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Frequency-Selective Sufaces Make Nimble Antennas

Reconfigurable antennas can overcome the limitations of conventional antennas as well as the shortcomings of smart or adaptive antennaarray systems. As a result, much attention has been paid to reconfigurable structures based on artificial materials. At the Universite de Quebec, a class of new, reconfigurable radiation-pattern antennas has been developed by Mahmoud Niroo Jazi and Tayeb A. Denidni. With one layer of frequency-selective-surface (FSS) sheet taking the place of several layers of active antenna elements, the antenna promises to provide low cost, power savings, compact size, and robustness.

The authors proposed two different activefrequency- selective screens that could be used to develop reconfigurable-agile radiation-pattern antennas. By precisely incorporating high-frequency PIN diodes into the screens, they reconfigured the surfaces' electromagnetic (EM) responses to imitate blocking of the transparent window for the incident EM waves. To verify performance, the researchers examined the DC-feed loading in the first screen and the PIN-diode parasitic effects. They also clarified the constraints of DC-fed lines for the first cylindrical screen.

The researchers found that the DC-feed line, which is required to bias the active elements, impacts the frequency response of the FSS sheet. Specifically, it changes the equivalent inductance and capacitance related to the electrical circuit model of the resonant strips. Another issue is the diodes' biasing network, which restricts the structure's potentials and applications to certain reconfigurable configurations. The parasitic capacitance of the diodes severely affects the FSS response as well. The stop-band position must therefore be changed to lower frequencies, which may limit the frequency operation of the proposed structures to a particular design range. See "Frequency Selective Surfaces and their Applications for Nimble-Radiation Patterns," IEEE Transactions On Antennas And Propagation, July 2010, p. 2227.

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