Effects of Polarization and Radiation Diagram of Antennas in RFID Systems for Positioning Purposes Mudrik Alaydrus Universitas Mercu Buana Jl. Meruya Selatan Jakarta, 11650 Indonesia Abstract- Radio Frequency Identification (RFID) is a wireless system designed to identify the presence of objects attached by tags. In recent times, RFID is also used for positioning purposes. We show a scenario of wireless propagation observed by eight antennas with different polarization located in different positions. In this way, the polarization and diagram radiation of the antennas will play a significant role in producing electromagnetic field in the region. Keyword: RFID, identification, positioning, wireless, antenna, polarization, radiation diagram. I. INTRODUCTION Nowadays Radio Frequency Identification (RFID) becomes a mature application of wireless technology [1]. RFID is ubiquitous, is used for different purposes [2]. An emerging application of RFID is positioning of objects, especially mobile robots [3, 4, 5] and communication networks [6, 7, 8]. For indoor propagation problem, RFID based positioning systems are preferred than the GPS based counterpart [9], due to the shadowing problem of the satellite signals. Another indoor positioning systems are given in [10, 11]. In [12,13] RFID systems are used for accurate positioning problems in indoor propagation. Most of publications concerning with wireless propagation problems used statistical data evaluations [5, 14, 15], and some few other used simple deterministic approach [16, 17, 18]. In this work we would like to observe the effects of polarization/orientation and diagram radiation of the antenna in an indoor positioning system. For estimating the position we use the fingerprinting approach. To produce the data base, a scenario in a free space region with dimension of 6 m x 6 m is observed. Around the region we set up eight antennas in different known positions and different polarization. The tag will be moved around the region. II. BASICS of WIRELESS POSITIONING There are three important signal characteristics can be used for the positioning purposes; the received signal strength (RSS), the angle of arrival (AOA) and the time of arrival (TOA) [19, 20]. With these characteristic quantities we can deduce information about the position of the tag attached on an object. To implement the method angle of arrival (AOA) we need directional antennas. AOA methods are the core of direction finding (DF), which has been used for years to locate illegal transmitters or for tracking wild animals that are tagged with tiny transmitters. It requires no cooperation from the target, and any type of signal can be used, including continuous wave (CW). It also is used over wide frequency bands and ranges— from high frequency (HF) through microwave and from direct true line-of-sight to long communications distances propagated through the ionosphere. AOA is a principle component in a radar system. Using radar, only one fixed station is required to determine the location of a target in two or three dimensions. The two methods of AOA and time of flight (TOF) are employed. When using AOA alone, at least two fixed terminals are required, or two separate measurements by a single terminal in motion. TOA (time of arrival) and TDOA (time difference of arrival) methods use relationships based on distances between a mobile station and a number of fixed terminals to determine the position coordinates of the mobile target. Data for distance estimations are derived from the arrival times of radio signal epochs at one or more receivers. The TOA method uses the transit time between transmitter and receiver directly to find distance, whereas the TDOA method calculates location from the differences of the arrival times measured on pairs of transmission paths between the target and fixed terminals. Both TOA and TDOA are based on the TOF principle of distance measurement, where the sensed parameter, time interval, is converted to distance by multiplication by the speed of propagation. In TOA, location estimates are found by determining the points of intersection of circles or spheres whose centers are located at the fixed stations and the radii are estimated distances to the target. TDOA locates the target at intersections of hyperbolas or hyperboloids that are generated with foci at each fixed station of a pair. In applying RSS we use the condition that, signal strength at a receiver decreases as distance from the transmitter increases. If the relationship between signal strength and distance is known, analytically or empirically, the distance between two terminals can be determined. When several base stations and a target are involved, triangularization can be applied to determine the target’s location. RSS has several advantages over the TOF methods. It can be implemented on an existing wireless communications system with little or no hardware