Electrical & Computer Engineering
https://hdl.handle.net/10365/32557
2023-09-28T10:40:02ZImpedances of a Cubical Quad Antenna
https://hdl.handle.net/10365/33225
Impedances of a Cubical Quad Antenna
Choong, Tsi-lung
Rectangular loop antennas and short electric dipoles
are two of the oldest antennas in existence. In 1888,
twenty years after Maxwell invented his famous Maxwell's equations,
Hertz used these two antennas to prove that
high frequency electric energy sources could radiate electro-
magnetic waves.
The "Cubical Quad" or, simply, "Quad" antenna is a
development of the rectangular loop antenna. It consists
of a pair of square loops, one-quarter wavelength on a
side or one wavelength around the periphery; one loop
being driven and the other used as a parasitic reflector.
The separation between the two is usually of the order of
0.15 to 0.2 wavelength, with the planes of the loops parallel.
While studying the properties of this antenna, it
was discovered that little had been done to develop it
from a theoretical aspect. The purpose of this thesis is
to obtain values of the self and mutual impedances existing
in such an antenna array. The values are obtained from mathematical
analysis and experimental measurements and may be
used in field pattern and gain calculations.
1965-01-01T00:00:00ZA Study of Inverter-Based Resources on Power Grid Operation Under Uncertain Operating Conditions
https://hdl.handle.net/10365/32766
A Study of Inverter-Based Resources on Power Grid Operation Under Uncertain Operating Conditions
Maharjan, Manisha
The electric power grid is undergoing a rapid change predominantly driven by high penetration levels of renewable energy resources (RERs) such as wind and solar. These resources are interfaced with the power grid through power electronic inverters that use control algorithms to define their performance characteristics. As a group, these types of resources are commonly referred to as inverter-based RERs (IB-RERs). While IB-RERs use power electronic controls to change active and reactive power injection, the fast inverter controls, separating the power source from the grid, have changed grid dynamics and posed new challenges to maintaining reliable and safe grid operation. Moreover, the variable nature of IB-RERs generation under uncertain weather conditions further challenge the grid operation under uncertain operating conditions resulting from an imbalance in electricity generation and demand. To effectively manage IB-RERs for providing reliable grid services, this dissertation studies the impact of IB-RERs on grid operation at the transmission- and distribution- levels while considering uncertain operating conditions. More specifically, the probabilistic collocation method is introduced to quantify the uncertainty of renewable generation and load demands on the distribution system operation. Also, the probabilistic collocation method is integrated with grid assessment to assess the grid stiffness under uncertain operating conditions. In addition, the impact of transmission-level disturbances on solar generator operation in distribution systems is investigated by a real-time electromagnetic simulator. The proposed method and analysis results are useful for guiding grid planning and operation to address the emerging issues of integrating the high penetration of IB-RERs into the power grid for reliable grid services.
2022-01-01T00:00:00ZA Study of Conformal Metasurfaces on Passive Beam Steering for Arrays
https://hdl.handle.net/10365/32760
A Study of Conformal Metasurfaces on Passive Beam Steering for Arrays
Ge, Ruisi
Beam-steering has drawn significant interest due to the expansion of network capacity. However, a traditional beam steering system involves active phase shifters and controlling networks which can be complex. This work proposes a passive conformal metasurface design on beam steering. The phase shifting is achieved by changing the curvature of a conformal metasurface. In addition, three conformal prototypes were fabricated and tested using different techniques such as 3D printing. The simulations and test results indicate up to 20° of beam shifting. This study can be extended to higher frequency bands for lower power consumption beam steering systems.
2022-01-01T00:00:00ZTransformation Electromagnetics/Optics for Designing and Scanning Antenna Arrays
https://hdl.handle.net/10365/32741
Transformation Electromagnetics/Optics for Designing and Scanning Antenna Arrays
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.
2021-01-01T00:00:00Z