In January 2015 we delivered a novel Quasi-Optical bench to SAC, Indian Space Research Organization, in Ahmadabad in Gujarat, India.

Designed for both accurate complex material measurements and the characterisation of Dichroic Plates (DCP's), our circuit allow both normal incidence, but - unusually - also specular and scattering  reflection measurements. SAC are developing a range of DCP's for use in future meteorological satellite radiometers.

Thanks to Dr S B Chakrabarty and Ila Agnihotri  (The latter pictured on the left of Richard Wylde [The bald chap] in this image) and their colleagues for their hard work and enthusiasm during the design and installation of the project.

 

The bench: The V-band horns are connected to the Agilent (sorry Keysight) VNA with Gore cables - only a few dB each Metre.

Both the sample holder and the swing arm can be independently adjusted in angle, to allow both transmission and specular/scattering reflection measurements to be made.

QO losses are very low, as the two S12 transmission plots - calibrated to the waveguide inputs - show.

First V-Band - losses at the 1dB level

and at W-band, only slightly higher, reaching only -1.5dB at the lower band edge.

Although currently configured to work only at V-band (50-75 GHz) and W-band (75-110 GHz), ISRO is expected to add additional bands in the future, through the addition of higher frequency corrugated horns. The precision of the optics should allow measurement to be performed to 400 GHz and beyond.

More details of the bench - designed in Pro/Engineer by Stuart Froud  - can be seen in these images

The beams at the W and 2W level are ghosted in here:

The sample holding mechanism with graduated scale:

The optics operating just about 60 GHz:

and the waist sizes (1/e amplitude radii) at the sample are - in mm: