Combinations of low∕high permittivity and∕or permeability substrates for highly directive planar metamaterial antennas

G Lovat,P Burghignoli,D.R Jackson,F Capolino

doi:10.1049/iet-map:20050353

G Lovat, P Burghignoli + Show 2 more

Open Access

https://doi.org/10.1049/iet-map:20050353

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Abstract

An investigation of planar metamaterial antennas consisting of grounded metamaterial substrates with low and/or high values of the electric permittivity and/or the magnetic permeability excited by dipole sources is presented. Their performances are characterised in terms of their capability to radiate high levels of power density in the broadside direction and to produce narrow pencil beams pointing at broadside with high directivity. To achieve a high directivity, a pair of weakly attenuated cylindrical leaky waves is excited along the metamaterial substrate; sufficient conditions are established for the existence of such leaky waves in terms of the values of the substrate permittivity and permeability. Approximate closed-form expressions are derived for the phase and attenuation constants of the leaky waves. Numerical results are given in order to illustrate the radiative features of this class of antennas and to validate the theoretical analysis.

Highlights

Periodic structures made of metallic and/or dielectric inclusions in a uniform host medium may be represented, in suitable frequency ranges, as homogeneous artificial materials that show novel and interesting electromagnetic features
The metamaterial antennas considered in this work are similar in terms of the mechanism of radiation: all the antennas in [1 – 11] radiate a narrow beam because the feed excites slowly attenuating leaky waves, as demonstrated in the work of Lovat et al [4] and Jackson and Oliner [6]
Grounded metamaterial slabs have been studied with the aim of designing planar antennas with enhanced broadside radiation and/or high broadside directivity

Summary

Introduction

Periodic structures made of metallic and/or dielectric inclusions in a uniform host medium may be represented, in suitable frequency ranges, as homogeneous artificial materials (metamaterials) that show novel and interesting electromagnetic features. Metamaterials are not usually isotropic when practically implemented, but the general properties discussed in this paper for the isotropic case, assumed for simplicity, have been found assuming specific anisotropic models In this contribution, we focus on a comparison among antennas based on different realisations of substrates with high/low values of permittivity and/or permeability. The conclusions given in this paper provide guidelines for a more comprehensive investigation assuming a more realistic homogeneous anisotropic model, or even the still further realistic case of a metamaterial made of actual periodic inclusions Their importance rely on the fact that no other studies have been carried out so far on this topic, and that the example seen in the literature represents just one of the possible choices (a low-permittivity metamaterial) that can be adopted in order to realise a planar radiator with enhanced directivity or broadside radiation. MVL – mu very large, that is, jmrj ) 1; EVL – epsilon very large, that is,pj1rj ) 1; Low-impedance material – hr 1⁄4 p(mr/1r) ( 1; High-impedance material – phr 1⁄4 (mr/1r) ) 1; Low-index material – nr 1⁄4 p(mr1r) ( 1; High-index material – nr 1⁄4 (mr1r) ) 1

Maximisation of broadside radiation

Leaky waves and enhanced broadside directivity

Numerical examples

Conclusion