1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Concept Demonstrator for MeerKAT Operation from 14.5 to 20 GHz

In this thesis, a proof of concept receiver system operating from 14.5 to 20 GHz for the MeerKAT Radio Telescope is presented. MeerKAT is a 64 element telescope antenna array consisting of offset-fed Gregorian reflector antennas with a 13.5 m main reflector and 3.8 m sub-reflector. Currently, the MeerKAT is planned to operate up to 14.5 GHz. However, the reflector surface accuracy of 0.6 mm RMS achieved for the MeerKAT potentially allows it to operate at much higher frequencies. The system design consists of a feed horn antenna and front-end down conversion receiver ready for integration with back-end digital signal processing. The antenna design was carried out using electromagnetic simulation software and system level simulation software was used for the front-end receiver. A single polarization wide-axially corrugated horn with low side-lobes and cross-polarization has been designed for the proof of concept with a predicted aperture efficiency of 60% including surface accuracy loss when illuminating the MeerKAT reflector. The measured results for the antenna show a return loss better than 15 dB in the operational band and boresight gain of 12 dB. The measured E- and H-plane cross-polarization for the antenna is lower than -40 dB. The measured edge taper at the halfsubtended angle of the sub-reflector is between -11.8 dB and -13.2 dB. The front-end receiver was designed to use a single down-conversion stage to a 4.5 GHz IF with an instantaneous bandwidth of 2.5 GHz to be bandpass sampled at 6 Giga-samples per second (GSPS). The receiver was designed using off-the-shelf connectorized modules and custom designed microstrip filters for image rejection and anti-aliasing. Laboratory measurements of the receiver show a maximum gain of 76 dB, 40 dB image rejection and 27 dB spurious free dynamic range (SFDR). The simulated noise figure of the system using the measured noise figure of the LNA is 1.74 dB. The measured gain flatness of the receiver is ±7 dB due to poor performance of one of the amplifier modules used in the system

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

Engineering evaluations and studies. Volume 3: Exhibit C

High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed

Proceedings of the Third International Mobile Satellite Conference (IMSC 1993)

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial cellular communications services. While the first and second International Mobile Satellite Conferences (IMSC) mostly concentrated on technical advances, this Third IMSC also focuses on the increasing worldwide commercial activities in Mobile Satellite Services. Because of the large service areas provided by such systems, it is important to consider political and regulatory issues in addition to technical and user requirements issues. Topics covered include: the direct broadcast of audio programming from satellites; spacecraft technology; regulatory and policy considerations; advanced system concepts and analysis; propagation; and user requirements and applications

Multi-Polarized Spiral Antennas for RF Sensing

Spiral antennas are capable of dual polarized operation if the currents can propagate along their arms by going either out or in through the radiation region of the spiral. The wrapping sense of the spiral determines the polarization of the radiated field resulting from this current flow. There are two ways to accomplish this phenomenon over very wide bandwidths. Specifically, either have a feed point for the spiral both outside and inside the radiation region, or use of the modulated arm width (MAW) spiral antenna. The MAW spiral antenna has not been widely accepted and is seldom reported in open literature. Its geometry is however sufficiently unique from the other planar frequency independent (FI) antennas to require a complete explanation of where it fits for different applications, specifically RF sensing. The design of the MAW spiral antenna is detailed herein including geometry described by modulation period, modulation magnitude, expansion rate, total number of arms, feed point structure, termination, cavity, feeding and dielectric effects. The emphasis is on detailed understanding of its performance characteristics such as impedance, pattern control and quality. The relevance of these characteristics to the antenna being used as a sensor is explained. The specific concerns being quantified are location by angle of arrival techniques and polarization detection. The use of a four-arm MAW spiral for angle of arrival as well as polarization sensing is demonstrated theoretically and experimentally. This combined capability has not been mentioned in any literature previously and was investigated thoroughly under this thesis to determine the limitations since as found herein no other four-arm FI planar antenna has this capability. In addition, the application of several geometries of the MAW spiral are examined as possible improvements over the original equiangular geometry including Archimedean, bi-layer, and structures that are not self-complementary due to either the modulation ratio or the period. In particular, pattern performance improvement is demonstrated for modulation periods that do not produce self-complementary geometries while having minimal impact on impedance. Finally, an investigation into the asymmetric modes for an arbitrary number of arms was conducted to evaluate the performance limits of the highest available mode (mode with the largest phase change between arms) of a MAW spiral. Typically, this highest mode has significantly poorer performance than the other modes due to the inability of the MAW spiral to separate it from the modes that are not controlled by the beamformer

Reconfigurable antennas for wireless network security

Large scale proliferation of wireless technology coupled with the increasingly hostile information security landscape is of serious concern as organizations continue to widely adopt wireless networks to access and distribute critical and con dential information. Private users also face more risks than ever as they exchange more and more sensitive information over home and public networks through their ubiquitous wireless-enabled laptops and hand held devices. The fundamental broadcast nature of wireless data transmission aggravates the situation, since unlike wired networks, it introduces multiple avenues for attack and penetration into a network. Though several traditional mechanisms do exist to protect wireless networks against threats, such schemes are a carryover from the traditional wire based systems. Hence vulnerabilities continue to exist, and have been repeatedly demonstrated to be susceptible to failure under di erent circumstances.The resulting uncertainties have led to a signi cant paradigm shift in the design and implementation of wireless security in recent times, among which wireless channel based security schemes have shown the most promise. Channel based security schemes are rooted on the simple fact that a legitimate user and an adversary cannot be physically co-located and hence the underlying multi-path structure corresponding to the two links cannot be the same. However most wireless systems are constrained in terms of bandwidth, power and number of transceivers, which seriously limit the performance of such channel based security implementations. To overcome these limitations, this thesis proposes a new dimension to the channel based security approach by introducing the capabilities of recon gurable antennas. The main objective of this work is to demonstrate that the ability of recon gurable antennas to generate di erent channel realizations that are uncorrelated between di erent modes will lead to signi cant improvements in intrusion detection rates.To this end, two di erent schemes that make use of channels generated by a recon gurable antenna are proposed and evaluated through measurements. The rstscheme is based on associating a channel based ngerprint to the legitimate user to prevent intrusion. The three main components of this scheme are i ) a ngerprint derived from the di erent modes of the antenna, ii ) a metric to compare two ngerprints and iii ) a hypothesis test based on the proposed metric to classify intruders and legitimate transmitters. The second scheme relies on monitoring the statistics of the channels for the legitimate transmitters' links since any intrusion will result in an observable change in the channel's statistics. The problem is posed as a generalized likelihood ratio test (GLRT) which responds to any change in the channel statistics by a large spike in the likelihood ratio's value. The detector's performance is studied as a function of pattern correlation coe cient for both schemes to provide insights on designing appropriate antenna modes for better performance.Moreover this thesis takes a holistic approach to studying the antenna based security schemes. A novel channel modeling approach which combines the cluster channel model and site speci c ray tracer results is proposed and validated to facilitate the analysis of such schemes through simulations without resorting to comprehensive channel measurements. This approach is motivated by the lack of an intuitive and simple channel model to study systems that use recon gurable antennas for any application.Finally the design of a metamaterial based substrate that can help miniaturize antenna arrays and recon gurable antennas is presented. The magnetic permeabilityenhanced metamaterial's capability to miniaturize an antenna's size while maintaining an acceptable level of isolation between elements in an array is experimentallydemonstrated. The bene ts gained in a wireless communication system that uses a patch antenna arrray built on this substrate is quanti ed in terms of mean e ective gain, correlation between the antennas and channel capacity through channel measurements.Despite their capability to signi cantly improve spectral e ciency, the widespread adoption of recon gurable antennas in wireless devices has been hampered by their complexity, cost and size. The work presented in this thesis is therefore intended to serve as a catalyst to the widespread adoption of recon gurable antenna technology by i ) adding value to such antennas by utilizing them for enhancing system security and ii ) providing a mechanism to miniaturize them to facilitate their integration into modern space constrained wireless devices.Ph.D., Electrical Engineering -- Drexel University, 201

Significant Accomplishments in Science and Technology at Goddard Space Flight Center, 1969

Aerospace scientific and technological studies in 1969 for satellite systems and spacecraft mission

A Multi-Band Far-Infrared Survey with a Balloon-Borne Telescope

Nine additional radiation sources, above a 3-sigma confidence level of 1300 Jy, were identified at 100 microns by far infrared photometry of the galactic plane using a 0.4 meter aperture, liquid helium cooled, multichannel far infrared balloon-borne telescope. The instrument is described, including its electronics, pointing and suspension systems, and ground support equipment. Testing procedures and flight staging are discussed along with the reduction and analysis of the data acquired. The history of infrared astronomy is reviewed. General infrared techniques and the concerns of balloon astronomers are explored