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This paper is an extension of the recent work of Gupta (1968) in which the properties of a thin resonant antenna in a plasma are analysed using linearized hydrodynamic theory and assuming a general propagation constant for the current distribution, for an antenna having feed points displaced by /2.
In this paper the analysis is extended to include non-resonant antenna and also the dependence of the properties of both types of antennas on the size of the displacement and value of the propagation, constant. The field patterns in the plasma are calculated for two different values of the general propagation constant and for various lengths of the antennas. The results are compared with the free space radiation field strengths which are evaluated by setting the plasma frequency to zero. It is shown that the maximum field strength of both the resonant and the non-resonant types of antenna in free space increases considerably when the feed points are displaced to a certain optimum value. The variation of the magnitude of the field strength and of the radiation resistance on the ratio of the plasma frequency to the source frequency are also investigated. [ABSTRACT FROM AUTHOR]

In an earlier paper, Nair et al. (1968) derived an expression for the radiation pattern due to a primary aperture antenna and two secondary sources excited by the primary, introducing different possible asymmetric conditions in the system. Apart from the asymmetries in length and orientation of the axis of the flange elements considered by them, it is quite possible to occur an asymmetry in the amplitude of excitation of the secondary sources. Due to their heterogeneous conditions, the secondary radiators might be excited by the primary source to different amplitudes k and k relative to the primary amplitude which is taken as unity. Under such conditions the vector diagram assumes a different form, yielding to a new expression for the radiation pattern. This note presents the derivation for this radiation pattern. The symbols used in this note are the same used by Nair et al. (1968) in the earlier paper. [ABSTRACT FROM AUTHOR]

Expressions for the radiation fields in a compressible electron plasma medium are derived pertaining to the helical antenna of finite size immersed in it. The current distribution on the helical antenna is assumed to be an out-going travelling wave with an arbitrary phase propagation constant. From these general expressions fields of circular loop and linear antennas can be deduced as particular cases. Further, by letting the plasma frequency approach zero in these general expressions, the electromagnetic fields of the usual helical antenna theory can be obtained. It is, therefore, concluded that the radiation field expressions for a helical antenna given in this paper are of a general nature and cover the cases of circular loops and linear antennas in an electron plasma medium and of the helical antenna in vacuum. [ABSTRACT FROM AUTHOR]

The radiation properties of perfectly conducting filamentary circular loops of arbitrary dimensions immersed in a uniform isotropic, compressible electron plasma are studied theoretically. The current distribution on the circumference of the loop is assumed to be a travelling wave with arbitrary phase propagation constant. The far zone fields of the circular loop are obtained and the radiation resistance is then evaluated for both the electromagnetic and electroacoustic modes. From these general results, the problem is reduced to that of the circular loop in vacuum and the consequent results are found to tally with those available in literature. From the detailed study of fields and radiation resistances as put out in this paper, it is shown that the radiation resistance of both the modes is higher in the case of travelling wave loop than in the case of standing wave loop. It is, therefore, concluded that loop antennas on space vehicles may be fed with travelling wave currents rather than with the usual standing wave currents, since in the former case radiation resistance of the electromagnetic mode is enhanced. [ABSTRACT FROM AUTHOR]

It is found from experimental investigations that the normal mode helical antenna used with a ground plane may be used in the medium and short wave region. In this paper, analytical expressions for the radiation field (EΦ and Eθ) of this antenna are found from the appropriate vector potential for the helix. The analytical expressions are derived on the assumption of a sinusoidal current distribution. The helix is considered to be cylindrical. The theoretical results are in good agreement with experimental observations. [ABSTRACT FROM AUTHOR]

Metallic grills arranged at certain optimum positions of an E-plane sectoral horn are found to be very effective in sharpening the E-plane radiation patterns of the horns. Experimental data for a good number of horns operating at varying frequencies are presented. It has been proved that the grills do not adversely affect the impedance conditions of the horns. These experimental results are explained theoretically on the assumption of secondary radiators situated at the edges of the grills. The radiation patterns computed using this theory are found to be in very good agreement with the experimental patterns.
This paper presents the results of a more elaborate experimental study of the above phenomenon together with a theoretical analysis to explain the action of the grills. The experimental data have been collected using a good number of E-plane sectoral horns operating at a wide range of frequencies. The validity of the theory is tested by comparing the theoretically computed patterns with the experimental ones. [ABSTRACT FROM AUTHOR]

This note deals with the power radiated into the air by a vertical monopole on a lossy ground and comments on a previous paper concerning the calculation of radiation resistance by Poynting's vector method.
In a recent paper, Singh and Shukla (1972) have obtained analytical expressions for the radiation resistance of a monopole antenna on an imperfect homogeneous ground. The method is based on the analytical integration of Poynting's vector over a hemisphere enclosing the antenna using sinusoidal current distribution.
The above integration gives only the power radiated into air and may not be used to calculate the radiation resistance of the monopole. Consequently, one must also consider the power radiated into the ground. Sommerfeld and Renner (1942) have integrated Poynting's vector over a plane just above the ground in order to find the change in the radiation resistance resulting from the imperfect ground. [ABSTRACT FROM AUTHOR]