Mechanically short single and multi-carriage impedance tuners use a dielectrically filled slabline. 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 factor is 40%. Using dielectric low loss oil also 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. The method is most effective for wideband tuners with lowest frequency of operation between 100 and 200 MHz and harmonic tuners with lowest frequency between 200 and 400 MHz.
Filed: 13 March 2013