Broadband Rectangular Waveguide TE10–TE20 Mode Converter With In-Line Ports and Compact Structure

Abstract

This letter presents a compact and broadband TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{10}$</tex-math> </inline-formula> –TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{20}$</tex-math> </inline-formula> mode converter for millimeter-wave and terahertz applications. The input rectangular waveguide (RWG) and output over-mode waveguide (OMWG) are in-line and orthogonal in arrangement. In this converter, the waveguide mode is converted in the short height-reduced and width-widened gradient waveguides. A simple cuboid matching structure is employed to improve bandwidth and conversion efficiency, and a bed of nails is applied to the waveguide profile to suppress electromagnetic (EM) leakage and facilitate assembly at high frequencies. For further verification, a pair of WR-4.3 band prototypes were fabricated and measured. In the range of 170–252 GHz (38.9%-bandwidth), the measured insertion loss of the back-to-back converters is found to be around 0.86 dB with the worst return loss of 14 dB except for a slight deterioration at 172 GHz. Deducting the waveguide insertion loss, the conversion efficiency is higher than 98%.