Wilkinson Microwave Anisotropy Probe

Product Name
Far-Sidelobe Beam Maps
Coord. System
Spacecraft Coordinates
Projection Type
HEALPix, nested, res 7 (Nside=128)


These are resolution 7 maps of the antenna gain response over 4π steradians for each of the 10 WMAP differencing assemblies. While WMAP's optical system gain drops very rapidly when moving away from the main beam line-of-sight, the emission of the extended Galactic foreground can be 1000 times brighter than the fluctuations of the CMB and can cover very large solid angles. It is therefore extremely important to fully characterize the antenna gain response. The Far-Sidelobe Maps are based on compilations of data from the following sources:

  • GSFC anechoic chamber antenna range
  • Princeton outdoor antenna range
  • In-flight lunar data
  • Physical Optics Code theoretical predictions

The gain pattern is provided in spacecraft coordinates, such that the X axis is parallel to the plane of the radiators, -Z is the anti-sun direction of the spin axis, and Y is perpendicular to both. Gain is in dimensionless units, 4π/(beam solid angle). Positive values refer to A-side pickup, and negative values to B-side pickup.

These maps are in units of directive gain, gi, where i is a pixel; these are the linear units that correspond to dBi. The normalization is such that i(|gi|) = 2 * Npix, or it would equal 2*Npix if the full antenna pattern were represented rather than being cut off at the radius chosen to define the main beam/far-sidelobe boundary.

These maps are the same as were delivered in the third data release. The boundary between the main beam lobe and the far sidelobes did not change and therefore these maps did not change.

Additional Information

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A service of the HEASARC and of the Astrophysics Science Division at NASA/GSFC
Goddard Space Flight Center, National Aeronautics and Space Administration
HEASARC Director: Dr. Alan P. Smale
LAMBDA Director: Dr. Eric R. Switzer
NASA Official: Dr. Eric R. Switzer
Web Curator: Mr. Michael R. Greason