Compact Low-Profile Dual-Band Tag Antenna for Indoor Positioning Systems

A compact, dual-band, dual-port, and linearly polarized tag antenna is proposed for indoor positioning systems. It operates in both UHF and UWB bands, covering 881–913 MHz for the lower band and 2.9–5.35 GHz for the upper band. U-shaped planar inverted-F antenna for the UHF band is designed to surround the dipole for the UWB band so that both bands can share the same radiating aperture and a compact structure $(100 \times 50 \times 9 {\text{ mm}}^3)$ is realized. In order to obtain a wideband and stable radiation performance in the upper band, a novel differential feeding structure is proposed to excite the ellipse-shaped dipole that exhibits good impulse performance. Meanwhile, the isolation between both ports is greatly improved to be better than 20 dB through loaded inductors. Measurements of a prototype show stable radiation patterns at both bands. With attractive features, this antenna can be potentially useful for indoor positioning systems.