The increase of the operating frequency in order to fulfill the requirements for high speed digital applications makes the electromagnetic compatibility an important issue in the design stage. This paper studies the reflection, transmission and coupling parameters of two singled ended microstrip lines as a function of the separation between them, in the frequency band 0.5-50 GHz. The microstrip traces are printed on high frequency, low loss microwave substrate, Rogers 4003 C. Full wave electromagnetic method had been employed for the study.