There is interest in developing phased array radiometers for space based applications. The limitations and the optimum topology for beam forming network in radiometric systems, however, are not well understood. In this work, two phased array total power radiometer front end topologies are compared in terms of gain and noise temperature stability. It is shown that a phased array radiometer topology incorporating amplifiers at each branch reduces the front end gain and noise figure fluctuation. The dependence of the front-end gain fluctuation on the number of the elements in the array, N, is shown to be ▲G/G ∝ 1/√N. Thus, it is demonstrated that the gain fluctuation contribution of the front-end is reduced as the array size gets larger. This results in a larger maximum usable calibration interval under the condition that the gain variation effects not dominate radiometer ∝T. Such a system also has a lower noise temperature by virtue of the frontend amplification. This work indicates that total power phased array radiometers have significant potential for space based applications.