Broadband microstrip-to-parallel strip transition balun with reduced size

A tapered balun of broadband microstrip-to-parallel strip transition using triangular structure with linear transition for a dipole antenna is proposed. The original balun consists of linear profile with the size of one quarter wavelength for both the height and width. By studying the current distributions at balun surface, it can be reduced to 25%, 50%, and 75% from the original size. Measured results based on return loss and insertion loss for all baluns were found to be better than -10 dB and -3 dB, respectively, from 400 MHz to 3.5 GHz.