IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 57, NO. 5, MAY 2009 1341 UHF RF Identification of People in Indoor and Open Areas Milan Polívka, Member, IEEE, Milan ˇ Svanda, Student Member, IEEE, Pˇ remysl Hudec, and Stanislav Zvánovec, Member, IEEE Abstract—The performance of an ultra-high-frequency RF identification (ID) system operating at 869 MHz, intended for the ID of persons in both indoor and open areas, has been val- idated using the propagation models, as well as the series of practical measurements. A two-ray propagation model and the 3-D ray-tracing model were used for calculations of all important system parameters in open and indoor areas, respectively. For the application mentioned above, a novel (electrically small and, at the same time, low-profile) wearable TAG antenna was designed. It was used in order to carry out the necessary tests as well. The antenna in question is based on an artificial-like surface. The latter provides an important screening effect and avoids detuning. Another virtue of the surface used is represented by the fact that it ensures the minimum loss of the antenna efficiency (resulting from the presence of a nearby human body). The simulations and measurements show that the optimized system can guarantee a reliable ID at distances up to 9 m in open areas and up to 16 m in corridors. Index Terms—Artificial surface, electrically small antenna, iden- tification (ID) of people, loop antenna, RF identification (RFID) system, TAG antenna. I. INTRODUCTION T O DATE, given the growing stress put on security as- pects, the identification (ID) systems intended for mon- itoring of people in both indoor and outdoor areas have become increasingly important. The efficient and reliable tracking of the motion of many people in either large buildings or outdoor areas belongs to the relatively difficult tasks. Standard mon- itoring-ID systems, working in either low-frequency (LF) or high-frequency (HF) bands (125 kHz, 13.56 MHz), which are based on inductive coupling, suffer from a low read distance (i.e., typically up to 1 m [1]). Therefore, during the ID process, the person has to, more or less, touch the reader or even insert Manuscript received June 09, 2008; revised October 26, 2008. First published April 14, 2009; current version published May 06, 2009. This work was sup- ported in part by the Czech Science Foundation under Project 102/08/1282: “Artificial electromagnetic structures for miniaturization of high-frequency and microwave radiation and circuit elements” and Project 102/08/H018: “Mod- eling and simulation of fields,” by the Czech Ministry of Education, Youth and Sports under the “Research in the Area of the Prospective Information and Nav- igation Technologies” MSM 6840770014 and “Research of Methods and Sys- tems for Measurement of Physical Quantities and Measured Data Processing” MSMT6840770015 research programs and under COST Project IC0603. The authors are with the Faculty of Electrical Engineering, Department of Electromagnetic Fields, Czech Technical University, 16627 Prague 6, Czech Republic (e-mail: polivka@fel.cvut.cz; svandm1@fel.cvut.cz; hudecp@fel.cvut.cz; xzvanove@fel.cvut.cz). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMTT.2009.2017305 the ID card into the reader. This requires the installation of rel- atively narrow gates, where anyone that intends to pass through the gate, is obliged to stop and activate the reader. This kind of ID process is, in general, inconvenient and time consuming. Fur- thermore, in cases of heavy traffic or multiple accesses, it gives rise to unacceptable time delays. As a result, RF identification (RFID) systems operating at ei- ther ultra-high-frequency (UHF) or microwave frequencies (i.e., at 860–930 MHz or 2.4 GHz) that use electromagnetic wave propagation as a coupling mechanism seem to be more suitable than inductive coupling systems. It is possible to monitor and identify persons at moderate distances, usually over several me- ters. In addition, the persons that are being monitored are not required to perform any action during the ID process. The mon- itoring and ID processes do not have any negative repercussions on the fluency of the traffic; in fact, people can even move rather quickly. Such ID systems can be used in manufacturing plants, offices, warehouses, prisons, etc. A specific application of the UHF RFID system, consisting of the ID of sportsmen in mass races, is described in [2]. The performance of any UHF or microwave RFID system is dominantly influenced by the parameters of antennas used and also by the propagation of electromagnetic waves in the in- tended ID area. This paper is focused on the ID of people in open areas and inside buildings (especially in corridors). The objec- tive is to reach as high a read distance as possible. To handle the RF ID task exactly, the evaluation of the electromagnetic field coverage in the treated area is required. Usually there is not much space for raising the gain of the reader antennas. High-gain antennas are relatively large and can show too narrow radiation patterns. Due to this, the parame- ters of TAG antennas are of prime importance. Since their di- mensions must be small, while their radiation patterns are re- quired to be wide, it is necessary to optimize their efficiency in order to ensure a long read distance. This is especially impor- tant in case of wearable antennas because their parameters can be strongly influenced by the close vicinity of a human body. The new dual-loop antenna designed for the ID of people, pre- sented here, employs a special screening substrate that preserves the acceptable antenna efficiency while guaranteeing a high im- munity against the influence of the human body. The propagation of electromagnetic waves substantially dif- fers in open areas and inside the buildings. In open spaces, it is usually accurate to take into account only the first reflec- tion from the ground. Owing to this, a relatively simple analyt- ical propagation model can be used. On the contrary, in case of indoor applications, the multiple reflections from many walls, 0018-9480/$25.00 © 2009 IEEE Authorized licensed use limited to: CZECH TECHNICAL UNIVERSITY. Downloaded on May 7, 2009 at 06:21 from IEEE Xplore. Restrictions apply.