Couplers

What is an RF coupler?

An RF coupler is a passive component that transfers a defined portion of an RF signal from a main transmission path to a secondary port. RF couplers are commonly used for signal monitoring, power detection, signal routing, and power distribution. Johanson Technology offers compact surface-mount directional couplers, directional coupler-filters, hybrid couplers, and high-power hybrid couplers.
How do I select the correct RF coupler?

Select an RF coupler by evaluating:

• Operating-frequency range
• Coupling requirement
• Insertion loss
• Directivity
• Isolation
• Power-handling requirement
• Impedance
• Phase relationship
• Package size
• Operating environment
• Product qualification requirements

The selected coupler should provide the required sampled or divided signal while minimizing its effect on the main RF path. Review the applicable Johanson datasheet and S-parameters under the intended system conditions before completing the design.

What is the difference between a directional coupler and a hybrid coupler?

A directional coupler samples a defined portion of a signal traveling through a transmission path and is commonly used for RF monitoring and power detection. A hybrid coupler divides or combines RF power between ports with a defined phase relationship and is commonly used in antenna networks, power distribution, and amplifier circuits. Johanson offers both directional and hybrid coupler configurations.

What is coupling factor in an RF directional coupler?

Coupling factor describes the relationship between the signal level in the main transmission path and the signal delivered to the coupled port. It indicates how much of the main RF signal is sampled. The required coupling value depends on the detector sensitivity, measurement range, transmitted power, and signal-monitoring objective

What is directivity in an RF coupler?

Directivity indicates how effectively a directional coupler distinguishes between signals traveling in opposite directions through the main transmission path. Higher directivity improves separation between forward and reflected signals, which can be important when monitoring transmitted power, reflected power, or impedance mismatch.

When should I use a directional coupler-filter instead of a standard directional coupler?

A directional coupler-filter may be appropriate when the circuit requires both signal sampling and frequency filtering in the same RF path. The integrated component can reduce the need for a separate coupler and filter when its frequency response, coupling, insertion loss, directivity, rejection, and power-handling characteristics meet the system requirements.

Can RF couplers be used in power-amplifier circuits?

Yes. Johanson identifies power amplification as an application for its RF coupler portfolio. A coupler may be used for output-power monitoring, reflected-power detection, signal division, signal combining, or power distribution. The selected component must meet the amplifier’s operating-frequency, power, coupling, insertion-loss, isolation, and thermal requirements.

What applications use Johanson RF couplers?

Johanson Technology identifies RF couplers for:

• Wireless communication systems
• RF signal monitoring
• Power detection
• Power amplifiers
• Antenna networks
• Signal-routing networks
• Power-distribution networks
• Base stations
• Microwave and other high-frequency systems
• MRI equipment requiring high-power RF handling

The appropriate coupler depends on the power level, frequency range, coupling function, phase requirement, and system architecture

Are S-parameter files available for Johanson RF couplers?

Yes. Johanson states that S-parameter files are available through the Info link next to each applicable part number. These files can be used to evaluate and simulate the coupler’s RF behavior within the intended circuit