Design of Microfabricated Rectangular Coaxial Lines and Components for mm-Wave Applications

Miniature 310μm tall copper-air rectangular coaxial lines (RCL) with the inner conductor supported by periodic dielectric straps are demonstrated in this paper. The measured line loss is about 0.2dB/cm at 26GHz, while the isolation between two parallel lines with a center-to-center separation of 700μm is better than 60dB. Several quasi-planar components are designed and fabricated on the same wafer, and presented here are a branch line hybrid, a cavity resonator, and a cavity-backed patch antenna. The through and coupled port transmissions for the hybrid at 26GHz are 3.25dB and 3.35dB, respectively, with an output phase misbalance below 0.2°. The fabricated resonator has an unloaded Q-factor of 530 at 26GHz. The measured bandwidth of the antenna is 4.5% near 35GHz. The coaxial lines and other passive components are built with a new sequential micromachining process capable of utilizing copper as structural material, and polymer for the support of the inner conductor. A detailed description of the analysis, design, fabrication and performance is provided. Keywords—Coaxial line, Computer aided design, Branch line hybrid, Transmission Line Resonator.