This paper is devoted to an amplitude control device with compensated phase component based on the Q control of a microstrip resonator, so that the amplitude of S21 can be controlled without phase shifting at a certain frequency. The device consists of a PIN diode and two microstrip lines coupled by an aperture slot on a ground plane. In this paper, the authors have studied both numerically and experimentally the phase compensated variable attenuator. This can be applied to an adaptive array antenna to control the nulls with a fixed main beam directivity.