Complementary RFID tag antennas

This thesis is mainly concerned with the investigation of a systematic approach to selecting tag antennas whose electromagnetic properties are compatible with the platforms on which they are supported and the immediate environment in which they are to be operated. The work is divided into three parts. The first two explore the design and optimisation of Radio Frequency Identification (RFID) tag antennas: firstly, in this section, behaviour of an electric dipole is explored. Secondly, a novel dual band Slot Patch Antenna (SPA) antenna is designed and developed, which employs various resonant slots to perturb the tuning and impedance of a conventional slotline. The third investigates its operation within a roll cage.

Complementary dipole and Slot Patch Antennas (SPA) are investigated to obtain a range of options on antenna configurations that, at certain selected frequency bands, give optimum interaction with the antenna support material. This requires that the regions of Perfect Electric Conductor (PEC) and free space dielectric substrate in both antennas be interchanged. The antennas are truncated of the otherwise infinite perfect electric conductor and dielectric substrate.

The radar cross sections (RCS) are predicted under various load conditions and orientations when the models are illuminated with plane wave. The convergence of this method has been found to depend on the load conditions and the substrate thickness and permittivity. The RCS at boresight is found to depend on the radiating elements. The effects of various possible mounting platforms are predicted.

The feasibility of reading tags through wire meshes such as those on a roll cage is investigated. The cages, of various mesh sizes, exhibit transmission responses characterised by frequency spacing of approximately half the first resonant frequency. The insertion loss is found to decrease with increasing mesh size. Also, the standing waves inside the cage exhibit nulls whose voltage standing wave ratio (v.s.w.r.) decreases with increasing mesh sizes. The distance, or range, over which the tag surveillance operates, is approximated in proportion to the amplitude of the standing wave at the position of the tag with peaks and nulls occurring at every half wavelength. The effects on the read range of either electromagnetic absorber or scatterer packing the space with the roll cage are also investigated.