Cavity backed slot antenna covering entire Ku-band satellite communications frequency band (10.5-14.5 GHz) is designed and manufactured using both 3D printing and traditional metal milling for performance comparison. Four cavity backed radiating slots are fed with a waveguide aperture and a stub along the aperture magnetic field is placed to improve the antenna gain and to reduce the mutual coupling among the slots. Measured fractional bandwidth is 38% for both antennas. Measured gain in the target bandwidth is up to 13.1 dBi and 13.5 dBi for 3D-printed and all-metallic variant, respectively. Average HPBW in E-plane is 34 degrees throughout the band. Antenna height is only 0.78 lambda. at the center frequency including the stub and the feed waveguide, and its transverse dimensions are 1.51 lambda by 1.82 lambda. Wideband, high-gain, light weight, and small form factor features of the proposed antenna can be used in array form for satellite and radiolink communications.