Controlling Surface Waves on Finite FSS Groundplanes

in the following we shall use the finite FSS groundplane and accept the greater complexity due to the more intricate presence of surface waves. 

In the next section we shall examine these surface waves in more detail and also ways to alleviate them. 

By inspection of Fig. 5.9 we chose the frequency 5.7 GHz (more or less arbitrarily) as a representative of a range of frequencies with strong surface waves. The actual column currents obtained from the SPLAT program are shown in Fig. 5.10. Indeed, we observe very strong surface waves at that frequency. 

We shall attempt to suppress these surface currents similarly as we did in Chapter 4, namely by loading the edge columns only with resistors located at the center of each element. Two examples are shown in Figs. 5.11 and 5.12, respectively. In the first case we have loaded the three outermost columns with the load resistors 200, 100, and 50 ohms, respectively, as shown in the insert of Fig. 5.11, bottom. Similarly, the example in Fig. 5.12 has the seven outermost columns loaded with resistors as indicated in the figure. In the following we shall refer to these as the lightly and heavily loaded cases, respectively. 

Finally we should remind ourselves that a practical antenna probably will be made with a groundplane comprised of a finite perfectly conducting groundplane rather than using a finite FSS (except perhaps at the edges see later). Thus, in that event our interest in surface waves associated with the finite FSS groundplane has been reduced to be of merely academic interest. 

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