Compact rectangular-waveguide (WR-12) transition for coherent photonic mixers

A compact E-band (71–76 GHz) conductor-backed coplanar waveguide (CBCPW) to hollow metallic waveguide (WR-12) transition has been designed and fabricated. The fully-planar two-layer transition makes use of a double-slot antenna, which efficiently couples the millimeter-wave (mm-wave) signal from the CBCPW to the WR-12 waveguide. The introduced transition, together with an integrated high-speed balanced photodetector (BPD), enables the development of a compact coherent photonic mixer featuring a WR-12 output (WR12-CPX). The mm-wave generation is realized by heterodyne coherent optical detection in the BPD chip. The WR12-CPX allows direct optical-to-wireless conversion, enabling fiber-to-the-antenna connectivity for mobile backhauling. The transition is designed and fabricated on a 127 μm thick ROGERS RT/duroid 5880 laminate (er = 2.2). The experimental results of the fabricated transition show a maximum insertion loss of 3 dB and an average return loss of ∼20 dB. In addition to that, the packaged transition is presented as part of a novel WR12-CPX module.