71-76 GHz grounded CPW to WR-12 transition for quasi-hermetic RoF wireless transmitter

A grounded coplanar waveguide (GCPW) to rectangular waveguide (WR) transition is presented for operation in the E-band from 71 to 76 GHz, a worldwide allocated frequency slot for wireless communication. The GCPW-to-WR transition is designated for the E-band radio-over-fibre (RoF) wireless transmitter where it connects the 50 coplanar waveguide (CPW) output of a high-frequency photodiode chip to a WR-12 waveguide. The presented transition is implemented on a ROGERS RT/Duroid 5880 RF laminate, it allows for quasi-hermetic packaging without the need of radomes and enables the use of a commercially available WR without the need for any mechanical modifications. Full-wave electromagnetic simulations show that the optimised transition presents a return loss of at least 30 dB and an insertion loss (IL) of only 2 dB. Experimental results confirm an average IL of only 2.5 dB. The key role of via-holes in reducing the IL is experimentally proven.