A new low cost and easy tuning compact GPS microstrip antenna structure has been proposed. RHCP (right-hand circular polarized) radiation is realized with corner truncated on a square patch as the radiating element. The size of the antenna is reduced by cutting the central slot and marginal slits, which force the current to follow extra paths. Coaxial single- probe center feed loaded with microstrip stub is used to achieve impedance matching. The best operating frequency tuning can be achieved by varying the marginal slits. The design and tuning method is given. The final optimized antenna dimension has been obtained after a large of electromagnetic simulations. The simulated results show that the antenna has a good matching and CP radiation performance.