Frequency selective surfaces with very low loss and cross-polarisation levels

Frequency selective surfaces have been used to increase the capacity of multifrequency reflector antenna systems by means of dichroic subreflectors. In modem satellite communications, multifrequency antennas need a quite low cross-polarisation level to cope with frequency reuse requirements and dichroic surfaces with low-losses are necessary in a cascade configuration to separate several frequency bands. The authors describe the design of an inductive frequency selective surface with a separation between transmission and reflection frequency bands of 1:1.2 and with very low loss and cross-polarisation levels. The design criteria for the choice of the proper lattice, the number of grids, the spacing among them and the geometry of the selective element are discussed