Finite x Infinite Array With an FSS Groundplane

A top view of the array layout with the FSS groundplane is shown in the insert of both Figs. 5.2 and 5.3. It is comprised of 20 columns of active elements and twice as many FSS elements. The reason for more passive than active elements is simply to make the FSS groundplane more broadbanded. (In general, the closer the elements, the greater the bandwidth cf. the Gangbuster array in reference 91.) 

Putting the FSS elements closer together raises the resonance frequency somewhat. Since the elements cannot be made longer without disturbing the periodicity, all the passive elements have instead been loaded with Zl = j20S ohms (note Here we do not use interlaced elements of the type shown in Fig. 5.1a, just 

A plane wave is incident broadside to this array—that is, at 0°. The bistatic scattered field is obtained from the SPLAT program in the entire range fi om —90° to 270°. Furthermore, we show the bistatic fields for various load conditions of the active elements. 

First in Fig. 5.2 we show two curves, one where the active elements are short-circuited and denoted S.C. and another where Zl = 315 ohms. Note that for Zi = 0 the backscattered field looks like it is coming from a groundplane the size of the array. Furthermore, for Z/, = 315 ohms and with Z = 195 — jl5 ohms we obtain a reflection coefficient 

Furthermore, in Fig. 5.3 we show the bistatic scattered field when Zl = 195 + 7 75ohms—that is, conjugate-matched. We also repeat the case Zl = 315 ohms to facilitate comparisons. 

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