4-layer inductive grid FSS at 45 deg incidence

Situations in which single-layer frequency-selective surfaces are required to produce reasonably close spacings between the transmission and reflection bands are considered. The choice of array element for linear polarization includes the Jerusalem cross, the concentric ring, and the double square. An alternative approach is to synthesize the required transmission curves using multiple layers of simpler structures, such as capacitive or inductive grids. The present investigation is concerned with results for two structures to illustrate some of the problems which can arise experimentally. Attention is given to an inductive mesh used in a 45 deg incidence diplexer, copolar losses in the case of a 4-layer inductive grid and 2-layer concentric rings, and linear crosspolar levels.