Vector measurement of modulated RF signals by an in-phase and quadrature referencing technique

Vector measurements of modulated RF signals are demonstrated using a sampling oscilloscope with in-phase and quadrature referencing. Certain sampling oscilloscope designs exhibit sub-picosecond time-correlation between channels. This correlation allows independent referencing of the carrier frequency and the modulation signals. This measurement technique, which can be implemented using simple RF components, provides an alternative to real-time digitising oscilloscopes or real-time spectrum analysers and can be used at higher RF frequencies than is currently possible with these other methods for repetitive RF waveforms. Experimental results are presented for a pulsed RF power application and for 4QAM, 16QAM and DQPSK wireless communication coding schemes.