Abstract-Both branch-line and rat-race couplers are easily realized using planar circuit technology as they employ only transmission lines without additional components. However, as the electrical lengths of the transmission line elements are either 90 or 270 , such couplers consume a significant amount of circuit area. This paper shows the development of branch-line and rat-race couplers that use artificial transmission lines (ATLs) in place of conventional transmission lines resulting in significant size reduction. As the ATLs are constructed entirely from microstriplines, the couplers are easily fabricated using conventional printed-circuit processes. The design formulas developed for the ATLs are explicit. Full-wave simulation and experimental results were used to confirm the design approach for hybrids operating at 1.8 GHz. The frequency response of the proposed hybrids is similar to conventional hybrids.

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A balanced amplifier employing two identical single‐ended dual‐fed distributed amplifiers is demonstrated to be a viable approach for combining FET output power. The FETs are spaced 180° to ensure all FETs have identical load lines, which are chosen optimally. The configuration uses all FET output power and has good port match. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 42–45, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10510

Abstract-The dual-fed distributed amplifier (DFDA) allows efficient combining of field-effect transistors (FETs) at the device level without using -way power combiners. However, the FETs must be spaced 180 , resulting in physically large circuits. In this paper, meandered artificial transmission lines (TLs) comprised of microstrip lines periodically loaded with short open-circuit stubs can be used in place of TLs to reduce the size. The approach incorporates FET input and output capacitances with the artificial TLs, thereby eliminating their detrimental effects on bandwidth and performance. Both simulation and experimental results of a class-A three-FET single-ended DFDA designed to operate at 1.8 GHz demonstrate the feasibility of this approach and the validity of the design method. The size reduction is approximately one-third compared to realization using microstrip lines only, and the maximum efficiency is greater than 35% over a bandwidth of 15%.Index Terms-Distributed amplifiers, microstrip circuits, microwave field-effect transistor (FET) amplifiers, microwave power FET amplifiers.