Directional Coupler Calculator

A directional coupler is a passive RF/microwave component that splits a signal between a main transmission path and a coupled port — used in signal monitoring, power measurement, and antenna systems. Enter your Input Power (P1), Output Power (P2), Isolated Port Power (P3), and Coupled Power (P4) — in dBm or Watts — into the Directional Coupler Calculator to get the primary Coupling value in dB. Secondary outputs include Coupling Loss, Insertion Loss, and Directivity. Also try the Radar Cross Section Calculator.

Results

Coupling

Coupling Loss

Insertion Loss

Directivity

What is a directional coupler and how does it work?

A directional coupler is a passive microwave device that samples a portion of the signal traveling in one direction while providing isolation for signals traveling in the opposite direction. It has four ports: input, output, coupled, and isolated. See also our Smith Chart Calculator.

How is coupling calculated in a directional coupler?

Coupling is calculated as the ratio of input power to coupled power, expressed in dB. It represents how much signal is coupled from the main transmission line to the coupled port.

What is the difference between coupling loss and insertion loss?

Coupling loss is the difference between input and coupled power, while insertion loss is the difference between input and output power. Insertion loss represents the signal loss in the main transmission path.

What does directivity mean in directional couplers?

Directivity is the ability of the coupler to distinguish between forward and reverse signals. It's calculated as the difference between coupling and isolation, expressed in dB. Higher directivity indicates better performance. You might also find our calculate Series Resistor (R1), Parallel Resistor (R2) & Total Impedance — L-Pad Attenuator useful.

Can I use both dBm and Watts units in the same calculation?

Yes, you can mix units for different power measurements. The calculator automatically converts between dBm and Watts as needed for accurate calculations.

What are typical coupling values for directional couplers?

Common coupling values range from 3 dB to 30 dB. Tighter coupling (lower dB values) provides more coupled power but higher insertion loss, while looser coupling provides less coupled power with lower insertion loss.

How do I interpret the isolation port measurement?

The isolation port (P3) should ideally have very low power, indicating good isolation between the coupled and output ports. High isolation values (low power) indicate better coupler performance.