We describe the design and characterisation of a cryogenic millimetre/sub-millimetre wave calibration load, cooled by
use of a closed cycle refrigerator that is used to test the performance of the ALMA receiver front-end system. Use of the
refrigerator removes the need for liquid cryogen (nitrogen) cooling and allows for long duration, and unattended
operation independent of orientation angle. Key requirements of the load include provision of a well-characterised and
constant brightness temperature over a wide frequency range (from ~100 GHz to ~1 THz) polarisation insensitivity, high
emissivity and mechanical stability. Test and verification of the load performance characteristics is achieved by using
several measurement techniques; these are presented and compared with measurements made using a liquid cryogen load
(cooled reference).
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