Design, fabrication, testing, and application of a sub-wavelength microwave lens

Abstract

This thesis presents the design and experimental validation of a photonic band gap (PBG) graded-index lens. PBGs can be used to achieve sub-wavelength focusing, which is not possible with lenses made from conventional dielectric materials. Subwavelength focusing is attractive for a variety of applications, including medicine, optics, and mining. By creating a focal spot smaller than the traditional diffraction-limited size, higher power density can be achieved in the focal spot. Further, subwavelength focusing is useful in imaging applications to view objects smaller than one wavelength. Using metamaterials is a common method for creating lenses that can beat the diffraction limit, and such devices have proven to be very successful. However, metamaterials are ill-suited for high-power microwave (HPM) applications because they can have very high electric fields in the metamaterial elements that can cause breakdown. PBG structures are capable of handling substantially higher power without facing problems with breakdown or arcing. The lens presented in this thesis is an attempt to create a PBG lens capable of sub-wavelength focusing specifically for use with HPM. Testing showed the lens achieved very good sub-wavelength focusing near the design frequency of 2.05 GHz, with focal spot widths between 0.58-0.75 times the traditional diffraction-limited size. The lens is capable of achieving subwavelength focusing over a range of frequencies of roughly 400 MHz, which is a additional advantage over low bandwidth metamaterial lenses. These results demonstrate significant progress in the development of novel electromagnetic materials suitable for high power applications.