Let $K = 10^{\frac{A_{dB}}{20}}$ (Voltage ratio)

Pi Network:

$R_{shunt} = Z_0 \cdot \frac{K+1}{K-1} \quad ; \quad R_{series} = Z_0 \cdot \frac{K^2-1}{2K}$

Tee Network:

$R_{series} = Z_0 \cdot \frac{K-1}{K+1} \quad ; \quad R_{shunt} = Z_0 \cdot \frac{2K}{K^2-1}$