Thomas Keating supplied to ESTEC a 310 GHz Illuminator, with best performance comning from the use of a Faraday 45 degree rotator.
TK has supplied an "illuminator" to the ESTEC/Alcatel team responsible for aligning the focal plane array with respect to the pimary dish of Planck.
The illuminator acts as a monotatic transmit/receive device, coupling, on the same boresite, a transmitter and receiver (supplied by Farran) to the Alcatel Compact Range in Cannes.
These two images show the design, prepared by TK designer, Stuart Froud:
The alignment stratergy involves placing a modulating diode in a low gain horn - also supplied by TK - in the Focal Plane Array, and measuring its cross section as the Planck telescope is rotated. Predicted patterns are compared with the measured result to determing if the two components are properly aligned.
The modulator horn with a diode in its single moded waveguide - mounted on the Planck RFQM - is shown here in the foreground. The wire carries the modulating current to the diode
Measurements on the performance of the illuminator confirmed that a TK designed Faraday rotator (shown below) gave a two way Tx/Rx loss of 4dB, some 2dB better than the raw double grid system which
was baselined. That converts to a 2dB single path loss at 310 GHz for the 45 degree rotator.
The illuminator undergoing tests in Cannes.