This study presents the results of an optimization technique in order to determine the best design parameters of a plasma analyzer with planar geometry. The instrument is considered to be used in PolarBeeSat which is a CubeSat with 4U designed to study the Earth's space environment. It will carry a magnetometer and a plasma analyzer. The plasma analyzer will be used to measure the energetic electron, ion and neutral particles as PolarBee moves through the polar regions of the magnetosphere Since the design of the instruments is strongly depended upon the characteristics of the region where the spacecraft flies and the mission's purpose, there is no one detector that is perfectly suitable for all space regions. Therefore, different types of instrument designs are used to study the space environment. In this study we consider two types of plasma analyzer and compare them and decide for the appropriate one to place on PolarBee. Depending on the scientific mission, various criteria are used to determine the type of the instrument is determined. In this work, different design considerations are addressed, and the initial design is optimized by a genetic algorithm used with a particle trajectory tracing program for performance evaluation. The preliminary results from the optimization technique will be presented and discussed for its suitability for the PolarBee's scientific mission. Optimization results will be used in our future laboratory tests of the instrument as a start and further optimization will be applied according to the necessities in accordance with the environmental factors.