Planar Luneburg lens design and characterisation

• Main Author: Xue, X.
• Published: Queen's University Belfast 2008
• Subjects: 621.3841
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492176

In this thesis, the design procedures, implementation methods and performance characteristics for various fan beam planar lens antennas mainly synthesized using Luneburg lens principles are developed with regard to acceptable radiation performance and ease of low cost fabrication. The lenses presented are characterised at 24 GHz for industrial, scientific, and medical (ISM) band (24 - 24.25 GHz) or for wide-band automotive short-range radar systems (21.65 - 26.65 GHz), and at 27 GHz for potential millimetre wave applications. The derivation of the original Luneburg lens equations are illustrated using ray tracing theory. Then the problems associated with conventional discrete 3D spherical LL fabrication are presented and summarised. The realization of the gradient refractive index of a cylindrical Luneburg lens achieved by three novel techniques is reported. These are: (1) use of a combination method of improved artificial refractive index grading in the lens central region together with the application of the transverse resonance method (TRM) in the lens outer region; (2) use photo lithographically etched holes of different sizes into one side of a standard low loss PCB ground plane in order to introduce a local inductive variation which partially neutralizes the intrinsic permittivity of the material in prespecified localized regions of the lens; (3) use a shape contoured fixed dielectric constant disc with no metal plates. Further the design and performance of two planar extended hemi-elliptical polystyrene lens operated at 28.5 GHz are given. This type of lens, though Supplied by The British Library - 'The world's knowledge' homogeneous, has similar characteristics to that of the planar inhomogeneous Luneburg lens. Finally the general theoretical properties of two types of reconfigurable spherically symmetrical lenses are analyzed and their potential summarized for future electronic scanning applications.