Design of a Narrowband 2.45 GHz Unidirectional Microstrip Antenna with a Reversed ‘Arrow’ Shaped Slot for Fixed RFID Tag and Reader Md. Saad-Bin-Alam 1 , Mohammad Sakib Ullah 1 and Sanjida Moury 1 1 Department of Electrical Engineering and Computer Science, North South University, Dhaka, Bangladesh 2 Faculty of Engineering & Applied Science, Memorial University of Newfoundland, St. John's, NL, Canada E-mail: sadbinalam.nsu.bd@gmail.com Abstract— In this paper, we have designed a newly shaped narrowband microstrip antenna operating at nearly 2.45 GHz based on transmission-line model. We have created a reversed ‘Arrow’ shaped slot at the edge of opposite side of microstrip line feed to improve return loss and minimize VSWR, which are required for better impedance matching. After simulating the design, we have got higher return loss (approximately -41 dB) and lower VSWR (approximately 1.02:1) at 2.442 GHz. The radiation pattern of the antenna is unidirectional, which is suitable for both fixed RFID tag and reader. The gain of this antenna is 9.67 dB. The design has been simulated in CST Microwave Studio 2011. Keywords- Microstrip; Narrowband; RFID; Return-loss; VSWR I. INTRODUCTION The necessity of using fixed RFID tag and reader is still alive today. According to [1], fixed readers are designed to streamline processes at the major mandatory read points in a facility like warehouse dock doors to capture incoming and outgoing inventory movement, work in process (WIP) to track every step of the manufacturing process, parts tracking to ensure adequate inventory levels and protect against loss and theft, conveyor belt of the manufacturing production line to document the ‘birth’ of a product from the moment of its creation (required in some industries due to government regulations, such as pharmaceutical) etc. In the case of designing antenna for RFID systems, most of the times the frequency band is either UHF or microwave band. In [2], a 865 MHz microstrip patch antenna fed by a microstrip line designed on a substrate is considerably studied and thoroughly analyzed. The final optimized design of [2] achieved a total antenna gain of 5.6 dBi and a return loss or reflection coefficient (S11) of -35 dB at 865 MHz for 116 mm patch length. In this paper, we choose nearly 2.45 GHz frequency (microwave ISM band) as RFID frequency band because data speed of this band is higher than UHF bands [3]. The another advantage of choosing microwave band instead of UHF band for designing a microstrip patch is it requires less space to design and manufacture the patch antenna. Our main target in this paper is to design a microstrip antenna operating at nearly 2.45 GHz ISM band for fixed RFID system with increased impedance matching performance. Figure 1. The initial design of the microstrip antenna based on transmission-line model II. ANTENNA CONFIGURATION AND DESIGN The initial configuration of the microstrip antenna is shown in Fig. 1. The microstrip Antenna is designed by two stages. At first stage, the basic shape of the rectangular patch of the antenna is designed by transmission-line model. It is very easy to analyze using the transmission-line model, which are most accurate for thin substrates [4] [5]. This patch is designed on a Rogers RT5880 substrate with dielectric constant of =2.2. The thickness of the substrate is 0.787mm. As shown in the Fig. 1 the dimensions of the substrate is Ws = 49.384mm and Ls = 42.629mm. The patch has the following parameters for initial design (Table 1). In this paper, the units of all parameters are given in millimeter (mm). Table 1 Initial Parameters of the Patch L s W s L p W P W W 42.629 49.384 41.798 49.384 21.08 L g W g L f W f L in W in 12.06 2.408 3.618875 3.408 8.856625 2.408 Here, L p and W p are the main length and width of the patch respectively. W f and L f is the width and length of the X Y Z