In this paper, a novel double-layer multiband circularly polarized microstrip patch antenna is proposed. The design employs the concept of slotted patch fed with proximity coupled feed having defected ground plane (DGS). The proposed antenna achieves multiple operating frequency bands including FB1 (11.15 GHz), FB2 (4.17 GHz), FB3 (4.87 GHz) and FB4 (1.98 GHz). The proposed antenna has obtained bandwidth of 12.98%, 4.7%, 4.69% and 5.39% at FB1, FB2, FB3 and FB4 bands, respectively. The proposed antenna also exhibits circular polarization in the frequency band FB4. The 3dB ARBW of the antenna is 9.23% at 11.2 GHz. Finally, a metallic cavity is used with the antenna to achieve a unidirectional radiation pattern. The designed antenna radiation characteristics are verified with the experimental results.