Wireless communication for the future will use 5G standards, supported by an antenna system with Massive MIMO technology incorporating subarrays. A subarray microstrip antenna that has small element spacing will result in mutual coupling effects. This paper proposes design of a two rectangular subarray antenna with coaxial feeding for massive MIMO development and analysis the effect of mutual coupling at varying spacing element. Antennas are designed and simulated, namely a single antenna, a two element antenna arrayed in the E-plane and a two element antenna arrayed in the H-plane. The simulation results show that the mutual coupling of the two antenna elements arrayed in the E-plane for all element spacing is less than -20 dB, which means the mutual coupling effect can be ignored. Whereas the mutual coupling of the two antenna elements arrayed in the H-plane for all spacing elements is greater than -20 dB, which means the value of the mutual coupling must be considered. The bandwidth of the two element subarrays on E and H-plane is 77.3-88.5 MHz depending on the element spacing, which is still below 100 MHz required for 5G application.