© 2018 Institution of Engineering and Technology.All Rights Reserved.Harmonic Motion Microwave Doppler Imaging method (HMMDI), proposed as an alternative noninvasive method for breast tumor detection, is a combination of focused ultrasound and radar techniques to obtain data based on mechanical and electrical properties of the tissue. Two main limitations on the sensitivity of the method are the phase noise of the transmitter source and the coupling between transmitting and receiving antennas. In this study, we used a signal cancellation circuit to suppress the coupled signal and increased the signal to noise ratio (SNR) of the Doppler component. The transmit signal coupled to the receiving antenna was decreased by 33.2 dB, enhancing the SNR about 17 dB. Two hard inclusions inside fat phantom were resolved using the HMMDI system with the signal cancellation circuit.