Pico-second time domain reflectometry response of a microstripline embedded in various liquids

摘要

A microstripline having 50 ohms characteristic impedance has been delineated on PCB type FR-4 board material, by using standard three layer dry film lamination and chemical photo-etching technology. The dielectric constant and dissipation factor for FR-4 substrate material is 4.6 and 0.018 at 1MHz respectively. The fringing fields arising from free end of a microstripline have been employed to observe its free-end-dip liquid response. The microstripline has been vertically dipped in various liquids at different successive lengths. The response due to 40 pico second rise time pulse from free-end-dip of a microstripline in a liquid is observed on the TDR equipment in reflection mode at room temperature. The response waveform obtained is similar to the conventional co-axial transmission line connected to precision SMA cell containing liquid. The data analysis is carried out by standard Fourier transformation techniques. The microstripline of suitable length embedded in a liquid can be used as substitute to the SMA cell to determine the dielectric properties of various liquids.