A Dual Resonant Microstrip UHF RFID " Cargo" Tag with a CPW Structure for the Feed and Matching Circuit

Abstract

The container is at the core of a highly automated system used for moving goods from one geographic location to another. Containers usually contain pallets; pallets contain cases; cases contain items such as pharmaceuticals and electronic goods. Passive UHF RFID has been widely used for tracking goods at the pallet and case-level. Tracking goods at each level can improve efficiency and cut supply chain costs. A practical application for passive UHF RFID is tracking large metal assets such as cargo containers. In this thesis, we present a high gain, planar microstrip antenna for low-cost RFID tagging of large metal assets. The antenna is dual-resonant and utilizes a coplanar waveguide (CPW) feed structure and matching circuit. The tag can operate over 860-930 MHz, a major portion of the 860-960 MHz frequency spectrum allocated for UHF RFID applications world-wide. We present a rigorous analysis of the antenna along with the circuit model of the antenna which will accurately predict the impedance and performance characteristics. We introduce a polarization model to predict the vertical to horizontal polarization power ratio. The analysis gives insight to the working of the antenna and the feed structure. We present measurement results and data to verify our synthesis of the antenna design. There are still open questions regarding the feed structure of the tag. We model and run several simulation models to provide a better understanding of the feed structure.