Bi-directional coupler
Bi-directional coupler design
A bi-directional coupler can be designed in the same way that a “normal” directional coupler is designed. If you refer to the schematic for bi-directional coupler circuit, you will notice that the load that is connected to the isolated port is removed and becomes the coupled port for the output port. A bi-directional coupler is actually a 4-port coupler without the internal termination. In this way, the forward and reflected signals can be sampled simultaneously.
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Bi-directional coupler versus dual directional coupler
A dual directional coupler is not the same as a bi-directional coupler. A dual directional coupler is constructed by cascading two three-port directional coupler back-to-back but with the internal termination facing each other. In this way, a dual directional coupler allows the forward and reflected signals to be sampled simultaneously, but the coupled ports are independent of each other.
The main difference is that the directivity of a dual directional coupler is much better than the directivity of a bi-directional coupler. This is because the directivity of a coupler is greatly affected by the termination on the isolated port.
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Bi-directional Couplers – Tackling the Basics of the RF Component: A Short Guide
Couplers are RF and microwave components that are used in sampling the high frequency signals being transmitted; it produces two outputs by just sampling a single signal as the input. The two outputs produced are known to be as the normal output and the other one to be the paired output. There are different types of couplers that can be used in any system; a prime example of one is the directional coupler. This is a four-port component that has an input (Port 1) and output port (Port 2) that can carry a high amount of high frequencies, and the remaining ports (Ports 3 and 4) can only carry low signals.
However, there is another type of directional coupler that can perform double the task; that would be the dual directional coupler (A.K.A the bi-directional coupler). This coupler is made up of two directional couplers that are connected in the series; however, they are placed in the opposing direction. Another definition for this coupler is it’s a directional coupler that has one main line and has a pair of secondary lines meant for pairing frequency signals.
Generally speaking, the dual directional coupler has the same components as the single directional coupler. However, as mentioned above, they get input only from a single main line and the component simultaneously will examine and pair these signals for them to be turned into outputs.
The Basic Configurations of a Single Directional Coupler
Oftentimes, other people will think that the dual directional coupler will have a different configuration with that of the single directional coupler. As a matter of fact, the configurations of the dual directional coupler are exactly the same as the single directional coupler due to it being manufactured by using two single directional couplers.
The configuration of a single directional coupler has two parallel transmission line that stretches over a length of one-quarter wavelength, it responds with the operation’s core frequency. The main and secondary lines are apart with a calculated physical distance which identifies the coupling factor of the component.
The physically closer the lines are with one another, the more power will be welcomed on the secondary line. Plus, the term “coupling” signifies the amount of input power sampled to the coupled port and is usually defined as 10 times ratio of Incident Power and Forward Power.
The Main Difference between Single and Dual Directional Couplers
As mentioned over and over, single and dual directional coupler is made of the same component, that’s true. However, there is something that stands out in the circuit design of the dual directional coupler.
The single directional coupler are linked together back-to-back and shares a common mainline for the sampling of frequency signals and thus producing two outputs, that makes it a dual directional coupler (or a bi-directional coupler). However, these ports have a high amount of isolation compared to the single directional coupler. This is critical for the accuracy of the reflectometer set-ups that will, at the same time, test the input power to a device. On the other hand, it can load to provide signal ratios for the purpose of identifying the return loss in decibels.