Calibrated non-linear vector network measurement without using a multi-harmonic generator

The current generation of non-linear vector network analysers (NVNA) relies on a multi-harmonic generator to establish an absolute phase reference. Such a reference may not be readily available or, more importantly, may impose limitations on tone spacing in multi-tone testing for one type of NVNA based on a four-port VNA. The latter is a severe limitation when characterising memory behaviour in RF non-linear circuits. Here a hybrid NVNA is proposed that combines a sampling oscilloscope, a four-port VNA and phase-locked signal generators. A signal generator, phase locked to generators that are combined as the multi-tone excitation, provides the relative phase reference during swept power measurements using the VNA. The high dynamic range VNA-based measurements are corrected in absolute phase using the oscilloscope-based NVNA measurement at a specific power level. The hybrid NVNA has high dynamic range and the lower bound on tone spacing is determined by the memory depth of the oscilloscope, the windowing effect of the VNA receivers and the phase noise of the multi-tone sources. At 2 GHz, the hybrid NVNA has a dynamic range of 40 dB at 200 Hz tone spacing for a two-tone signal, increasing to more than 80 dB for tone spacings of 200 kHz and greater.