Design and manufacture of a directional coupler in LTCC

In this work, the design and fabrication process of a stripline 90 degree hybrid coupler using LTCC technology are presented. The main specifications required for the device developed were 1.03 GHz central operation frequency, isolation higher than 23dB and a maximum size of 15 mm x 10 mm. To obtain a starting point of physical parameters for the simplified DC configuration a transmission lines calculation program was used and design optimization was performed by simulation. Final design was developed according to specifications required, mentioned above, using LTCC material with k = 7.8 and 12 um thickness TF ink. The fabrication process required twelve LTCC 951 Dupont layers. Coupling lines and the earth planes were screen printed using Dupont 6148 Ag conductive paste. Standard lamination and firing process was applied.