Question

The gain margin for the system with open loop transfer function

 H(s) = G(s) =2(1+s) / s2 is

(a) 8

(b) 0

(c) 1

(d) -8

The question was asked during an interview.

This key question is from Polar Plots topic in section Frequency Response Analysis of Control Systems

Answer 1

The correct answer is (b) 0

Easiest explanation: Gain margin of a system is calculated at the phase cross over frequency and expressed in decibels.