# Is this phase response linear phase?

Would the following frequency response be considered linear phase? I know that linear phase is when the phase response is a linear function of frequency. However, the phase response is only linear from ~0.3 so I'm not sure if it is considered "linear".

• The phase seems to be non linear in the passband itself ...so I dont think the phase response is linear – DSP Novice Mar 14 '20 at 4:19

Another method is to look at the pole-zero diagram of the transfer function. If the system is causal then all poles must lie at the origin and all zeros must either lie on the unit circle, or they must occur in quadruples $$z_0$$, $$z_0^*$$, $$1/z_0$$, $$1/z_0^*$$.