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In this article, waveguide dual-band filter and diplexer working on W-band are synthesized through cascading mixed TE301- and TE102-mode cavities as well as TE101-mode resonators. Based on the discussion of top resonance modes in single cavity, the TE301&TE102 dual-mode resonator which features oversized dimension, technological insensitivity and high Q-factor is the strong candidate for designing high-frequency filters and diplexers. For dual-band filter, such dual-mode resonator can be shared by both bands as T-junction, and each band can be independently controlled. Besides, a W-band diplexer is proposed based on the analogous method. Two extra zeros have also been generated for each channel with adopting the singlet concept. Finally, the filter and diplexer prototypes are machined by CNC-milling. The filter has obtained 3-dB FBWs of 4% (86.7–90.2 GHz) and 6.3% (96.7–103 GHz), low insertion losses (ILs) of -0.9 dB and -0.5 dB, as well as less than -16 dB return loss, respectively. The diplexer has achieved 3-dB FBWs of 4.9% (86.3–90.6 GHz) and 6.5% (96.9–103.4 GHz), low ILs of -0.7 dB and -0.4 dB, high insolation with more than 40 dB, respectively. All the experimental results including transmission zeros on out-of-band are very close to the simulations in the full band. The performance of dual-band filter and diplexer is highlighted comparing with the reported ones too. [ABSTRACT FROM AUTHOR]