Precision microfabrication of millimetre wave components

Although conventional methods of metal milling are still capable of producing microwave components with high precision, the unit cost increases quite rapidly as the dimension gets smaller and structure more complex. Photolithography based micromachining technologies are therefore increasingly been explored by microwave community as an alternative method of producing high performance microwave components with a potentially much reduced unit cost. There are at least three micromachining technologies which are capable of producing accurately defined thick pieces (~0.5mm), namely SU8 photoresist, Si deep reactive ion etching (DRIE), and electroforming. In order to investigate their suitability for fabricating microwave components, all three technologies have been tried constructing various coaxial cables for 20 to 50GHz operation and excellent microwave performance were obtained for both SU8 and etched Si devices, but not for electroplated Ni ones.