An exact analysis for deriving closed-form expressions for the coefficients of free-space spherical modes radiated by typical linear, array, and aperture type of antennas is presented. This analysis is employed to determine the number of spherical modes required to reconstruct the near/ far fields (NF/FF) with a prescribed accuracy. The analysis developed together with the theory of probe-compensated spherical scanning is also employed to arrive at a criterion for the minimum distance of separation between the probe and test antenna which will enable accurate nonprobe corrected spherical scanning possible. © 1985 IEEE

M. S. Narasimhan

SOURCE OF EM RADIATION

SPHERICAL SCANNING

SPHERICAL WAVES

Antennas

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IIT Madras

Modal behavior of spherical waves from a source of EM radiation with application to spherical scanning

IEEE Transactions on Antennas and Propagation

An efficient technique for probe-directivity uncompensated spherical near-field to far-field (NF-FF) transformation is presented. The technique proposed does not make use of the spherical vector wave functions (SVWF) in the conventional manner, but seeks to obtain the NF-FF transformation exactly, viewing it as an electromagnetic scattering problem. The problem is formulated by considering the NF-FF transformation, when the FF observation points are restricted to a single ϕ plane at a time. The analytical expressions derived toward this end assume a considerably simplified form offering a high computational efficiency. The proposed technique is validated by considering arrays as test antennas with a maximum dimension of 150 X. Based on the principles employed for the spherical NF-FF transformation, an efficient technique for computing the FF patterns of a perfectly conducting scatterer illuminated by an arbitrary source using the technique of physical optics (PO) is also developed. In order to validate this, typical numerical computations are performed and the results obtained are discussed. © 1989 IEEE

An Efficient Technique for Spherical Near-Field to Far-Field Transformation and Evaluation of Far Fields of Perfectly Conducting Scatterers

An analysis of multiple scattering of electromagnetic (EM) waves by two loss-free dielectric spheres with radii greater than a wavelength and located in the near field of a source of radiation is presented. The incident field is expressed in terms of spherical vector wave functions (SVWF). Translational and rotational addition theorems are employed to express the SVWF of the incident field in the coordinate system associated with the dielectric scatterer. Numerical computations are performed for obtaining the amplitude and phase patterns of fields multiply scattered by two loss-free dielectric spheres, whose centers are located on the boresight axis and in the nearfield of an open-ended circular cylindrical waveguide excited in its dominant mode. Numerically computed results show good agreement with measured results obtained from a systematic experimental study on forward scatter performed in the X-band. Copyright © 1987 by The Institute of Electrical and Electronics Engineers, Inc.

Journal	IEEE Transactions on Antennas and Propagation
ISSN	0018926X
Open Access	No