Comments on "The design of coupled resonator bandpass filter with wide stop-band"

In the above letter [1], Wang, Wang, and Wang presented a coupled resonator bandpass filter with wide stop-band. Before [1] was published, the authors proposed various novel ring resonators among which a coupled double half-ring resonator had been realized by placing two identical open half-ring configuration, leading to suppression of multiple harmonics [2], [3]. Even though the above letter [1] designed a filter using only one element composed of a single ring resonator, the resonator used is conceptually the same as the single element filter in terms of the layout and resulting performance.