Switched-Antenna Low-Frequency (LF) Radio-Frequency Identification (RFID) for Ornithology

Although low-frequency (LF) radio-frequency identification (RFID) is the de facto standard for many ornithological tracking studies, it is hampered by low range (5-10 cm) and the multiple tag collision problem. The simple concept of augmenting existing RFID transceivers with a switched antenna array is explored to overcome these difficulties. Analysis shows that non-ideal behavior of the switch elements can lead to detuning and cross-talk effects that should be considered when designing the LF antennas. An open-source prototype RFID reader with an integrated switch array supporting up to 12 antennas is developed and presented. Controlled laboratory tests indicate good read reliability of an 8-element antenna matrix covering a 37 cm × 37 cm ground area and a 4-element array placed on a bird feeder, but relative tag-antenna orientation must be carefully considered. A four-hour field test with tagged house sparrows indicates detection reliability of 94% and 78% for the 4-element feeder and 8-element mat arrays, respectively.