Abstract:
Highly directive antennas are useful in applications such as satellite communications, radar systems and biomedical applications. Directivity is usually achieved using either large antenna apertures or array systems comprising many antenna elements. In recent times, metamaterials have been investigated for improving the directivity of different types of antennas such as linear wire antennas, patch antennas, horn antennas, slot antennas etc. In this work, we investigate the possibility of improving the directivity of a slot antenna with a metamaterial substrate and a source excitation within the substrate. The metamaterial substrate is modelled as a Debye medium with dispersive permittivity and permeability. The refractive index of the substrate is negative at frequencies below the plasma frequency, zero at the plasma frequency, positive at frequencies above the plasma frequency. We demonstrate a directive 3D (three-dimensional) two-slot antenna structure with a near zero refractive index substrate that is capable of directing the main lobe of the radiation away from the broadside based on the position of the source within the substrate, with respect to the two slot apertures. The effect of antenna parameters, such as material of the substrate, length of the aperture or slot length, width of the slot, spacing between the slots, height of the substrate and the choice of plasma frequency of the metamaterial, on the far- field radiation pattern and directivity of the antenna are studied. Transverse magnetic (TM) mode wave propagation is simulated using the finite difference time domain (FDTD) techniques with perfectly matched boundary conditions. The far- field radiation pattern of the 3D two-slot antenna is estimated from the electric fields at the aperture. The results indicate that reduced beam width is achieved for a bandwidth of frequencies around the plasma frequency when compared to a conventional slot antenna with the air substrate. These results imply that 3D two-slot antenna design could be extended to 3D multi-slot antenna design for better directivity and controllability in beam steering.
