A novel reconfigurable antenna with the capability of 360-degree polarization scanning and the diversity of boresight and conical radiation patterns switching is presented in this paper. Each shorting-post is connected and controlled by a PIN diode to achieve the desired distribution of electric field null(s) in the substrate, where transverse magnetic (TM) modes switching between TM₁₁ and TM₀₂ can be accordingly realized corresponding to boresight and conical patterns. The antenna is analyzed in a cavity model, which, in terms of electric field, theoretically explains the generation of TM₁₁ and TM₀₂ resonant modes, and provides the audience with an innovative method of designing pattern reconfigurable antennas for the applications such as multiple-input and multiple-output (MIMO), wireless body sensor network (WBSN), Wi-Fi and WiMAX. The proposed antenna is with a competitive radius of 0.32 λ_g. The antenna structure is very easy to be fabricated. The measurement shows that the antenna can realize a boresight and conical pattern reconfiguration at 2.4 GHz with a gain of 6 dBi and efficiency of 86.7% (boresight mode), and 4.39 dBi and efficiency of 82.4% (conical mode).