Microwave measurements - Non-linear measurements

The employment of an active-loop technique is utilized to effectively and economically control the device-under-test (DUT) load conditions in synthesizing loads. In such a technique, a portion of the DUT output signal is controlled in amplitude and phase by means of a directional coupler and sent back to the DUT. The technique offers great flexibility in load control and selection compared with approaches. Another approach uses the vector network analyzer (VNA) wherein calibration is done as a classical VNA error correction in linear conditions. This technique is employed in order to measure all of the quantities of interest in real-time while exciting the system in non-linear conditions. However, additional calibration step that exploits further power meter measurement is needed in order to achieve information on the magnitude of each wave as classical VNA calibrations can only correct the wave ratios in non-linear conditions. In harmonic characterization, passive and active solutions do exists. Passive tuners have three methods of characterization, including cascade tuners, stub resonators and a multiplexer with normal tuners. Cascade tuners have noticeable flexibility for frequency control and variation while a stub resonator produces very narrow band and has independent harmonic control. Multiplexers separate fundamental and harmonic signals in order to for them to be independently tuned.