Broadly tunable frequency division duplex transceiver: Theory and operation

Software defined radios (SDR) capable of supporting a wide range of legacy and future systems must be compatible with frequency division duplex (FDD) operation. We have recently demonstrated an FDD capable, integrated SDR (SD-FDD) that achieves >25dB isolation of TX and RX across a wide band while supporting high TX power. This transceiver employs an artificial transmission line and frequency selective TX degeneration to meet the various requirements of FDD-SDR. In this paper, this architecture is analyzed and methods to choose and calibrate the complex input weights of the transmitter are derived. The key degeneration parameters are characterized and how they affect noise is described.