A 2.45 GHz digital beam-forming antenna for RFID reader

Spatial filtering using adaptive or smart antennas has emerged as a promising technique to improve the performance of cellular mobile systems. Due to the digital nature of the control of spatial filtering a quantization error is readily present. This is due to the fact that weights and phase information is provided with the aid of finite wordlength processors. This paper presents the development of a five-element digital beam-forming antenna for RFID (radio frequency identification) reader operating on the 2.4 GHz ISM-band. The paper presents a detailed description of the operation of beam-form control including the analysis of 4-bit phase shifters. In addition, the result shows that the quantization error, even if it small, can degrade the pattern so dramatically making it unacceptable. However, we show that with as low number of control bits as four the desired radiation characteristics can be achieved.