| The design of a single layer dual band frequency selective surface (FSS) with close to an octave separation between the two bands is considered. Three design guidelines are given to specify about the location of the fundamental and harmonic resonances, the regularity of the elements, and the interelement spacing of an FSS. These guidelines are arrived at by studying the perturbation of an FSS and by examining the responses of several arrayed elements which have two resonant frequencies.; The perturbation study derives analytic expressions for typical perturbations that occur to a single band FSS when it is converted to a dual band FSS. Expressions are derived for the case when every second element of an array has a perturbation of the resonant frequency, the interelement spacing, the bandwidth, or the orientation of the elements. Additional expressions are obtained for the case when every third element of an array has a perturbation of the resonant frequency or the interelement spacing. Typical responses are calculated from all expressions. Also, the response of a tripole array is calculated when every fourth element is a different size or missing.; In addition to the perturbation study, responses are calculated for FSS's with elements having two resonant frequencies. The results show how some surfaces fail as dual band FSS's because of noncompliance with the guidelines. Finally, several compliant and successful dual band designs with dipoles and tripoles using a new type of capacitive loading are shown. |
