Design of a 74-MHz antenna for radio astronomy

Describes the design and construction of an 8000 m² 74-MHz phased array dedicated to measurement of the solar-wind velocity using the interplanetary scintillation (IPS) technique, and a simple and novel autocalibration system that measures and connects phase and amplitude errors to a level of 1° and 0.2 dB rms. In the IPS technique, intensity fluctuations of compact radio sources caused by plasma turbulence in the solar wind are observed with multiple antennas. The time lag between the antennas is estimated using a cross-correlation analysis. The primary requirement of such a system is sensitivity so that one may observe a large number of compact sources. A secondary requirement is high beam efficiency so that one may observe near the Sun. The scan angle was limited to allow the largest possible array element and thus the simplest feed system. The feed was designed to have independent phase and amplitude control of each element. Although this is not strictly necessary it permits the use of the feed as a phase switched interferometer with which any element can be correlated against any other group of elements. This provides a simple and accurate calibration of the entire array. The antenna was completely prefabricated, the site preparation was minimal, and the installation was quick and accurate. The system is remotely operated. The control information, system diagnostics, and data are transmitted over a leased telephone line. The entire system is powered by storage batteries charged by solar cells. In addition to IFS it has been used extensively for pulsar observations which have similar requirements