A X-K-KA band dichroic mirror for ESA deep space antennas

This paper presents a complete overview of the project activity for a new dichroic mirror to replace the actual unit (M6, currently installed in the DSA2, Cebreros, Spain). The required specifications and constraints, the analysis and design tools adopted and the design of the dichroic mirror are also discussed and the manufacturing, testing and measuring techniques adopted to fabricate, verify and measure this dichroic mirror are presented. The new dichroic mirror discussed in this paper is due to be installed at the same nominal incidence angle of the actual unit and it will transmit the Ka-band Rx and the Ka-band Tx channels while it will reflect the X-band Rx, X-band Tx channels and K-band (25.5–27 GHz). For all frequencies, the dichroic mirror will be able to operate with Left-Hand Circular Polarisation (LHCP) and Right-Hand Circular Polarisation (RHCP) simultaneously. A detailed mechanical model of the dichroic mirror has been implemented to simulate the thermo-elastic behaviour of the entire mirron in operation. The structure is modeled assuming two different elastic materials: the external ring composed of solid bulk material (aluminium alloy), and the perforated central part considered as a continuum orthotropic elastic material. In particular, the mechanical and thermal parameters of the perforated area have been retrieved by numerical simulation of a significant portion of the perforated area itself. The thermal analysis takes into account the internal conduction and the convection operated along the external surface of the mirror and through the perforated part of the plate by the surrounding air applying an ambient temperature of 20 °C.