This paper presents a miniaturized 28GHz-band 2-D Beamforming Network (BFN) design, implementation, and vertical integration with a 2x2 patch array antenna for mmWave communications. The antenna module is realized in a thin 5-layers Panasonic Megtron6 substrate. The substrate is composed of upper layers (4-5) for the antenna design and lower layers (1-4) which form the broadside coupled stripline structure used to design the 2-D BFN isolated from the array antenna. The broadside coupled stripline has the characteristic of tight coupling and low attenuation which allow the design of a compact and wideband 3dB/90° broadside stripline coupler. The proposed 2-D BFN consists of four 3dB/90° broadside stripline couplers interconnected by very short striplines and arranged to form a compact, planar and square topology BFN. The actual area of the 2-D BFN is only 0.3λ0×0.3λ0×0.08λ0 which is easily integrated under the 2x2 array antenna area (0.9λ0×0.8λ0×0.08λ0) realizing a miniaturized module structure. The element separation is set to 0.6λ0. A prototype of the 2-D BFN and the antenna module have been fabricated and measured, showing the validity of the simulation results.