Far-zone Radiation Fields Research Articles

On the computation of plane-wave impressed fields and far-zone fields of arbitrary current sources in planar multilayer dielectric and plasmonic media

A unified and succinct transmission line formulation is presented for the computation of the plane-wave impressed fields and far-zone radiation fields due to arbitrary electric and magnetic current source distributions embedded in planar layered media. The equivalence principle and the spectral-domain transmission-line network analogue of the multilayer medium are used to express the fields in terms of the voltage and current transmission-line Green functions. The new formulation is applied to sample problems involving both dielectric and plasmonic multilayer media.

Complete waveform model for compact binaries on eccentric orbits

We present a time domain waveform model that describes the inspiral-merger-ringdown (IMR) of compact binary systems whose components are non-spinning, and which evolve on orbits with low to moderate eccentricity. The inspiral evolution is described using third order post-Newtonian equations both for the equations of motion of the binary, and its far-zone radiation field. This latter component also includes instantaneous, tails and tails-of-tails contributions, and a contribution due to non-linear memory. This framework reduces to the post-Newtonian approximant TaylorT4 at third post-Newtonian order in the zero eccentricity limit. To improve phase accuracy, we incorporate higher-order post-Newtonian corrections for the energy flux of quasi-circular binaries and gravitational self-force corrections to the binding energy of compact binaries. This enhanced inspiral evolution prescription is combined with an analytical prescription for the merger-ringdown evolution using a catalog of numerical relativity simulations. This IMR waveform model reproduces effective-one-body waveforms for systems with mass-ratios between 1 to 15 in the zero eccentricity limit. Using a set of eccentric numerical relativity simulations, not used during calibration, we show that our eccentric model accurately reproduces the features of eccentric compact binary coalescence throughout the merger. Using this model we show that the gravitational wave transients GW150914 and GW151226 can be effectively recovered with template banks of quasi-circular, spin-aligned waveforms if the eccentricity $e_0$ of these systems when they enter the aLIGO band at a gravitational wave frequency of 14 Hz satisfies $e_0^{\rm GW150914}\leq0.15$ and $e_0^{\rm GW151226}\leq0.1$.

Radiation Characteristics of Antennas Embedded in a Medium With a Two-Temperature Electron Population

It is well-known that low-frequency electromagnetic (EM) signals are heavily attenuated in a medium with dense electron population. All signals below the plasma frequency of the medium get cut off. If we create in this medium, a small population of relatively hot electrons the composite medium then supports low-frequency electrostatic oscillations known as electron acoustic waves (EAW) [e.g., Gary and Tokar, Phys. Fluids 28, 2439]. The dispersion relation of this composite medium shows that it supports EAW in the frequency band where EM signals are cut off. Thus, it is possible, in principle, to employ EAW to transmit signals across an overdense plasma medium. Our primary interest in this paper is to study the radiation characteristics of a source current distribution embedded in a half-space of our composite medium. To enable this, we derive the Green's functions for our problem and, hence, study the radiation characteristics of antennas. When the source signal frequency is below the plasma frequency, only EAW exist in the composite medium, while only EM waves can exist in the free space above. We find that the far-zone radiation fields of any current distribution consist only of θ-polarized waves. Explicit expressions for the radiated fields are obtained for horizontally- and vertically-polarized Hertzian dipoles embedded in our composite medium. We, hence, find that in both cases the radiation patterns are skewed towards the horizon. In particular, we find that the radiation pattern of a horizontal dipole has two lobes as opposed to one in the underdense case.

Theory of waveguide light scattering in an integrated optical waveguide in the presence of noise

We develop a vector theory of waveguide monochromatic light scattering in an integrated optical waveguide with arbitrary three-dimensional irregularities in the presence of noise. The electrodynamical problem of laser radiation scattering in an irregular waveguide is solved by the method of coupled modes with the help of the theory of perturbations. The approximate solution of the inhomogeneous three-dimensional wave equation is derived by the method of modes and the method of Green’s functions. The obtained Green’s function is analyzed for the cases of propagating and evanescent modes of an irregular asymmetric optical waveguide. Analytical formulas for the near- and far-zone radiation fields are presented. A preliminary analysis of these formulas is given.

Radiation from multiple circumferential slots on a coaxial cable

Radiation from multiple circumferential slots on a coaxial cable is rigorously studied. The reflection coefficient and the far-zone radiation field are represented in a fast convergent series, and their characteristics are investigated in terms of slot geometry and frequency. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 160–162, 2000.

An integral equation and its application to spiral antennas on semi-infinite dielectric materials

This paper presents an integral equation that can handle wire antennas on a semi-infinite dielectric material. The integral equation is reduced to a set of linear equations by the method of moments. For efficiency, the impedance matrix element Z/sub m,n/ is divided into two parts on the basis of weighted Green's function extractions. The far-zone radiation field, which is formulated using the stationary phase method, is also described. After the validity of the presented numerical techniques is checked using a bow-tie antenna, a spiral antenna is analyzed. The current distribution, radiation pattern, axial ratio, power gain, and input impedance are discussed. It is found that the radiation field inside a dielectric material is circularly polarized. As the relative permittivity of the dielectric material increases, the angle coverage over which the axial ratio is less than 3 dB becomes narrower.

Electromagnetic radiation from line sources embedded in a uniaxial dielectric or plasma half-space backed by a medium of finite conductivity

This paper treats the problem of electromagnetic radiation from the electric and magnetic line sources embedded in a uniaxially anisotropic dielectric or plasma half-space backed by a finitely conducting medium. The anisotropy of the uniaxial medium is taken along the x direction and the line source is aligned parallel with the z axis. For the envisaged geometry, E and H modes are independently excited by a magnetic and an electric line source, respectively. Expressions for the far-zone radiation field and the radiation pattern are obtained via the saddle-point technique of integration. It is noted that the radiation from an electric line source remains unaffected by the anisotropy of the medium and possesses only a radial component of the Poynting vector. In contrast, the radiation from a magnetic line source not only depends on the anisotropy of the medium but has, in addition to the radial component, a circumferential component of the Poynting vector indicating deviation of the resultant energy flow from the radial direction. Numerical results for the radiation pattern and also for the angle of deviation of the power flow from the radial direction, for the magnetic line source, are presented for a wide range of parameters characterizing the anisotropy of the uniaxial medium, the location of the line source, electron-plasma density, and the conductivity of the half-space backing the uniaxial medium. It is revealed that in the case of a uniaxial plasma or dielectric backed by a perfect conductor, the radiation has a finite strength of unity both in directions ϑ=0 and ϑ=π, in contrast to the case of a medium backed by a finitely conducting medium.

Electromagnetic radiation from line sources interacting with a moving uniaxial dielectric or plasma half-space

The problem of electromagnetic radiation from electric and magnetic line sources interacting with a moving uniaxially anisotropic dielectric or plasma half-space is treated. The anisotropy of the plasma is due to an infinitely strong magnetizing field impressedparallel to the motion of plasma. The line source is oriented normal to the direction of medium motion. TheE and theH modes are excited independently in the medium by the magnetic and the electric line sources, respectively. Invoking the saddle-point method of integration, the far-zone radiation field and the radiation pattern are obtained for both line sources. It is found that the radiation from an electric line source is not affected by the anisotropy of the moving medium and that a magnetic line source invacuum has finite components of radiation in directions which are parallel and antiparallel to the direction of motion, for the case of a uniaxial plasma in contrast to the results for a uniaxial dielectric. Numerical results for the far-zone radiation pattern, referring to a magnetic line source, are presented for several values of parameters characterizing the non-dimensional velocity, the anisotropy of the medium, the electron-plasma density and the location of the line source.

Electromagnetic radiation from line sources embedded in a moving bounded magnetoplasma sheath

The problem of electromagnetic radiation from electric and magnetic line sources embedded in a moving bounded magrietoplasma sheath situated over a perfectly conducting plane is studied. The radiation fields due to the line sources consist of both E and H modes, excited simultaneously in the moving sheath. However, when the magnetic field lies parallel to the line source and is oriented normal to the direction of the sheath motion, the modes become decoupled. The far-zone radiation fields for both the electric and the magnetic line sources have been obtained, using the method of saddle-point approximation. The corresponding radiation patterns are also obtained and their variation studied as a function of the magnetic field, the location of the line source, the thickness and the velocity of the moving plasma sheath. It is found that the fields radiated by an electric line source remain unaffected by the presence of an ambient magnetic field and that, in the presence of a sufficiently intense magnetizing field, the magnetic line source over a perfectly conducting plane radiates as though surrounded by vacuum.

Electromagnetic radiation from line sources interacting with a moving magnetoplasma half-space

The problem of electromagnetic radiation from the electric and the magnetic line sources interacting with a cold collisionless moving magnetoplasma half-space has been treated. The ambient magnetic field lies parallel to the line source and is oriented normal to the direction of medium motion. For the configuration, the E and H modes become independent, being capable of becoming excited, respectively, by a magnetic and an electric line source. Using the saddle-point method of integration, we have obtained the far-zone radiation fields and the radiation patterns for both line sources. It is found that the fields radiated by an electric line source remain unaffected by the presence of an ambient magnetic field. Numerical results for the far-zone radiation pattern, referring to a magnetic line source, are presented for several values of the parameters characterizing the electron-plasma density, the local magnetic field, and the velocity of the moving medium.

Analysis of Travelling Wave Log-periodic Dipole Antenna

A generalized analysis of the log-periodic dipole antenna (LPDA) having travelling wave type current distribution in its constituent dipoles is presented. Mathematical expressions for the far-zone radiation fields, gain and aperture are derived. Results obtained from these expressions for the travelling wave LPDA are compared with the LPDA having sinusoidal current distribution. It is found that the LPDA with travelling wave type of current distribution gives narrower E-plane beam and better gain as compared to the LPDA with sinusoidal current distribution.

Theoretical investigations on the centre-fed full-wave dipole antenna with feed-points displaced along the axis of the dipole

An analysis of a centre-fed full-wave dipole antenna with feed-points displaced along the dipole axis is presented. Mathematical expressions for the far-zone radiation field, radiation resistance, power gain and effective length of the antenna are developed. The variation in the properties of the full-wave dipole for various values of feed-points displacement along the dipole axis are discussed.

A wide-band circularly polarized corner reflector antenna

A corner reflector excited by a tilted log-periodic dipole antenna is shown to radiate a circularly polarized unidirectional signal. Mathematical expressions for the radiation patterns have been developed using the image theory. Theoretical plots for the far-zone radiation fields are given.

A note on radiation in a gyro-electric-magnetic medium--An extension of bunkin's calculation

Some fundamental results on radiation in anisotropic media have been worked out by F. V. Bunkin for the case of a gyro-electric (or plasma) medium using the technique of tensorial Green's function. He obtained asymptotic expressions for the far-zone radiation fields in a gyro-electric medium and therefore demonstrated actually the validity of Sommerfield's radiation condition for a gyro-electric medium. The present paper extends Bunkin s calculation to a case of a gyro-electric-magnetic medium and thus justifies the validity of Sommerfeld's radiation condition in a gyro-electric-magnetic medium.

Radiation from a Rectangular Waveguide Filled with Ferrite

This paper presents an approximate analytical solution to the problem of radiation from a ferrite-filled rectangular waveguide. The field distribution at the mouth of the guide is assumed to be unaffected by the termination of the guide. The vector Huygens' principle is applied to find the far-zone radiation field from the determined aperture field. The solution to the problem is found in this manner for the cases of longitudinal and transverse magnetization of the ferrite. The transverse magnetization case is supplemented with a discussion of a specfic numerical example which includes plots of the aperture field distribution and the phase angle as well as plots of the far-zone radiation field. The experimentally known phenomenon of the effect of the applied magnetic field upon the shift of the main lobe is demonstrated and verified analytically.