CASSBEAM(1) | User Commands | CASSBEAM(1) |

**feed_x**- The x value of the phase center of the feed. If no value is provided, 0 is assumed. [double]

**feed_y**- The y value of the phase center of the feed. If no value is provided, 0 is assumed. [double]

**feed_z**- The z value of the phase center of the feed. If no value is provided, 0 is assumed. [double]

**geom**- This string points to a disk file containing the primary optical surface geometry. This file is a three column ascii text file, each containing space separated values for r, z, and dz/dr for the antenna. There is no limit (other than your computer's memory) to the number of lines in this file. It is assumed (but not checked!) that the values of r start at 0 and are equally spaced. The radius, R, of the primary is given by the value of r in the last row. Columns 1 and 2 are in meters, and column 3 is dimensionless. [string]

**hole_radius**- The radius (in meters) of an unpanelled area at the center of the primary. If omitted, no hole will be made. [double, > 0]

**legapex**- The z value where the legs (struts) intersect each other.
Note that the legs might terminate before reaching this point. The default
value is 1.2*
**sub_h**. [double, > 0]

**legfoot**- The r value where the legs (struts) intersect the primary surface. The default value is half the antenna radius. [double, > 0]

**legwidth**- The effective width of the legs, used to compute blockage. Note that currently a positive value indicates four equally spaced legs with one leg along the x axis. If the value is negative, its absolute value is used in the blockage calculations, but the legs are rotated 45°. If this parameter is not set, or if it is set to 0, then no legs will be generated. [double]

**name**- An optional name given to the antenna. If the name is ``VLBA'', then the true strut geometry for the VLBA antennas is used rather than equispaced struts. [string]

**roughness**- The RSS surface roughness in meters. This number represents the combined surface error for the primary and secondary. If no roughness is provided, the default value of 0 is used. [double, >= 0]

**sub_h**- This value is the z value of the intersection of the subreflector with the z axis. [double, > 0]

**feedangle**- Sets the reference angle for the feed taper. [double, > 0]

**feedpattern**- The name of the file containing the pattern of the feed. This file contains two space-separated columns of numbers: the angle in degrees and the taper in dB. The first angle must equal 0, and the angles must be uniformly spaced. [string]

**feedpatternscale**- The factor by which to scale the pattern defined in
**feedpattern**. [double, > 0]

**feedtaper**- This parameter sets the taper (in dB) of the feed at an
angle
**feedangle**from the feed axis to 10^-**feedtaper**/10. [double, > 0]

**dfeed_x**- Displacement of the feed along the x axis. [double]

**dfeed_y**- Displacement of the feed along the y axis. [double]

**dfeed_z**- Displacement of the feed along the z axis. [double]

**dsub_x**- Displacement of the subreflector along the x axis. [double]

**dsub_y**- Displacement of the subreflector along the y axis. [double]

**dsub_z**- Displacement of the subreflector along the z axis. [double]

**focus**- Displacement of the feed along the feed axis. A positive value moves the feed closer to the subreflector. [double]

**rfeed_x**- Rotation of the feed in degrees about the x axis. A positive value will rotate from the z axis through the y axis. [double]

**rfeed_y**- Rotation of the feed in degrees about the y axis. A positive value will rotate from the x axis through the z axis. [double]

**rfeed_z**- Rotation of the feed in degrees about the z axis. A positive value will rotate from the y axis through the x axis. [double]

**rsub_x**- Rotation of the subreflector in degrees about the x axis. A positive value will rotate from the z axis through the y axis. [double]

**rsub_y**- Rotation of the subreflector in degrees about the y axis. A positive value will rotate from the x axis through the z axis. [double]

**rsub_z**- Rotation of the subreflector in degrees about the z axis. A positive value will rotate from the y axis through the x axis. [double]

**subrotpoint**- Defines the point about which the rotation of the subreflector is performed. The contents of the vector depend on the number of elements are provided: either only the z value, or the x and y values, or the x, y, and z values. [vector (1 or 2 or 3)]

**compute**- A string to tell what output to produce. The string can be `all', `none', or a string containing flag characters. The default value is `all', meaning produce all possible output. `none' will produce only messages on the screen and no output files. The characters of the general string mean the following:

**a**Save the aperture images;

**j**Save the Jones matrices in a table;

**p**Save the parameters;

**s**Save the polarized beams.

- Note that the string is case insensitive. [string]

**diffeff**- A user supplied diffraction efficiency. If none is provided, an internal algorithm that is not very good is used. This needs to be upgraded! [double]

**freq**- The frequency in GHz at which the calculation will be run. [double, > 0]

**gridsize**- Specifies a fixed grid size. If odd, the next even number
will be used. This option overrides any setting of
**oversamp**and is the preferred method of setting the grid size. Setting it to a value less than 32 will result in a grid size of 32. [integer, >= 32]

**leggroundscatter**- The fraction of power that scatters off the struts toward the ground. The default value is 0.2. [double, >= 0, <= 1]

**misceff**- A factor of the efficiency calculation that contains ``everything else''. The user is responsible for choosing a realistic value for this. A default of 1 (i.e., 100%) is assumed if this parameter is not provided. [double, >= 0, <= 1]

**out**- The prefix for all output files. The default is
*cassbeam*. A dot will always separate the prefix from any trailing characters. [string]

**oversamp**- One way of specifying the grid size. This option will make
the grid on the primary fine enough to accommodate 4*
**oversamp***R/lambda points. The default is 1. Note that vastly ``undersampling'' is fine as the field is never calculated anywhere between the feed and the aperture plane. Normally blockage calculations and constancy of the illumination will dictate the required sampling. See**gridsize**for an alternate way of specifying the grid. This parameter is ignored if**gridsize**is set. [double, > 0]

**pixelsperbeam**- This is the approximate number of pixels that the core of the beam will occupy in the output images. [int, > 0]

**Tground**- The temperature in Kelvin of the ground. The default value is 290. [double, > 0]

**Trec**- The equivalent temperature of the receiver. This adds into the system temperature. The default value is 50. [double, > 0]

**Tsky**- The temperature in Kelvin of the sky. The default value is 3 for frequencies over 1 GHz, and 3 * 10^-2.5 nu for frequencies below 1 GHz. [double, > 0]

*out***.illumamp.pgm**- Raster image showing the amplitude of the illumination pattern of the primary. No blockage is done at this point. The scale is linear in flux.

*out***.illumphase.pgm**- Raster image showing the net phase (pathlength multiplied by wave vector) at each point on the primary. A phase gradient is removed. Portions of the image that correspond to zero flux have an arbitrary phase.

*out***.illumblock.pgm**- Raster image showing the blocked portion of the aperture. White means that this part of the dish is experiences either plane wave blockage from the sky or spherical wave blockage from the feed, and thus does not contribute to the gain of the antenna.

**Aeff**- The effective area of the antenna [m^2]. [double]

**Aeff_Tsys**- The effective area of the antenna divided by the system temperature [m^2/K]. [double]

**ampeff**- The amplitude efficiency. [double]

**beampixelscale**- The scale of the generated beam images [deg/pixel]. [double]

**blockeff**- The blockage efficiency. [double]

**diffeff**- The diffraction efficiency. [double]

**fwhm_l**- The full width at half max of the beam in the l direction. [double]

**fwhm_m**- The full width at half max of the beam in the m direction. [double]

**gain**- The gain G of the antenna. [double]

**illumeff**- The illumination efficiency. [double]

**peaksidelobe**- The directivity of the greatest sidelobe relative to the peak directivity of the beam. [double]

**phaseeff**- The phase efficiency. [double]

**point_l**- The l component of the pointing offset from the z axis measured in the image plane. [double]

**point_m**- The m component of the pointing offset from the z axis measured in the image plane. [double]

**prispilleff**- The primary spillover efficiency. [double]

**program**- The name of the program run, which is
*cassbeam*. [string]

**misceff**- The miscellaneous efficiency. [double]

**spilleff**- The spillover efficiency. [double]

**subspilleff**- The subreflector spillover efficiency. [double]

**surfeff**- The surface efficiency. [double]

**totaleff**- The total efficiency calculated for the antenna. [double]

**Tsys**- The system temperature. [double]

**version**- The software version number. [string]

*out***.I.pgm**- Stokes I - total intensity;

*out***.Q.pgm**- Stokes Q - excess linear polarization e_1 over e_2;

*out***.U.pgm**- Stokes U - excess linear polarization in e'_1 over e'_2

*out***.V.pgm**- Stokes V - excess right circular polarzation over left circular polarization;

*out***.QI.pgm**- The ratio of the Stokes Q image to the Stokes I image;

*out***.UI.pgm**- The ratio of the Sytokes U image to the Stokes I image;

*out***.VI.pgm**- The ratio of the Stokes V image to the Stokes I image;

18 Aug 2003 | 1.0 |