Improvement of crosstalk in coplanar transmission lines

Crosstalk that occurs between transmission lines in electronic circuit boards is a factor that negatively affects the operation of the circuit. In this study, crosstalk between two ungrounded coplanar waveguide (UCPW) transmission lines oriented side by side was investigated. For this purpose, two separate electronic circuit boards with flame retardant (FR4) and poly tetra fluoro ethylene (PTFE) dielectric materials were studied. Impedance, capacitance, inductance and transconductance, which are model parameters of the UCPW transmission line, were calculated for both FR4 and PTFE transmission lines. Crosstalk measurements were made with a vector network analyzer (VNA) in the range of 100 kHz - 3.2 GHz. An external capacitance or inductor was added from outside between the ground plane located between the designed transmission lines and the ground planes at the other end of the transmission line. These external components were placed at the beginning, middle and end of the line. Three different capacitor and inductor values were selected for each location. After the measurements, it was seen that the crosstalk in the transmission line designed with FR4 dielectric material decreased between 17.5 dB to 32.5 dB. It was observed that PTFE decreased between 20.8 dB to 32.5 dB. With the findings obtained, it has been observed that passive components such as capacitors and inductors, which are included externally in the transmission lines in two-layer electronic circuit boards, can reduce crosstalk and test results are given.