A Novel Transition from Grounded Coplanar Waveguide to Substrate Inte grated Waveguide for 60 GHz Radio-over-Fiber Photonic Transmitters

We present a novel transition from grounded coplanar waveguide (GCPW) to substrate integrated waveguide (SIW), designed on a ROGERS 5880 laminate for 60 GHz Radio-over-Fiber (RoF) photonic transmitters. The transition serves as connection between a 60 GHz photodiode (PD) chip and a suitable SIW antenna. In contrast to previous designs, our approach makes use of a quarter-wave coupled-lines (CL) section to transfer the signal carried by the GCPW to the SIW. This technique, creating a DC-block between the GCPW signal track and the ground layers, allows for correctly biasing the PD. In order to reduce the propagation of parasitic modes as well as the risk of interferences, the transition is fully enclosed by a fence of via holes. Simulations show that in the whole 57-64 GHz band, the return loss (RL) is higher than 17 dB, while the insertion loss (IL) is similar to 0.4 dB. To prevent the loss of RF power through the DC path, a planar RF-choke (RL > 22 dB, IL < 0.4 dB and RF-to-DC isolation (IS) higher than 28 dB) is additionally integrated.