Compact CPW-fed quasi-circular monopole with very wide bandwidth

Presented is a new CPW-fed quasi-circular monopole antenna, which is composed of a triangle and its tangent circle. This smooth monopole structure reduces the dimensions and improves impedance bandwidth dramatically. The CPW ground is bevelled to form a 50 to 100 Omega impedance transformer. The measured bandwidth defined by VSWR<2 is from 2.55 to 18.5 GHz, i.e. a ratio of about 7.3:1. The proposed monopole exhibits a nearly omnidirectional radiation pattern with very compact size and simple structure, which is suitable for various military and commercial wideband applications