Ultra-wideband Planar Marchand Balun Design for the Pyramidal Sinuous Antenna

This article presents the design of an ultra-wideband planar Marchand balun for the pyramidal sinuous antenna. Ground plane slots, placed beneath the coupled-line sections, increase the coupling factor of the coupled-line sections and ensure tight coupling. This results in wider bandwidths compared to standard implementations and relaxes the requirements on the trace width and gap spacing. The balanced output lines are placed on the same side of the substrate to facilitate straightforward integration with the antenna. The designed balun showcases a simulated return loss better than 10 dB, and an insertion loss better than 0.84 dB across the band from 2-6 GHz. The simulated amplitude and phase balance are better than 0.8 dB and -12° respectively. Manufactured performance corresponds well with simulated predictions with minor differences being attributed to manufacturing tolerances.