Prototype Antenna feed for Observations at Decimeter and Meter Wavelengths

Abstract

The objective of this work is to develop a prototype broadband radio antenna that can be used for observing the Sun and other astronomical sources in the 200–600 MHz band; the latter corresponds to a heliocentric height range of ~ 1.01-1.30 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{R}_{\odot} ( &gt;\mathrm{R}_{\odot}$</tex> = photospheric radius). In the case of non-solar targets, the above frequency range is well suited for the observations of Fast Radio Bursts (FRBs) and other transients. The Log Periodic Dipole Antenna (LPDA) is chosen as the feed because it has broadband, directional and uniform characteristics over its operating bandwidth as compared to other broadband antennas. Additionally, the antenna is fitted to a rotor system having minimal radio frequency interference <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\lesssim-100\ \text{dBm})$</tex> in order to track the Sun both in hour angle and declination. It also helps to achieve uniform antenna gain as a function of frequency throughout the observing time period as compared to a stationary zenith pointing system. Although a dish antenna with a broadband feed is preferred due to a larger collecting area and better sensitivity, its gain varies appreciably over the operating bandwidth and its return loss is greater than the nominal value <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\approx-9.5\ \text{dB})$</tex> . The performance of this new system (in the standalone receiving element mode at present) is better than a dish antenna feed in terms of uniform gain and return loss over the designed operating bandwidth.