Antennas for the next generation of low-frequency radio telescopes

The next generation of large telescopes for radio astronomy at frequencies below 100 MHz will consist of tens of thousands of wide-band dipole-like antennas, each individually instrumented with a receiver and combined using digital signal processing. At these frequencies, the sensitivity of a telescope is limited by Galactic noise, with the result that even simple dipoles can deliver extraordinary useable bandwidth. In this paper the necessary characteristics for these antennas are explained, some bounds on performance are developed, and a few candidate designs are analyzed. It is shown that antenna systems consisting of simple wire dipoles, a 360 K active balun, and a long coaxial feedline can achieve Galactic noise-limited performance over large portions of the range 10-100 MHz. It is further shown that when these antennas are used as elements in a compact array, their Galactic noise-limited characteristics are not significantly affected.