Abstract
We present an analysis on the performance of the Cassegrain and Gregorian on-axis, off-axis and offset antennas. In our study, we have adopted the design parameters for the Cassegrain configuration used in the Atacama Large Millimeter Array (ALMA) project. Modifications on the original parameters are made so as to meet the design requirement for the off-axis and offset configurations. To reduce spillover loss in the offset antennas, we have adjusted the angle between the axis of the primary reflector and that of the sub-reflector, so that the feed horn is placed right next to the edge of the primary reflector. This is to allow the offset antennas to receive the highest power at the feed horn. The results obtained from the physical optics simulation show that the radiation characteristics of both Cassegrain and Gregorian antennas are similar. The offset designs exhibit the best performance, followed by the on-axis, and, finally, the off-axis designs. Our analysis also shows that the performance of both offset Cassegrain and Gregorian antennas are comparable to each other.
Highlights
Radio telescopes are built to observe naturally occurring signal emission from cosmic sources, such as stars, galaxies, planet, quasars, etc [1 – 5]
A typical radio telescope consists of a parabolic primary reflector antenna and a hyperboloid or ellipsoid sub-reflector
To develop the offset configurations based on the original on-axis designs in [4], β is adjusted to move the positions of the feed horn and the reflectors
Summary
Radio telescopes are built to observe naturally occurring signal emission from cosmic sources, such as stars, galaxies, planet, quasars, etc [1 – 5]. Signals from distant celestial objects received at the surface of the earth are usually very faint. The size of a radio telescope has to be large so as to increase the signal energy received. A typical radio telescope consists of a parabolic primary reflector antenna and a hyperboloid or ellipsoid sub-reflector. The large circular parabolic reflector is to ensure that the telescope has a large signal collecting aperture and to give high angular resolution over a wide frequency range. Incoming signal collected by the primary reflector is focused onto a feed horn located behind or below the parabolic primary reflector. The incoming signal is coupled onto a detector mounted in the waveguide and processed to display the spectral and spatial information [6 – 9]
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