In This Paper the Resonant Frequency Fr and Effective Radius A, Are Obtained In Analytical Form For a Planner, Circular Shape Microstrip Patch Antenna Which Is Etched on a Printed- Circuit Hoard So That the Low Profile Antenna from the Ground Plane Only By a Thin Layer of Dielectric Material: the Formulas Are Found to Have an Error of Less Than 2.5 Percent When Compared With Experimental Data.