Ultra-Wideband Aperture Array Element Design for Low Frequency Radio Astronomy

21st century Radio Astronomy at frequencies below 1 GHz will be dominated by arrays of thousands or millions of elements in configurations which are dense or sparse, regular or random, delivering data to powerful digital back-ends. High performance, specified by parameters such as the effective aperture and system noise temperature, will be crucial to achieve the ambitious survey speeds and sensitivities demanded by astronomers. In this paper we analyze the different trade-offs and difficulties in the design of ultra-wideband array antenna elements for these radio telescopes at frequencies below 500 MHz. Bandwidths of 7:1 are desired while using low-profile elements to keep the overall cost within the budget.