RF Power Combiners/Splitters, sometimes referred to as either RF combiners, RF splitters, or RF dividers, are a fundamental passive RF component used to combine power from multiple inputs to a single output or split RF power from one input to multiple outputs. RF Power Combiners are often used to combine the output powers of several amplifiers to realize a higher output power level than is possible or viable with a single amplifier. An example of this is replacing high power traveling wave tube amplifiers (TWTAs) with a combined gang of solid-state power amplifiers (SSPAs).
Other applications include adding redundancy to critical transmission systems where the high-power output amplifiers may fail. Using a RF Power Combiner with several redundant amplifiers, only one of which is active at a time, can enable continuous transmission even in the event of an amplifier failure. Other use cases include splitting the input from an antenna or other source to multiple RF signal paths for the purpose of filtering or feeding different radio systems with the same antenna/source.
More recently, there are also emerging applications for RF Power Combiners/Splitters with modern advanced/active antenna systems (AAS). One such case is splitting the power from a single RF source to feed multiple AAS antenna elements in an analog phased array antenna. Another is using an RF Power Combiner/Splitter to divide/split the RF power from a single local oscillator (LO) and feed that RF source to the two sides of a quadrature demodulator.
Key RF Power Combiner/Splitter Performance Parameters
- Frequency Range (Hz)
- Port Count (input/output ports)
- Impedance (Ohms)
- Output VSWR
- Insert Loss (dB)
- Isolation (dB)
- Amplitude Balance (dB)
- Phase Balance (degrees)
- Power Handling Continuous Wave (Watts)
- Operating Temperature (C/F)
- Size/Weight
The three most common types of RF Power Combiner/Splitters are passive in nature (Resistive Combiner/Divider, Wilkinson Combiner/Divider, and Hybrid Combiner/Divider). Being passive, these combiners/dividers absorb some of the signal energy that passes through them, this is known as insertion loss. Moreover, If the component is used for dividing each output port will also be a fraction of the input power less the insertion loss per channel. Depending on the design and fabrication process, the tolerances of these dividers/combiners aren’t not perfect. These imperfections result in variations in the amplitude and phase balance among the output ports.
These components don’t have perfect isolation either, and some RF signal energy from each port will couple into the others. This could be an issue if the downstream RF electronics produce substantial reflections that could be coupled into the other signal paths of the combiner/divider.
Dividers/combiners also have an intrinsic trade-off between the frequency range of the circuit versus the power handling capability. The larger dimension conductors and spacing needed for higher power handling limit the high frequency performance. It is also more difficult to design a combiner/splitter that has both extremely broadband operation and good amplitude and phase balance.