A Ku-band rotating, fanbeam scatterometer (RFSCAT) will be used to measure the sea surface wind field from a polar-orbiting small satellite with a rotating, range-gated fanbeam radar scatterometer. The measurement principle and instrument are introduced in this article. An end-to-end simulation model is adopted to analyse and optimize the performances of the system, taking into account the radar observation conditions. Then two kinds of spatially coherent wind fields, namely a parallel wind field and a circular wind field, as well as an incoherently random wind are simulated to assess the system performances. The results show that with the chosen configurations, the performance for wind vector retrieval of the discussed scatterometer is roughly comparable to the pencil-beam radar scatterometers (e.g. SeaWinds on QuikSCAT), and exceeds it at some wind regimes over part of its swath. Particularly, it usually has a better performance for wind direction retrieval, though with a narrower swath.