  We present a method for measuring CMB polarization power spectra given
incomplete sky coverage and test it with simulated examples such as Boomerang
2001 and MAP. By augmenting the quadratic estimator method with an additional
step, we find that the E and B power spectra can be effectively disentangled on
angular scales substantially smaller than the width of the sky patch in the
narrowest direction. We find that the basic quadratic and maximum-likelihood
methods display a unneccesary sensitivity to systematic errors when T-E
cross-correlation is involved, and show how this problem can be eliminated at
negligible cost in increased error bars. We also test numerically the widely
used approximation that sample variance scales inversely with sky coverage, and
find it to be an excellent approximation on scales substantially smaller than
the sky patch.
