Coplanar Interdigital Delay Line Theory and Measurement

The authors have studied a coplanar interdigital delay line for different finger lengths. Using the conforming mapping theory and assming the pure TEM mode case the calculation of the phase velocity for an unit cell of the stucture is proposed and plotted as a function of the finger length. Coplanar strips interdigital delay lines have been fabricated and measured at a frequency range of 0.5-3 GHz. Both theoretical and experimental results are presented and compared with each other. Group velocity results decrease by about 70% as the finger length goes from 0.6mm to 4.2mm, which seem attractive to the design of coplanar istantaneous frequency measurement subsystem (IFM).