Significance of the Ground Plane Width and Frequency on the Patterns Radiated by Rectangular Slot Antennas

Abstract

This paper investigates how the width of the ground plane and operating frequency influence the patterns radiated by the slot antenna. Total field radiated by a slot antenna etched in a finite-sized ground plane, comprises the primary and secondary fields. Primary field is the field radiated by the slot when the ground plane dimension in which the slot is cut, is viewed as infinite dimension while the secondary field is due to diffractions from the edges of the ground plane when it is of finite extent. It is shown here that, variations in the width of a finite-sized ground plane are accompanied with differential E-plane patterns, at a given operating frequency. Simulated results show that E-plane patterns are characterised by pattern distortions in the forward direction and non-zero ripples pattern in the reverse direction. The number of these distortions and ripples increases with increase in the width of the ground plane while and the spacing between them reduces. However, in the case of H-plane, unlike what obtains in the E-plane, H-plane patterns of the slot in finite-sized ground planes remain identically the same irrespective of the width of the ground plane. Distortions and non-zero ripples in the reverse direction of E-plane patterns of the slot are due to contribution of edge diffraction into the total field pattern. The strength of the diffracted field decreases with increase in the width of the ground plane, making the pattern to approach the limit of the infinite ground consideration. Edge diffractions in the H-plane are inconsequentially small to make meaningful impact in the total pattern, hence identical patterns in all simulations. For the effects of the varying operating frequency at a given ground plane width, E-plane patterns are identical in all respect at all frequencies whereas H-plane patterns vary with varying operating frequencies. It is observed that so long the ratio of the slot length to the operating wavelength is not more than one; H-plane patterns of the slot assumes the characteristic half-of-figure-of eight shapes. However, whenever this ratio is greater than a unity, multi-lobes patterns emerge.