In this paper, we present a novel frequency-selective surface (FSS) design aimed at enhancing the performance of broad-band reconfigurable antenna apertures. In particular, reconfigurable printed dipole arrays are examined in the presence of a multilayer FSS. Of particular interest is the design of FSS structures whose reflection coefficient has prespecified phase response over a broad set of frequencies. Previous FSSs primarily considered designs on the basis of the reflection-coefficient amplitude and were intended for radome applications rather than substrates. Designing FSSs subject to phase requirements will be seen to require some compromise in the magnitude. Broad-band requirements also present us with a need for noncommensurate FSS designs.

Conformal slot arrays have been widely used in mobile communication systems due to their distinctive features such as compactness, ease of fabrication, high power handling, frequency-scanning capability and wideband/wide-scanning performance. So far, the focus has been on waveguide-fed slot arrays. On the other hand, cavity-backed slot (CBS) arrays have also been considered mainly because of their low-profile, flush-mountable features. Nevertheless, the bandwidth of CBS antennas has been very limited except for the traveling-wave slot configurations. Here, our goal is to achieve bandwidth enhancement for cavity-backed planar slot arrays by introducing a novel substrate/feed design. When conformal slots are placed over cavity-backed, planar or curved substrates, their bandwidth and radiation characteristics are altered due to the presence of undesired modes (surface-wave or parallel-plate modes) within the cavity. Hence, it is essential to use a frequency-dependent substrate to improve antenna performance. This can be achieved by using a multilayer frequency selective surface as an artificial substrate with a tailored frequency response.

Multilayer frequency selective surfaces (FSS) are needed for optimizing the performance of a broadband antenna. In this paper, we examine various designs of such layered periodic surfaces that can be used to enhance the performance of broadband reconfigurable arrays. Of particular interest is the development of frequency selective volumes which reflect, with pre-specified phase and amplitude of the reflection coefficient, over a broad set of frequencies. Previous emphasis on FSS has been on reflectivity performance, but in this application, the phase response is of more importance. Designing FSS subject to phase requirements is seen to involve some compromise in the reflection coefficient magnitude. A key aspect of the paper is the development of suitable criteria for FSS designs such that conformal antennas can be reconfigured to deliver broad bandwidths. A goal is to also design very thin FSS to serve as artificial substrates for reconfigurable slot arrays.