3 Port Directional Coupler

There’s no doubt that communications has grown a lot since people began looking for ways to stay in contact despite long distances and other physical barriers. With many technologies involved in communications, there are different bands in the electromagnetic spectrum to keep signals from interfering.

It isn’t just about transmission of signals, either. Other applications necessitate testing signal samples, or else combining signals for transmission through a single antenna. With the many tasks associated with communications, it’s no wonder that some would call for a 3 port directional coupler.

Terms to Know

There are several specifications that set the different types of couplers apart from each other, and for those who are largely unfamiliar with the field, this can get confusing. Here are some of the terms often used, explained in order to help choose the best directional coupler for one application or another.

• Coupling tolerance – the allowed unit-to-unit variation in nominal coupling, or how big or small a difference in power can be allowed without affecting the coupler.
• Coupling coefficient – the ratio of the power fed into the main port and what goes into the coupled port, assuming lines are terminated by reflection. Typically, this is expressed in dB (decibels)
• Coupling loss – the reduction in available power, due solely to transferred power over to the coupled line
• Bandwidth – the range of frequencies over which the coupler can operate, with its performance usually within specific limits.

Directional Couplers

At its most basic, a directional coupler is a network consisting of 4 ports, and its main role is combine two signals into a single one, or else take an input and produce two output signals. Normally, directional couplers have four ports, connecting to a main line and a coupled line, with both ends of the latter serving as coupled ports.

A model with 3 ports, however, is just as straightforward – a main line, and a coupled line that is internally terminated. One of the characteristics this gives the coupler is, the output signals are usually unequal, as far as amplitude is concerned, with the smaller signal being at the coupled port.

Companies such as AWG Tech do their best to provide clients with directional couplers that have as little insertion loss as possible. This is because the more power is lost when a signal is inserted into the device, the less power it puts out. This can cause inaccuracies when the coupler is used to test a system, or else it results in not enough power being directed where it needs to go.

While 4-port and 3-port directional couplers each see constant use in various applications, the latter are usually chosen, whether for commercial or military applications. This is due to the high performance associated with having an internally terminated port. When the port is terminated within the device, this positively affects the coupler’s directivity, and therefore its performance.

The casings holding the set-up, say experts, doesn’t really affect the coupler’s performance. However, at high frequencies, the smaller the casing, the better the performance.

So depending on the application you need it for, don’t be afraid to ask for either off-the-shelf or customized designs for the 3 port directional coupler. The better it fits, the better the results.