Matching Items (11)

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Analysis, design, simulation, and measurements of flexible high impedance surfaces

Description

High Impedance Surfaces (HISs), which have been investigated extensively, have proven to be very efficient ground planes for low profile antenna applications due to their unique reflection phase characteristics. Another

High Impedance Surfaces (HISs), which have been investigated extensively, have proven to be very efficient ground planes for low profile antenna applications due to their unique reflection phase characteristics. Another emerging research field among the microwave and antenna technologies is the design of flexible antennas and microwave circuits to be utilized in conformal applications. The combination of those two research topics gives birth to a third one, namely the design of Conformal or Flexible HISs (FHISs), which is the main subject of this dissertation. The problems associated with the FHISs are twofold: characterization and physical realization. The characterization involves the analysis of scattering properties of FHISs in the presence of plane wave and localized sources. For this purpose, an approximate analytical method is developed to characterize the reflection properties of a cylindrically curved FHIS. The effects of curvature on the reflection phase of the curved FHISs are examined. Furthermore, the effects of different types of currents, specifically the ones inherent to finite sized periodic structures, on the reflection phase characteristics are observed. After the reflection phase characterization of curved HISs, the performance of dipole antennas located in close proximity to a curved HIS are investigated, and the results are compared with the flat case. Different types of resonances that may occur for such a low-profile antenna application are discussed. The effects of curvature on the radiation performance of antennas are examined. Commercially available flexible materials are relatively thin which degrades the bandwidth of HISs. Another practical aspect, which is related to the substrate thickness, is the compactness of the surface. Because of the design limitations of conventional HISs, it is not possible to miniaturize the HIS and increase the bandwidth, simultaneously. To overcome this drawback, a novel HIS is proposed with a periodically perforated ground plane. Copper plated through holes are extremely vulnerable to bending and should be avoided at the bending parts of flexible circuits. Fortunately, if designed properly, the perforations on the ground plane may result in suppression of surface waves. Hence, metallic posts can be eliminated without hindering the surface wave suppression properties of HISs.

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Created

Date Created
  • 2013

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Terahertz Micro-Doppler Radar for Detection and Characterization of Multicopters

Description

The micromotions (e.g. vibration, rotation, etc.,) of a target induce time-varying frequency modulations on the reflected signal, called the micro-Doppler modulations. Micro-Doppler modulations are target specific and may contain information

The micromotions (e.g. vibration, rotation, etc.,) of a target induce time-varying frequency modulations on the reflected signal, called the micro-Doppler modulations. Micro-Doppler modulations are target specific and may contain information needed to detect and characterize the target. Thus, unlike conventional Doppler radars, Fourier transform cannot be used for the analysis of these time dependent frequency modulations. While Doppler radars can detect the presence of a target and deduce if it is approaching or receding from the radar location, they cannot identify the target. Meaning, for a Doppler radar, a small commercial aircraft and a fighter plane when gliding at the same velocity exhibit similar radar signature. However, using a micro-Doppler radar, the time dependent frequency variations caused by the vibrational and rotational micromotions of the two aircrafts can be captured and analyzed to discern between them. Similarly, micro-Doppler signature can be used to distinguish a multicopter from a bird, a quadcopter from a hexacopter or a octacopter, a bus from a car or a truck and even one person from another. In all these scenarios, joint time-frequency transforms must be employed for the analysis of micro-Doppler variations, in order to extract the targets’ features.

Due to ample bandwidth, THz radiation provides richer radar signals than the microwave systems. Thus, a Terahertz (THz) micro-Doppler radar is developed in this work for the detection and characterization of the micro-Doppler signatures of quadcopters. The radar is implemented as a continuous-wave (CW) radar in monostatic configuration and operates at a low-THz frequency of 270 GHz. A linear time-frequency transform, the short-time Fourier transform (STFT) is used for the analysis the micro-Doppler signature. The designed radar has been built and measurements are carried out using a quadcopter to detect the micro-Doppler modulations caused by the rotation of its propellers. The spectrograms are obtained for a quadcopter hovering in front of the radar and analysis methods are developed for characterizing the frequency variations caused by the rotational and vibrational micromotions of the quadcopter. The proposed method can be effective for distinguishing the quadcopters from other flying targets like birds which lack the rotational micromotions.

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Date Created
  • 2018

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Gain and loss factor for conical horns, and impact of ground plane edge diffractions on radiation patterns of uncoated and coated circular aperture antennas

Description

Horn antennas have been used for over a hundred years. They have a wide variety of uses where they are a basic and popular microwave antenna for many practical applications,

Horn antennas have been used for over a hundred years. They have a wide variety of uses where they are a basic and popular microwave antenna for many practical applications, such as feed elements for communication reflector dishes on satellite or point-to-point relay antennas. They are also widely utilized as gain standards for calibration and gain measurement of other antennas.

The gain and loss factor of conical horns are revisited in this dissertation based on

spherical and quadratic aperture phase distributions. The gain is compared with published classical data in an attempt to confirm their validity and accuracy and to determine whether they were derived based on spherical or quadratic aperture phase distributions. In this work, it is demonstrated that the gain of a conical horn antenna obtained by using a spherical phase distribution is in close agreement with published classical data. Moreover, more accurate expressions for the loss factor, to account for amplitude and phase tapers over the horn aperture, are derived. New formulas for the design of optimum gain conical horns, based on the more accurate spherical aperture phase distribution, are derived.

To better understand the impact of edge diffractions on aperture antenna performance, an extensive investigation of the edge diffractions impact is undertaken in this dissertation for commercial aperture antennas. The impact of finite uncoated and coated PEC ground plane edge diffractions on the amplitude patterns in the principal planes of circular apertures is intensively examined. Similarly, aperture edge diffractions of aperture antennas without ground planes are examined. Computational results obtained by the analytical model are compared with experimental and HFSS-simulated results for all cases studied. In addition, the impact of the ground plane size, coating thickness, and relative permittivity of the dielectric layer on the radiation amplitude in the back region has been examined.

This investigation indicates that the edge diffractions do impact the main forward lobe pattern, especially in the E plane. Their most significant contribution appears in far side and back lobes. This work demonstrates that the finite edge contributors must be considered to obtain more accurate amplitude patterns of aperture antennas.

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Created

Date Created
  • 2014

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Thin film transistor control circuitry for MEMS acoustic transducers

Description

ABSTRACT This work seeks to develop a practical solution for short range ultrasonic communications and produce an integrated array of acoustic transmitters on a flexible substrate. This is done using

ABSTRACT This work seeks to develop a practical solution for short range ultrasonic communications and produce an integrated array of acoustic transmitters on a flexible substrate. This is done using flexible thin film transistor (TFT) and micro electromechanical systems (MEMS). The goal is to develop a flexible system capable of communicating in the ultrasonic frequency range at a distance of 10 - 100 meters. This requires a great deal of innovation on the part of the FDC team developing the TFT driving circuitry and the MEMS team adapting the technology for fabrication on a flexible substrate. The technologies required for this research are independently developed. The TFT development is driven primarily by research into flexible displays. The MEMS development is driving by research in biosensors and micro actuators. This project involves the integration of TFT flexible circuit capabilities with MEMS micro actuators in the novel area of flexible acoustic transmitter arrays. This thesis focuses on the design, testing and analysis of the circuit components required for this project.

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Created

Date Created
  • 2012

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Low Frequency Electric Field Imaging

Description

Electric field imaging allows for a low cost, compact, non-invasive, non-ionizing alternative to other methods of imaging. It has many promising industrial applications including security, safely imaging power lines

Electric field imaging allows for a low cost, compact, non-invasive, non-ionizing alternative to other methods of imaging. It has many promising industrial applications including security, safely imaging power lines at construction sites, finding sources of electromagnetic interference, geo-prospecting, and medical imaging. The work presented in this dissertation concerns low frequency electric field imaging: the physics, hardware, and various methods of achieving it.

Electric fields have historically been notoriously difficult to work with due to how intrinsically noisy the data is in electric field sensors. As a first contribution, an in-depth study demonstrates just how prevalent electric field noise is. In field tests, various cables were placed underneath power lines. Despite being shielded, the 60 Hz power line signal readily penetrated several types of cables.

The challenges of high noise levels were largely addressed by connecting the output of an electric field sensor to a lock-in amplifier. Using the more accurate means of collecting electric field data, D-dot sensors were arrayed in a compact grid to resolve electric field images as a second contribution. This imager has successfully captured electric field images of live concealed wires and electromagnetic interference.

An active method was developed as a third contribution. In this method, distortions created by objects when placed in a known electric field are read. This expands the domain of what can be imaged because the object does not need to be a time-varying electric field source. Images of dielectrics (e.g. bodies of water) and DC wires were captured using this new method.

The final contribution uses a collection of one-dimensional electric field images, i.e. projections, to reconstruct a two-dimensional image. This was achieved using algorithms based in computed tomography such as filtered backprojection. An algebraic approach was also used to enforce sparsity regularization with the L1 norm, further improving the quality of some images.

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Date Created
  • 2017

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High-Directive Metasurface Printed Antennas for Low-Profile Applications

Description

Since the advent of High Impedance Surfaces (HISs) and metasurfaces, researchers

have proposed many low profile antenna configurations. HISs possess in-phase reflection, which reinforces the radiation, and enhances the directivity and

Since the advent of High Impedance Surfaces (HISs) and metasurfaces, researchers

have proposed many low profile antenna configurations. HISs possess in-phase reflection, which reinforces the radiation, and enhances the directivity and matching bandwidth of radiating elements. Most of the proposed dipole and loop element designs that have used HISs as a ground plane, have attained a maximum directivity of 8 dBi. While HISs are more attractive ground planes for low profile antennas, these HISs result in a low directivity as compared to PEC ground planes. Various studies have shown that Perfect Electric Conductor (PEC) ground planes are capable of achieving higher directivity, at the expense of matching efficiency, when the spacing

between the radiating element and the PEC ground plane is less than 0.25 lambda. To establish an efficient ground plane for low profile applications, PEC (Perfect Electric Conductor) and PMC (Perfect Magnetic Conductor) ground planes are examined in the vicinity of electric and magnetic radiating elements. The limitation of the two ground planes, in terms of radiation efficiency and the impedance matching, are discussed. Far-field analytical formulations are derived and the results are compared with full-wave EM simulations performed using the High-Frequency Structure Simulator (HFSS). Based on PEC and PMC designs, two engineered ground planes are proposed.

The designed ground planes depend on two metasurface properties; namely in-phase reflection and excitation of surface waves. Two ground plane geometries are considered. The first one is designed for a circular loop radiating element, which utilizes a

circular HIS ring deployed on a circular ground plane. The integration of the loop element with the circular HIS ground plane enhances the maximum directivity up to 10.5 dB with a 13% fractional bandwidth. The second ground plane is designed for a square loop radiating element. Unlike the first design, rectangular HIS patches are utilized to control the excitation of surface waves in the principal planes. The final design operates from 3.8 to 5 GHz (27% fractional bandwidth) with a stable broadside maximum realized gain up to 11.9 dBi. To verify the proposed designs, a prototype was fabricated and measurements were conducted. A good agreement between simulations and measurements was observed. Furthermore, multiple square ring elements are embedded within the periodic patches to form a surface wave planar antenna array. Linear and circular polarizations are proposed and compared to a conventional square ring array. The implementation of periodic patches results in a better matching bandwidth and higher broadside gain compared to a conventional array.

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Created

Date Created
  • 2020

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Output bandwidth limitations of basestation power amplifier design and its implementation using Doherty amplifier

Description

This thesis is a study of Bandwidth limitation of basestation power amplifier and its Doherty application. Fundamentally, bandwidth of a power amplifier (PA) is limited by both its input and

This thesis is a study of Bandwidth limitation of basestation power amplifier and its Doherty application. Fundamentally, bandwidth of a power amplifier (PA) is limited by both its input and output prematch networks and its Doherty architecture, specifically the impedance inverter between the main and auxiliary amplifier. In this study, only the output prematch network and the Doherty architecture follows are being investigated. A new proposed impedance inverter in the Doherty architecture exhibits an extended bandwidth compared to traditional quarterwave line.

Base on the loadline analysis, output impedance of the power amplifier can be represented by a loadline resistor and an output shunt capacitor. Base on this simple model, the maximum allowed bandwidth of the output impedance of the power amplifier can be estimated using the Bode-Fano method. However, since power amplifier is in fact nonlinear, harmonic balance simulation is used to loadpull the device across a broad range of frequencies. Base on the simulated large signal impedance at maximum power, the prematch circuitry can be designed. On a system level, the prematch power amplifier is used in Doherty amplifier. Two different prematch circuitries, T- section and shunt L methods are investigated along with their comparison in the Doherty architecture at both back off power and peak power condition. The last section of the thesis will be incorporating the proposed impedance inverter structure between the main and auxiliary amplifiers.

The simulated results showed the shunt L prematch topology has the least impedance dispersion across frequency. Along with the new impedance inverter structure, the 65% efficiency bandwidth improves by 50% compared to the original impedance inverter structure at back off power level.

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Date Created
  • 2014

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Feasibility demonstration of a massively parallelizable near-field sensor for sub-wavelength defect detection and imaging

Description

To detect and resolve sub-wavelength features at optical frequencies, beyond the diffraction limit, requires sensors that interact with the electromagnetic near-field of those features. Most instruments operating in this modality

To detect and resolve sub-wavelength features at optical frequencies, beyond the diffraction limit, requires sensors that interact with the electromagnetic near-field of those features. Most instruments operating in this modality scan a single detector element across the surface under inspection because the scattered signals from a multiplicity of such elements would end up interfering with each other. However, an alternative massively parallelized configuration, consisting of a remotely interrogating array of dipoles, capable of interrogating multiple adjacent areas of the surface at the same time, was proposed in 2002.

In the present work a remotely interrogating slot antenna inside a 60nm silver slab is designed which increases the signal to noise ratio of the original system. The antenna is tuned to resonance at 600nm range by taking advantage of the plasmon resonance properties of the metal’s negative permittivity and judicious shaping of the slot element. Full-physics simulations show the capability of detecting an 8nm particle using red light illumination. The sensitivity to the λ/78 particle is attained by detecting the change induced on the antenna’s far field signature by the proximate particle, a change that is 15dB greater than the scattering signature of the particle by itself.

To verify the capabilities of this technology in a readily accessible experimental environment, a radiofrequency scale model is designed using a meta-material to mimic the optical properties of silver in the 2GHz to 5GHz range. Various approaches to the replication of the metal’s behavior are explored in a trade-off between fidelity to the metal’s natural plasmon response, desired bandwidth of the demonstration, and

ii

manufacturability of the meta-material. The simulation and experimental results successfully verify the capability of the proposed near-field sensor in sub-wavelength detection and imaging not only as a proof of concept for optical frequencies but also as a potential imaging device for radio frequencies.

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Created

Date Created
  • 2016

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Analysis, design and measurements of flat and curved circularly symmetric high impedance surfaces for curvilinear antenna applications

Description

In this dissertation a new wideband circular HIS is proposed. The circular periodicity made it possible to illuminate the surface with a cylindrical TEMz wave and; a novel technique is

In this dissertation a new wideband circular HIS is proposed. The circular periodicity made it possible to illuminate the surface with a cylindrical TEMz wave and; a novel technique is utilized to make it wideband. Two models are developed to analyze the

reflection characteristics of the proposed HIS.

The circularly symmetric high impedance surface is used as a ground plane for the design of a low-profile loop and spiral radiating elements. It is shown that a HIS with circular periodicity provides a wider operational bandwidth for curvilinear radiating elements such, such as loops and spirals, compared to canonical rectangular HISs.

It is also observed that, with the aid of a circular HIS ground plane the gain of a loop and a spiral increases compared to when a perfect magnetic conductor (PMC) or rectangular HIS is used as a ground plane. The circular HIS was fabricated and the loop and spiral elements were placed individually in close proximity to it.

Also, due to the growing demand for low-radar signature (RCS) antennas for advanced airborne vehicles, curved and flexible HIS ground planes, which meet both the aerodynamic and low RCS requirements, have recently become popular candidates within the antenna and microwave technology. This encouraged us, to propose a spherical HIS where a 2-D curvature is introduced to the previously designed flat HIS.

The major problem associated with spherical HIS is the impact of the curvature on its reflection properties. After characterization of the flat circular HIS, which is addressed in the first part of this dissertation, a spherical curvature is introduced to the flat circular HIS and its impact on the reflection properties was examined when it was illuminated with the same cylindrical TEMz wave. The same technique, as for the flat HIS ground plane, is utilized to make the spherical HIS wideband. A loop and spiral element were placed in the vicinity of the curved HIS and their performanceswere investigated. The HISs were also fabricated and measurements were conducted to verify the simulations. An excellent agreement was observed.

Contributors

Agent

Created

Date Created
  • 2018

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Performance enhancement of space-time adaptive processing for GPS and microstrip antenna design using ferrite rings

Description

Global Positioning System (GPS) is a navigation system widely used in civilian and military application, but its accuracy is highly impacted with consequential fading, and possible loss of communication due

Global Positioning System (GPS) is a navigation system widely used in civilian and military application, but its accuracy is highly impacted with consequential fading, and possible loss of communication due to multipath propagation and high power interferences. This dissertation proposes alternatives to improve the performance of the GPS receivers to obtain a system that can be reliable in critical situations. The basic performance of the GPS receiver consists of receiving the signal with an antenna array, delaying the signal at each antenna element, weighting the delayed replicas, and finally, combining the weighted replicas to estimate the desired signal. Based on these, three modifications are proposed to improve the performance of the system. The first proposed modification is the use of the Least Mean Squares (LMS) algorithm with two variations to decrease the convergence time of the classic LMS while achieving good system stability. The results obtained by the proposed LMS demonstrate that the algorithm can achieve the same stability as the classic LMS using a small step size, and its convergence rate is better than the classic LMS using a large step size. The second proposed modification is to replace the uniform distribution of the time delays (or taps) by an exponential distribution that decreases the bit-error rate (BER) of the system without impacting the computational efficiency of the uniform taps. The results show that, for a BER of 0.001, the system can operate with a 1 to 2 dB lower signal-to-noise ratio (SNR) when an exponential distribution is used rather than a uniform distribution. Finally, the third modification is implemented in the design of the antenna array. In this case, the gain of each microstrip element is enhanced by embedding ferrite rings in the substrate, creating a hybrid substrate. The ferrite rings generates constructive interference between the incident and reflected fields; consequently, the gain of a single microstrip element is enhanced by up to 4 dB. When hybrid substrates are used in microstrip element arrays, a significant enhancement in angle range is achieved for a given reflection coefficient compared to using a conventional substrate.

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Created

Date Created
  • 2013