I am studying a book called RF Circuit Design by Reinhold Ludwig and Gene Bogdanov (2nd Edition).
In the first chapter on capacitors, they introduce the loss tangent and equivalent series resistance, with \$ESR=\frac{tan\Delta}{\omega C}\$.
This seems to make sense to me, with the loss angle \$\Delta\$ being the angle between the real and complex components of the impedance of a capacitor in series with a resistance.
However, just before that, they also define the loss tangent relative to the leakage conductance \$G_e=\omega Ctan\Delta\$. This leads to an interesting connection between series resistance and parallel conductance: \$ESR=\frac{G_e}{\omega^2 C^2}\$.
After thinking about this quite a bit, I suspect what they've done is calculate the impedance of the capacitor and leakage conductance in parallel, and make an approximation for very small conductance:
$$Z=\frac{1}{G_e+j\omega C} \approx \frac{G_e}{\omega^2 C^2}-\frac{j}{\omega C}$$
with the assumption \$\omega C >> G_e\$.
Firstly, am I understanding this correctly? If so, what this tells me is that parallel resistance can be modelled as an equivalent series resistance. Is this a standard way of calculating ESR? All other references I have seen on equivalent circuits for capacitors include two separate resistors, one in series and one in parallel, equating ESR with the resistor in series. Is it normal to lump the parallel resistance in with the ESR like this book seems to be doing?