Knowing the Basics of Directional Couplers and Small Insights on the S-Band

Couplers are passive components that are utilized for the sampling of high frequency signals. It takes a single signal as the input and grants two outputs – one being the regular output and the other would be the coupled output. A prime example of these couplers are directional couplers, a four-port device – each with an input and output port, one port for the coupled signal and the other port that can be terminated anytime from the inside of the circuitry.

Aside from the general functionality definition of the directional coupler, there are some directional couplers who uses the frequency bands in order for them to serve different purposes. One of which is the S-band directional coupler. The S-band is a frequency band on the electromagnetic spectrum that has a frequency range from 2 to 4 GHz. The S-band is widely used in weather radar systems, surface ship radars and some forms of satellite communications. This is the frequency band used by NASA to send transmissions to both the Space Shuttle and the International Space Station.

Directional Couplers: The Four Ports and the Specifications

As mentioned above, a single directional coupler has four ports in its circuit design, they are listed down below:

• The Input (The Incident Port and Port #1)
• The Transmitted (The Output Port and Port #2)
• The Coupled (The Forward Coupled Port and Port #3)
• The Isolated (The Reverse Coupled Port and Port #4)

Upon closer inspection of the four ports, they have alternative names. These are so because users of the component often refer to them as such.

As for the specifications of the directional coupler, they are summarized below:

• The Directivity: This refers to the level of power difference between port 3 and 4 (in-line with isolation). This is a measure of how independent both ports 3 and 4 are. It’s all because it’s practically impossible to establish the best coupler, there will always be an unintended amount of coupling between every single signal paths.

• The Coupling Loss: This refers to the amount of power that’s being lost to ports 3 and 4. Assuming a reasonable directivity, the power that’s being transferred unintentionally to port 4 will be negligible in comparison to the ones transferred on purpose to port 3.

• The Isolation: This refers to the level difference between ports 1 and 4 (in-line with directivity).

• The Main Line Loss: This refers to the resistive loss that’s caused by heating (different and segregated from coupling loss). This value is added to the theoretical power reduction that is being ported over to ports 3 and 4 (the coupling loss).

How can the S-band Help Improve Services?

As mentioned above, the S-band frequency used in the S-band directional coupler is a band in the electromagnetic spectrum that has a frequency range from 2 to 4 GHz. According to experts, 2.1 GHz is the preferred band for 3G operations all over the world and a lot of operators have rolled out 3G networks in the S-band. However, this band is quite limited in some countries due to the amount of 3G users.