Radio frequency (RF) splitters and combiners are key components used to distribute and combine signals in RF circuits. They play an important role in wireless communication systems, test equipment, and other applications where a single signal source needs to be distributed to multiple destinations or multiple input ports need to be combined into one output. 4

　　The following is a detailed introduction to these two devices, including their working principles, types, and application scenarios.

　　1. RF Splitters

　　1.1 Definition and Function

　　An RF splitter is a three-port or multi-port network that can distribute an input signal to two or more output ports in a certain proportion. Ideally, if it is a half-power splitter, the power at each output port will be half of the input power minus 3 dB (i.e. power loss). Splitters ensure good isolation between all output ports and are usually designed so that there is no reflection at the input port when all output ports are connected to matched loads. 2

　　1.2 Main types

　　Resistive type: Use three equal-value resistors to form a star configuration, suitable for broadband applications but with large insertion loss.

　　Wilkinson type: By introducing a terminal resistor to achieve good port-to-port isolation, it has low insertion loss and is suitable for narrowband applications.

　　Hybrid type: Combining the advantages of transmission lines and resistors, it can provide better performance over a wider frequency range, such as branch line directional couplers7

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　　1.3 Application scenarios

　　Splitter is widely used in phased array antenna systems, where a single RF source is evenly distributed to multiple antenna units; in addition, in the orthogonal demodulator, the local oscillator also needs to provide in-phase and quadrature component signals for two mixers4

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　　2. RF Combiners

　　2.1 Definition and Function

　　The function of the combiner is exactly the opposite of the splitter. It can receive multiple input signals from different sources and combine them into one output signal. In order to ensure the quality of the output signal, the combiner must correctly handle the relative amplitude and phase relationship between the input signals to avoid unnecessary interference or distortion. At the same time, it is also necessary to consider how to effectively manage heat dissipation, because the energy of multiple input signals will be concentrated at the output end2

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　　2.2 Types

　　Combiners can be divided into passive and active types. Passive combiners are mainly composed of passive components, such as inductors, capacitors, and transmission lines. They are simple and stable in structure, but may cause certain insertion losses. Active combiners, on the other hand, contain active components such as amplifiers. Although they increase complexity and cost, they can provide gain and improve isolation2

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　　2.3 Application Examples

　　In multi-carrier power amplifiers, combiners are used to combine signals from different channels into the same power amplifier for amplification before transmitting them out. Another example is that in the receiving part of a base station, the outputs of multiple low-power receivers can be aggregated together through a combiner and then sent to a subsequent processing unit4

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　　3. The relationship and difference between the two

　　Power dividers/splitters and power combiners are actually devices that can be used inversely. For example, a standard Wilkinson splitter can also be used as a combiner, as long as the port originally defined as input is now regarded as output. However, in actual applications, there may be subtle differences between the two due to different specific design parameters. For example, some products designed for splitting may not perform well in high-power combining scenarios10

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　　4. Selection Guide

　　When choosing a suitable RF splitter or combiner, you should consider the specific needs of the system, such as the operating frequency range, the required maximum power capacity, the expected insertion loss level, and whether additional functional features (such as polarization maintenance) are required. In addition, you should also check the product's electrical specification sheet to ensure that the selected product meets your project requirements13

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