Abstract
A fully planar antenna design incorporating a high impedance surface (HIS) is presented. The HIS is composed by a periodic array of subwavelength dogbone-shaped conductors printed on top of a thin dielectric substrate and backed by a metallic ground plane. First, the characteristics of a dipole over PEC or PMC layers, a dielectric slab, and the HIS are compared and studied in detail, highlighting the advantages provided by the use of the HIS. Then, the design of a low profile folded dipole antenna working at 5.5 GHz on top of the HIS is described. The surface provides close to 6% antenna impedance bandwidth and increased gain up to 7 dBi, while shielding the lower half space from radiation. The antenna structure comprises three metal layers without any vias between them, and its overall thickness is 0.059λ0. The dipole is fed by a balanced twin lead line through a balun transformer integrated in the same antenna layer. A prototype has been built and measurements confirming simulation results are provided.
Highlights
S INCE the advent of electromagnetic bandgap (EBG) materials and metamaterials, researchers have tried to realize artificial magnetic conductors (AMCs) [1]–[5] that can provide an effective shielding of radiation without requiring the vanishing of the tangential electric field
The so called magnetic resonance frequency [13] is very close to the frequency where the reflection phase value reaches zero degrees and the surface behaves as an AMC
The reflection coefficient and input impedance de-embedded to the folded dipole terminals for variable high impedance surface (HIS) and ground plane sizes are shown in Fig. 21 and Fig. 22, respectively
Summary
S INCE the advent of electromagnetic bandgap (EBG) materials and metamaterials, researchers have tried to realize artificial magnetic conductors (AMCs) [1]–[5] that can provide an effective shielding of radiation without requiring the vanishing of the tangential electric field. One important application of AMCs is, for example, as the ground plane of an electric dipole for a low profile design with increased forward directivity [6]–[13] In this context, according to different terminologies in use, the metamaterial surface is denoted either as EBG ground plane [7], [8], [10], [14], reactive impedance substrate [9], magnetic ground plane, or high impedance surface (HIS) [5]. In this work an artificial reactive impedance surface is realized using a periodic structure printed on a planar grounded substrate without any via This structure is similar to the one presented in [5] though its modeling is substantially different since in this case a subwavelength thickness is used for the dielectric layer. Red and green colors indicate strong and weak field intensity, respectively
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