Experimental studies of high impedance surfaces and suppression of spatial dispersion
Olli Luukkonen, Pekka Alitalo, Filippo Costa, Constantin Simovski, Agostino Monorchio, and Sergei Tretyakov
Introduction
Artificial impedance surfaces are man-made surfaces with conductive and dielectric elements designed to have a certain electromagnetic response. Artificial impedance surfaces can be used in low-profile antennas, absorbers, quasi-TEM waveguides, filters, et cetera.
There are several types of artificial impedance surfaces, including a “Fakir’s bed of nails”, an array of patches over a grounded dielectric slab, and a mushroom-type impedance surface.
Spatial dispersion means that the permittivity depends on the angle of propagation. In analytical equations spatially dispersive terms may be neglected if the mushrooms are electrically thin and patches are large enough.
Measurement setup
The high impedance surface is measured in the measurement room.
The measurement setup contains two antennas and a rotation unit that turns the sample. The receiving antenna is moving.
Patch array on top of a grounded dielectric slab
In this experiment the surface is simply an array of square shaped patches on top of a dielectric substrate. Beneath the dielectric substrate there is a ground plane. Phase shift on ideal high impedance surface is 0o in contrast to the phase shift on PEC, which is 180o. In man-made structures this happens only at certain frequencies.
Results for experiment 1 - TE 30o Analytical results are denoted with black dashed line, experimental results are denoted with red solid line with error bars. Simulation results are denoted with circles.
Mushroom surface with suppressed spatial dispersion
In the second experiment the surface is so called mushroom structure where the patches are connected to ground plane with vias. In mushroom-type impedance surfaces it is possible to obtain a resonance due to the plasma frequency of the wire medium if the spatial dispersion is supressed. This additional resonance can be used in many applications.
The picture of mushroom structure from the side.
Results for experiment 2 - TM 20o.
Results for experiment 2 - TM 30o.
References
- O. Luukkonen et al., “Simple and accurate analytical model of planar grids and high-impedance surfaces comprising metal strips or patches,” IEEE Trans. Antennas Propag., vol. 56, no. 6, pp. 1624–1632, June 2008.
- O. Luukkonen et al., “Effects of spatial dispersion on reflection from mushroom-type artificial impedance surfaces,” to appear in IEEE Trans. Microwave Theory Tech.
- O. Luukkonen, P. Alitalo, C.R. Simovski, and S.A. Tretyakov, “Experimental verification of analytical model for high impedance surfaces,” Electronics Lett., vol. 45, no. 14, pp. 720-721, 2009. (requires subscription to IEEE Xplore)