Take note when learning about Hybrid Mixtures

If you've ever wondered which one to use for a reflection test, or struggled with splitting the output signal from an amplifier, this is an article worth taking a few minutes to read.

Why do many people still confuse hybrid coupler and directional coupler?

If you’ve ever searched for “RF signal splitter” and come up with a bunch of results with the names hybrid coupler and directional coupler, you’re not the only one who’s confused. They both look very similar, have multiple signal ports, and fall into the category of passive devices that split or route signals. The problem is: they’re designed to do two completely different things. But in practice, many young engineers or people who aren’t RF experts use them interchangeably, thinking that as long as they can get the signal out of multiple ports, it’s good enough.

This confusion often comes from the way the devices are named and described on the market. Many places simply state "power splitter" or "for signal measurement", but do not clearly state the specific role of each type. Meanwhile, the nature of a directional coupler is to separate the reflected signal from the main transmission line to serve measurements such as VSWR or Return Loss. A hybrid coupler, on the other hand, is designed to split the input signal into two signals with a phase difference of 90 or 180 degrees, a specific requirement in antenna systems or RF mixers.

Can the directional couple also be used when measuring reflected signals?

This is also a question we have received a lot recently. Directional couplers are commonly used to measure reflected signals, but not all types can be used for that purpose. The problem lies in the directivity parameter and the suitability of the frequency range with the measuring device such as VNA. If you choose a coupler with low directivity or not optimized for the working frequency, the reflected signal will be mixed with noise from the incoming signal, causing the measurement data to be significantly distorted. In other words, not all directional couplers can be used for reflection measurement by default, but the coupler must be good enough and of the right type for the measurement system you are operating.

Application of Hybrid Coupler in phased array antenna system

If you are looking into designing a phased array antenna system and wondering how to control the phase between antenna elements accurately and consistently, then a hybrid coupler is a good fit. 

Unlike conventional splitters, hybrid couplers split the power evenly, creating a precise phase shift between the output ports, usually 90° or 180°, depending on the coupler type. This makes them extremely useful in phased array antenna systems, where controlling the phase between antenna elements is key to beam steering and beam optimization.

In a phased array system, hybrid couplers are used to:

Create a fixed phase difference between transmission channels, ensuring phase synchronization or anti-phase according to design requirements.

Combine signals from multiple antennas without causing reflections back to the source, thanks to the ability to isolate between ports.

Increase the directionality of the antenna through phase control - helping the system to transmit strong signals in the desired direction and eliminate signals in unnecessary directions.