Large-Signal Calculations for the Overdriven Varactor Upper-Sideband Upconverter Operating an Maximum Power Output

Varactor upconverters are finding increased application in solid-state microwave transmitters. In this application a frequency modulated IF signal is mixed with an unmodulated microwave signal to obtain a frequency modulated output signal. 1 Because of the varactor's low loss and high power handling capacity, this output signal can be used as the transmitter output signal without further amplification. Microwave conversion efficiencies in a varactor upconverter are typically greater than 50 percent. 2 A varactor upconverter can be either an upper-sideband or a lowersideband upconverter. However, since the lower-sideband upconverter can present stability problems, 3 the upper-sideband upconverter is generally preferred for the above application. 1223 1224 T H E BELL SYSTEM TECHNICAL JOURNAL, JULY-fAUGUST 19G7 This paper presents a general analysis of lossy varactor uppersideband upconverters, using both graded- and abrupt-junction varactors. Results will be presented for operation at maximum power output for a prescribed drive level. The two input signals and the output signal are all three "large" signals in this mode of operation. Penfield and Rafuse have presented a theory for nonoverdriven abrupt-junction varactors; 3 however, their analysis gives a conservative value of output power, as explained by Nelson. 4 Nelson presents an improved upper bound on the varactor charge coefficients, which results in 25 to 54 percent greater output power than that given by Penfield and Rafuse.