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 (<; λ_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 μ_r = 3 a 6.6:1 instantaneous bandwidth (VSWR <; 2) is achieved without mode suppression and extends to 7.75:1 using μ_r = 7 with mode suppression. The corresponding array thickness is λ_L/46, where λ_L is the wavelength at the lowest frequency of operation.