Unilateral finline transition at THz frequencies
Abstract:
We present a new type of waveguide to microstrip transition designs for a 700 GHz SIS mixer. The transition comprised a unilateral finline taper and the RF power from the finline slot is coupled through coplanar waveguide to microstrip using two radial stubs. This transition is significantly easier to design and fabricate than the conventional antipodal finline taper since the fins do not overlap at any stage. A key feature of this design is that it can be deposited on Silicon-on-Insulator resulting in a finline mixer chip on approximately 15 µm silicon substrate. This allows the mixer chip to be held in the E-plane of the waveguide without a supporting groove in the waveguide wall, avoiding the excitation of higher order modes. The chip is simply supported by gold leads deposited on the substrate. It should be emphasized that the employment of such substrate will also decrease the loss and allow finline mixers design to be extended to the THz region.