RECIPROCITY IN SIMULATIONS OF BOLOMETRIC DETECTORS IN TRANSMITTING MODE

Abstract

Bolometric detectors used in radio-astronomical instruments such as the ESA Planck Surveyor, operate as incoherent receivers of electromagnetic radiation. Meanwhile, the optical (quasi-optical) parts of the instruments (feed horns, telescope mirrors) are conventionally designed in transmitting mode when a coherent source of radiation (supposedly, equivalent to the bolometric detector) replaces the detector and radiates the electromagnetic waves through the optical system to the sky. The rules of reciprocity in such a replacement of a detector by an “equivalent transmitter” located in a lossy (open) structure (a bolometric cavity coupled via the feed horn with the outer space) are not obvious and usually ignored. A conventional simplistic approach used in this problem may cause errors in the design of such systems. By considering simple, analytically solvable models that simulate bolometric detectors surrounded by some structures, we find the rules of reciprocity providing the necessary equivalence in replacing the receiver by an appropriate transmitter as needed for the rigorous simulations of infrared and submillimetre-wave bolometric systems.