Ultra- Wideband Balun Design Based on Double-Sided Parallel Strip Lines

This paper presents a balun with more than ten octaves. The novel balun is an implanted conductor plane multilayer double-sided parallel-strip line. To isolate the various circuits on the upper and lower layers and convert into two immediate microstrip circuits, a conductor plane is inserted into the centre of the platform of the double-sided parallel-strip line in the multilayer construction. The method results in an extremely simple balun construction with superior broadband performance. From 1 GHz to above 10GHz, the developed switch circuit exhibits mismatch in degrees and amplitude of less than $\pm 1.8^{\circ}$ and $\pm 0.17\text{dB}$, respectively. The balun measures 29 $\text{mm}\times 20 \text{mm}\times 1.128$ mm in size.