High performance dichroic design for orbiting VLBI Earth station antenna applications

The National Radio Astronomy Observatory is constructing an Earth station at Green Bank to communicate with two orbiting VLBI satellites, RADIOASTRON and VSOP. The frequency allocations for the communication between this Earth station and the two satellites are in the X and Ku bands. To meet this dual-band communication requirement, the reflector antenna with a frequency selective surface (FSS) or dichoric has been selected. This FSS should be designed to reflect Ku-band signals (13.5 to 15.5 GHz) and to pass X-band signals (7 to 9 GHz). In order to reduce the antenna´s noise temperature, the RF loss (including the ohmic loss) of the FSS should also be minimized. The authors describe the selected FSS design and the good agreement between the predicted and measured FSS performance.<>