TABLE I:

Accuracy of ${\mathcal{H}}_{\text{N}-1}-{\mathcal{H}}_{\text{N}-\text{M}-1}$ Approximation

Approximation Form	Error, dB
${\mathcal{H}}_{\text{a}}-{\mathcal{H}}_{\text{b}}=\ln (\frac{\text{a}}{\text{b}})$	−47.3 dB
${\mathcal{H}}_{\text{a}}-{\mathcal{H}}_{\text{b}}=\ln (\frac{\text{a}}{\text{b}})+\frac{{\text{a}}^{-1}-{\text{b}}^{-1}}{2}$	−98.1 dB
${\mathcal{H}}_{\text{a}}-{\mathcal{H}}_{\text{b}}=\ln (\frac{\text{a}}{\text{b}})+\frac{{\text{a}}^{-1}-{\text{b}}^{-1}}{2}-\frac{{\text{a}}^{-2}-{\text{b}}^{-2}}{12}$	−194.7 dB