Small-Size Uniplanar WWAN Tablet Computer Antenna Using a Parallel-Resonant Strip for Bandwidth Enhancement

The technique of using a parallel-resonant (PR) strip for bandwidth enhancement of a small-size uniplanar tablet computer antenna for the WWAN operation (824-960/1710-2170 MHz) is presented. The antenna is printed on a thin FR4 substrate of small size 12 × 40 mm², and has a simple uniplanar structure of comprising a feeding strip, a shorted strip, and a PR strip. The antenna's wide lower band is formed by the quarter-wavelength resonant mode of the shorted strip and an additional resonant mode generated owing to the presence of the PR strip, which occupies a very small area of about 7 × 7 mm² only. The PR strip contributes a parallel resonance at about 1100 MHz which in turn generates an additional resonance near the quarter-wavelength mode of the shorted strip, thereby resulting in a new resonant mode to greatly enhance or double the bandwidth of the antenna's lower band for the GSM850/900 operation. For the antenna's upper band, it is formed by a higher-order mode of the shorted strip and a quarter-wavelength mode of the feeding strip, and covers the GSM1800/1900/UMTS operation. Details of the proposed antenna are presented.