This thesis presents a miniaturization of single-feed reconfigurable antenna which is proposed to achieve circular polarization diversity for wireless communication systems. With the state of the diodes, that is ON state and OFF state, this miniaturized antenna radiates with either left hand circular polarization (LHCP) or right hand circular polarization. In order to achieve size reduction on the circularly polarized performance with single-feed structure, two shorting pins and wider square loops slots are incorporated into the square patch antenna. Since a diode can be regarded as an equivalent low resistance under forward bias and capacitance under reverse bias, the impedance of diode changes, which results in different resonant modes and thus the circular polarization can be obtained. Simulated and experimental results of the design are presented to confirm the feasibility. Moreover, the operating mechanism, parametric analysis and design flow are also discussed in detail.