A THEORETICAL ANALYSIS AND EXPERIMENTAL CONFIRMATION OF THE OPTIMALLY LOADED AND OVERDRIVEN RF POWER AMPLIFIER
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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Although the textbook Class B approach to rf amplifier design yields high output power and reasonable collector efficiency 78.5 percent at maximum output power, neither the power nor the efficiency are optimum, and both are dependent on rf drive level. This report presents an analysis of appropriately selected collector voltage and current waveforms which determine the load impedance at the fundamental and harmonically related frequencies these conditions define the Class B optimum efficiency case with 100 percent collector efficiency and 1.27 times the textbook Class B value of output power. If the rf drive level is increased and the collector voltage and current waveforms are appropriately selected so that the amplifier is overdriven, a different load impedance is determined these conditions define the optimum power case with 1.46 times the textbook Class B value of output power and 88 percent collector efficiency. The optimum power case has the added advantage of resulting in an output power and collector frequency that are essentially constant over a predetermined range of drive level. Finally, the theory is verified by the construction and testing of a UHF power amplifier having a power output of 46 watts and an overall dc to rf conversion efficiency of 65 percent with an output power insensitivity to rf drive of 1 db for 10.5 db.
- Electrical and Electronic Equipment