The radar cross section(RCS) of a coated cylinder with two plates is measured at 10GHz. Prior to measurement, it is necessary to calculate the RCS value. Even though there are many ways to estimate the RCS value, the physical optics(PO) method is used in this paper. In the PO method, the current source is approximated by the incident geometrical optics(GO) field and the reflection coefficient, and then the electric field is obtained. In order to obtain the reflection coefficient of dielectrics, it is essential to know the permittivity. For this purpose, the method to calculate the permittivity is suggested in the case of the low loss material. In actual measurement of the RCS, the most important considerations are the nulling and the calibration. For the nulling, a tuner and a circulator are employed to remove scattering from the background, and for the calibration, a bronze sphere is used as a reference. The measured RCS of the target with varying incident angle is compared with the calculated value from the physical optics. It is shown that the measured data are very close to the calculated within $45\Box$ of the incident angle. Over this range, however, the difference between those values becomes conspicuous because edge effects are not took in account.
