The $z$-parameter matrix for the two-port network shown is $$\begin{bmatrix} 2j\omega &j\omega \\ j\omega & 3+2j\omega \end{bmatrix},$$ where the entries are in $\Omega$. Suppose $Z_{b}\left ( j\omega \right )=R_{b}+j\omega .$

Then the value of $R_{b}$ (in $\Omega$) equals ________