**All-Stokes Parameterization of the Main Beam and First Sidelobe for the Arecibo Radio Telescope**

*Authors:* Carl Heiles, Phil Perillat, Michael Nolan, Duncan Lorimer, Ramesh Bhat, Tapasi Ghosh, E. Howell, Murray Lewis, Karen O'Neil, Chris Salter, Snezana Stanimirovic

*Published:* Publications of the Astronomical Society of the Pacific, accepted (2001)

*Abstract:*

We describe a scheme that characterizes the main beam
and sidelobe in all Stokes parameters employing
parameters that allow reconstruction of the complete beam
patterns and, also, afford an easy way to see how the
beam changes with azimuth, zenith angle, and time. For the
main beam in Stokes I the parameters include the beam
width, ellipticity and its orientation, coma and its orientation,
the point-source gain, the integrated gain (or, equivalently,
the main beam efficiency); for the other Stokes parameters
the beam parameters include beam squint and beam
squash. For the first sidelobe ring in Stokes I the
parameters include an 8-term Fourier series describing
the height, radius, and radial width; for the other Stokes
parameters they include only the sidelobe's fractional
polarization.
We illustrate the technique by applying it to the Arecibo
telescope. The main beam width is smaller and the
sidelobe levels higher than for a uniformly-illuminated
aperture of the same effective area. These effects are
modeled modestly well by a blocked aperture, with the
blocked area equal to about 10% of the effective area (this
corresponds to 5% physical blockage). In polarized
emission, the effects of beam squint (difference in pointing
direction between orthogonal polarizations) and squash
(difference in beamwidth between orthogonal polarizations)
do not correspond to theoretical expectation and are
higher than expected; these effects are almost certainly
caused by the blockage. The first sidelobe is highly
polarized because of blockage.

Paper (postscript, with figures - 141.1 kb)