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A study is made of the radiation from a phased array of circular loop antennas in a resonant magnetoplasma. The loops are assumed to have a finite radius and be located on a circumference in such a manner that their axes are aligned with a static magnetic field superimposed on the plasma. The emphasis is placed on determining the total radiated power of such an array and the partial powers going to different azimuthal field harmonics. For these quantities, rigorous integral representations are obtained using an expansion of the excited field in terms of cylindrical vector eigenfunctions of a magnetized plasma medium. Numerical results are reported for the radiation characteristics of the phased array in the whistler frequency range under conditions of the Earth's ionosphere. It is shown that an appropriately phased array is capable of selectively exciting waves with the desired helicity of the phase front and can be useful as a source of twisted whistler-mode waves in a magnetoplasma. [ABSTRACT FROM AUTHOR]

Guided propagation of whistler waves and their excitation by a loop antenna in the presence of a field-aligned cylindrical duct with enhanced density in a magnetoplasma are studied below the lower hybrid resonance frequency. The emphasis is placed on the case where the duct is transversely nonuniform such that the plasma density in it decreases monotonically from a constant value in the near-axis inner region to the lower background value in the outer medium. Conditions are determined under which the dispersion characteristics and field structures of the modes guided by such a duct allow an approximate description within the framework of perturbation theory. The approximate results are shown to be in good agreement with the numerical results obtained using a full-wave approach. It is also found that the radiation resistance of a loop antenna located in the smooth-walled enhanced density duct can be notably greater than that of the same antenna immersed in the background magnetoplasma due to the excitation of the modes guided by the duct. The reported results extend previous analyses performed for sharp-walled uniform ducts to the case of a more realistic plasma density profile in the duct and can be useful in understanding the basic features of whistler wave guidance and excitation as well as in planning the related experiments. [ABSTRACT FROM AUTHOR]

(In,Fe)Sb layers with a Fe content up to 13 at. % have been grown on (001) GaAs substrates using the pulsed laser deposition. Transmission electron microscopy shows that the layers are epitaxial and free of second-phase inclusions. The observation of hysteretic magnetoresistance curves at temperatures up to 300K and the investigations of magnetic circular dichroism reveal that the Curie point lies above room temperature. The resonant character of magnetic circular dichroism confirms the intrinsic ferromagnetism in the (In,Fe)Sb matrix. We suggest that the ferromagnetism of the (In,Fe)Sb matrix is not carrier-mediated and is apparently determined by the mechanism of superexchange interaction between Fe atoms. [ABSTRACT FROM AUTHOR]

A study is made of the radiation of whistler waves with helical phase fronts from nonsymmetric sources immersed in a homogeneous cold magnetoplasma. The emphasis is placed on calculating the radiation resistance of an antenna in the form of two orthogonally crossed circular loops with quadrature-phased currents using an approach that is based on an eigenfunction expansion representation of the excited field. Analytical and numerical results are reported for the radiation characteristics of such an antenna in the whistler range and differences in the behavior of the radiation resistance below and above the lower hybrid resonance frequency are revealed. The results obtained can be useful in understanding the basic features of excitation of twisted whistler waves in a magnetoplasma. [ABSTRACT FROM AUTHOR]

Scattering of a normally incident extraordinary (Z mode) wave by a cylindrical density depletion aligned with an external static magnetic field in a magnetoplasma is studied. This problem is of importance for wave diagnostics of plasma density irregularities that can be formed under natural conditions of near-Earth space or during the modification of the ionosphere by high-power radio waves. The emphasis is placed on the behavior of scattering characteristics of the density depletion in the case where the frequency of the incident plane wave coincides with one of the resonant frequencies of such a plasma structure. The field patterns observed in the resonance scattering regimes are calculated and analyzed. The results obtained can be helpful in understanding the basic properties of resonance scattering of electromagnetic waves from the field-aligned density irregularities and planning the related ionospheric and laboratory experiments. [ABSTRACT FROM AUTHOR]

Whistler wave radiation from a loop antenna located in a cylindrical duct with enhanced plasma density is considered in the case where the wave frequency is less than the lower hybrid frequency. Using the full-wave formulation, the total radiation resistance and the partial radiation resistances corresponding to guided eigenmodes of such a duct and unguided waves radiating to the background magnetoplasma are calculated and analyzed as functions of the plasma and source parameters. The emphasis is placed on the radiation characteristics of the considered source in the presence of an artificial near-antenna duct that can be created during active experiments in the ionosphere. Conditions are revealed under which the total radiation resistance is predominantly determined by the excitation of the eigenmodes of the duct. It is shown that the presence of an enhanced density duct can lead to a notable increase in the radiation resistance of a loop antenna in the discussed frequency range even if the duct is rather narrow and capable of guiding only a single low-order eigenmode. The results obtained can be helpful in understanding the basic features of excitation of the ducted whistlers and planning the related ionospheric and laboratory experiments. [ABSTRACT FROM AUTHOR]

Pulsed radiation from a loop antenna located in a cylindrical duct with enhanced plasma density is studied. The radiated energy and its distribution over the spatial and frequency spectra of the excited waves are derived and analyzed as functions of the antenna and duct parameters. Numerical results referring to the case where the frequency spectrum of the antenna current is concentrated in the whistler range are reported. It is shown that under ionospheric conditions, the presence of an artificial duct with enhanced density can lead to a significant increase in the energy radiated from a pulsed loop antenna compared with the case where the same source is immersed in the surrounding uniform magnetoplasma. The results obtained can be useful in planning active ionospheric experiments with pulsed electromagnetic sources operated in the presence of artificial field-aligned plasma density irregularities that are capable of guiding whistler waves. [ABSTRACT FROM AUTHOR]

A study is made of the radiation from a pulsed loop antenna immersed in a cold collisionless magnetoplasma. Using a rigorous solution for the total field of such an antenna, the energy characteristics of its radiation are determined. The radiated energy and its distribution over the spatial and frequency spectra of the excited waves are analyzed as functions of the antenna and plasma parameters. Numerical results referring to the case where the frequency spectrum of the antenna current is concentrated in the whistler frequency range are reported. The results obtained can be useful in understanding the basic features of wave excitation by pulsed sources in a magnetoplasma. [ABSTRACT FROM AUTHOR]

Electromagnetic radiation from sources in a magnetoplasma containing a radially nonuniform cylindrical density depletion is considered. Using a rigorous solution for the total field comprising both the discrete and continuous parts of the spatial spectrum of excited waves, the radiation resistance of a loop antenna and the efficiency of excitation of different modes by such a source are determined in the whistler range. Based on the numerical results, conditions are revealed under which the power radiated from a loop antenna located in a density depletion is dominated by the contribution of either discrete- or continuous-spectrum modes. It is found that the radiation resistance of the loop antenna in a weakly nonuniform density depletion can be notably greater than that in a homogeneous magnetoplasma whose parameters coincide with those near the depletion axis. The results are relevant to the basic properties of whistler wave excitation in the presence of field-aligned plasma density irregularities and can be useful for wave diagnostics in laboratory and space plasmas. [ABSTRACT FROM AUTHOR]

A study is made of the electromagnetic radiation from a thin modulated electron beam of finite length injected parallel to an external magnetic field in a magnetic-field-aligned cylindrical density duct immersed in a uniform ambient magnetoplasma. A rigorous solution for the beam-excited field is obtained and the power lost by the beam in the presence of the duct is examined. Although a general theory is developed, attention is focused on ducts with enhanced density and modulation frequencies belonging to the whistler band. Expressions for the time-averaged power emitted from the beam are derived as a function of the beam and duct parameters. A significant difference between the features of whistler wave emission in the presence of a duct and in the case of a homogeneous unbounded plasma is revealed. Estimates of the power emitted in the whistler band are given for representative examples of artificial density ducts in the laboratory and space plasmas. It is shown that the power lost by the beam in the presence of an enhanced-density duct can increase noticeably due to Cerenkov excitation of guided whistler modes. [ABSTRACT FROM AUTHOR]