Endfire Transition from Coplanar Waveguide-to-WR3 Rectangular Waveguide for Monolithic Integration with THz Photodiodes

In this paper, an endfire transition from coplanar-to-rectangular waveguide (CPW-to-WR3) for operation in the WR3-band (220-320 GHz) is presented. The transition is designed for providing connectivity between a monolithically integrated InP-based terahertz photodiode (PD) to a WR3 rectangular waveguide. The presented transition is based on a CPW-fed planar dipole antenna designed on InP substrate which placed in the E-plane of the rectangular waveguide. The dipole-based transition converts the direct coupled quasi-TEM CPW mode of the PD output to the TE10 mode of the rectangular waveguide. The proposed design provides a simple approach avoiding complex integration and packaging techniques like air bridges, ribbon-bonds, or via holes. Numerical analysis of the designed transition shows a wideband performance with a 3 dB insertion loss (IL) over 88 GHz bandwidth and a 10 dB return loss (RL) over 53 GHz bandwidth within the WR3-band.