Tracking of metallic targets using a retro-reflective array at 26 GHz

This paper presents a design concept to aid in the detection and tracking of objects in a cluttered environment. The goal is to uniquely identify large, relatively cylindrical metallic objects in a warehouse setting. In addition to the challenge of determining the object's precise location, it is also desirable to uniquely identify each cylinder. The application is similar to RFID but differs in that much longer range of operation is needed and operation on metallic objects is required. Target tracking can generally be accomplished with the use of retro-reflectors which are able to return an incident signal back in the same direction with an RCS that is independent of angle of arrival for a large range of incidence angles. In free space applications corner reflectors adequately accomplish this task. In a cluttered environment, target tracking may be accomplished by modulating the backscatter. Corner reflectors' purely passive nature does not allow for external modulation and, as such, they cannot be employed in situations where range gating alone is insufficient for target identification. The current application requires the use of a planar retro-reflective structure which is capable of providing large RCS, signal modulation, and can operate on metallic surfaces. To achieve small dimensions, a RF tag with large RCS operation in the frequency range from 25.5–26.5 GHz is proposed. A particular planar patch antenna retro-reflective array is used. The design of the retro-reflective array itself is discussed in a separate conference submission. Herein, the incorporation of modulation into the RF tag and system level performance are discussed.