At a named reference plane, reflection coefficient Γ is the reflected-to-incident voltage-wave ratio. Return loss is -20 log10|Γ| in dB, and VSWR is (1+|Γ|)/(1-|Γ|). Reflected power fraction is |Γ| squared; mismatch loss is -10 log10(1-|Γ| squared). A 2:1 VSWR corresponds to |Γ| about 0.333, return loss about 9.54 dB and mismatch loss about 0.51 dB.
These relations apply at the same impedance and plane. A cable, adapter, balun or matching network can transform the observed result, so state whether it is included and preserve calibration details. Wideband acceptance should use limits over the continuous band, not one marker.
Good match does not prove that accepted power is radiated efficiently or in the required directions. Review match, realized gain, efficiency, pattern and polarization as separate evidence, then evaluate installed effects.