Low-Profile Ferrite Loaded UWB Tightly Coupled Dipole Array

Tightly coupled dipole arrays are quickly becoming a viable replacement to thick egg crate Vivaldi arrays as they are planar and low-profile (<lambda(H)/2), but currently are limited to bandwidths around 4.5:1 (VSWR < 2) without using dielectric superstrates. This paper investigates ferrite loading to overcome the bandwidth limitation without using dielectric materials. Full wave simulation is used to study the miniaturization and bandwidth improvements achieved with ferrite substrate loading. For this initial work, lossless ferrites with constant permeability are placed between the antenna aperture and ground plane. An undesired TM210 ferrite material mode is shown to limit the arrays high frequency bandwidth and is predicted within 5% using simple resonate cavity analysis. Using a ferrite substrate with mu(r) = 3 a 6.6:1 instantaneous bandwidth (VSWR < 2) is achieved without mode suppression and extends to 7.75:1 using mu(r) = 7 with mode suppression. The corresponding array thickness is lambda(L)/46, where lambda(L) is the wavelength at the lowest frequency of operation.