Abstract: In this paper, a compact W-band broadband waveguide diplexer for diplex communication systems working on the millimeter wave band is developed, which can achieve the aggregation and separation of uplink and downlink channels. The diplexer is realized by E-plane Y-type power splitter integrated with two-channel bandpass filter. The overall structure is compact and easy to CNC machining of E-plane splitting. This paper mainly includes the proposal of a compact diplexer network structure, then introduces performance requirement and implementation of the Y-junction, implementation of dual channel Chebyshev filters, and the integration of compact broadband diplexers. This W-band diplexer is processed based on CNC technology. The measured performance shows that the diplexer achieves frequency division/combination performance in two frequency bands of 78.5 GHz~87.5 GHz and 94.4 GHz~105.0 GHz (the relative bandwidth are 10.8% and 10.6% respectively). The insertion loss in two channels is about 0.4 dB, and the isolation between channels is better than 35 dB. The measured results are in good agreement with the simulations. The above results verify the wideband, low loss, robust feasibility, and easy scalability of the W-band diplexer.