A novel mobile antenna structure is presented to relay stress and strain data on railroad tracks. The antenna structure is a unique design employing dual probe-fed radiating cavities integrated with a Zigbee IEEE 802.15.4 wireless transceiver. This structure is mounted against the rail web and has a compact design to ensure survivability. A dielectric filler is employed inside each radiating cavity to minimize cavity width and protect the integrity of the mobile antenna structure. Measurements are given for a fabricated prototype to verify simulated performance characteristics.Index Terms-IEEE 802.15.4, ISM 2.4 GHz band, cavity radiator, rail stress, wireless sensor, Zigbee transceiver.