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A nanoplasmonic loop-stub structure is proposed. Its fundamental properties are studied and compared with those of single-stub and double-stub structures of similar structural parameters. The results show that loop-stub structure has two sets of resonances. One set is similar to the resonances of single-stub and double-stub structures; these resonances are tunable by varying the widths of vertical branches. In contrast, other sets of resonances, which are unique to this structure, can be independently controlled by varying the width of the horizontal branch. The advantage of the loop-stub design over conventional stubs is that it can support traveling-wave-like modes in addition of the standing-wave modes. This feature offers a potential to realize directional add/drop filters for either forward or backward dropping. Moreover, it can provide efficient coupling between waveguides of different widths.