Study on the Characteristics of A Compact Ultra Wideband Antenna

Abstract

A new kind of Ultra Wideband (UWB) antenna, which consists of a leaf-like dipole and a dielectric block, is proposed and analyzed. The dielectric block is parallelly attached to the feed point of the leaf-like dipole, so the near field can be attracted to the side where dielectric block located, this leads to a focusing effect of the energy in the far zone. The leaf-like dipole itself is a wideband antenna, with proper resistance loading on the leaf-like elements, the impedance bandwidth of the antenna defined by VSWR less than 2.3 achieves 6.9 GHz (from 3.1GHz to 10 GHz), which satisfies the UWB requirement given by FCC. The characteristic impedance of the feeding cable is 50 Q. I INDRODUCTIONThe commercial Ultra Wideband (UWB) attracts more and more interests since the first release of authorization by FCC in February 2002. In the UWB systems, the antenna is an important component and should have low profile, compact and integratable properties. Dipole antenna is a single structure antenna, but for UWB use, techniques should be introduced to widen the bandwidth. Recently, several successful designs of dipole antenna for UWB systems are reported [1-3], where the dipole configurations are bow-tie, circular and elliptical, etc. In [4], the transmission characteristics of the pulse voltage and current on dipole antenna and the pulse radiation mechanism of the dipole antenna are studied. Based on the analysis, the author proposed, in the last of the paper, a dipole with smooth distributed capacitance, which may be suitable for pulse radiation. Based on the work in [4], a new sort of wideband antenna is proposed in this paper. The proposed antenna is composed of a leaf-like dipole and a dielectric block. The geometry of the antenna is introduced in detail in Section II. This antenna has compact structure, and is easy to be fabricated by PCB technique. The input and radiation characteristics of the antenna are studied by FDTD method and PML absorbing boundary condition. Simulation results show that the antenna has the expected directive property and a suitable radiation pattern. The bandwidth of the antenna is from 3.1 to 10 GHz with VSWR less than 2.3.Gaussian monocycle pulse is fed to the antenna by a cable line with the characteristic impedance of 50 Q. II THEORY AND METHODReference [5] indicated that, the late-time ringing of an antenna, which brings the narrowband nature, is mainly caused by the current reflections. References [4] indicated that the rapid variation of the distributed unit length capacitance along the dipole rods is one of the reasons of current reflection and impedance mismatch. To compensate the distributed capacitance along dipole rods is a good means for decreasing the reflection. The biconical antenna, obtained by increasing diameter along dipole rods, has wonderfully capacitance compensating effect. But the biconical antenna with relatively large size and weight is not fit to mobile and miniaturizing equipment. Based on theoretical analysis, the author proposed, in the last of the paper, the...