Abstract: The receiving link of satellite communication is often interfered by the transmitter of 5G mobile communication. One solution to eliminate interference is to add a high suppression filter to the existing antenna feed system, and introduce transmission zeros to increase the suppression of the specified frequency band. For the compactness of the whole system, filter miniaturization is necessary, but there is often a contradiction between high performance and miniaturization. To solve this problem, a C-band coaxial cavity filter with high out-of-band rejection is proposed. Direct input coupling from BJ-40 standard waveguide to multiple resonators to reduce size for miniaturization. Non resonant nodes and triangular structures with redundant resonant modes do not introduce negative coupling to generate low frequency transmission zeros to suppress irrelevant signals, which eliminates the processing impact of the traditional implementation of filter low end transmission zeros (negative coupling). The return loss of the designed coaxial cavity filter is greater than 18dB. The out-of-band suppression is greater than 37dB in 3.5~36GHz, greater than 53dB in 3.45~3.5GHz, greater than 60dB in 3.2~3.4GHz and greater than 70dB in 4.4~4.8GHz. The whole structure is compact. The C-band filter has a simple structure without negative coupling introduction, is easy to process, and has a compact structure with source coupling to multiple resonators, making it suitable for anti-jamming applications in satellite communication systems.