Feed networks for antenna-array coupled TES bolometers for CMB polarimetry

Summary form only given. Measurements of the Cosmic Mirowave Background's (CMB) temperature have provided new insight into the origins of our universe, and these experimental successes have been driven by advancements in detector technology. The next generation of experiments have just started measuring the CMB's polarization with monolithic detector arrays that integrate an antenna and filtering on-chip with the detectors. Caltech and JPL are playing a leading role in this effort through their antenna-coupled TES-bolometers. Each pixel of a focal-plane imaging array contains an antenna that itself is an array of coherently driven slot-dipoles. We feed each polarization of this dual-polarized antenna with separate microstrip summing trees that pass power through in-line band-defining filters before termination at the bolometers. We can control the angular response of the antenna with the summing tree design. In particular, the closely packed microstrips seem to couple, which introduces phase errors that steer the two polarizations' beams differentially off boresight. We have introduced extra lags in parts of the tree to correct for this effect and will report on these efforts. Our original summing tree designs also drive the slots with a simple uniform (top-hat) excitation, but this generates strong side-lobes and surface waves. We are currently modifying the tree to drive the antenna with a Gaussian-profile taper to suppress these losses and will report on those efforts as well.