Compact Wideband and Variable Impedance Transformation Ratio Balun for Folded Dipole

Aiming at dipoles with different impedances, a wideband balun with adjustable impedance for the balanced port is proposed in this communication. The balun is directly connected to the dipole to form an antenna element, so it also needs to meet: no connection line is required; the overall size is less than a quarter of the wavelength. The proposed balun realizes balanced–unbalanced conversion through aperture coupling, and dual slot ensures its wide-band characteristics. Due to the high-impedance characteristics of the folded dipole (FD), the balun has achieved impedance conversion ratios of 6:1, 8:1, 10:1, and 12:1, and the corresponding bandwidths are 82.1%, 67.1%, 53.7%, and 44.4%, respectively. Finally, three types of wideband dipoles with different characteristic impedances are fabricated to verify the versatility of the balun.