Browsing by Author "Mitra, Dipankar"

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Transformation Electromagnetics/Optics for Designing and Scanning Antenna Arrays
(North Dakota State University, 2021) Mitra, Dipankar
Recent developments in engineered electromagnetic materials, also known as metamaterials paved the way for new design approaches of unique and incomprehensible electromagnetic devices and structures using electromagnetic properties which are usually not available in nature. By taking advantage of Maxwell’s equation’s “form-invariance” under coordinate transformations, lately, a coordinate transformation-based approach was introduced to manipulate electromagnetic waves at will, which resulted in a non-homogeneous, anisotropic transformation media dictated by the coordinate transformation. This design approach is known as “transformation electromagnetics/optics (TE/TO)” and has steered many unconventional and seemingly-impossible unique electromagnetic devices such as, the electromagnetic invisibility cloak. The concepts of TE/TO can be extended to a region containing electromagnetic sources, which is known as source transformations. This research focused on the understanding of the theoretical and mathematical foundation of the “transformation electromagnetics/optics” and based on the understanding of the TE/TO concepts, a phased array antenna with new elements where antenna performance is a function of structural and mechanical constraints is proposed using source transformations, where each antenna element is “pinwheel” shaped antenna element transformed from a dipole element in free-space using appropriate coordinate transformations. The transformed materials are derived and through numerical simulations the radiation properties of the proposed array are demonstrated. It is anticipated that the proposed complex-geometry array will have great potential for future applications in structurally integrated and conformal arrays for wireless communications, radars, and sensing. Additionally, the TE/TO technique is employed to design a TO-based beam-steerer which enables beam-scanning with a single antenna element and an antenna array without using phase control circuits. The proposed beam-steerer is a TE/TO-based non-homogeneous, anisotropic material shell theoretically computed using coordinate transformations. Through full-wave simulations the beam-scanning performances of the TO-based beam-rotator was demonstrated and validated. Since the practical metamaterial implementation involves losses, numerical simulations are performed incorporating losses to the derived material parameters. While currently, numerical verifications are provided, in practice, these TO-approaches will require actively tunable material parameters. Significant advancements have been made by the material scientists to design tunable materials using different approaches, which could enable the implementation of the TO-based approach practically.
A Variable High Gain and High Dynamics Range CMOS Phase Shifter for Phased Array Antenna Applications
(North Dakota State University, 2016) Mitra, Dipankar
Phase shifters can adjust phases electronically and hence is very popular for phased array antenna applications where radiation angle can be scanned electronically avoiding bulky mechanical rotation arrangement. In this research a variable gain phase shifter was investigated, capable of controlling precisely both phase and gain simultaneously. The phase shifter was fabricated using 0.18um CMOS process and the measured results showed continuous phase shift of 3030 with 9-dB variable gain at 3.5 GHz. Based on the measured results, a modified phase shifter was proposed and designed which can achieve continuous phase rotation of 3600 with small 22.50 steps, a low RMS phase error of 20 providing high resolution, a very high conversion gain of 14.2 dB with dynamic gain control range of 20 dB. These performances will create a potential future for smart communication radar applications where both beamforming and nulling can be achieved.