Question

Consider the following statements: The gain margin and phase margin of an unstable system may respectively be 1. Positive, positive 2. Positive, negative 3. Negative, positive 4. Negative, negative Of these statements

(a) 1 and 4 are correct

(b) 1 and 2 are correct

(c) 1, 2 and 3 are correct

(d) 2,3 and 4 are correct

I had been asked this question during an interview.

The above asked question is from Polar Plots in portion Frequency Response Analysis of Control Systems

Answer 1

Correct choice is (d) 2,3 and 4 are correct

For explanation: For unstable system the signs of gain margin and phase margin are always different or they can both be negative.