Lossless Broadband Microwave Switches

摘要

The GaAs dual-gate MESFET is a very powerful microwave device offering more gain and a wider range of functional capabilities than a conventional single-gate FET (field effect transistor). It has also been demonstrated that the dual-gate FET can be switched from full off to full on in less than 50 psec. Combining the high gain and fast switching speed of this device with its inherently high isolation makes it an attractive candidate for microwave switching applications. This report describes the results of a 21 month effort to demonstrate the feasibility of using dual-gate FETs as high-speed, broadband, lossless microwave switches. During this period, we have designed and fabricated two different dual-gate FET structures which functionally operate as multipole, multithrow switches with gain. We have measured gains as high as 18 dB at 10 GHz from simple dual-gate structures. We have also measured on-off ratios in excess of 30 dB and channel-to-channel isolation in excess of 25 dB in multiport structures. We have developed various characterization and measurement techniques adapted to handle the complex structures being studied. From the data thus taken, an equivalent circuit model of the dual-gate structure has been derived and applied to multiport devices. Finally, a prototype broadband double-pole, double-throw switch was designed. This hybrid circuit was built, and it demonstrated a capability of switching microwave signals while providing gain. (Author)