Combined HF and UHF RFID device

A wearable RFID device is configured with a geometry and materials that allow an HF RFID system and a UHF RFID system to operate in close proximity to a human body and to each other with minimal impact on performance. An RFID device may have a three-dimensional, multi-planar UHF antenna incorporated into a dielectric core with an HF antenna, or a single-plane UHF antenna separated from an HF antenna by a rigid spacer. A conductive metal backplane is disposed adjacent the wearable RFID device to improve antenna performance when disposed in close proximity to an absorbing body, such as a human being.