94 GHz CPW branch-line bandpass filter for planar integrated millimeter-wave circuits

We report the 94 GHz CPW branch-line bandpass filter for planar integrated millimeter- wave circuits. The basic idea is to use the branch-line coupler as a transversal filtering section by connecting the coupled ports to the open load stubs and taking the isolated port as the output node. The 94 GHz bandpass filter exhibits an insertion loss of 2.5 dB with an 11.7 % 3 dB relative bandwidth at a center frequency of 94 GHz and the return loss is better than -18 dB at a center frequency. The designed and fabricated 94 GHz bandpass filter shows the good performance for planar integrated millimeter-wave circuits.