Introduction

Introduction The Radio Frequency Identification (RFID) system is become popular in many applications such as industrial automation and supply chain management because it can provide fast and automation operating. Tags in contactless smart cards used in building-access and anti-theft systems. In practice, these tags are oriented in many directions. Conventionally, the rectangular or circular loop reader antennas are always employed, but they cannot provide sufficient magnetic field intensities in some required directions. Therefore, a large number of publications and patents are available in the literature for loop antenna in various configurations. Most techniques can improve the magnetic field distribution but antenna structure is complicated. In this paper, the flat spiral rectangular loop antenna arranged as a walk-through gate is proposed for the anti-theft system. Anti-theft system is also expected to be applied in the shop or store to protect the thievery. A typical RFID anti-theft system as shown in Fig. 1 consists of three main parts: antenna system, reader and computer. This propose reader antenna is low cost and simple structure, including ability to communicate with various tag orientations.