Abstract: A Ku band high efficiency rectangular filtering waveguide slot array antenna is proposed in this paper. The filtering characteristic of the antenna is realized by zigzag metal posts loaded in rectangular waveguide. Based on the analysis of the filtering characteristics of the filtering unit by equivalent circuit and electromagnetic field, a filtering waveguide slot array antenna is designed, fabricated and tested. The measured results show that the –15dB impedance bandwidth of the filtering waveguide slot array antenna is about 6.8%(12.06-12.91 GHz), covering the downlink band of Ku band satellite communication(12.25-12.75 GHz), and the in-band gain is about 13.5-14.4 dBi, with a cross-polarization level lower than –38 dB. At the same time, the antenna obtains high suppression of more than 29.8 dB in the uplink band of Ku band satellite communication(14-14.5 GHz).