Hello everyone,

It is reported that the non-constant group delay of phase modulator in a polar transmitter would cause spectral distortion. I wonder how the group delay of phase modulator has an impact on the output RF spectrum of 8PSK or any other variant envelop modulation.

Can I comprehend it in this way? The variant group delay makes the phase component not combine its corresponding amplitude component, so the spectrum becomes distorted.

Does the group delay only affect the spectrum in non-constant envelop modulation?

With GMSK modulation, there is only frequency modulation in OPLL, then the group delay of OPLL would not affect the output spectrum, would it?

Best,
Yutao