RF Power Splitter / Divider & Combiner

Passive RF splitters / dividers and combiners are just the reverse of each other - they are just used the other way round.

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RF Combiner Splitter Couplers & Hybrids Includes:
Combiner, splitter, coupler hybrids overview Splitters & Combiners Resistive splitter & combiner Hybrid splitter & combiner Wilkinson splitter & combiner Directional coupler

As the name implies RF power splitters / dividers and combiners are used to split a single RF line into more than one line and divide the power, and similarly combiners are used to combine more than one feed line into a single one.

RF power combiners and RF splitters are the same items. The same circuits can be used to combine and split RF power, the only difference being that RF power is applied to one port and extracted from other in the case of the RF splitter, and for the RF combiner, power is applied in the opposite direction.

Typical microwave connectorised splitter / combiner — Typical commercially available microwave splitter / divider

RF power splitter & combiner types

There are two broad categories of RF splitters:

Resistive power splitters: As the name implies, these power splitters and combiners use resistors. While they are able to maintain the characteristic impedance of the system, the use of resistors introduces loss above that of the minimum caused any splitting action. They are cheap and easy to make.
Hybrid power splitters: Hybrid splitters use transformers and are able to provide low levels of loss. Although there are some physical losses in the transformer, the major "loss" is that arising from the splitting process as the same signal is shared between a number of outputs.

Splitter and combiner symbols

A variety of circut symbols may be used for splitters or dividers and combiners. They are typically quite self explanatory, and may even have a function description on the symbol.

Splitter / power divider circuit symbol — Splitter / divide symbol

Where there is a requirement for splitting the power into more than two ways, the following symbol may be used.

n way splitter / power divider circuit symbol — n-way splitter / divide symbol

The combiner symbol is just the reverse of the splitter symbol.

Power combiner circuit symbol — Combiner symbol

Power splitter insertion loss

When a splitter is inserted into a circuit, there are naturally some losses resulting from the fact that no component is perfectly lossless. These losses are generally minimised and cannot be calculated exactly.

Typical microwave connectorised 8-way splitter / combiner — Typical commercially available microwave 8 way splitter / divider

However there are also "losses" resulting from the fact that the signal is being divided between several outputs. This should more accurately be described as a division signal reduction as none of the signal is actually lost. Instead there is a level reduction from the fact that the input power is being shared amongst several outputs.

This signal power division reduction can be calculated and table of the levels for power splitters with different numbers of outputs is given below.

Splitter Division Reduction Loss Table
Number of Output Ports	Theoretical Division Reduction (dB)
2	3.0
3	4.8
4	6.0
5	7.0
6	7.8
8	9.0
10	10.0

The losses tabulated above provide the signal division level reduction and these figures are theoretical. In reality, all components are imperfect and will introduce some real losses. These will need to be accommodated in any loss calculations.