Antenna characteristics of the Dwingeloo 25-metre paraboloid at 820 MHz

For a survey of celestial radio emission in absolute units, the spill-over and side-lobe characteristics of the radio telescope must be well determined. In connection with such a survey planned by Leiden Observatory, the antenna pattern of the 25-metre paraboloid at Dwingeloo, the Netherlands, has been determined experimentally at this frequency. The response of the antenna has been measured, down to a level of -65db with respect to the main beam, at 1\ub0 intervals over an area of 2\u3c0 steradians. A circularly polarized transmitter on a 300-metre tower at a distance of 10km was used for these measurements, and a receiver whih effectively measured the average power in two orthogonal polarizations. The response within the main beam was determined using astronomical radio sources. It was found that the observations were rather severely affected by trees between the antenna and the test transmitter and approximate correction factors were applied. The effective solid angle, stay factor, and aperture efficiency have been computed from this corrected pattern. In addition, components of antenna temperature due to atmospheric and ground emission, on the basis of a simple model, have been calculated for various orientations of the antenna.NRC publication: Ye