Near-Field Far-Field RFID Reader Antenna for European UHF Band

Radio Frequency Identification (RFID) technology is used for identifying near or distant objects wirelessly. Near-field or far-field operations are performed to detect the tags depending on the objects and applications. UHF near-field reading is preferred for item-level tagging of small, sensitive, and expensive objects. Far-field operation is required to identify the objects farther than half a meter. Both of these reading performances may be required for inventory control of different products in supply chain management system. This thesis report presents two RFID reader antennas each working for both the near field and far field at European UHF band. Loop is used for inductively coupled near-field performance. Segmentation of the loop and insertion of capacitors in between the segments is done to make the loop size electrically small at UHF band so as to provide uniform magnetic field over the loop surface nearby. This enables loop to detect near-field tags effectively. The first antenna implements the loop structure for near-field operation and patch structure for far-field operation. With 8 mm button type near-field tag, read range varies from 0 (at center) to 9 cm (at periphery). The far-field performance is good with realized gain of about 4 dBi and read-range of greater than 5 m with UPM short dipole tag. The antenna works from 864 to 873 MHz with 〖|S〗_11 | at least 10 dB. The second antenna has only the segmented loop. The segments connected to the feed are treated as a dipole for far-field operation. The maximum near-field and far-field read range toward +z-axis with the abovementioned tags are 15 cm and 2.5 m respectively. The near-field performance is more stable than that of the first antenna. Both of these antennas can be used in inventory control purpose requiring both the near-field and far-field operations. However, use of reflector is better for unidirectional radiation pattern in the second design and miniaturized technique of patch design can be implemented for reducing the effect of patch on near-field performance for the first design. /Kir1