The IUP Journal of Electrical and Electronics Engineering:
Calibration of the Beam Pointing Accuracy
of an Antenna Array
Using the Celestial Radio Source
The IUP Journal of Electrical
and Electronics Engineering
Madhu G C and Jhansi J
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The paper explains a method to calibrate the beam pointing accuracy of the MST radar-phased antenna array present in the National Atmospheric Research Laboratory (NARL) in Gadanki, India. Phase switched interferometer is used to receive the radio frequency radiations from a celestial radio source called Virgo-A (M87) during its transit time over the coordinates of the antenna array. The radar beam is oriented in a specific direction to receive the radiation pattern generated by the Virgo-A, through which it is possible to determine the error in the beam pointing accuracy.
A phased antenna array consists of an array of elements for transmission or reception of the radiation. The radiating elements are fed with one or more signals whose amplitudes and phases are determined to form a beam in a specified direction. Since accurate pointing of a beam of a phased array antenna demands precise control of phase and amplitude, exact knowledge of the gain and phase of the electronics is essential. However, the parameters of electronic components vary with temperature and can drift over time. Hence, periodic calibration of a phased array may be necessary to ascertain phase and amplitude corrections for each element (Ron, 2001).
The calibration of the beam pointing accuracy of an antenna array can be determined by observing the received radiation pattern. The radiation pattern of an antenna is a three-dimensional pattern of field intensity over the spatial angles. The traditional method of generating the radiation pattern requires two antenna systems. Out of two antennas, the phased-antenna array is assumed to be the antenna under test which is a fixed one. Another antenna setup should be established at some distance away to illuminate the phased-antenna array. It is usual to the antenna system under test as a receiver of radiation which should be illuminated by the second antenna system.