For applications ranging from public-safety to targeted mobile advertising, the need for indoor real-time location systems is quickly rising. Although solutions are available commercially, they are costly and not completely reliable. While optical and infrared systems are very accurate, for example, they require line of sight. Hybrid systems that merge optical imaging with infrared and ultrasound are generally accurate, but limited in the number of objects that they can simultaneously track. To provide a more well-rounded solution, a hybrid passive ultra-high-frequency (UHF)/ultrawideband (UWB) RF-identification (RFID) concept has been proposed by Catarina C. Cruz, Jorge R. Costa, and Carlos A. Fernandes from Portugal’s Technical University of Lisbon.
Their design combines the potential of high-resolution UWB impulse radio with the typical range of UHF-RFID systems. For this design, the team developed a new planar antenna for hybrid passive tag systems. It operates in both the UHF-RFID and Federal Communications Commission (FCC) UWB bands. In a system, the reader may activate the tag’s chip through a narrowband UHF signal. The tag could then answer with short UWB pulses, determining position with centimeter-class resolution. The co-designed UHG and UWB antenna elements are printed back to back on each side of a common substrate, which paves the way for integration onto a single UHF-UWB RFID chip. In experimental results, the hybrid antenna performed comparably to available solutions working on just a single band. See “Hybrid UHF/UWB Antenna for Passive Indoor Identification and Localization Systems,” IEEE Transactions On Antennas And Propagation, Jan. 2013, p. 354.