Electromagnetic inversion strategies for antenna design and characterization
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In this work, we use the electromagnetic inversion (EI) framework to develop/improve algorithms for the purpose of antenna design and characterization. Broadly speaking, antennas are any device, object, or system that can transform energy in the form of guided waves to energy in the form of radiated waves in space. In our increasingly wireless technology landscape, many different types of antennas are being analyzed and developed for a variety of applications. Therefore a flexible design/characterization methodology is required to support our future wireless engineering needs. To this end, we employ an EI methodology that allows the flexibility to develop novel antenna characterization and design algorithms in a variety of applications. In general, electromagnetic inversion enables the determination of an electromagnetic property of interest (e.g., relative permittivity or equivalent current distribution) in an investigation domain by processing some type of electromagnetic data (e.g., complex electric field, phaseless data, or far-field performance criteria) on a separate measurement/desired data domain wherein the investigation and data domains can be arbitrarily shaped; our methodology allows for this flexibility to be utilized. Through the use of this methodology and the electromagnetic surface and volume equivalence principles we develop EI algorithms to contribute to the areas of metasurface design, microwave imaging, and dielectric lens/antenna design. Specifically, (i) we develop and demonstrate a gradient-based EI algorithm that can directly design the circuit admittance profiles of metasurfaces from desired complex or phaseless (magnitude-only) magnetic field data on an external data domain, (ii) we develop and verify inverse scattering algorithms to reconstruct dielectric profiles from phaseless synthetic and experimentally measured data, and finally (iii) we introduce a combined inverse source and scattering technique to tailor electromagnetic fields by designing passive, lossless, and reflectionless dielectric profiles to transform an existing electromagnetic field distribution from a known feed to one that satisfies desired far-field performance criteria such as main beam directions, null locations, and half-power beamwidth.