  Between the BICEP2 and Keck Array experiments, we have deployed over 1500
dual polarized antenna coupled bolometers to map the Cosmic Microwave
Background's polarization. We have been able to rapidly deploy these detectors
because they are completely planar with an integrated phased-array antenna.
Through our experience in these experiments, we have learned of several
challenges with this technology- specifically the beam synthesis in the
antenna- and in this paper we report on how we have modified our designs to
mitigate these challenges. In particular, we discus differential steering
errors between the polarization pairs' beam centroids due to microstrip cross
talk and gradients of penetration depth in the niobium thin films of our
millimeter wave circuits. We also discuss how we have suppressed side lobe
response with a Gaussian taper of our antenna illumination pattern. These
improvements will be used in Spider, Polar-1, and this season's retrofit of
Keck Array.
