Journal ArticleDOI
The radiation efficiency of a dipole antenna located above an imperfectly conducting ground
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In this paper, the dyadic Green's function was used to develop integral expressions for the radiation efficiency of three types of dipole antennas located above an imperfectly conducting, infinite ground plane.Abstract:
The dyadic Green's function technique is used to develop integral expressions for the radiation efficiency of three types of dipole antennas located above an imperfectly conducting, infinite ground plane. The three antennas treated are: 1) vertical Hertzian dipole, 2) horizontal Hertzian dipole, and 3) a vertical half-wave dipole with sinusoidal current distribution. The results of numerical evaluation of the integral expressions for several values of ground constants are presented in graphical form. The radiation efficiency of a vertical Hertzian dipole is found to exhibit a distinct peak when located at a height of one-eighth wavelength.read more
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Journal ArticleDOI
Holographic free-electron light source
Guanhai Li,Brendan P. Clarke,Jin-Kyu So,Jin-Kyu So,Kevin F. MacDonald,Nikolay I. Zheludev,Nikolay I. Zheludev +6 more
TL;DR: This work introduces a universal approach allowing generation of light with prescribed wavelength, direction, divergence and topological charge via point-excitation of holographic plasmonic metasurfaces to offer novel applications in nano-spectroscopy, nano-chemistry and sensing.
Journal ArticleDOI
Sensitivity of an Active Antenna Array Element for the Low-Frequency Radio Telescope GURT
TL;DR: In this article, the parameters of the active antenna used as array element are studied, with special attention paid to sensitivity, and the results of numerical calculations of the sensitivity are given in terms of the sky noise dominance and system equivalent flux density of the GURT element within 10−80 MHz.
ReportDOI
Performance of Ground-Based High-Frequency Receiving Arrays with Electrically-Small Ground Planes
TL;DR: In this article, the performance degradation of ground-based high-frequency receiving arrays due to ground losses and external currents on the element feed cables was investigated, including a reduction in element directive gain near the horizon, distortion of the element azimuthal pattern, an increase in the system internal noise factor, and increases in the array factor root-mean-squared (rms) phase error and beam-pointing errors.
Journal ArticleDOI
A method to assess the loss of a dipole antenna for ultra‐high‐field MRI
TL;DR: A new bench measurement based on quality (Q) factors to estimate the coil noise relative to the sample noise of dipole antennas at 7 T is described.
Journal ArticleDOI
An Active Antenna Subarray for the Low-Frequency Radio Telescope GURT—Part I: Design and Theoretical Model
TL;DR: In this article, the electrical and noise parameters of the subarray of the giant Ukrainian Radio Telescope (GURT) have been studied by numerical and experimental ways, and a theoretical model based on the wave theory of noisy multiport networks that takes into account the mutual coupling in the dipole array placed over imperfect ground and the correlation between all existing noise sources is proposed.
References
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Journal ArticleDOI
On the theory of electromagnetic wave diffraction by an aperture in an infinite plane conducting screen
TL;DR: In this article, a defect in the Kirchhoff procedure is revealed by its failure to duplicate the assumed boundary values at the conducting screen, leading to a lack of self-consistency.
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Input resistances of horizontal electric and vertical magnetic dipoles over a homogeneous ground
TL;DR: In this paper, a comparison between a horizontal electric dipole and a vertical magnetic dipole is made, so far as their input resistances are concerned, and the theoretical curves of the input resistance are drawn for the two cases as a function of the normalized height of the antenna above the ground for fixed values of permittivity and the ratio of conduction and displacement currents.
Journal ArticleDOI
Theory of a vertical tubular antenna located above a conducting half-space
David C. Chang,James R. Wait +1 more
TL;DR: In this article, an integral equation for the current on the surface of the antenna was formulated and subsequently solved by numerical evaluation of associated moment functions in the Fourier transform plane, and the magnitude, but not the distribution, of the current was found to be strongly affected by the presence of the dissipative medium.
Journal ArticleDOI
Radiation Resistance of a Small Circular Loop in the Presence of a Conducting Ground
TL;DR: In this article, the total power flow from an oscillating magnetic dipole, situated above a flat homogeneous conducting ground and oriented in the vertical direction, was derived for the radiation resistance of a small wire loop whose axis is perpendicular to the ground.