A Circularly Polarized Printed Antenna with Modified Slots and Slits for RFID Reader

The paper discusses a new design of RFID reader antenna. The proposed antenna is operating in UHF Band (902-928 MHz), which is one of the bands used for RFID applications. Various techniques are used for enhancing the antenna parameters, to achieve compact size, increase the bandwidth and ensure circular polarization. Matching is achieved by choosing the appropriate point for feeding instead of using a reactive matching circuit. Increasing the axial ratio bandwidth to maintain circular polarization transmission and reception is done by using different slot sizes and positions, alongside slits. These slots and slits on the patch lead to the increase of the 10 dB impedance bandwidth to cover the whole bandwidth required for RFID applications. The slits also reduce the antenna size to around 87% of the conventional patch. In order to add another benefit to the design, FR4 is used as the dielectric substrate to decrease the cost. However, this means the size can be further reduced using a substrate with higher permittivity. The proposed design and parameters are simulated and optimized using the full wave simulation software package IE3D, which is based on the method of moments (MOM), which is ideal for planar structures. The design is fabricated using photo-lithographic technique. The reflection coefficient Sit is measured from the feeding port using Rhode and Shwartz ZVL Network Analyzer and the results obtained are compared with the simulated ones. Good agreement is found between simulated and measured results. The simulated radiation pattern, gain and axial ratio bandwidth are obtained and plotted.