“…According to the comparisons, although the return losses of the filters in [24,25] are quite good, their insertion losses are much higher than that of the proposed one, which is mainly contributed by the transmission loss of inter-coupling between adjacent cavities and the radiation loss. Compared with the proposed filter, due to the narrow band, the cross-layer aperture coupling and multilayered structure, the multilayered filters reported in [9,10,12,27] have higher insertion loss, larger sizes and higher fabrication price. Although the SIW-DGS filter in [26]-2 and the SIW-CSRR filter in [28] have good performance on the whole, as a tradeoff of insertion loss, return loss and size, they are inconvenient to do system integration owing to their DGS and CSRR etched into the bottom metal cover.…”