Abstract: A very compact orthomode transducer design in Ku-band is established, which is suited for complex multi-feed network integration system, the common port is square waveguide and the maximum size is 36 mm. The polarization filtering of electromagnetic wave is realized through a series of ladder transformation and side wall gap coupling. The two output ports correspond to one kind of polarization wave respectively. The coupler is processed and tested. The measured port standing wave in the 15% band range is less than 1.6, the isolation degree of the two ports is less than -50 dB, and the measured result is agree with the simulation result.