and simulation of a simple C-band circular waveguide adapter that converts the TEM mode to the TE11 mode. The studies are carried out using CST software. Simulation results show the adapter's insertion loss and return loss to be -0.019 dB and 27.556 dB, respectively, at the operating frequency. Obtained bandwidth is 1.85 GHz, i.e., the waveguide adapter covers 46 % of C-band frequencies.