Spherical wave strut blockage in high gain reflector antennas

High gain antennas for space applications sometimes require a multiple band operation in a constrained environment that imposes complex feeding configurations inside the main reflector (typically, a centered dual reflector system). In such cases the blockage and the diffraction effects cannot be ignored during the design process, since they affect parameters of primary interest such as the antenna efficiency, the sidelobes and the cross-polar level. This paper is concerned with the spherical wave blockage (SWB) of the struts. When the attachment of the struts are located deeply inside the main reflector surface, the interference of the primary field with such structures may create a rather extended masking of the reflector surface when the strut diameter is large in terms of a wavelength. Even for thin struts, the diffraction of the primary field cannot be neglected since the reflector induced currents may be significantly modified, as is shown.