However, it has a 180° phase difference between outputs, while the power dividers have 0° phase difference and quad hybrids have 90° phase difference. A balun has equal power outputs just like a Wilkinson power divider, resistive power divider, or quadrature hybrid coupler. However, this description obscures the simplicity of the balun. The term balun is a portmanteau of balanced and unbalanced, indicating that a balun will transition between a balanced (also called ‘differential’) transmission line (where opposite currents both travel in transmission lines) and an unbalanced (also called ‘single ended’) transmission line (where the return current travels in the ground).
Finally we will discuss the applications of baluns and how to determine what kind of balun is required for a several different purposes.Ī balun is any three port device with a matched input and differential outputs. Next we will define generic balun specs, which we then use to discuss the different types of baluns and their properties. First we will define what a balun is, what it does, and how it is different from other components. The need for high speed, low noise data transfer has driven the advancement of the balun to higher frequencies and superior performance.ĭespite these advancements, information about baluns remains scattered and confusing this application note seeks to resolve this problem by clarifying the basic characteristics of baluns. Baluns have long been ubiquitous in low frequency audio, video, and antenna driving applications. Since then designs have evolved dramatically, and applications have evolved beyond driving differential antennas to include balanced mixers, amplifiers, and signaling lines of all types. The balun has a long and illustrious history, first documented in the literature as a device to feed the television transmitting antenna for the Empire State Building1 in 1939.