1. Field of the Invention
The present invention relates to electronic devices, and, more particularly, to microwave travelling-wave (distributed) devices.
2. Description of the Related Art
The availability of high-gain, high-frequency microwave transistors has revived the old "distributed" or "travelling-wave" approach for broadband microwave amplification but using GaAs FETs; see Y. Ayasli et al, Monolithic GaAs Travelling-Wave Amplifier, 17 Electronics Letters 413 (1981). Such amplifiers are similar to the distributed amplifier using electron tubes, as described in E. L. Ginzton et al. Distributed Amplification, 36 Proc. IRE 956 (1948), in that the intrinsic gate and drain capacitances serve as parts of the shunt elements of two artificial transmission lines: the gate and drain transmission lines. If the line element values (inductances) are chosen properly, wideband amplification can be obtained with more reasonable VSWRs than is possible for an FET having the same total gate width. The Ayasli article reported results of broadband travelling-wave amplification in the 0.5 to 14 GHz band using four discrete 300 .mu.m gate width FETs in a distributed amplifier configuration. See also U.S. Pat. No. 4,486,719 to Ayasli.
McIver, A Traveling-Wave Transistor, 53 Proc. IEEE 1747 (1965), described a travelling-wave transistor structure using distributed active elements (i.e., both the gate and drain were transmission lines with an extended channel region linking the two lines). In the theoretical treatment, the losses associated with the gate and drain resistances were not taken into account, nor was a detailed, practical device realization given either. Several publications have dealt with the distributed effects of the gate transmission line. Due to the use of submicron gate length (for high frequency operation), the gate line has high series as well as shunt resistances, which renders it unusable as an input transmission line of the travelling-wave transistor because the line attenuation is prohibitably high.
Thus it is a problem in the known travelling-wave transistors to obtain broadband high-frequency response.