NEAR FIELD OF SLOT RADIATORS

Abstract

In this paper, the cosinusoidal slot aperture distribution is replaced with a two term approximation. Using this two term approximation, the slot fields are evaluated in closed form and explicit expressions are given in terms of sine and cosine integrals. The two term approximation and the near fields derived therefrom agree closely with the cosinusoidal distribution for slot lengths upto 0.65λ ,w ith an error of less than 3.3% with respect to the numerical results for distances Rnearest ≥ 0.05λ from the slot in the near field, where Rnearest is the distance of the nearest point on the slot from the field point. The formulation given here is of practical use in estimating mutual coupling in an array or in estimating radiated emissions for Electromagnetic Compatibility (EMC) analysis. Slots are commonly used as radiating elements in antennas or antenna arrays. Mutual coupling between slots needs to be taken into account for accurately predicting the performance of slotted array antennas. In Electromagnetic Compatibility (EMC) analysis, radiation from slots needs to be taken into account for estimating leakage and interference from apertures used for ventilation, seams, display windows etc. In Radiated Emissions measurement, fields radiated from an Equipment Under Test (EUT) are often measured at a distance of 1 m or 3 m, over a frequency range where the far field criterion may not be fully satisfied. The near field of dipoles with piecewise sinusoidal (PWS) distribution of the form sin(k(l −| z|)), where 2l is the length of the slot and k is the wavenumber, is well known (1, 2). The near field for similar