This paper presents a new class of dual-band filters and diplexers, realized based on dual-band resonators. The proposed dual-band filter and diplexer do not require junctions and can achieve equivalent performance with fewer cavities, thus offering a significant reduction in size compared with traditional approaches. The concept is potentially applicable to most dual-band cavities and is demonstrated in this paper using elliptical and rectangular waveguide cavities. The first design is an inline structure employing elliptical cavities, whereas the second design is implemented through a unique layout that combines the use of dual-band and single-band rectangular cavities. The result is a group of highly compact dual-band filters and diplexers that offer increased Q and an improved spurious-free window. To verify the concept, an eighth-order Ku-band elliptical dual-band filter and a fourth-order Ku-band rectangular diplexer are designed, manufactured, and tested to allow comparisons with traditional designs.