Bandwidth Enhancement and Size Reduction of Printed Monopole Antenna Using Bounding Box Structure

A printed monopole antenna with enhanced bandwidth and reduced size using a bounding box structure is presented in this paper. The initial design comprises a microstrip-fed rectangular monopole with a partial ground structure. A feed line offset, a slit etched on the feed line, an asymmetric transition connecting the feed line and the monopole, and an inverted T-slot embedded in the ground are used to ensure good impedance matching. The design is modified by incorporating a bounding box structure, which introduces additional resonances hence an enhanced impedance fractional bandwidth reaching 156% (0.28 to 2.27 GHz) is obtained as compared to only 72% (0.75–1.60 GHz) realised for a conventional monopole. The electrical size of the proposed antenna is also reduced from 1.01 λ l × 0.60 λ l to 0.39λl  × 0.24 λ l (where λ l denotes the wavelength corresponding to the lowest operating frequency of the antenna) using the bounding box configuration. The experimental and predicted results are in good agreement, and the proposed antenna demonstrates good radiation characteristics over the operating bandwidth. The proposed antenna can be applied in DVB (530–860 MHz), GSM850 (824–894 MHz), GSM900 (880–960 MHz) DCS (1710–1880 MHz), PCS (1850–1990 MHz), and UMTS (1920–2170 MHz) systems.