Tunable 200 GHz lens-coupled annular-slot antennas using Schottky varactor diodes for all-electronic reconfigurable terahertz circuits

A tunable lens-coupled annular-slot antenna using a Schottky varactor diode has been designed, fabricated and characterised at 140 to 220 GHz. Simulation results show that the resonant frequency of the annular-slot antenna can be effectively tuned by varying the capacitance of the imbedded varactor diode, with an average tunability of ˜2.5 GHz/fF. Prototype demonstration using a varactor with zero-bias capacitance of 3.8 fF has shown a frequency tuning range from 197 to 202.7 GHz by varying the diode DC bias voltage from 1 to -5 V (corresponding to a diode capacitance change from 4.97 to 2.4 fF). The measured tunability is 2.22 GHz/fF, which agrees well with simulation. Projections indicate tuning ranges of ˜50 GHz in the G-band should be possible using varactor diodes with ˜20 fF zero-bias capacitance.