Matching Items (11)

158760-Thumbnail Image.png

Physical Optics Modeling of AMC Checkerboard Surfaces for RCS-Reduction and Low Backscattering Retrodirective Array

Description

Artificial magnetic conductor (AMC) surfaces have the unique electromagnetic property that the phase of the reflected fields imitate those of perfect magnetic conductors (PMCs). When a perfect electric conductor

Artificial magnetic conductor (AMC) surfaces have the unique electromagnetic property that the phase of the reflected fields imitate those of perfect magnetic conductors (PMCs). When a perfect electric conductor (PEC) and an AMC surface are placed on the same plane and illuminated by a plane wave, destructive interference occurs between the fields (due to 180 degrees phase difference between the reflected fields of each surface).

In this dissertation, a design procedure is introduced where a refined algorithm is developed and employed on single-band AMCs leading to a 10-dB RCS-reduction bandwidth of 80%. The AMC circuit model is judiciously utilized to reduce the substrate thickness while simultaneously increasing the bandwidth of the AMC surfaces. Furthermore, dual-band AMC surfaces are synthesized and utilized in combination with single-band AMC surfaces to extend the 10-dB RCS-reduction bandwidth from 80% to about 99%. Employing the proposed design procedure, a 99% bandwidth of 10-dB RCS-reduction bandwidth is achieved while reducing the thickness of the substrate by 20%.

The second topic of this dissertation aims at analytically modeling the scattering of planar checkerboard surfaces. The high-frequency asymptotic method, Physical Optics (PO), is utilized to analyze the scattering characteristics of complex structures since the PO is computationally efficient and provides intuitive physical insight. Closed-form formulations developed using PO are used to predict the scattering patterns of checkerboard planar surfaces. The PO-based data compare well, along and near specular directions, with simulations by the full-wave Finite Element Method (FEM).

Finally, a Van Atta retrodirective reflector with low backscattering is designed and developed using a microstrip antenna array. Conventional retrodirective reflectors are sensitive to interference by the fields scattered by the antenna structure. By using a virtual feeding network, structural mode scattering is identified and canceled using AMC technology.

Contributors

Agent

Created

Date Created
  • 2020

158751-Thumbnail Image.png

Metasurface-Based Techniques for Broadband Radar Cross-Section Reduction of Complex Structures

Description

Within the past two decades, metasurfaces, with their unique ability to tailor the wavefront, have attracted scientific attention. Along with many other research areas, RADAR cross-section (RCS)-reduction techniques have also

Within the past two decades, metasurfaces, with their unique ability to tailor the wavefront, have attracted scientific attention. Along with many other research areas, RADAR cross-section (RCS)-reduction techniques have also benefited from metasurface technology.

In this dissertation, a novel technique to synthesize the RCS-reduction metasurfaces is presented. This technique unifies the two most widely studied and two well-established modern RCS-reduction methods: checkerboard RCS-reduction andgradient-index RCS-reduction. It also overcomes the limitations associated with these RCS-reduction methods. It synthesizes the RCS-reduction metasurfaces, which can be juxtaposed with almost any existing metasurface, to reduce its RCS. The proposed technique is fundamentally based on scattering cancellation. Finally, an example of the RCS-reduction metasurface has been synthesized and introduced to reduce the RCS of an existing high-gain metasurface ground plane.

After that, various ways of obtaining ultrabroadband RCS-reduction using the same technique are proposed, which overcome the fundamental limitation of the conventional checkerboard metasurfaces, where the reflection phase difference of (180+-37) degrees is required to achieve 10-dB RCS reduction. First, the guideline on how to select Artificial Magnetic Conductors (AMCs) is explained with an example of a blended checkerboard architecture where a 10-dB RCS reduction is observed over 83% of the bandwidth. Further, by modifying the architecture of the blended checkerboard metasurface, the 10-dB RCS reduction bandwidth increased to 91% fractional bandwidth. All the proposed architectures are validated using measured data for fabricated prototypes. Critical steps for designing the ultrabroadband RCS reduction checkerboard surface are summarized.

Finally, a broadband technique to reduce the RCS of complex targets is presented. By using the proposed technique, the problem of reducing the RCS contribution from such multiple-bounces simplifies to identifying and implementing a set of orthogonal functions. Robust guidelines for avoiding grating lobes are provided using array theory. The 90 degree dihedral corner is used to verify the proposed technique. Measurements are reported for a fabricated prototype, where a 70% RCS-reduction bandwidth is observed. To generalize the method, a 45 degree dihedral corner, with a quadruple-bounce mechanism, is considered. Generalized guidelines are summarized and applied to reduce the RCS of complex targets using the proposed method.

Contributors

Agent

Created

Date Created
  • 2020

158105-Thumbnail Image.png

Impedance Modulated Metasurface Antennas

Description

Impedance-modulated metasurfaces are compact artificially-engineered surfaces whose surface-impedance profile is modulated with a periodic function. These metasurfaces function as leaky-wave antennas (LWAs) that are capable of achieving high gains and

Impedance-modulated metasurfaces are compact artificially-engineered surfaces whose surface-impedance profile is modulated with a periodic function. These metasurfaces function as leaky-wave antennas (LWAs) that are capable of achieving high gains and narrow beamwidths with thin and light-weight structures. The surface-impedance modulation function for the desired radiation characteristics can be obtained using the holographic principle, whose application in antennas has been investigated extensively.

On account of their radiation and physical characteristics, modulated metasurfaces can be employed in automotive radar, 5G, and imaging applications. Automotive radar applications might require the antennas to be flush-mounted on the vehicular bodies that can be curved. Hence, it is necessary to analyze and design conformal metasurface antennas. The surface-impedance modulation function is derived for cylindrically-curved metasurfaces, where the impedance modulation is along the cylinder axis. These metasurface antennas are referred to as axially-modulated cylindrical metasurface LWAs (AMCLWAs). The effect of curvature is modeled, the radiation characteristics are predicted analytically, and they are validated by simulations and measurements.

Communication-based applications, like 5G and 6G, require the generation of multiple beams with polarization diversity, which can be achieved using a class of impedance-modulated metasurfaces referred to as polarization-diverse holographic metasurfaces (PDHMs). PDHMs can form, one at a time, a pencil beam in the desired direction with horizontal polarization, vertical polarization, left-hand circular polarization (LHCP), or right-hand circular polarization (RHCP). These metasurface antennas are analyzed, designed, measured, and improved to include the ability to frequency scan.

In automotive radar and other imaging applications, the performance of metasurface antennas can be impacted by the formation of standing waves due to multiple reflections between the antenna and the target. The monostatic RCS of the metasurface antenna is reduced by modulating its surface impedance with a square wave, to avert multiple reflections. These square-wave-modulated metasurfaces are referred to as checkerboard metasurface LWAs, whose radiation and scattering characteristics, for normal incidence parallel polarization, are analyzed and measured.

Contributors

Agent

Created

Date Created
  • 2020

150815-Thumbnail Image.png

Analysis, simulation and measurements of CBS antennas loaded with non-uniformly biased ferrite material

Description

When ferrite materials are used in antenna designs, they introduce some interesting and unique performance characteristics. One of the attractive features, for example, is the ability to reconfigure the center

When ferrite materials are used in antenna designs, they introduce some interesting and unique performance characteristics. One of the attractive features, for example, is the ability to reconfigure the center frequency of the antenna. In addition, ferrite materials also introduce a number of challenges in the modeling and simulation of such antennas. In order for the ferrite material to be useful in an antenna design, it usually is subjected to an external magnetic field. This field induces the internal magnetic field inside the ferrite material. The internal field plays a pivotal role in the radiation characteristics of the antenna. Thus, from the numerical point of view, accurate computation of this field is critical to the overall accuracy of the analysis. Usually the internal field is non-uniform and its computation is often a rather complex and non-trivial task. Therefore, to facilitate the modeling, simplifying assumptions, which introduce some kind of averaging, are often made. In this study, ferrite-loaded cavity-backed slot antennas are used to demonstrate that averaging procedures can lead to very unsatisfactory results. For instance, it is common practice to assume that the external field is uniform by averaging its distribution. One of the pivotal points in this study is the demonstration that the external magnetic field plays a very significant role and should be included in the modeling without averaging, if the accurate results are to be attained. Results presented in this study clearly support this argument. A procedure which avoids such averaging is presented and verified by comparing simulations with measurements. In contrast to the previous formulations, the modeling methodology developed in this dissertation leads to accurate results which compare very well with measurements for both uniform and non-uniform field distributions. The utility of this methodology is especially evident for the case when the magnetic field is severely non-uniform.

Contributors

Agent

Created

Date Created
  • 2012

155883-Thumbnail Image.png

Flexible, Reconfigurable and Wearable Antennas Integrated with Artificial Magnetic Conducting Surfaces

Description

Flexibility, reconfigurability and wearability technologies for antenna designs are presented, investigated and merged in this work. Prior to the design of these radiating elements, a study is conducted on several

Flexibility, reconfigurability and wearability technologies for antenna designs are presented, investigated and merged in this work. Prior to the design of these radiating elements, a study is conducted on several flexible substrates and how to fabricate flexible devices. Furthermore, the integration of active devices into the flexible substrates is also investigated. A new approach of designing inkjet-printed flexible reconfigurable antennas, based on the concept of printed slot elements, is proposed. An alternate technique to reconfigure the folded slot antenna is also reported. The proposed radiator works for both Wireless Local Area Network (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX) applications. The flexible reconfigurable antenna is also redesigned to resonate at both (2.4/5.2 GHz) for WLAN devices and its Multiple-Input Multiple-Output (MIMO) configuration is reported. Two orthogonal elements are used to form the MIMO antenna system for better isolation.

The wearability of the proposed flexible reconfigurable radiator is also discussed. Since wearable antennas operate close to the human body, which is considered as a lossy tissue, an isolation between the radiating elements and human body is required to improve the radiation characteristics and to reduce the Specific Absorption Rate (SAR). The proposed antenna is redesigned on an Artificial Magnetic Conductor (AMC) surface that also functions as a ground plane to isolate the radiator from the human body. To examine its performance as a body-worn device, it is measured at different positions on the human body. Furthermore, simulations show that the SAR level is reduced when using the AMC surface. The proposed wearable antenna works for both Wireless Body Area Network (WBAN) and WiMAX body-worn wireless devices.

Electromagnetic bandgap (EBG) structures are used to suppress surface wave propagation in printed antennas. However, due to the presence of vias, not all of them can be utilized in flexible radiators. Thus, a Perforated High Impedance Surface (PHIS) is proposed which suppresses the surface waves without the need of vias, and it also serves as a ground plane for flexible antennas. The surface wave suppression and the antenna applications of the proposed PHIS surface are discussed.

Contributors

Agent

Created

Date Created
  • 2017

157540-Thumbnail Image.png

A double-sided planar transmission medium design for ultra-low loss planar orthomode transducers

Description

Microwave circuits are an essential part of technology in the modern day. Everything from cell phone communications, television and radio reception, medical imaging, and radar surveillance depend on microwave circuitry.

Microwave circuits are an essential part of technology in the modern day. Everything from cell phone communications, television and radio reception, medical imaging, and radar surveillance depend on microwave circuitry. Constant efforts are being made to introduce new methods of implementing more efficient microwave circuitry while maintaining well known fabrication methods. These improvements typically focus on lower loss, smaller size, and higher operating frequencies [1-6]. This thesis will focus on the specific application of a planar orthomode transducer (OMT) in Home Direct Broadcast (DBS) Systems used in residential satellite receivers. The need for low-loss circuitry becomes increasingly important in the realm of satellite reception, as the carrier to noise levels at the receiver can be as low as 10dB [7]. Interference and loss of signal integrity can occur very easily if the receiving network is not properly designed.

This thesis will investigate the design of a planar transmission media that produces ultra-low losses when compared to more conventional planar transmission media. This design, which is called Double Sided Suspended Stripline (DSSL), utilizes air as its primary propagation medium. The design will be similar to standard suspended stripline in geometry, but has signal traces on the top and bottom of the substrate. The traces are connected using plated through-hole vias. This geometry is hugely beneficial because it virtually eliminates one of the major loss mechanisms in classical microwave structures: dielectric loss. This thesis will focus mainly on empirically derived equations and performance metrics obtained through rigorous simulation.

Contributors

Agent

Created

Date Created
  • 2019

156222-Thumbnail Image.png

Novel Multicarrier Memory Channel Architecture Using Microwave Interconnects: Alleviating the Memory Wall

Description

The increase in computing power has simultaneously increased the demand for input/output (I/O) bandwidth. Unfortunately, the speed of I/O and memory interconnects have not kept pace. Thus, processor-based systems are

The increase in computing power has simultaneously increased the demand for input/output (I/O) bandwidth. Unfortunately, the speed of I/O and memory interconnects have not kept pace. Thus, processor-based systems are I/O and interconnect limited. The memory aggregated bandwidth is not scaling fast enough to keep up with increasing bandwidth demands. The term "memory wall" has been coined to describe this phenomenon.

A new memory bus concept that has the potential to push double data rate (DDR) memory speed to 30 Gbit/s is presented. We propose to map the conventional DDR bus to a microwave link using a multicarrier frequency division multiplexing scheme. The memory bus is formed using a microwave signal carried within a waveguide. We call this approach multicarrier memory channel architecture (MCMCA). In MCMCA, each memory signal is modulated onto an RF carrier using 64-QAM format or higher. The carriers are then routed using substrate integrated waveguide (SIW) interconnects. At the receiver, the memory signals are demodulated and then delivered to SDRAM devices. We pioneered the usage of SIW as memory channel interconnects and demonstrated that it alleviates the memory bandwidth bottleneck. We demonstrated SIW performance superiority over conventional transmission line in immunity to cross-talk and electromagnetic interference. We developed a methodology based on design of experiment (DOE) and response surface method techniques that optimizes the design of SIW interconnects and minimizes its performance fluctuations under material and manufacturing variations. Along with using SIW, we implemented a multicarrier architecture which enabled the aggregated DDR bandwidth to reach 30 Gbit/s. We developed an end-to-end system model in Simulink and demonstrated the MCMCA performance for ultra-high throughput memory channel.

Experimental characterization of the new channel shows that by using judicious frequency division multiplexing, as few as one SIW interconnect is sufficient to transmit the 64 DDR bits. Overall aggregated bus data rate achieves 240 GBytes/s data transfer with EVM not exceeding 2.26% and phase error of 1.07 degree or less.

Contributors

Agent

Created

Date Created
  • 2018

155120-Thumbnail Image.png

Radar cross section reduction using electromagnetic band-gap checkerboard surfaces

Description

Electromagnetic band-gap (EBG) structures have noteworthy electromagnetic characteristics that include their phase variations with frequency. When combining perfect electric conductor (PEC) and EBG structures on the same ground plane, the

Electromagnetic band-gap (EBG) structures have noteworthy electromagnetic characteristics that include their phase variations with frequency. When combining perfect electric conductor (PEC) and EBG structures on the same ground plane, the scattering fields of the ground plane are altered because of the scattering properties of EBG structures. The scattering fields are cancelled along the principal planes because PEC and EBG structures are anti-phase at the resonant frequency. To make the scattered fields symmetrical under plane wave incidence, a square checkerboard surface is designed to form constructive and destructive interference scattering patterns to reduce the intensity of the scattered fields toward the observer; thus reducing the radar cross section (RCS). To increase the 10-dB RCS reduction (compared to a PEC surface) bandwidth, checkerboard surfaces of two different EBG structures on the same ground plane are designed. Thus, significant RCS reduction over a wider frequency bandwidth of about 63% is achieved.

Another design is a hexagonal checkerboard surface that achieves the same RCS reduction bandwidth because it combines the same EBG designs. The hexagonal checkerboard design further reduce the RCS than square checkerboard designs because the reflected energy is re-directed toward six directions and a null remains in the normal direction.

A dual frequency band checkerboard surface with 10-dB RCS reduction bandwidths of 61% and 24% is realized by utilizing two dual-band EBG structures, while the surfaces maintain scattering in four quadrants. The first RCS reduction bandwidth of the dual band is basically the same as in the square checkerboard design; however, the present surface exhibits a second frequency band of 10-dB RCS reduction.

Finally, cylindrically curved checkerboard surfaces are designed and examined for three different radii of curvature. Both narrow and wide band curved checkerboard surfaces are evaluated under normal incidence for both horizontal and vertical polarizations. Simulated bistatic RCS patterns of the cylindrical checkerboard surfaces are presented.

For all designs, bistatic and monostatic RCS of each checkerboard surface design are compared to that of the corresponding PEC surface. The monostatic simulations are also compared with measurements as a function of frequency and polarization. A very good agreement has been attained throughout.

Contributors

Agent

Created

Date Created
  • 2016

152830-Thumbnail Image.png

Modelings, simulations, measurements and comparisons of monopole-type blade antennas

Description

Two commercial blade antennas for aircraft applications are investigated. The computed results are compared with measurements performed in the ASU ElectroMagnetic Anechoic Chamber (EMAC). The antennas are modeled as mounted

Two commercial blade antennas for aircraft applications are investigated. The computed results are compared with measurements performed in the ASU ElectroMagnetic Anechoic Chamber (EMAC). The antennas are modeled as mounted on a 13-inch diameter circular ground plane, which corresponds to that of the measurements. Two electromagnetic modeling codes are used in this project to model the antennas and predict their radiation and impedance characteristics: FEKO and WIPL-D Pro. A useful tool of WIPL-D Pro, referred to as WIPL-D Pro CAD, has proven to be convenient for modeling complex geometries. The classical wire monopole was also modeled using high-frequency methods, GO and GTD/UTD, mounted on both a rectangular and a circular ground plane. A good agreement between the patterns of this model and FEKO has been obtained. The final versions of the solvers used in this work are FEKO (Suit 6.2), WIPL-D Pro v11 and WIPL-D Pro CAD 2013. Features of the simulation solvers are presented and compared. Simulation results of FEKO and WIPL-D Pro have good agreements with the measurements for radiation and impedance characteristics. WIPL-D Pro has a much higher computational efficiency than FEKO.

Contributors

Agent

Created

Date Created
  • 2014

151908-Thumbnail Image.png

Gain and bandwidth enhancement of ferrite-loaded CBS antenna using material shaping and positioning

Description

Loading a cavity-backed slot (CBS) antenna with ferrite material and applying a biasing static magnetic field can be used to control its resonant frequency. Such a mechanism results in a

Loading a cavity-backed slot (CBS) antenna with ferrite material and applying a biasing static magnetic field can be used to control its resonant frequency. Such a mechanism results in a frequency reconfigurable antenna. However, placing a lossy ferrite material inside the cavity can reduce the gain or negatively impact the impedance bandwidth. This thesis develops guidelines, based on a non-uniform applied magnetic field and non-uniform magnetic field internal to the ferrite specimen, for the design of ferrite-loaded CBS antennas which enhance their gain and tunable bandwidth by shaping the ferrite specimen and judiciously locating it within the cavity. To achieve these objectives, it is necessary to examine the influence of the shape and relative location of the ferrite material, and also the proximity of the ferrite specimen from the probe on the DC magnetic field and RF electric field distributions inside the cavity. The geometry of the probe and its impacts on figures-of-merit of the antenna is of interest as well. Two common cavity backed-slot antennas (rectangular and circular cross-section) were designed, and corresponding simulations and measurements were performed and compared. The cavities were mounted on 30 cm $\times$ 30 cm perfect electric conductor (PEC) ground planes and partially loaded with ferrite material. The ferrites were biased with an external magnetic field produced by either an electromagnet or permanent magnets. Simulations were performed using FEM-based commercial software, Ansys' Maxwell 3D and HFSS. Maxwell 3D is utilized to model the non-uniform DC applied magnetic field and non-uniform magnetic field internal to the ferrite specimen; HFSS however, is used to simulate and obtain the RF characteristics of the antenna. To validate the simulations they were compared with measurements performed in ASU's EM Anechoic Chamber. After many examinations using simulations and measurements, some optimal designs guidelines with respect to the gain, return loss and tunable impedance bandwidth, were obtained and recommended for ferrite-loaded CBS antennas.

Contributors

Agent

Created

Date Created
  • 2013