71–76GHz grounded-coplanar-waveguide-to-rectangular-waveguide transition with integrated planar bias tee for quasi-hermetic radio-over-fiber wireless transmitter

A grounded coplanar waveguide (GCPW) to rectangular waveguide (WR) transition featuring an integrated planar bias tee is presented for operation in the E-band from 71 GHz to 76 GHz, a frequency slot which has been worldwide allocated for wireless communication applications. The GCPW-to-WR transition is implemented on high-frequency laminate (ROGERS RT Duroid 5880) and has been optimized for E-band Radio-over-Fiber (RoF) wireless transmitter, in order to connect the 50 Ω coplanar waveguide (CPW) output of a high-frequency InP photodiode (PD) chip to a WR-12 waveguide. The presented transition concept allows for quasi-hermetic packaging without the need of radomes and enables the use of commercially available WR without the need for any mechanical modifications. Furthermore, the built-in bias tee allows packaging of PDs without on-chip bias networks for a more efficient use of the PD chip area. Full-wave electromagnetic simulations show that the optimized transition presents a return loss (RL) of at least 25 dB, an insertion loss (IL) of only 2 dB, and a RF-to-DC path isolation (IS) of at least 34 dB.