Design of 0.8-3.7 GHz Broadband asymmetric multi-node directional coupler

In this paper, a 15 dB asymmetric broadband directional coupler for 4G and 5G communication is designed. The physical size of the coupler is
$13\ \text{mm}\times 60\ \text{mm}$
. The dielectric constant is 4.4 and the thickness of single layer plate is 2 mm. The couplers operate in the 0.8-3.7 GHz band. The coupler has the advantages of bandwidth width, convenient processing and installation. ANSYS HFSS 2019 simulation results shows that in the 0.8-3.7 GHz band, the return loss (S
11
) is more than 16.4 dB, the insertion loss (S
21
) is from 0.14 dB to 1.18 dB, the coupling degree (S
31
) is about 15 dB, and the isolation degree (S
41
) is more than 29 dB. The method of multi-section coupling line cascade is adopted, to achieve the requirements of bandwidth width. The directivity of the coupler is increased by loading the branches to meet the design requirements of the 15 dB coupler.