Calibration Challenges for Future Radio Telescopes

Instruments for radio astronomical observations have come a long way. While the first telescopes were based on very large dishes and 2-antenna interferometers, current instruments consist of dozens of steerable dishes, whereas future instruments will be even larger distributed sensor arrays with a hierarchy of phased array elements. For such arrays to provide meaningful output (images), accurate calibration is of critical importance. Calibration must solve for the unknown antenna gains and phases, as well as the unknown atmospheric and ionospheric disturbances. Future telescopes will have a large number of elements and a large field of view. In this case the parameters are strongly direction dependent, resulting in a large number of unknown parameters even if appropriately constrained physical or phenomenological descriptions are used. This makes calibration a daunting parameter estimation task, that is reviewed from a signal processing perspective in this article.Comment: 12 pages, 7 figures, 20 subfigures The title quoted in the meta-data is the title after release / final editing

Radio wave blind zone in a duct: an analytical approach

Electromagnetic (EM) waves propagate through the atmosphere where they are refracted depending on the composition of the atmosphere. This refraction highly influences the propagation of the EM-waves. Certain atmospheric conditions can cause EM-waves to get trapped within a duct. In these ducts blind zones may occur, where there is no EM-wave coverage. These blind zones show up in the results of ray tracing simulations. However, these codes provide no insight into the dependence of the blind zone on the atmospheric conditions and the transmitter height. In this research analytical expressions are derived for the range of these blind zones. The expressions have been verified by ray trace simulations for several transmitter heights under ducting conditions. Results show that the blind zone range can be accurately predicted. </p

Radio wave blind zone in a duct: an analytical approach

Electromagnetic (EM) waves propagate through the atmosphere where they are refracted depending on the composition of the atmosphere. This refraction highly influences the propagation of the EM-waves. Certain atmospheric conditions can cause EM-waves to get trapped within a duct. In these ducts blind zones may occur, where there is no EM-wave coverage. These blind zones show up in the results of ray tracing simulations. However, these codes provide no insight into the dependence of the blind zone on the atmospheric conditions and the transmitter height. In this research analytical expressions are derived for the range of these blind zones. The expressions have been verified by ray trace simulations for several transmitter heights under ducting conditions. Results show that the blind zone range can be accurately predicted. Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Microwave Sensing, Signals & System