The version in the Kent Academic Repository may differ from the final published version. Users are advised to check http://kar.kent.ac.uk for the status of the paper. Users should always cite the published version of record.

The version in the Kent Academic Repository may differ from the final published version. Users are advised to check http://kar.kent.ac.uk for the status of the paper. Users should always cite the published version of record.

A novel biasing technique is described for active frequency selective slot arrays. The bandpass response can be switched between transmitting and reflecting modes, or tuned over a predetermined frequency range using two different biasing circuit configurations based on the same technology. The biasing layer is separated from the slot layer by a very thin, flexible, substrate while pin and varactor diodes are employed for switching and tuning, respectively. One application is the time-dependent modification of the EM architecture of buildings, permitting access to frequency bands as desired.Introduction: There is increasing research interest in employing frequency selective surfaces (FSS) to modify radio propagation in the built environment [1,2]. As most of the mobile and wireless technologies used indoors work between about 300 MHz and 6 GHz, the FSS designed for this application needs to operate in a very wide frequency band [2].Active frequency selective surfaces can add a higher level of control over the electromagnetic wave propagation in buildings. Two related procedures can be considered when applying active devices to frequency selective surfaces: switching and tuning. Switching FSS between transmitting and reflecting modes using pin diodes on metallic dipole patches is well known [3]. The development of switching and tuning on slot FSS, however, has been reported more recently [4,5]. Bandpass active FSS consisted of slots etched on one side of an FR4 substrate, with the biasing circuit on the other side, and metallic vias connected both.In this Letter we propose a double-sided structure, sandwiching a very thin, flexible dielectric material. The thin substrate allows the biasing circuit to be placed with the active devices on its rear side without physical connection to the front surface which contains the slots. These in turn could lay on a second, thick dielectric layer if necessary for support, or for additional bandpass shaping. We describe the application of this biasing technique to two well known basic active configurations using singularly-polarised dipole slots. The first is a switchable structure in which the applied biasing circuit uses pin diodes connected in series. In the second, the capacitance of varactor diodes, placed in parallel, is varied by an applied external voltage.

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