Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Glenn S. Smith; Committee Member: Andrew F. Peterson; Committee Member: Gregory D. Durgin; Committee Member: John W. Schultz; Committee Member: Waymond R. Scott, Jr.. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Transmitarrays have been shown to be viable architectures for achieving high-directivity reconfigurable apertures. The existing work on reconfigurable transmitarrays is sparse, with only a few experimental demonstrations of reconfigurable implementations. Furthermore, of the designs that have been presented, different approaches have been proposed, but the advantages and drawbacks of these approaches have not been compared. Therefore, in this thesis we present a systematic study of the different approaches to designing reconfigurable transmitarrays, and present designs following these approaches with experimental validation. First, we investigate the distributed-scatterer approach, which is modeled with layers of identical scattering surfaces. We characterize the beamforming capabilities and then present a Method of Moments technique for analyzing and optimizing designs that follow this approach. Then, we present experimental results for a unit cell with varactor-loaded dipoles following this approach. From these results, we demonstrate that the structure thickness following this approach is problematic for beamforming applications. Taking the coupled-resonator approach, we next present a slot-coupled patch design that is significantly thinner and easier to fabricate than designs that follow the first approach. Implementing this design in a fully reconfigurable transmitarray, we demonstrate two-dimensional beamforming. An advantage of this design is that it can also operate as a reflectarray. Next, following the guided-wave approach, we present a transmitarray design that uses a bridged-T phase shifter and proximity-coupled differentially-fed stacked patches. Not only does this design not require vias, it is has a large fractional bandwidth of 10 percent, which is unprecedented in reconfigurable transmitarrays. Implementing this design in a full transmitarray, we experimentally demonstrate reconfigurable two-dimensional beamsteering, as well as shaped-beam synthesis. The main contributions of this thesis are two-fold. First, we thoroughly and systematically compare the transmitarray approaches, which has not been previously done in literature. Secondly, we experimentally demonstrate a reconfigurable array design that achieves better bandwidth, scan angle range, and beam-shaping capability, than existing designs, with reduced fabrication complexity and physical profile.

Transmitarrays have been shown to be viable architectures for achieving high-directivity reconfigurable apertures. The existing work on reconfigurable transmitarrays is sparse, with only a few experimental demonstrations of reconfigurable implementations. Furthermore, of the designs that have been presented, different approaches have been proposed, but the advantages and drawbacks of these approaches have not been compared. Therefore, in this thesis we present a systematic study of the different approaches to designing reconfigurable transmitarrays, and present designs following these approaches with experimental validation. First, we investigate the distributed-scatterer approach, which is modeled with layers of identical scattering surfaces. We characterize the beamforming capabilities and then present a Method of Moments technique for analyzing and optimizing designs that follow this approach. Then, we present experimental results for a unit cell with varactor-loaded dipoles following this approach. From these results, we demonstrate that the structure thickness following this approach is problematic for beamforming applications. Taking the coupled-resonator approach, we next present a slot-coupled patch design that is significantly thinner and easier to fabricate than designs that follow the first approach. Implementing this design in a fully reconfigurable transmitarray, we demonstrate two-dimensional beamforming. An advantage of this design is that it can also operate as a reflectarray. Next, following the guided-wave approach, we present a transmitarray design that uses a bridged-T phase shifter and proximity-coupled differentially-fed stacked patches. Not only does this design not require vias, it is has a large fractional bandwidth of 10 percent, which is unprecedented in reconfigurable transmitarrays. Implementing this design in a full transmitarray, we experimentally demonstrate reconfigurable two-dimensional beamsteering, as well as shaped-beam synthesis. The main contributions of this thesis are two-fold. First, we thoroughly and systematically compare the transmitarray approaches, which has not been previously done in literature. Secondly, we experimentally demonstrate a reconfigurable array design that achieves better bandwidth, scan angle range, and beam-shaping capability, than existing designs, with reduced fabrication complexity and physical profile.

To increase capacity, lower latency, and boostdata rates, new higher gain antennas that can transmitmillimeter-waves are needed. Dielectric lens antennas arean attractive potential solution. The J1-project investigatedthe permittivity and losses of four 3D printing filamentsin four frequency bands, to better design a hyperboliclens antenna in the Ka-band with a WR-28 StandardGain Horn Antenna acting as a feed. To measure thedielectric filaments, the TRL calibration method wasevaluated in simulation and employed in measurementstogether with the NRW method for permittivity extraction.Shortcomings of these methods near resonant frequencieswere marginally analyzed in simulation, and the results ofthe processed measured permittivities were shown to havesignificant uncertainty in the loss tangent. Nevertheless thedatasheet specified<(r) =3 was shown to have meanrelative permittivity∗r= 3.53−0.13jin the Ka-band.Using the measurement data, a hyperbolic lens antennawas designed and optimized in simulation for the centerfrequency of the Ka-band at 33.25 GHz. The simulatedresults show an aperture efficiency of 36.2% and a gainof 30.4 dBi. / För att öka kapaciteten, sänka för- dröjningen samt höja datahastigheterna så behövs högre förstärkta antenner som kan transmittera millimetervågor. Här är dielektriska linsantenner en attraktiv, potentiell lösning. J1-projektet undersökte permittiviteten och förlusterna av fyra 3D-utskriftsfilament i fyra frekvensband, för att bättre designa en hyperbolisk linsantenn i Ka- bandet för en matande WR-28 “Standard Gain Horn Antenna”. För att kunna mäta de dielektriska filamenten så var TRL-kalibreringsmetoden utvärderad i simulering och nyttjad vid mätning tillsammans med NRW-metoden för att betsämma permittiviteten. Nackdelarna bakom dessa metoder nära resonanta frekvenser var marginellt analyserade i simulering och resultaten av de behandlade, mätta permittiviteterna visade sig ha märkbara osäker- heter i deras förlusttangens. Oavsett så blev medelvärdet på det uppmätta resultatet; av det databladsspecificerade materialet R (∈r) = 3; ∈*r = 3,53 -0,13j i Ka-bandet. Med hjälp av databladsspecifikationerna, så designades samt optimiserades en hyperbolisk linsantenn i simulering för Ka-bandets mittfrekvens på 33,25 GHz. De simulerade resultaten visar på en apertureffektivitet på 36,2% och en förstärkning på 30,4 dBi. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm

This thesis describes an electrically thin surface used for electromagnetic applications in the microwave regime. The surface is free-standing and its primary purpose is to modify the phase distribution, or the phase and amplitude distribution of electromagnetic fields propagating through it: it is called phase shifting surface (PSS) in the first case, and phase and amplitude shifting surface (PASS) in the second case. For practical applications, the surface typically comprises three or four layers of metallic patterns spaced by dielectric layers. The patterns of the metallic layers are designed to locally alter the phase (and amplitude in the case of the PASS) of an incoming wave to a prescribed set of desired values for the outgoing wave. The PSS/PASS takes advantage of the reactive coupling by closely spacing of the metallic layers, which results in a larger phase shift range while keeping the structure significantly thin. The PSS concept is used to design components such as gratings and lens antennas which are presented in this document. The components are designed for an operating frequency of 30 GHz. The PSS phase grating gives high diffraction efficiency, even higher than a dielectric phase grating. Several types of lens antennas are also presented, which show comparable performance to that of a conventional dielectric plano-hyperbolic lens antenna with similar parameters. The PASS concept is used in a beam shaping application in which a flat-topped beam antenna is designed. This work demonstrates the potential for realising thin, lightweight and low-cost antennas at Ka band, in particular for substituting higher-gain antenna technologies such as conventional dielectric shaped lens antennas.

This thesis describes an electrically thin surface used for electromagnetic applications in the microwave regime. The surface is free-standing and its primary purpose is to modify the phase distribution, or the phase and amplitude distribution of electromagnetic fields propagating through it: it is called phase shifting surface (PSS) in the first case, and phase and amplitude shifting surface (PASS) in the second case. For practical applications, the surface typically comprises three or four layers of metallic patterns spaced by dielectric layers. The patterns of the metallic layers are designed to locally alter the phase (and amplitude in the case of the PASS) of an incoming wave to a prescribed set of desired values for the outgoing wave. The PSS/PASS takes advantage of the reactive coupling by closely spacing of the metallic layers, which results in a larger phase shift range while keeping the structure significantly thin. The PSS concept is used to design components such as gratings and lens antennas which are presented in this document. The components are designed for an operating frequency of 30 GHz. The PSS phase grating gives high diffraction efficiency, even higher than a dielectric phase grating. Several types of lens antennas are also presented, which show comparable performance to that of a conventional dielectric plano-hyperbolic lens antenna with similar parameters. The PASS concept is used in a beam shaping application in which a flat-topped beam antenna is designed. This work demonstrates the potential for realising thin, lightweight and low-cost antennas at Ka band, in particular for substituting higher-gain antenna technologies such as conventional dielectric shaped lens antennas.

This thesis describes an electrically thin surface used for electromagnetic applications in the microwave regime. The surface is free-standing and its primary purpose is to modify the phase distribution, or the phase and amplitude distribution of electromagnetic fields propagating through it: it is called phase shifting surface (PSS) in the first case, and phase and amplitude shifting surface (PASS) in the second case. For practical applications, the surface typically comprises three or four layers of metallic patterns spaced by dielectric layers. The patterns of the metallic layers are designed to locally alter the phase (and amplitude in the case of the PASS) of an incoming wave to a prescribed set of desired values for the outgoing wave. The PSS/PASS takes advantage of the reactive coupling by closely spacing of the metallic layers, which results in a larger phase shift range while keeping the structure significantly thin. The PSS concept is used to design components such as gratings and lens antennas which are presented in this document. The components are designed for an operating frequency of 30 GHz. The PSS phase grating gives high diffraction efficiency, even higher than a dielectric phase grating. Several types of lens antennas are also presented, which show comparable performance to that of a conventional dielectric plano-hyperbolic lens antenna with similar parameters. The PASS concept is used in a beam shaping application in which a flat-topped beam antenna is designed. This work demonstrates the potential for realising thin, lightweight and low-cost antennas at Ka band, in particular for substituting higher-gain antenna technologies such as conventional dielectric shaped lens antennas.

This thesis describes an electrically thin surface used for electromagnetic applications in the microwave regime. The surface is free-standing and its primary purpose is to modify the phase distribution, or the phase and amplitude distribution of electromagnetic fields propagating through it: it is called phase shifting surface (PSS) in the first case, and phase and amplitude shifting surface (PASS) in the second case. For practical applications, the surface typically comprises three or four layers of metallic patterns spaced by dielectric layers. The patterns of the metallic layers are designed to locally alter the phase (and amplitude in the case of the PASS) of an incoming wave to a prescribed set of desired values for the outgoing wave. The PSS/PASS takes advantage of the reactive coupling by closely spacing of the metallic layers, which results in a larger phase shift range while keeping the structure significantly thin. The PSS concept is used to design components such as gratings and lens antennas which are presented in this document. The components are designed for an operating frequency of 30 GHz. The PSS phase grating gives high diffraction efficiency, even higher than a dielectric phase grating. Several types of lens antennas are also presented, which show comparable performance to that of a conventional dielectric plano-hyperbolic lens antenna with similar parameters. The PASS concept is used in a beam shaping application in which a flat-topped beam antenna is designed. This work demonstrates the potential for realising thin, lightweight and low-cost antennas at Ka band, in particular for substituting higher-gain antenna technologies such as conventional dielectric shaped lens antennas.

This thesis presents an efficient self-consistent Hybrid Spectral Ray Tracing (HSRT) technique for analysis and design of multi-scale sub-millimeter wave problems, where sub-wavelength features are modeled using rigorous methods, and complex structures with dimensions in the order of tens or even hundreds of wavelengths are modeled by asymptotic methods. Quasi-optical devices are used in imaging arrays for sub-millimeter and terahertz applications, THz time-domain spectroscopy (THz-TDS), high-speed wireless communications, and space applications to couple terahertz radiation from space to a hot electron bolometer. These devices and structures, as physically small they have become, are very large in terms of the wavelength of the driving quasi-optical sources and may have dimension in the tens or even hundreds of wavelengths. Simulation and design optimization of these devices and structures is an extremely challenging electromagnetic problem. The analysis of complex electrically large unbounded wave structures using rigorous methods such as method of moments (MoM), finite element method (FEM), and finite difference time domain (FDTD) method can become almost impossible due to the need for large computational resources. Asymptotic high-frequency techniques are used for analysis of electrically large quasi-optical systems and hybrid methods for solving multi-scale problems. Spectral Ray Tracing (SRT) has a number of unique advantages as a candidate for hybridization. The SRT method has the advantages of Spectral Theory of Diffraction (STD). STD can model reflection, refraction and diffraction of an arbitrary wave incident on the complex structure, which is not the case for diffraction theories such as Geometrical Theory of Diffraction (GTD), Uniform theory of Diffraction (UTD) and Uniform Asymptotic Theory (UAT). By including complex rays, SRT can effectively analyze both near-fields and far-fields accurately with minimal approximations. In this thesis, a novel matrix representation of SRT is presented that uses only one spectral integration per observation point and applied to modeling a hemispherical and hyper-hemispherical lens. The hybridization of SRT with commercially available FEM and MoM software is proposed in this work to solve the complexity of multi-scale analysis. This yields a computationally efficient self-consistent HSRT algorithm. Various arrangements of the Hybrid SRT method such as FEM-SRT, and MoM-SRT, are investigated and validated through comparison of radiation patterns with Ansoft HFSS for the FEM method, FEKO for MoM, Multi-level Fast Multipole Method (MLFMM) and physical optics. For that a bow-tie terahertz antenna backed by hyper-hemispherical silicon lens, an on-chip planar dipole fabricated in SiGe:C BiCMOS technology and attached to a hyper-hemispherical silicon lens and a double-slot antenna backed by silica lens will be used as sample structures to be analyzed using the HSRT. Computational performance (memory requirement, CPU/GPU time) of developed algorithm is compared to other methods in commercially available software. It is shown that the MoM-SRT, in its present implementation, is more accurate than MoM-PO but comparable in speed. However, as shown in this thesis, MoM-SRT can take advantage of parallel processing and GPU. The HSRT algorithm is applied to simulation of on-chip dipole antenna backed by Silicon lens and integrated with a 180-GHz VCO and radiation pattern compared with measurements. The radiation pattern is measured in a quasi-optical configuration using a power detector. In addition, it is shown that the matrix formulation of SRT and HSRT are promising approaches for solving complex electrically large problems with high accuracy. This thesis also expounds on new measurement setup specifically developed for measuring integrated antennas, radiation pattern and gain of the embedded on-chip antenna in the mmW/ terahertz range. In this method, the radiation pattern is first measured in a quasi-optical configuration using a power detector. Subsequently, the radiated power is estimated form the integration over the radiation pattern. Finally, the antenna gain is obtained from the measurement of a two-antenna system.

This thesis presents an efficient self-consistent Hybrid Spectral Ray Tracing (HSRT) technique for analysis and design of multi-scale sub-millimeter wave problems, where sub-wavelength features are modeled using rigorous methods, and complex structures with dimensions in the order of tens or even hundreds of wavelengths are modeled by asymptotic methods. Quasi-optical devices are used in imaging arrays for sub-millimeter and terahertz applications, THz time-domain spectroscopy (THz-TDS), high-speed wireless communications, and space applications to couple terahertz radiation from space to a hot electron bolometer. These devices and structures, as physically small they have become, are very large in terms of the wavelength of the driving quasi-optical sources and may have dimension in the tens or even hundreds of wavelengths. Simulation and design optimization of these devices and structures is an extremely challenging electromagnetic problem. The analysis of complex electrically large unbounded wave structures using rigorous methods such as method of moments (MoM), finite element method (FEM), and finite difference time domain (FDTD) method can become almost impossible due to the need for large computational resources. Asymptotic high-frequency techniques are used for analysis of electrically large quasi-optical systems and hybrid methods for solving multi-scale problems. Spectral Ray Tracing (SRT) has a number of unique advantages as a candidate for hybridization. The SRT method has the advantages of Spectral Theory of Diffraction (STD). STD can model reflection, refraction and diffraction of an arbitrary wave incident on the complex structure, which is not the case for diffraction theories such as Geometrical Theory of Diffraction (GTD), Uniform theory of Diffraction (UTD) and Uniform Asymptotic Theory (UAT). By including complex rays, SRT can effectively analyze both near-fields and far-fields accurately with minimal approximations. In this thesis, a novel matrix representation of SRT is presented that uses only one spectral integration per observation point and applied to modeling a hemispherical and hyper-hemispherical lens. The hybridization of SRT with commercially available FEM and MoM software is proposed in this work to solve the complexity of multi-scale analysis. This yields a computationally efficient self-consistent HSRT algorithm. Various arrangements of the Hybrid SRT method such as FEM-SRT, and MoM-SRT, are investigated and validated through comparison of radiation patterns with Ansoft HFSS for the FEM method, FEKO for MoM, Multi-level Fast Multipole Method (MLFMM) and physical optics. For that a bow-tie terahertz antenna backed by hyper-hemispherical silicon lens, an on-chip planar dipole fabricated in SiGe:C BiCMOS technology and attached to a hyper-hemispherical silicon lens and a double-slot antenna backed by silica lens will be used as sample structures to be analyzed using the HSRT. Computational performance (memory requirement, CPU/GPU time) of developed algorithm is compared to other methods in commercially available software. It is shown that the MoM-SRT, in its present implementation, is more accurate than MoM-PO but comparable in speed. However, as shown in this thesis, MoM-SRT can take advantage of parallel processing and GPU. The HSRT algorithm is applied to simulation of on-chip dipole antenna backed by Silicon lens and integrated with a 180-GHz VCO and radiation pattern compared with measurements. The radiation pattern is measured in a quasi-optical configuration using a power detector. In addition, it is shown that the matrix formulation of SRT and HSRT are promising approaches for solving complex electrically large problems with high accuracy. This thesis also expounds on new measurement setup specifically developed for measuring integrated antennas, radiation pattern and gain of the embedded on-chip antenna in the mmW/ terahertz range. In this method, the radiation pattern is first measured in a quasi-optical configuration using a power detector. Subsequently, the radiated power is estimated form the integration over the radiation pattern. Finally, the antenna gain is obtained from the measurement of a two-antenna system.