function pixel_beam_function, ell, res_arcmin

;from: http://xxx.lanl.gov/abs/astro-ph/0007212

;calculate pixel beam function for square pixels                                

;res_arcmin is the side of the square pixel

;effect on power, square the return

pix = res_arcmin/60.*!dtor

out=( exp(-1./18.1*(ell*pix[0])^2.04 ) * ( 1. - .0272*(ell*pix[0])^2 ) )
return, out

end