Design of an Ultrawideband Planar Guanella Balun

This article presents the design and implementation of an ultrawideband multioctave planar Guanella balun (balanced-to-unbalanced) using double-sided parallel strip lines (DSPSLs). The operating frequency of the balun is found to be 0.5–2.6 GHz. The DSPSL is a type of balanced transmission line where two metal strips are present on the opposite sides of a flat dielectric substrate. Wideband transition between these balanced lines to a microstrip line has also been implemented. The measured amplitude and phase imbalance between the output signals at the balanced ports are less than 0.75 dB and 7°, respectively. The impact of these amplitude and phase imbalances on the combining loss of the balun has been presented. In order to understand the behavior of the balun with respect to differential and common mode signals, the mixed-mode $S$ -parameters have been calculated. The physical size of the fabricated balun is 27.25 mm $\times\,\,49$ mm. The design has been validated with the help of its measurement results.