Employment of New Techniques for Characterizing Indian MST Radar Phased Array

摘要

Scientific investigations of dynamical processes in the earth's atmosphere are being performed over the past two decades using a 53 MHz mesosphere-stratosphere-troposphere (MST) radar, which is located at Gadanki, India. This radar consists of a phased antenna array of 1024 Yagi-Uda antennas. Antenna phase calibration is an important aspect for accurate measurements of atmospheric parameters by phased array MST/ST radars. In this paper, we describe two newly employed techniques to calibrate the large phased array antenna system of the Indian MST radar and the results obtained by these techniques. A total power radiometer technique has been employed for the first time to calibrate the antenna pattern in the receive mode. Radio source Virgo-A has been used as source in the far field for this purpose. The new technique has enabled us to characterize for the first time the first side lobe level of the antenna pattern and also the beam pointing accuracy in the E-plane. In the receive mode, antenna pattern is characterized with a 3 dB full beam width of 2.8(o), first side lobe level of -18 dB, beam pointing accuracy is better than 0.12(o). While the beam width and beam pointing accuracy are found to be close to the design values, the first side lobe level is 2 dB higher than that expected. To characterize the two-way antenna beam, active radar experiments are conducted and beam pointing accuracy has been estimated to be approximate to 0.1(o) using radar echoes from the moon; again for the first time. Improvement of signal-to-noise-ratio is observed with the newly developed antenna phase calibration method that used receiver quadrature detector. The agreement in comparison of wind vector derived from radar observations and Global Positioning System (GPS)-radiosonde measurements shows the performance status of the array antenna with the applied phase calibration.