Novel compact balun based on slotted square patch

In this paper, a novel patch based balun with compact size is presented. This balun consists of a simple square patch etched by a pair of asymmetric slots. The unbalanced input port is orthogonally arranged in-between two balanced output ports along the patch. Asymmetrical width and length of the cross-loaded slots perturb the field of the patch and prolong the flow of the current path for miniaturization, simultaneously. For demonstration, a prototype balun is designed and fabricated at 2.4 GHz. Measured results achieve a good performance with an amplitude imbalance smaller than 0.7 dB and a phase difference of 180°±10° with a fractional bandwidth of 8.3%.