Micromachined rectangular coaxial line to ridge waveguide transition

This paper discusses a new micromachined rectangular coaxial line to ridge waveguide transition operating in the frequency range from 60 to 90 GHz. The micromachining techniques are used to provide accurate device dimensions for millimeter wave distributed circuits. A 50 Omega coaxial line output is coupled to a relatively high impedance ridge waveguide. A balun (balanced to un-balanced) concept is considered in order to transform TEM mode in the coaxial line to TE mode in the waveguide [4]. The design has been simulated using CST Microwave Studio 3D simulator. The structure is constructed by bonding five layers of gold coated photoresist (SU-8) each 200 microns thick. The experimental result shows a good wideband response with return loss below -19 dB between 60 GHz to 90 GHz. The measurements show a 1 dB insertion loss and the S parameter response giving a good agreement with the simulation result.