A four harmonic wideband impedance tuner

A slide screw microwave impedance tuner is presented which has four independent carriages, which slide across a low loss slabline. Each carriage has one or two vertical axes and associated stepper motors and gear, allowing the precise positioning of RF probes (slugs) into the slot of the slabline at any horizontal or vertical position. Each RF probe generates wideband reflection when approaching the center conductor. The associated calibration and tuning software can identify combinations of tuner probe positions corresponding to reflection factors such as to create independent tuning at up to four different frequencies. In case of harmonic frequencies the coverage of the RF probes has to be at least two octaves, i.e.: maximum∶ minimum frequency ≥ 4∶1; in practice frequency coverage is higher than 4∶1, since most applications require a certain operation bandwidth; in the typical case of a fundamental frequency band of 1.8–2.5 GHz the frequency range covered by the RF probes needs to be 1.8 to 10 GHz, the maximum frequency being 4 • 2.5 GHz = 10 GHz..