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Multifocal Metasurface Lens for Use in Continuous Wave Doppler Radar
Purpose of the Study: A multifocal metasurface lens for continuous wave Doppler radar was designed for the K band to be used 0.5 mm away from a patch array antenna. The metaparticle structure used was a 2 layer dogbone structure for its simplicity and its proven control of the phase of an incident wave. This thesis was an exploration into the feasibility of developing an easily manufacturable and small profile metalens to enhance the gain of a patch array antenna. Procedure: The dogbone metaparticle was used and simulations were run with varying dimensions to gather information on its effect on an incident wave. The phase and magnitude of the output wave were measured with 4 variable dimensions of the dogbone structure. Once an adequate range of phase shifts and magnitudes was found, they were placed in such a way to focus the wave in 1 dimension then in 2 dimensions. The simulations provided promising results in the gain across a large range and the metalenses were then fabricated and tested. Findings: Due to limited resources available in early 2020 the lenses were not tested as thoroughly as they could have been. The test that were conducted gave some insight as well as provided evidence for some of the findings from simulation, such as the effectiveness of a dogbone metalens in one orientation over another. The tests confirmed that a structure of dogbones set up with varying phase shifts vertically interacted with the field much more effectively than if they were set up horizontally. Using Babinet’s principle to alter the phase shift of a metaparticle was shown to be possible, however, it was also shown that this effect does not occur symmetrically. This means that when one side was inverted, the observed phase shift reversed in one direction as expected, but did not in the other. The metaparticles seemed to enhance the gain at a higher frequency than originally intended in one orientation, but when flipped the gain pattern shifted to a lower frequency, suggesting that the phase shifts that the asymmetric metaparticles imposed on the incident wave were slightly off from each other. Conclusions: The difference in the gain pattern shows that a chemically etched lens performed better than a mechanically etched lens of the same pattern. The 2-layer dogbone metaparticle has potential to be used in the application of a metalens, however, the control of the field only occurs in one orientation. This means that it can create a cylindrical phase front well, but not a spherical one.