A Waveguide-to-Balanced-Line Transition with embedded Balun for mm-Wave Measurement Setups

Differential signaling has been the preferred choice in radio-frequency circuits due to its inherent immunity towards common mode noise and cross-talk. However, the standard lab equipment is available with single-ended coaxial connectors or rectangular waveguide (WR) interface. It makes baluns and WR-to-planar transitions the essential blocks in the measurement setups for chipsets and antennas with differential microstrip line (DMSL) feeds. For this purpose, the authors propose a novel co-design of waveguide transistion and planar balun at 60GHz on a RF PCB with WR flange interface. The PCB design acts as a balun converting 100Ω DMSL to 50Ω single-ended microstrip without involving the flange. Whereas, when the flange is attached to the PCB, it redirects the signal from DMSL to the waveguide, disconnecting the single-ended microstrip port. In this way, a single differential device under test can be tested using both single-ended coaxial and WR lab equipment. In this work, the design as well as validating simulations are presented at 60GHz license-free band. To the best of the authors’ knowledge, this type of structure has not been previously reported in the literature.