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In this work thin narrow band and wideband electromagnetic absorbers based on the resonant behavior of a high‐impedance surface (HIS) are proposed. The absorbing structures consist of a resistive frequency selective surface over a grounded dielectric substrate. In this configuration, the HIS input impedance is equal to the parallel connection between the capacitive impedance of the FSS and the inductive impedance of the grounded dielectric. Simulated results are compared to experimental ones to validate the proposed methodology.

Measurement results are in good agreement with the simulation results. The relatively small amount of mismatch between the two patterns is mostly attributed to constructive imperfections and edge effects. Essentially, the antenna demonstrates predictable radiation characteristics and verifies the effectiveness of the proposed layout. CONCLUSIONS AND FUTURE WORKIn this paper, a novel concept is introduced: the use of conductive fluid as structural element in order to extend the features of a single monopole antenna. It is shown that by controlling the level of the fluid round the driven element it is possible to control the resonant frequency of the antenna. This capability enables both the operation at different frequencies and at the same time the filtering of interference and the background noise. Additionally, by controlling the heights of the parasitic elements it is possible to control the radiation pattern of the antenna. In essence, this last capability targets at the creation of notch zones concerning the radiation of the antenna, rather than increasing the gain of it. This characteristic is particularly useful in applications where multiple wireless links coexist and the interferences between them decrease the SNIR (signal-to-noise-andinterference-ratio). Future work regarding this topic includes the optimization of the antenna's design parameters (e.g., the dimensions and the materials used) as well as the research for different variations of the antenna layout in an attempt to achieve better emission characteristics. ABSTRACT: Periodic structures are widely used in order to provide different behavior on devices that operate in high frequencies. Some of them, are capable to change the constitutive parameters e and m, so that, the incident wave can assume a different behavior. Therefore, in this work, the tripole array is presented as an alternative tool to improve the performance of microwave systems, in terms of bandwidth, gain and resonance frequency. The equivalent circuit method in conjunction with the full-wave simulation method was used in order to characterize the tripole array topology, for normal and oblique incidence. Measurements and simulated results are compared.

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