Scanning in the E Plane

Small faceted radomes can be made by flat panels containing no discontinuities. Larger ones will in general be constructed of large flat panels comprised of smaller panels. A pertinent question then becomes how precise must these small panels be joined together in order to avoid excitation of surface waves. 

Considering the complexity of the typical periodic surfaces used today, we must state that a precise answer to this question is not possible, nor do we need it. Here we shall limit ourselves to investigating the effect of introducing discontinuities somewhere in the flat panels. 

More specifically we show in Fig. 4.30 the case shown earher in Fig. 4.28 but where a discontinuity has been introduced in each of the two front panels by simply removing one of the unloaded columns located in the middle of the two front panels. Similarly we show in Fig. 4.31 the case where two unloaded columns have been removed from each of the side panels. We note a considerable effect when the discontinuity is at the two front panels and very minor when it is at the sides. Part of the explanation for this observation might be that the surface waves are considerably stronger in the side panels already. 

Based on our observations earlier in this chapter, we may conclude that the amplitudes of the surface waves in these examples are sufficiently low not to warrant any significant radiation and thereby raise the RCS level. Unfortunately, precise numbers of the RCS level cannot be reported. 

So far in this chapter we have considered plane waves incident in the H plane only. In general this is the plane where the most important phenomena occurs. However, one should be cognizant of the fact that surface waves characteristic for finite structures can also exist for E-plane incidence. We shall explore this case in some detail in the following. 

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