Usage of characteristic modes with specific boundary conditions for wide-band antenna design: application to a cage loaded monopole antenna

Abstract : In this article, a technique to design a compact wideband antenna with the optimization of the input impedance is proposed. This technique is based on the use of two sets of characteristic modes. The first one is associated to an open circuit at the antenna input port while the second is associated to a short circuit at the antenna input port. The link of this analyze with a classical modal approach by a rational fraction approximation of the input impedance is demonstrated. This technique is firstly applied to a basic folded monopole antenna, then to a disc-loaded folded monopole antenna in the aim to optimize its bandwidth and radiation pattern while reducing its size. The disc-loaded folded monopole antenna is modeled and measured. Its VSWR performances are equivalent to thus of the Goubau antenna for equivalent dimensions. The radiation pattern is monopole-like on the full bandwidth.