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In this paper, the autofocus compressed sensing (ACS) imaging method is proposed to obtain the imagery with some unknown parameters in the forward model. The proposed method updates the unknown parameters of the measurement matrix and constructs the imagery alternately within an iterative framework. The unknown parameters, denoted as hyperparameters, are estimated using the nonlinear conjugate gradient...
HERA is a highly-redundant transit interferometer with 14m-diameter parabolic dish elements. We exploit the fact that the Galactic centre transits through the main beam of the telescope to attempt a conventional self-calibration approach to imaging and calibration. The Galactic centre provides a bright source which, we show, can be approximated as a point source sufficiently well to initialise the...
To meet 5G networks challenges in terms of high data rates and spectral efficiency, one solution might be using multicarrier modulations (MCM)s. However, using MCMs is synonymous with low energy efficiency due to their high peak-to-average power ratio (PAPR). Indeed, high PAPR signals drive power amplifiers to operate most of the time in the linear zone. This latter corresponds to low power efficiency...
This paper studies diffraction of a plane electromagnetic wave by a uniformly moving, anisotropic impedance wedge and presents an exact solution in closed form to a class of impedance wedges based on frame hopping [1] and earlier results for diffraction by such obstacles at rest [2, 3].
Fresnel reflection and transmission coefficients are well known for the two idealized cases when the two media are either perfect dielectrics [1] or one is a dielectric and the other is a perfect electric conductor (PEC) [2]. However, such is not the case when either one or both media have loss. In a recent paper, Besieris [3] showed that Canning's criticism [4] of the different approaches to the...
This paper presents a novel RF rectifier that compresses RF input impedance fluctuation caused by DC load change for reducing return loss at RF input power. The proposed rectifier connects twin basic RF rectifiers and a quarter-wave impedance transformer. The proposed rectifier automatically switches the two rectifiers according to DC load resistance. As the result, the rectifier can keep low deviation...
In this paper, a broadband rectenna, for ambient RF energy harvesting applications, is presented. It is composed of a broadband spiral antenna with its balun, optimized to cover the principal frequency bands where there is RF energy to harvest (GSM900, GSM1800, UMTS2100 and WIFI). This antenna will be associated, in a first step, with a dual-band rectifier (GSM900-GSM1800) to do a complete rectenna...
This paper describes the design and measurement of a full-bridge rectifier and a receiving antenna array operating at 2.4 GHz for wireless power transmission system applications, and with motivations to wirelessly charge an electronic device in the radiating near-field. A retrodirective antenna array (RDA) was also used in the system with high power gain to boost the overall received RF power at the...
Besides the radiation and reflection performance of wearable antennas, arguably one of the most important parameters is their Specific Absorption Rate (SAR). This work aims to evaluate SAR for wearable antennas integrated with Artificial Magnetic Conductor (AMC) plane made using different material categories — textiles and a flexible polymer,. Two types of textiles, felt and ShieldIt Super are used...
Very low frequency (VLF) radio waves propagate over long distances within the Earth-ionosphere waveguide, reflected off the Earth's surface and the ionospheric D-region. The characteristics of these signals depend on several parameters along the path, which apart from the D-region's properties, are fairly constant over short periods of time. This allows probing of perturbations in the lower ionosphere...
The exact and asymptotic solutions to the scattering of a complex-source beam (CSB) by an acoustically soft or hard semi-infinite circular cone are explored. The exact solution, expressed as a spherical-harmonics expansion, is compared with the complex geometrical optics (CGO) solution augmented by a complex ray diffraction at the tip.
Rubidium atomic frequency standards are currently the most common atomic clocks in global navigation satellite systems. Their frequency is affected by the light-shift effect due to the lamplight used for the optical pumping process, so that lamplight instabilities turn into frequency instabilities setting a limit to the navigation performance. Here we present the outcome of a study covering years...
The scattering properties of a finite array of magnetized plasma cylinders are studied theoretically by using the multiple scattering approach. It is assumed that the array, whose elements are aligned with an external static magnetic field and located equidistantly in free space, is illuminated by an obliquely incident H-polarized plane electromagnetic wave. The far-zone scattering patterns for the...
Dynamic spectrum access (DSA) paradigm has shown significant potential to improve the electromagnetic spectrum utilization. For DSA in the multi-user decentralized networks, frequency band characterization and allocation among unlicensed users is a non-trivial task and various decision making policies (DMPs) have been proposed recently. Though auction based DMPs have shown to offer better performance...
In this paper, two kinds of artificial magnetic conductors (AMC) are formed in a chessboard to reduce the radar cross section (RCS). Considering a 180+37° phase difference between reflection coefficients of both the AMC unit cells, frequency bandwidth of 55% from 2S.5GHz to 50GHz is obtained. In order to redirect energy and reduce RCS, the AMC structures are configured on chessboard surface. In addition,...
Multi-layered spherical nanoparticles are known to be able to achieve large electric field enhancements via highly resonant electrically small geometries. While the resonant properties of these nanoparticles can be tailored by altering their material geometries, their scattered far-fields can subsequently be tailored as well. This is accomplished through a fortuitous superposition of electric and...
Ground Based Augmentation Systems (GBAS) monitor the ionosphere locally for giving measurement integrity information to nearby users. Monitoring systems use ionospheric threat models to calculate the integrity information and contain ionospheric gradients estimated from the ionospheric slant delays through the maximum gradient observed days. These models show only maximum gradient estimates according...
Since their first realization the development of metamaterial based devices and applications has gained an increasing level of interest. These materials offer the opportunity to specifically engineer the materials ability to, control, enhance and suppress EM wave propagation though and near these materials, either in a specific direction or altogether. These materials have been used to construct a...
Log-periodic antenna is a special antenna type utilized with great success in many broadband applications due to its ability to achieve nearly constant gain over a wide frequency range. Such antennas are extensively used in electromagnetic compatibility measurements, spectrum monitoring and TV reception. In this study, a log-periodic dipole array is measured, simulated, and then optimized in the 470–860...
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