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This paper proposes a new nth order two-input/output filter in module for two-phase signal processing. The filter can make the distinction between positive and negative frequencies of two-phase signals and can allow for processing of the signals based on frequency polarity. The filter can also change dynamically its filtering characteristics by simply injecting a shift signal to the filter. The filtering effects equivalent to ones by parallel-arranged filters with vector rotators can be obtained, but in a much simpler manner. Unified analyses about attractive general properties of the proposed filter are given for easy designs and realizations as well. Effectiveness of the analyses and usefulness of the filter are examined and confirmed through numerical experiments. The proposed two-input/output filter in the module has potential usefulness in a variety of polyphase signal filtering applications, including three-phase power systems with active filtering function and sensorless vector controls of three-phase AC motors.