  We present a novel design of a waveguide to microstrip or coplanar waveguide
transition using a unilateral finline taper. The transition from the unilateral
finline mode to the TEM microstrip mode is done directly, avoiding the
antipodal finline tapers that have commonly been employed. This results in
significant simplification of the design and fabrication, and shortening of the
chip length, thereby reducing insertion loss. In this paper we shall present
designs at 90 GHz that can be employed in superconducting tunnel junction
mixers or Transition Edge Sensor bolometers, and scale-model measurements at 15
GHz.
