Study of an Ultrawideband Omnidirectional Rolled Monopole Antenna With Trapezoidal Cuts

An ultrawideband (UWB) omnidirectional monopole antenna is presented. It is shaped by symmetrically wrapping a PEC sheet that has two trapezoidal cuts at the bottom corners. The antenna features about 132% impedance bandwidth and a stable as well as omnidirectional gain versus frequency response over the UWB band. The monopole antenna is investigated both experimentally and numerically by using an FDTD method. A parametric study is carried out for the monopole above an infinite ground plane to obtain an optimal design. The effects of a finite ground plane on both the impedance matching and gain of the antenna are discussed. Particularly, a simple expression is derived based on ground plane size to estimate the ripples appearing in the gain versus frequency response. Furthermore, ground plane edge loading with resistive sheet is proposed to eliminate the edge diffraction effects on the antenna gain, and thus improves the antenna performance.