US Patent 7522274 Radiometers

Radiometers detect radio wavelength electromagnetic radiation and typically have an antenna (16), an amplifier (18) and a detector (20). All three of these components have response characteristics that may be dependent on temperature, and in the case of systems using radiometer arrays dependent upon temperatures throughout the system. Different temperatures across a multi-channel antenna and differential channel temperature response can result in poor image quality from imaging radiometers. Resolution of a linear array of detector horns is limited by the size of the horns. An imaging radiometer (10) uses a focusing polariser (36), a quarter wave plate (32), a rotating inclined disk (28), and a detector feed array (16) to perform a conical scan, and compensates for variation in operating temperature of a radiometer using one or more of a variety of techniques including calibrating channels relative to each other, calibrating channels using reference temperatures in-situo, and calibrating channels using temperature response predictions stored in the radiometer signal processor (22). Aspects of the invention also optimise image resolution, image quality and allow calibration.