A broadband Circularly Polarized (CP) Aperture Coupled Microstrip Antenna (ACMSA) is described herein. In order to decrease the back radiation of the antenna due to resonant coupling slots (a cross-slot) in the ground plane, a three-layer structure with a screen is proposed. As a result, the back radiation of the antenna is reduced by more than 12 dB and its gain is increased by about 1.3 dB compared to the conventional two-layer ACMSA with non-resonant coupling slots. The antenna is designed to operate within the Ku-band. Keeping its simple and compact construction and high mechanical characteristics it can be used as an element of CP microstrip antenna arrays with various applications in the contemporary communication systems.