Power Divider / Antenna Combiner: Why a T-Adapter Is the Wrong Choice

Do not use a "T connection" to get one AP to service two antennas from One Radio

A common mistake in RF installations is attempting to connect one access point (AP) or radio to two antennas using a simple T-adapter. This approach may appear convenient, but it introduces serious electrical problems that can degrade performance and potentially damage equipment.

By a “T connection,” we mean a basic T-adapter used to combine two antennas onto a single antenna cable. This method should not be used.

This causes many problems, further described below. By "T connection," we mean T-adapter to combine two antennas onto the same antenna cable.

A "T" is the incorrect way to split to antennas or transmitters. It results in a 2:1 impedance mismatch. That in turn, will cause signal degradation and probably equipment failure. You must use a "power divider" or "antenna combiner" device to operate two antennas from one transmitter. These devices are not expensive, and they are necessary. There are many variations on the concept, but the end result is that a 50 ohm load is presented to the transmitter, and each antenna "sees" a 50 ohm transmitter as well.

The common TV "splitter" does work for exactly the reasons above. At 2.4 GHz, our requirements are more stringent than at TV frequencies, but the approach is exactly the same.

Why a T-Adapter Causes Problems

A T-adapter is not designed to split RF power correctly between antennas. When two 50-ohm antennas are connected in parallel through a T-adapter, the resulting impedance seen by the radio is approximately 25 ohms, not 50 ohms. This creates a 2:1 impedance mismatch.

This mismatch leads to:

• Increased reflected power (high VSWR)
• Signal degradation
• Reduced transmitter efficiency
• Possible long-term damage to the radio’s output stage

In short, a T-adapter is the incorrect way to split power between antennas or transmitters.

The Correct Solution: Power Dividers and Antenna Combiners

To properly operate two antennas from one transmitter, you must use a power divider (also called an antenna combiner, depending on direction of use).

Power dividers are specifically designed RF devices that:

• Maintain a 50-ohm load to the transmitter
• Split power evenly between antennas
• Minimize signal reflections
• Provide isolation between antenna ports

These devices are not expensive, and they are essential for reliable system performance. There are many variations on the design (including Wilkinson power dividers), but the end result is the same:
the transmitter sees a proper 50-ohm load, and each antenna sees a properly matched source.

What About TV Splitters?

The common TV splitter works on the same basic RF principles as a power divider, which is why it functions correctly at broadcast TV frequencies.

However, at 2.4 GHz, 5 GHz, LTE, or other wireless data bands, requirements are more stringent:

• Tighter impedance tolerances
• Lower allowable insertion loss
• Higher isolation requirements

A splitter must be frequency-rated for the band in use. A generic TV splitter is not suitable unless it is explicitly specified for the operating frequency.

Power Divider vs. T-Adapter: Key Differences

1. Design and Purpose

Power Divider / Antenna Combiner
Designed specifically for RF systems, these devices distribute power evenly while maintaining impedance matching and isolation.

T-Adapter
Not designed for RF power division. It does not ensure impedance matching or equal power distribution.

2. Reflection and Signal Loss

Power Divider / Antenna Combiner
Minimizes reflections and standing waves, ensuring efficient power transfer.

T-Adapter
High risk of reflections due to impedance mismatch, leading to signal loss and stress on the transmitter.

3. Impedance Matching

Power Divider / Antenna Combiner
Maintains system impedance at 50 ohms (or the required standard).

T-Adapter
Does not maintain impedance, resulting in poor RF performance.

4. Isolation Between Antennas

Power Divider / Antenna Combiner
Provides isolation so one antenna does not affect the other.

T-Adapter
Offers no isolation, allowing antennas to interact and degrade performance.

Why You Should Not Use a T-Adapter

Using a T-adapter may seem like a simple or low-cost solution, but it introduces multiple risks:

• Signal Degradation: Poor impedance matching and reflections reduce effective radiated power.
• Potential Equipment Damage: Reflected power can damage sensitive RF output stages.
• Reduced System Performance: Lack of isolation allows antenna interaction and unpredictable behavior.

Conclusion

When operating multiple antennas from a single radio, using the correct RF components is critical. While a T-adapter may appear to work in the short term, it is not suitable for this application.

A properly designed power divider or antenna combiner ensures:

• Correct impedance
• Minimal signal loss
• Long-term equipment reliability
• Predictable, professional-grade performance

Using the right tool for the job always delivers better results.