RL

Return Loss

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Return loss is the ratio of incident power to reflected power at a port, expressed in dB. It quantifies how well a device is impedance matched. Higher return loss means less reflected power and a better match. A perfect match has infinite return loss (zero reflection). A return loss of 20 dB means only 1% of power is reflected. Return loss is directly related to VSWR and S11: RL = -20 log10(|S11|).

Category: Measurement & Characterization

Related to: VSWR, S11, Reflection Coefficient, Impedance

Units: dB

Understanding Return Loss

Return loss is one of the most universally specified RF parameters. Every connector, cable, component, and antenna has a return loss specification. It is the primary metric for impedance match quality and is measured with a vector network analyzer (VNA) or scalar network analyzer.

Return Loss vs. VSWR vs. Reflection Coefficient

These three parameters describe the same physical phenomenon (impedance mismatch) using different mathematical representations:

Return loss (RL): Expressed in dB. Higher is better. RL = -20 log10(|Gamma|).
VSWR: A ratio, always greater than or equal to 1. Lower is better. VSWR = (1+|Gamma|)/(1-|Gamma|).
Reflection coefficient (Gamma): A complex number with magnitude 0 to 1. Lower magnitude is better.

Why Return Loss Matters

Power delivery: Reflected power is not delivered to the load, reducing system efficiency.
Amplifier stability: Reflections from the load can cause oscillation in amplifiers that are not unconditionally stable.
Measurement accuracy: In a test system, connector and cable mismatches create measurement uncertainty (ripple).
System intermodulation: In multi-carrier systems, reflections at nonlinear junctions generate passive intermodulation (PIM).

Return Loss (dB):
RL = -20 × log10(|Γ|)
RL = -20 × log10(|S11|)

From VSWR:
RL = -20 × log10((VSWR-1)/(VSWR+1))

Reflected power (%):
P_refl = |Γ|² × 100%

Mismatch loss (dB):
ML = -10 × log10(1 - |Γ|²)

Return Loss Quick Reference

Return Loss	VSWR	\|Γ\|	Reflected Power	Mismatch Loss
6 dB	3.01	0.501	25.1%	1.26 dB
10 dB	1.92	0.316	10.0%	0.46 dB
14 dB	1.50	0.200	4.0%	0.18 dB
20 dB	1.22	0.100	1.0%	0.04 dB
26 dB	1.10	0.050	0.25%	0.01 dB
30 dB	1.07	0.032	0.1%	0.004 dB

⚡ VSWR / Return Loss Calculator →

Common Questions

Frequently Asked Questions

What is a good return loss?

It depends on the application. For precision test components, 26 dB or better (VSWR 1.10) is expected. For waveguide components, 20 dB (VSWR 1.22) is typical. For antennas, 10 dB (VSWR 1.92) is often acceptable. Higher return loss always means a better impedance match.

What is the difference between return loss and insertion loss?

Return loss measures reflected power at a single port (how well matched the device is). Insertion loss measures transmitted power through the device (how much signal is lost passing through it). Both are expressed in dB, but they describe different phenomena. A well-matched device can still have high insertion loss.

Is higher or lower return loss better?

Higher return loss is better. It means less power is reflected. A return loss of 30 dB means only 0.1% of power is reflected, while 10 dB means 10% is reflected. Note: some instruments display return loss as a negative number (e.g., -20 dB), which is technically the reflection coefficient in dB.

Related Terms

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