The Dielectric Properties Measurements of some Dielectric Materials, Used In Microwave and Millimeter Wave Technology, Are Performed In F Band (90-140 Ghz) By Using Free Space Technique. a System, Which Consist a Performance Network Analyzer, Two Pyramidal Horn Antennas, a Quasi-Optical Bench and an In House Developed Code Ttds Are Used In Measurements. the Measurement Results Are Also Verified By the Simulation Results Obtained By Cst-Microwave Studio