What S-Parameter Data Should I Check for an RF Circulator?

When evaluating an RF circulator, S-parameter data provides the most important insight into its RF performance. A complete S-parameter report, typically measured with a Vector Network Analyzer (VNA), allows you to verify whether the circulator meets your system requirements across the intended frequency band.

The key S-parameters to examine include:

• S21 (Insertion Loss): Measures how much signal is transmitted from Port 1 to Port 2. Lower insertion loss means more power reaches the intended output and improves overall system efficiency.
• S31 (Isolation): Indicates how well the circulator prevents signal leakage from Port 1 to Port 3. Higher isolation minimizes interference, protects sensitive components, and improves signal integrity.
• S11 (Return Loss): Reflects the impedance matching at Port 1. A higher return loss (or lower VSWR) indicates less reflected power and better matching to the system.
• S12, S23, and S13 (Reverse Transmission): These parameters help confirm the circulator's non-reciprocal behavior by showing signal suppression in the reverse direction. Good reverse isolation is critical in applications such as radar, satellite communications, and power amplifiers.

When reviewing S-parameter plots, make sure the specified performance is maintained across the entire operating frequency range, not just at the center frequency. Also check for performance consistency at your required operating power and temperature if those conditions are critical to your application.

For most RF circulators, the following values are considered good starting benchmarks:

Ultimately, the acceptable S-parameter values depend on your application. High-power radar systems, satellite communications, test equipment, and 5G infrastructure may each require different performance levels. Reviewing the complete S-parameter dataset—not just a few headline specifications—is the best way to ensure the RF circulator will perform reliably in your system.