Planar 71–76 GHz laminate integration platform for connecting millimeter wave photodiodes to WR-12 waveguides

Here, a millimeter wave photodiode (mm-wave PD) integration platform for development of high-power Radio-over-Fiber (RoF) wireless photonic transmitters (PTs) is presented. The platform features a novel planar bias-tee network design making use of a single quarter-wave coupled-line (CL) technique and two slotted split-ring resonators (SRRs) integrated in the DC bias line. The introduced bias-tee network enables proper biasing for mm-wave PDs, e.g. the triple transit region photodiode (TTR-PD), and protects the hybrid integrated RF amplifier from being damaged by the bias voltage.

The 3D full-wave electromagnetic field simulations of the designed bias-tee network show that in the whole 71–76 GHz band, the return loss (RL) is higher than 20 dB, the RF signal suppression level (IS) is higher than 30 dB, while the insertion loss (IL) is lower than 0.6 dB. A fence of via holes surrounds the bias-tee network to reduce the RF propagation losses into the laminate and to ensure that the grounded coplanar waveguide (GCPW) supports only a quasi-static transverse electromagnetic mode (TEM). The bias-tee network integrated together with high-electron-mobility transistor (HEMT) RF amplifiers and GCPW-to-rectangular waveguide (WR) transition enables the development of high-power (>17 dBm) PTs with WR-12 output. The IL of the complete integration platform is ∼2.2 dB.