Frequency-independent antennas for low-frequency radio telescope

Abstract

Exploring the universe at low frequencies for sensitive and broadband polarization studies of a range of radio sources is expected to open up a new dimension to radio astronomical observation. Building a low-frequency radio telescope (LFRT) to operate over the frequency band of 30–360 MHz with a wide field-of-view (FOV) capability and an instantaneous bandwidth of 300 MHz is considered most rewarding for observing the low-frequency universe. For this telescope, two reflector-based dipole antennas have been designed with 1:3 bandwidth to operate in the frequency bands of 30–90 MHz and 120–360 MHz to simultaneously cover the frequency band of 30–360 MHz. They are planar, profiled, and tilted to achieve larger bandwidth and frequency-independent radiation and impedance characteristics. The frequency-independent characteristic is expected to ease the calibration of the antenna bandpass response. The antennas have i) a moderate reflection coefficient of less than −4 dB over their operating bands with a smooth spectral response and ii) frequency-independent E-plane radiation patterns having a maximum dispersion in their half-power beamwidths of less than 10% across their operating bands. The structural parameters of the antennas have been optimized using electromagnetic modeling, and the designs have been validated by constructing prototypes.