U-band micromachined coaxial filter

This paper presents a micromachined filter for millimeter-wave applications operating at U-band. The structure was designed using a rectangular coaxial line with the center conductor suspended in air. The rectangular coaxial cables have been optimized to provide a low attenuation constant. The design includes a coplanar waveguide (CPW)-to-coaxial transition to interface the device with other components, or coplanar probes for measurements. The filter has been designed with a center frequency of 42 GHz and a 10% fractional bandwidth. A measured insertion loss of 0.77 dB has been obtained. This structure involves a low-cost micromachining manufacturing process using SU-8 photo resist which is very attractive for the implementation of integrated millimeter wave subsystems.