An Integrated Planar Guanella Balun with the Quasi-Coaxial Structure on GaAs Substrate

This paper proposes a planar Guanella balun with the quasi-coaxial structure. This is the first report of the Guanella balun fabricated on a GaAs substrate. The quasi-coaxial structure is configured with metal layers on three thin dielectric layers of a few micrometers thickness. These layers are laminated on the GaAs substrate. The metal on the second layer (the second metal) is an inner conductor, which is surrounded by the first and third metals correspond to an outer conductor. The first and third metals are split lines to widen the inner conductor. The fabricated Guanella balun has a spiral shape, and its size is ${4 2 5}\mu\mathrm{m}$ by ${3 4 5} \mu\mathrm{m}$. The fabricated Guanella balun shows less than $0.7\mathrm{~dB}$ of amplitude imbalance and 7.3 degrees of phase imbalance from 5 GHz to 15GHz. The fabricated Guanella balun is realized with half elements of a Marchand balun and achieves good performance with small size.