Compact Folded-Patch With Orthogonal Tuning Slots for On-Metal Tag Design

A highly miniaturized semi-flexible tag antenna, with dimensions 23 mm × 7.5 mm × 3.2 mm (0.0702λ × 0.0229λ × 0.0098λ), is designed for tagging small metallic objects. It consists of three patches and two foams which are tactfully folded to form a very compact three-layer structure. Multiple slots are etched on the top and middle patches for increasing the current paths, where the slots on the top patch are made orthogonal to those in the middle one so that the currents on the two patches do not affect each other. This enables the currents on the two patches to be tuned independently without affecting the tag performances. Despite its small size, the proposed tag is able to generate sufficient antenna resistance to match the impedance of the microchip. As a result, it is able to achieve a good conjugate match with a power transmission coefficient of -.1. The tag has a very compact size of -.λ/14. It can be read from a distance of 5.0 m when tested on a metal surface with reference to a transmitted power of 4 W effective isotropic radiated power. To the best of our knowledge, as compared to most of the contemporary tags, this is the best performing tag antenna in terms of size-ratio (read distance/tag volume).