New Narrow-Band Dual-Mode Bandstop Waveguide Filters (Comments)

I have read the above paper with interest, but find some possible discrepancies between the data presented in Fig. 4 and the data presented in Fig. 6. It seems to me that the data in Fig. 4 is probably accurate, reflecting as it does the rejection obtainable through a single pair of ports coupling to a dominant mode propagating waveguide. No matter how the multiple pole filter is synthesized in the concept discussed by the authors, the shunt coupled bandpass filter is coupled only by a pair of couplings to the main line. Thus, the limitation on the depth of the obtainable rejection is determined by two factors: 1) orthogonality of the two coupling irises, and 2) return loss of the two coupling irises.