In this letter, a 2 x 2 pyramidal horn antenna array is presented to accomplish linear and circular polarizations with suppressed grating lobes using removable grid cover structures (GCSs) mounted on the top of the antenna array. The spacing between the unit cells becomes farther than a wavelength due to electrically large pyramidal horns and the feeding network. The proposed GCSs, called linear and circular GCS, in this arrangement act as a spacing reducer between the apertures of the horn antennas without the need of physical change of the spacings. Thereby, the desired array factor with newly created apertures can be realized. Although using both GCSs benefit to suppress the highest-level grating lobe, the circular GCS also converts the polarization to circular. The feeding network, which also prevents a formal array factor due to its massive structure, is made up of equal power dividers with T-junction waveguides. The proposed horn arrays, the feeding network, and both GCSs are fabricated, and the total antenna is measured to validate the simulation results. A good agreement is achieved between simulations and measurements.