A Study on FDTD Analysis Method of Differential Lines Including Dielectric Loss at GHz Band

In order to process the large amount data, the a few GHz band signal is used on the printed circuit board (PCB). The glass epoxy (Flame Retardant Type 4: FR-4) substrate is mainly used at PCB of general electronic devices. However, the transmission signal decreases due to the dielectric loss of the FR-4 substrate at GHz band. This study is discussed the influence of the dielectric loss with respect to the transmission characteristics S dd21 for the differential line. The complex permittivity of actual substrate is measured by balanced disk resonator and incorporated to Finite-Difference Time-Domain (FDTD) method. The transmission characteristics S dd21 is measured by vector network analyzer (VNA) and calculated by FDTD method. The relative permittivity depends on the frequency. On the other hand, the value of dielectric loss is uniform with respect to the frequency. The results of the transmission characteristics S dd21 by measured and calculated are in good agreement. Since the dielectric loss of actual substrate is incorporated to FDTD method, it can be possible to get accurate analysis coincided with measurement results. The complex permittivity measured by balanced disk resonator is necessary to calculate at GHz band.