An antenna-coupled field effect transistor (FET) as a plasma wave terahertz detector is used with the current steering to record separately the gate-source and gate-drain photoresponses and their phase sensitive combination. This method is based on the observation that the plasmon-terminal coupling is cut off in saturation, resulting in only one-sided sensitivity. A polarimetric example is presented with intensity and polarization angle reconstruction using a single three-terminal antenna-coupled Si-metal-oxide semiconductor FET (MOSFET). The technique is applicable to various detection schemes and technologies (high electron mobility transistors and GaAs-, GaN-, and Si-MOSFETs), and other application possibilities are discussed.