Effect of antenna mutual coupling on the UHF passive RFID tag detection

In this paper we experimentally and numerically investigate how the antenna spacing, load condition, antenna orientation, and antenna arrangement of closely spaced tags affect the tag reception and backscattering. We found that the induced terminal voltage and the backscattered field will be greatly reduced when the antenna separation is smaller than 0.3 wavelength and when the other antennas are in short or in load condition. We also found that for closely-spaced tag antennas the terminal voltage at the center antenna is much smaller than that at the side antennas. The reduction in the induced terminal voltage and backscattering will degrade the RFID detection performance and the detection range.