There have been many different techniques over the years which have sought to bring about the physical manifestation of such a thing as a dual directional coupler. This article will seek to break down a bit exactly what one of these is and exactly what it does.
The most basic directional coupler will consist of four ports. It is mainly used in microwave systems. They are used to fulfill requirements of reporting any instances of sampling and any microwave power being reflected with very little disruption to the line of transmission.
At the input port, when power is introduced, it will reappear at the port of output, except for the portion left behind to be sampled. If there is a reflection of power from the output port, it can be appearing on the secondary line. The flatness of a coupler, otherwise known as the frequency sensitivity, measures the frequency range and how the coupler varies over the length of it. Within what is known as an interesting band, there will be centering of the specifics. There will also be another consideration which must be taken into account.
There should be a minimal loss when it comes to mainline insertion. This is why it is important to specify a coupler. This is because of the very nature of how they are designed. The rule of thumb as to how these are manufactured is that at higher frequencies the loss of signal will increase exponentially. This mainly is because higher power increases the frequency and higher frequency is considerably more expensive than lower frequency.
As you can see, there are some very interesting facts to remember about directional couplers. They are a great source of power when you need to split and there is really no reason to not ever use one.