Field of view (FOV) and effective aperture area are always limited by a reciprocal relationship in conventional heterodyne receiving antenna system of synthetic aperture imaging ladar, leading that the final signal-to-noise ratio (SNR) can't be improved via unilateral increasing one. From key aspects of receiving viewing angle, detectable ability of signal light and SNR, relative merits of three typical heterodyne receiving structures are discussed, which are telescope for heterodyne receiving, focusing lens for heterodyne receiving, and telescope for self-heterodyne receiving. Qualitative analysis results, compared with telescope receiving structure, show that the heterodyne receiver using a lens and a detector can expand the system′s receiving viewing angle and reduce the emission signal power, but can′t enhance the SNR actually, while the heterodyne receiver using a lens and an array detector with larger FOV and stronger detection ability has a reduction to 1/N in transmitting power and N times improvment in final SNR.The conculusions of this study meet with Siegman′s optical heterodyne receiving antenna theory and provide a certain reference to the parameter choosing of other heterodyne detection systems working in the photo-limited regime.