This paper identifies the most challenging re quirements for weather observations that a future Polarimetric Phased Array Radar (PPAR) should meet. These are routed in the current capabilities of the US national network of Doppler Weather Radars (WSR-88D). Biases in polarimetric variables are related to the PPAR designs and polarimetric mode of operations. A planar-array PPAR being used for resolving some technical challenges is described.