A Plasma-Switch Impedance Tuner With Microsecond Reconfiguration

With many frequency bands previously allocated solely for radar now being reallocated for sharing, radar transmitters must be frequency-agile, able to quickly change operating frequency while maintaining detection range. This article details the design of a 2–4-GHz reconfigurable impedance tuner using 35-W plasma switches. The tuner consists of switched shunt capacitor and inductor branches loading a series microstrip line. For many RF matching applications, a reconfigurable impedance tuner must have a broad tuning bandwidth, real-time switching speeds, high power handling, low loss, and broad Smith chart coverage. The implementation of the tuner using semiconductor plasma switches illuminated by laser diodes is described. The tuner is demonstrated in measurements using a custom search algorithm, adjusting and optimizing the tuner settings to provide maximum output power in approximately $300~\mu \text{s}$ upon changes in operating frequency or antenna impedance. This tuner provides superior reconfiguration times over other high-power tuners in the literature. The tuner possesses losses as low as 0.77 dB and at least 30% Smith chart coverage over the entire tunable bandwidth. With a 26.7- $\mu \text{s}$ switching speed, the impedance tuner is also demonstrated to handle 20 W of power at all frequencies and states with over 40 W of power for greater than half of the octave bandwidth and power handling measured as high as 70 W. The combination of fast reconfiguration and high power handling in an impedance tuner can enable cognitive radar systems to adapt to a congested and dynamic environment in real time.