The Nyquist plot of a stable transfer function $G(s)$ is shown in the figure. We are interested in the stability of the closed loop system in the feedback configuration shown.
The gain and phase margins of $G(s)$ for closed loop stability are
- $6 \mathrm{~dB}$ and $180^{\circ}$
- $3 \mathrm{~dB}$ and $180^{\circ}$
- $6 \mathrm{~dB}$ and $90^{\circ}$
- $3 \mathrm{~dB}$ and $90^{\circ}$