Six-port direct conversion receiver: Novel calibration for multi-port nonlinear circuits

An RF front-end using a six-port circuit is a promising technology for realization of a compact software defined radio (SDR) receiver. Such a receiver, called a six-port direct conversion receiver (DCR), consists of analog circuit and digital signal processing components. The six-port DCR itself outputs four different linear combinations of received and local signals. The output powers are measured at each port, and the received signal is recovered by solving a set of linear equations. This receiver can easily cover a wide frequency band unlike the conventional DCR since it does not require the precise orthogonality that the conventional one does. In this paper, we propose a novel calibration method for a six-port system that includes nonlinear circuits such as diode detectors. We demonstrated the demodulation performance of a six-port DCR by computer simulation and experiments at 1.9, 2.45, and 5.85 GHz.