TABLE OF CONTENTS Power splitters and combiners are an indispensable signal-processing component in RF and microwave systems. Mixers, balanced amplifiers, baluns, unbalanced-to-balanced converters, phase shifters, and many other applications employ splitters and combiners as a component. Some of the more commonly used splitter/combiners include Wilkinson 0 , balun/unbal 180 , and 90 branch-line couplers. Some recent microwave engineering designs have focused on using uniplanar transmission line to simplify MMIC implementations and require active splitter/combiners with arbitrary phase relationships.
The most common signal splitter application is for signal preparation for the inputs of mixers that perform frequency translation. Mixers are used in communication transmitters and receivers. Mixer configurations are categorized as single-ended, single-balanced, double-balanced, and balanced quadrature. Single-ended mixers are based on the nonlinear properties of a single active device (transistor) and suffer insufficient isolation between the mixer RF, LO, and intermediate frequency (IF) ports. This results in frequency translation of all in-band spurious signals. The single-balanced mixer has the RF or LO split into a differential or push-pull signal to improve isolation and spurious rejection by about 30 dB. A double-balanced mixer splits both RF and LO into balanced signals to improve isolation and second-order spurious rejection. A balanced quadrature mixer splits the RF and the LO are four ways into a differential quadrature signal set, and the IF is combined into a differential signal, to obtain sideband suppression or image rejection. The amount of second-order spurious attenuation, sideband suppression, or image rejection is a function of the balance of the signal. How...
