Radio Link Budgets for 915 Mhz Rfid Antennas Placed on Various Objects

Passive radio frequency (RF) tags in the UHF and microwave bands have recently drawn considerable attention with their great potential for use in inventory management, parcel and postal tracking, as remote sensors, and in a host of other radio frequency identification (RFID) applications [1, 2, 3]. However, much more basic research is needed to increase the range and reliability of a passive RF tag’s power and communication link, particularly when the RF tag is placed onto a lossy dielectric object or a metallic surface [4]. This paper presents the results of a radio assay, a series of tests for measuring the excess link loss of an RF tag antenna when placed on a variety of common materials. Using radio assay measurements for thin, flexible 915 MHz antennas, the results document the far-field pattern and gain change as the RF tag antenna is attached to cardboard, wood, acrylic, de-ionized water, ethylene glycol, ground beef, and an aluminum slab. It is shown that more than 18 dB of excess loss on the backscatter link is added when RF tag antennas are placed onto lossy and metallic surfaces.