Design of multiband centimetre wave antennas for an OFDM based RFID system

Abstract

In the era of object marking, radio frequency identification (RFID) has attracted wide attention. RFID is suitable not only for indoor but also for outdoor environment providing long distance object identification facilities. The major components of an RFID system are the RFID reader and the tag with the antenna for wireless data transfer between them. Little research has been done so far to analyze the fading effect for outdoor applications in the context of RFID. This research focuses on the development of an RFID reader antenna for outdoor scenarios. Two multiband patch antennas and an array antenna operating at centimetre band are proposed for an orthogonal frequency division multiplexing (OFDM) based radio-frequency identification (RFID) reader. The first one is a dual band antenna with centre frequencies of 7.30 GHz and 9.50 GHz, while the second one is a triple band antenna centred at 7.75 GHz, 9.70 GHz and 11.90 GHz. Both the patch antennas are designed with equal-width horizontal arms as radiating elements and a microstrip feeding line as the feeder. The simulated radiation efficiency of the multiband patch antennas is above 80% at each resonance frequency. The antennas are moderately small sized with dimensions of 40.30 mm by 35.10 mm. The designed double E-shaped array antenna provides resonance at frequencies of 7.23 GHz, 10 GHz, and, 11.748 GHz with dimensions of 86.584 mm by 35.117 mm. The spacing between the array elements of the proposed array antenna is 12 mm that minimizes grating lobe and mutual coupling between the array elements. The simulated antenna performance metrics such as (gain and directivity) of the designed array antenna at these three different frequencies are (9.81 dB and 10.13 dBi), (8.01 dB and 8.308 dBi) and (8.12 dB and 8.681 dBi) respectively. Simulations with Computer Simulation Technology (CST) Microwave Studio tool indicate that competitive values of different antenna parameters are achieved when compared with centimetre band antennas described in the literature. With the use of MATLAB tool, the bit error rate (BER) performance of the multiband antennas are simulated for outdoor Rayleigh and Rician fading channels. Simulation results for the proposed antennas indicate that for a given number of OFDM subcarriers, the larger the bandwidth of the signals received by the RFID reader, larger the BER degradation.