Comparison of two candidate elements for a 30-90 MHz radio telescope array

The long wavelength array (LWA) is radio telescope array now in the planning stage designed for operation between 30 MHz and 90 MHz. The array will consist of approximately 13000 dipole-like elements organized into "stations" of 256 dipoles each, distributed over a region about 400 km in diameter in the USA southwest. Requirements for the element include broad, slowly varying patterns over the tuning range; dimensions on the order of one-half wavelength or less at the highest frequency of operation to facilitate alias-free beamforming; mechanical simplicity; and low cost. When used with a 288 K preamplifier with 100Ω input impedance and 25 dB gain, it is desired for the element-preamplifier combination to deliver galactic noise at a level about 10 dB greater than the preamplifier noise. In this paper we present and compare two candidate element designs, and find that they come close to meeting these goals.