Proceedings with Extended Abstracts (single PDF file) - Radio ...

ANTENNA BEAM VERIFICATION USING COSMIC NOISET. K. Carey-Smith, A. J. McDonald, W. J. Baggaley, R. G. Bennett,G. J. Fraser and G. E. PlankDepartment of Physics and Astronomy, University of Canterbury,Christchurch, New Zealand.To obtain accurate vertical wind measurements using a VHF radar, the pointing direction ofthe antenna beam must be known precisely. Antenna beam patterns can be investigated usingaircraft, satellites [Sato et al., 1989], the sun [Graf et al., 1971] and extra-solar radio sources[Campistron et al., 2001]. In this study, different methods of beam verification using cosmicnoise sources have been investigated. With data obtained from the new Canterbury UniversityStratosphere Troposphere Atmospheric Radar (CUSTAR) in Christchurch, New Zealand(43 49.5 ¡ S, 172 41.5 ¡ E), the antenna’s pointing direction has been derived by comparisonwith discrete radio sources and also a 45 MHz sky map. The comparison has been performedby fitting Gaussian curves to the individual noise sources and also by performing a crosscorrelationover the whole sky map. The pointing direction of the beam has also been investigatedusing measurements of the vertical velocity. The results indicate that if a sky survey isavailable at a similar frequency and latitude to that of the radar then the optimum method ofverifying the beam pattern is to compare the right ascensions and widths of individual noisesources with corresponding peaks in the radar sky noise profile.1 Calculating the sky noiseCUSTAR operates at 42.5 MHz and uses a square antenna array made up of 128 individualelements. The theoretical half-power full-width of the main beam is 6.35 and the largest sidelobeis 13 dB below the main peak. The sky noise measured by the radar was calculated fromthe background noise, which was obtained using the method of Hildebrand and Sekhon [1974].On a typical day, for ranges less than 5 km the background noise is contaminated by instrumentalnoise, mainly due to leakage of the transmitter pulse through to the receiver input.Above 5 km, sky noise becomes the dominant feature. However, enhancements can be observedin this region and are due to other events such as reflections from aircraft. For theCUSTAR data these areas were removed by averaging over the 25 range bins (at each timepoint) that contained the lowest noise level. Approximately half of the total number of binswere used so that the time series is smoothed considerably, while the possibility of includingareas of unwanted noise, such as aircraft reflections, is minimized.2 Comparison with discrete radio sourcesThree strong radio sources pass through the beam of the CUSTAR antenna array, these arethe Vela-Puppis region (Vela XYZ), Centaurus A and part of the galactic equator. The galacticequator is a broad ridge of high radio emission so does not have exact coordinates, but391