To widen the bandwidth of a printed dipole antenna, many attempts have been made such
as inductively-loaded, double-sided printed method and series-fed technique, et al. [7{12]. Di®erent
element geometries have also been researched to improve the operating impedance bandwidth including
circular, elliptical, bowtie and so on [13{18]. Antenna miniaturization is an important trend for wireless
applications. Thus some small printed dipoles have also been investigated. A wideband low pro¯le
dipole fed by coplanar stripline is presented in [19]. A planar wideband balun based on microstrip to
coplanar stripline is designed to feed this dipole antenna. Unfortunately, a larger size is required to
realize this type balun, which will increase the antenna size. An ultrawideband printed dipole antenna
with shorting bridge is designed in [20]. A wideband microstrip balun with three-section transformer
is used to feed the printed dipole antenna. However, the bandwidth of the dipole antenna is limited by
using this balun. The antenna size is also increased due to the additional balun.