Abstract: Phased array feed（PAF)is a small twodimensional phased array antenna as the multibeam feed.The most prominent merit of PAF is the capability of synthesizing closely overlapped beams，leading to continuous fieldofview coverage and faster survey speed.In this paper， the relationship between focal field matching and antenna efficiency is analyzed，radiation performance both in singlepixel and multibeam applications are compared between PAF and waveguide feeds，and the SNR model of phased array fed radio telescope is introduced.As an emerging feed technology，PAF exhibits more flexibility and better performance.