Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976rsci...47..222p&link_type=abstract
Review of Scientific Instruments, vol. 47, Feb. 1976, p. 222, 223.
Astronomy and Astrophysics
Astronomy
5
Beam Switching, Cassegrain Antennas, Millimeter Waves, Radio Astronomy, Subreflectors, Antenna Feeds, Block Diagrams, Horn Antennas, Noise Reduction, Servomechanisms, Signal To Noise Ratios, Square Waves, Switching Circuits
Scientific paper
A method is described for switching the beam of a radio-astronomical antenna by tilting the subreflector, rather than using a RF switch coupled to an off-axis feed horn. It is noted that this method is more advantagenous because the switching system is virtually lossless and switching for all frequencies is accomplished by one simple mechanism. It is shown that a square-wave movement of the beam is desirable in order to provide an optimum S/N ratio, that the frequency of the square wave should be greater than 2 Hz and as high as 5 Hz, and that the transition time should be less than 31 msec (preferably, less than 12 msec). The required performance of the switching subreflector used with the NRAO 11-m millimeter-wave antenna is outlined, block diagrams of the subreflector and servo systems are presented, and switching waveforms at 5 Hz are illustrated for the case when the beam is switched 4 arcmin.
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