Characteristics measurements of supersensitive low temperature direct detector receivers of submillimeter waveband region using Planck radiation source

During the investigation and development of supersensitive low temperature direct detector receivers of submillimeter waveband region a need of measurements of their spectral and sensitivity characteristics is arising. We interpret the receiver as the direct detector, for instance the bolometer, and the matching antenna into which the direct detector is incorporated (coupled) together with filters, resonance circuit etc. or without them. Said direct detectors have to work at very low temperatures to achieve super high sensitivity. The radiation feeding in from outside to a refrigerator with measurement purposes is a problem because it is difficult to filter ambient background thermal radiation which will overheat the refrigerator strongly. The radiation power coming, for instance from a spectrum analyzer, has to be below of higher level of receiver dynamic range, i.e. before the beginning of non-linear portion of its signal characteristic. This limit may be two-three orders higher than receiver noise equivalent power. To overcome said difficulties we propose to mount the black body source in cold area of receiver cryogenic system, for instance, inside of the precooling cryostat at temperature 4.2 K, or in another place at lower temperature with characteristics measurements purposes.