a microwave measurement system is utilized for the determination of displacement of a piston in a fluid filled cylindrical structure . the piston plus cylindrical encasement of the hydraulic system is modeled as a uniform cylindrical waveguide terminated in a metal plate . a novel shaped probe antenna to measure the slope of the relative phase of the reflected equivalent voltage wave with respect to frequency . the idea to measure the slope of the relative phase is novel and requires a new antenna structure . instead of using the phase slope with respect to frequency , the total phase shift in a given frequency range is used to determine the location of the piston in the cylindrical chamber . simulation and measurement will be used to determine the impedance of the antenna as well as the electromagnetic field at different locations inside the cylinder . in addition , the antenna will be analyzed to optimize its design , which ought to result in minimizing the reflections .