Frequency reconfigurable RF circuits using photoconducting switches

Designs for a frequency switchable dual-band branch-line coupler and a reconfigurable S-band power amplifier input matching network with photoconducting switches are presented. Frequency switching is achieved by increasing the power of the laser applied to the highly resistive silicon wafer and changing the properties of silicon under optical illumination. The advantages of this approach are high-speed switching, electromagnetic transparency (no interference) and thermal and electrical isolation between the device and the control circuit. A branch-line coupler frequency shift of 35% and 10% has been achieved from all switches off to all switches on in lower (900 MHz) and upper (1800 MHz) frequency bands, respectively. Frequency switchable class AB power amplifier with silicon switch in the input matching circuit has obtained the frequency tuning range of 2.5-3.5 GHz with no significant loss in efficiency and linearity.