A Novel 90° Filtering Coupler With Low Amplitude Imbalance

In this article, a novel 90° filtering coupler with low amplitude imbalance is proposed. This novel design is based on the traditional filtering coupler, placing two waveguide-height discontinuity in the middle of the coupler symmetrically, which can introduce controllable ripple in the whole working frequency band, then achieve better amplitude imbalance. The center frequency of the filtering coupler is 140 GHz, which works in 138-142GHz. in the range of 138-142Ghz band, |S
11
| and |S
43
| are lower than −20 dB and |S
33
| and |S
21
| are lower than −20dB. The maximum magnitude imbalance is 0.148 dB, and the maximum phase error is 0.2°, Compared with the traditional structure, the amplitude imbalance is reduced to a great extent.