The terms RF combiners, splitters, couplers and hybrids refer to slightly different items. Each item is used in RF design and all are important to the RF designer.
● RF combiner: An RF combiner is used to combine RF from a number of different sources. This is achieved while maintaining the characteristic impedance of the system. Dependent upon the type of combiner it may introduce additional loss by using resistors, or it may be use transformers in which case it could in theory be lossless.
RF combiners can be used in a number of different applications. They are used for sending several signals along a single feeder, and they may also be used for circuits where several RF signals need to be brought together.
● RF splitter: An RF splitter is the reverse of a combiner - in fact splitters and combiners utilise exactly the same circuits - the inputs for one form the outputs for the other. As the signal is split a number of ways, there is an associated reduction in signal level between the input and the output dependent upon the number of outputs for which the signal is shared.
● RF directional coupler: Directional couplers have many similarities with splitters. They are often used to sample signals and they may have directional properties. Rather than being based upon transformer technology they use capacitive coupling to achieve their aims. As the name implies a key feature of directional couplers is that they only couple power flowing in one direction. Power entering the output port is coupled to the isolated port but not to the coupled port.
● RF hybrid: A number of circuits are referred to as hybrids. RF hybrids are based on transformers, and as such RF splitters or RF combiners may be referred to as hybrids when they use transformer technology rather than just resistive technology. This gives many advantages, dependent upon the actual circuit, but one of the main ones is that hybrids do not have the resistive losses of the resistive ones.
