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

The analysis of, and derivation of design equations for, a class-B balanced single-ended dual-fed distributed amplifier is presented. This approach allows efficient combining of FET output power without multi-way power combiners, has a good port match, and is easy to design as the gate and drain transmission lines are uniform. The design method ensures that all FETs are optimally used and the efficiency is comparable to that of a conventional single-transistor class-B power amplifier using the same FET type. The design method was applied to a class-B four-FET balanced single-ended dual-fed distributed amplifier designed to operate at 1.8 GHz. Large-signal measurements revealed 8% downward shift of the centre frequency. The measured output power and drain efficiency was consistent with the simulations. The efficiency of the amplifier was comparable to a conventional single-transistor class-B power amplifier using the same type of FET.

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This paper analyzes the effect of proximal metallic objects on the energy transfer efficiency of magnetic resonance coupling based wireless charging systems for electric vehicles. It is observed from both the experiment and simulation that the optimum energy transfer efficiency changes dramatically in the presence of a metallic copper sheet in close proximity to the receiving coil. This effect on the efficiency is also seen to be different for different physical spacing between the transmitting and receiving coils. The results show that the presence of metallic objects in the vicinity of the receiving coil have to be carefully considered for each possible usage scenario in order to maintain good energy transfer efficiencies.