Wideband low frequency impedance tuner / 8,212,629

Tuesday, July 3, 2012

An electro-mechanical impedance tuner generates wideband and complete Smith chart reflection factor coverage at frequencies as low as 1 MHz. It comprises an in-line adjustable linear phase shifter and a variable capacitor connected in parallel to ground. The transmission line, which serves as an adjustable phase shifter of variable electrical length, is made as a cylindrical rotating spiral wire-over-ground transmission line, on which runs a sliding contact, connected with a variable capacitor; the capacitor can be, depending on the frequency, immersed in a dielectric liquid, such as oil (.di-elect cons..sub.r.apprxeq.3) or alcohol (.di-elect cons..sub.r.apprxeq.20) for increased capacitance. The cylindrical structure of the spiral transmission line allows for a compact, 1 meter long apparatus at 1 MHz, whereas the required linear electrical length for this type of impedance tuner would be 150 meters in air, or 100 meters when low cost polyethylene dielectric (.di-elect cons..sub.r.apprxeq.2.25) is used. Cascading two or more tuners allows pre-matching and harmonic tuning.