Abstract: With the rapid development of modern radar systems, the system components are also developing in the direction of high performance and miniaturization. At the same time, by adjusting the electromagnetic coupling parameters between the adjacent resonators of the filter, the frequency-variable coupling is introduced to produce a controllable transmission zero point in the stop band, which realizes the performance that can only be achieved by the original four resonators or a larger volume, and achieves the purpose of miniaturization and low loss.