New Cold FET I-Q Linear Vector Modulator Topology

This paper presents the design, manufacture and test of a new cold FET monolithic I-Q vector modulator, The circuit has been developed in 8-8.4 GHz X band but can be transposed at any frequency range. The innovation is that the IF data signals are applied to the FET gates. The use of cold FETs allows achieving a 0.8 dB and 6° accuracy with only one voltage tuning on the whole bandwidth and the ¿25°C to +50°C temperature range. There is no DC consumption for the microwave modulator, The accuracy achieved at this first run is yet compatible with new coding and modulating systems and we have investigated several ways to improve the design.