Design and Error Analysis of W-Band SIW Cruciform Directional Coupler

In this paper, a substrate integrated Waveguide (SIW) directional coupler operating at W-band is designed and fabricated. The experimental results show that the relative bandwidth of the coupler is 27.1% when the return loss S
11
and the isolation S
41
are better than 15dB, and the output amplitude unbalance of the coupling end and the straight-through end is within the performance index of 0.5dB. The test results of the coupler are in good agreement with the simulation results, but the loss is deteriorated and a certain frequency offset is generated. Therefore, the error analysis is carried out, and the main sources of error include dielectric loss, conductor loss, machining accuracy and so on.