Membrane supported Yagi-Uda antennae for millimetre-wave applications

This paper addresses for the first time the design, fabrication and ´on wafer´ characterisation of membrane supported Yagi-Uda coplanar waveguide fed antenna structures, operating in the 45 GHz frequency range. The antennae were fabricated on 1.4 μm thin SiO₂/Si₃N₄ membranes obtained by micromachining of high resistivity silicon, using a backside reactive ion etching process. This approach has assured almost free-space operating conditions for the Yagi-Uda antennae and the dry backside etching process has allowed the effect of the bulk silicon wall that supports the membrane in the main radiation direction to be minimised. The design was based on electromagnetic simulations made using the Zeland IE3D software package. The antenna structures, measured ´on wafer´, have shown a minimum return loss of 15 dB and a gain of about 7 dBi. Very good agreement has been observed between experimental and simulated results.