Fibre-optic illumination of GaAs MESFETs for use in phased-array antennas

Experimental and theoretical results are reported for fiber-optic links using MESFETs as light detectors for application in monolithic microwave integrated circuit (MMIC)-based phased-array antennas. Since MESFETs are compatible with MMICs, it is easy to implement a MESFET receiver in MMIC transmit-and-receive (T/R) modules. A receiver design using MESFET detection is less complicated and occupies less area than a PINFET receiver. The use of single-mode (SM) and multimode graded-index (MMGI) fiber to illuminate microwave devices is examined. The keys to this investigation are the high responsivity (R) values obtained by illuminating MESFETS with fibers (R/sub SM/=1.87 mA/mW; R/sub MMGI/=1.18 mA/mW) and the phase coherency demonstration of MESFET fiber-optic links at microwave frequencies using an antenna array and measuring its radiation pattern RF link loss improvements of 9 to 13 dB with respect to links using p-i-n photodiodes were measured.<>