SQUARE AND circular monopole antennas for ultra-wideband (UWB) applications are known for providing a relatively small impedance bandwidth. Numerous techniques have been proposed to improve the matching over a broad bandwidth. One alternative introduces radiator-width and feed-position control. The resulting printed monopole antenna, which measures just 30 x 36 x 0.4 mm, provides a -10-dB impedance bandwidth from 2.82 to 13.60 GHz. This antenna is the work of Cheol Yoon, Woo-Su Kim, and Hyo-Dal Park from Inha University together with Suk-Youb Kang from Korea Maritime University School and Hwa-Choon Lee from Chodang University.
The antenna comprises a coplanar radiator and groundplane on a thin FR-4 substrate. Despite its compact size, the antenna offers a wide impedance bandwidth and good radiation patterns and characteristics. The researchers defined the impedance bandwidth by a voltage standing wave ratio (VSWR) of 2.0:1 or less at 10.78 GHz (the relative midband of 2.82 to 13.60 GHz). They also showed that they can attain omnidirectional radiation patterns with appreciable gain across the operating band. For example, the antenna gain was approximately 0.28 to 3.94 dBi (with 3.94 dBi being the peak at 9 GHz). See "Printed Monopole Antenna on a Thin Substrate for UWB Applications," Microwave And Optical Technology Letters, June 2011, p. 1262.