Improved Design Equations for Asymmetric Coplanar Strip Folded Dipoles on a Dielectric Slab

Design equations for the input impedance of the asymmetric strip folded dipole, developed by Lampe, [2,3], depend, amongst others, on the characteristic impedance of an asymmetric coplanar strip (CPS) transmission line. Lampe assumes a homogeneous surrounding medium. In practice, the antenna will be realised on a dielectric slab. Employing the Lampe equations for this inhomogeneous case may lead to relative errors in the CPS characteristic impedance as much as 32% and therefore to large errors in the input impedance. Improved design equations for the input impedance are discussed for the inhomogeneous case. These improved design equations rely on an accurate calculation of the characteristic impedance of an asymmetric CPS on a dielectric slab and further employ correction factors applied to the homogeneous case dipole length and equivalent radius.