An Air Dielectric Semi-Coaxial Line for mm-wave Applications

This paper reports on the design and fabrication of a surface micromachined air dielectric transmission line. The center conductor covers around 20 μm tall SU-8 support, while a semi-cylindrical air cavity (104μm diameter) acts as an outer shield. The device has been fabricated on a glass substrate with copper conductors and shows a line loss of 0.12 dB/mm at 50 GHz and 0.39 dB/mm at 100 GHz and a return loss of −30 dB at 52 GHz while it is better than −12 dB for the whole frequency band.