Microwave Photonic Image-Reject Mixer Based on a Tunable Microwave Photonic Filter With High Rejection

In a heterodyne receiver, the image can interfere with the desired signal and must be eliminated at the mixing stage. This paper presents a flexible microwave photonic image-reject mixer based on a widely tunable microwave photonic filter (MPF), which is used to select the desired signal and suppress the image. The MPF is realized by using stimulated Brillouin scattering, which offers significant advantages of wideband tunability, high selectivity, and large image rejection. In this work, a theoretical model is established to describe the operation principle of the proposed mixer at first. Then, in the experiment, a 7.8-GHz radio frequency (RF) signal is successfully down-converted to an intermediate frequency signal between 0.2 and 1.5 GHz, with an image rejection of larger than 40 dB. Additionally, when the RF frequency is tuned from 1.8 to 19.8 GHz, the image rejection remains above 40 dB.