Subject and Purpose. The current research projects in astrophysics are in need of high-sensitivity scientific instruments. The accuracy and sensitivity of observations can be enhanced through the use of large radio telescopes and other radio frequency systems, as well as via application of diagnostic instruments intended for exploring the radio propagation conditions along the signal paths. The paths traverse all of the Earth’s outer structural shells, from the atmosphere to remote layers of the magnetosphere. The present work is aimed at developing a highly sensitive off-set radiometer, operable in the frequency range of 20…25 GHz (1.35 cm waveband) and capable of monitoring the atmosphere above large centimeter-wavelength radio astronomical instruments, such as the recently developed radio telescope RT-32. The instruments like that should help making account of the integrated tropospheric absorption of the signals arriving from space radio sources and artificial objects in the near space. Methods and Methodology. The modern software that is used for simulating operation of microwave circuits, and the high quality models of microwave units available on the market, allow analyzing various circuit options, thus enabling a full-fledged development of such devices. As long as the intended implementations of the radiometer suggest the use of exclusively standard, commercially available and preferably off-the-shelf components, the development was based on analyzing the parameters and layout of such units. Results. An ultra-high sensitivity, broadband radiometer for the 1.35 cm range has been developed, which is intended for measuring integrated tropospheric absorption of the relevant radio waves. The calculated noise factor of the instrument is 2.3 dB. The extended bandwidth and high stability of the radiometer elements will provide for a sufficient sensitivity of the instrument as operated in conjunction with the receive system of the RT-32 radio telescope. Conclusions. The high-sensitivity, broadband radiometer that has been developed will provide for a much greater operative accuracy of radio astronomical and radio physical research projects. The radiometer, which has potential for further modernization, has been designed for use with the multi-band, high-tech radio telescope RT-32 in the interests of radio astronomy and space science, in particular for monitoring and forecasting the state of atmospheric and space weather systems.
