Received: 10 January 2018 DOI: 10.1002/mop.31322 A comparative performances analysis of UHF RFID two crossed dipoles antenna based on FR4 substrate E. Ben Abdallah 1,2 | M. Egels 1,2 | E. Bergeret 1,2 | O. Benzaim 1,2 | P. Pannier 1,2 1 Institut Mat  eriaux Micro electronique Nanosciences de Provence, UMR CNRS, 7334, France 2 Aix-Marseille Universit  e, Technop^ ole de Ch^ ateau-Gombert, 5 rue Enrico Fermi, B^ atiment N eel, 13453 Marseille, France Correspondence Essia Ben Abdallah, Institut des Materiaux de Microelectronique et des Nanosciences de Provence, Technop^ ole de Ch^ ateau Gombert, 5 rue Enrico Fermi, Marseille 13453, France. Email: benabdallahassia@gmail.com Abstract The design of an FR4-based UHF RFID portable quasi- isotropic reader antenna with a circular polarization is reported. This low-cost small size antenna consists of two crossed dipoles with dimensions of 50 3 80 3 1.6 mm 3 . A 3-dB axial ratio bandwidth of 10 MHz can be obtained and a quasi-isotropic radiation pattern is achieved. The designed antenna performances are investigated for 6 pro- totypes using the same substrate and different boards. A performances comparison and analysis between the differ- ent realizations are presented in this article. Results demonstrate that inaccuracies in FR4 characteristics have effects on the antenna performances. Therefore, the key parameters of this type of antennas are identified. KEYWORDS UHF RFID, reader antenna, CP, quasi-isotropic radiation, small size, low cost, FR4 1 | INTRODUCTION Radio frequency identification (RFID) systems operating in the ultrahigh frequency (UHF) band (860–960 MHz) have been widely applied in a number of scientific and technical fields, such as medicine, industries, and engineering. 1 Anten- nas are an important component to establish the communica- tion between the tag and the transceiver. In practical situations for indoor or outdoor, the orientation of the reader cannot remain aligned. Therefore, to increase orientation diversity and to overcome co-polarization losses, circular polarized (CP) reader antennas are required. 2–5 Also quasi- isotropic antenna is very attractive in RFID, 6 where full spa- tial coverage is preferred. Furthermore, the antenna is required to be small sized to be embedded and integrated in small portable RFID reader. On the other hand, the major challenge that could potentially hinder the practical implementation of RFID is the cost. In fact, RFID systems have to be inexpensive to be successfully commercialized, which imposes cost restrictions on the implementation of RFID antennas. 7,8 FR4_epoxy is an excel- lent candidate as low-cost substrate for antennas. The most serious drawbacks of FR4 are some variability in permittivity and loss tangent parameters, which may affect the antenna performances. This will be discussed in this article. A quasi-isotropic CP antenna using FR4 substrate with a low profile and small size is designed in this article. The main objective is to investigate the antenna sensitivity to the manufacturing process and validate results by realizations. This study first focuses on the design of a low-cost small size quasi-isotropic circularly polarized two crossed dipoles antenna (Section 2.1). By adjusting the lengths of the two dipoles, the UHF band could be addressed. This reader antenna allows a CP radiation in the UHF band from 860 to 870 MHz which responds to the specificities of the European frequency band ETSI (865–868 MHz). 9 Then, the study focuses on parametric studies (dipoles lengths, PCB dimen- sion, and substrate parameters) and experimental results to TABLE 1 Antenna dimension (mm) L s W s W d L 1d L 1d1 L 1d2 L 2d L 2d1 L 2d2 e 80 50 1.5 22 36.5 15 35.5 21 9 0.035 FIGURE 1 Configuration of the proposed antenna [Color figure can be viewed at wileyonlinelibrary.com] BEN ABDALLAH ET AL. | 2217