A controllable phase coherent pulsed RF signal generator for microwave network analyzer measurements

In this paper, a method is proposed to build a phase coherent modulated radio-frequency (RF) signal with high modulation depth, which can be used as an excitation signal for nonlinear pulsed-RF network analyzer measurements. The source consist of an RF carrier modulated by an arbitrary waveform generator whose sampling clock is phase coherent to the carrier. A software feedback technique is used to eliminate spurious modulation harmonics and to correct the amplitude and phase distortions in the IF signal path. This technique allows to create a modulated excitation signal with a known modulation spectrum (in amplitude and phase). Such a “controlled modulation” signal is required to fully characterize a device-under-test under noncontinuous wave (modulated or pulsed) test conditions with a sampling downconvertor. The measurement of a controlled pulsed-RF spectrum shows the obtained performance (the modulation bandwidth is limited to 4 MHz at this moment)