Single and multi-probe slide screw impedance tuners use a slabline filled with dielectric and the same probe and center conductor as in air. The dielectric filling reduces the overall tuner length by a factor of 1/√εr. The increase in loss, and associated reduction in reflection factor, is partly compensated by the shorter size and travel of the probes. A typical length reduction is 40%. Using low loss oil reduces the electric field between probe and center conductor and increases Corona threshold; lubrication of sliding contact between probe and slabline walls and cooling of the center conductor are additional benefits. Probe grounding is established either by adjustable top mounted conductive slabs or spring loaded grounding contact on the probes. The method is most effective for tuners with lowest frequency between 100 and 200 MHz and harmonic tuners with lowest frequency between 200 and 400 MHz.
An Impedance Tuner with Adjustable Electrical Length / 9,325,290
Tuesday, April 26, 2016