A six bit, 6–18 GHz, RF-MEMS impedance tuner for 50 Ω systems

A six bit impedance tuner is presented. The tuner consists of six switched RF-MEMS capacitors distributed along a length of CPW transmission line, producing 64 different impedance states. This tuner is capable of tuning to a VSWR of 30:1 at 6 GHz and to VSWR of 110:1 at 16 GHz, with a loss better than 0.7 dB. The impedance tuner is designed to have a 50 Ω impedance from 6 to 18 GHz with all the switches in their upstate. By introducing capacitive loading between the RF-MEMS capacitors a better control of the impedance coverage was achieved without sacrificing the 50 Ω upstate impedance. In this state the return loss in a 50 Ω system is better than 22 dB from 6 to 18 GHz, with an insertion loss better than 0.6 dB. An alternative calculation of loss in impedance matching circuits is presented.