Design of Efficient Broadband Varactor Upconverters

In many microwave radio relay systems the transmitted microwave signal is obtained by upconverting the IF signal in a mixer or modulator and amplifying it in a microwave power amplifier, such as a traveling wave tube, to a power level set by system requirements. By use of a varactor upconverter as a microwave power amplifier the func1623 1638 TI-IE BELL SYSTEM TECHNICAL JOURNAL, JULY-AUGUST 1969 tions of upconversion and amplification can be performed by one device. In fact, for all-solid-state radio systems the varactor upconverter is the only broadband microwave power amplifier available. Therefore, in radio systems such as those described in companion papers, broadband, efficient, rugged varactor upconverters are required as power amplifiers.1-2 Although several analyses of varactor upconverters have been published, design has required a trial and error procedure with its inherently uncertain results. In this paper we describe a design procedure for optimizing the performance of an upper sideband varactor upconverter with respect to maximum pump efficiency. This procedure gives diode and circuit parameters explicitly in terms of operating power levels. We also describe a method of obtaining broadband operation. Although the procedure is derived using specific frequencies and the maximum efficiency optimization, the basic method can be used for any frequency and optimization. The design procedure and broadbanding method are illustrated by the design of an upconverter for the experimental radio system described by Ruthroff and others.3 The system requires a bandwidth of 120 MHz between 1 dB points and has an intermediate frequency of 300 MHz.