A Wideband DRWG Balun With Low Loss and Compact Size

A wideband double ridge waveguide (DRWG) balun is proposed in this letter. The DRWG, as a variation of rectangular waveguides, provides low transmission loss. Meanwhile, it exhibits frequency-independent out-of-phase and equal power splits between its two ridges, ensuring low-amplitude imbalance and antiphase in the balun. By analysis of the DRWG structural parameters, the cutoff frequency is reduced while the bandwidth between fundamental and higher mode cutoff frequencies is expanded simultaneously, resulting in a compact design and the wideband operation of the proposed balun. For demonstration, the DRWG balun is designed and fabricated, and the simulated and measured results with good agreement are presented. The balun centered at 2.75 GHz illustrates a 76.4% bandwidth with a return loss of more than 15 dB. Within the wide bandwidth, the insertion loss is less than 0.25 dB, and the amplitude imbalance is ±0.17 dB while the phase difference between the two outputs is 180° ± 0.8°.