In recent years, a new spatial multiplexing transmission scheme using the orthogonality of orbital angular momentum (OAM) modes has attracted attention with growth of the millimeter wave technology and demands for further high-speed large capacity transmission. A uniform circular array (UCA) is one of the candidates for generating multiple OAM modes. However, each mode’s quality changes with distance when a single UCA of fixed diameter is used due to a property of Laguerre-Gaussian beam. In this paper, we propose maximum ratio transmission method by using multiple UCAs at the transmitter side for improving the quality and stability of each mode. Adjusting the amplitude and phase for each mode of all UCA, we can increase the received power and reduce the fluctuation depending on the transmission distance. The simulation results assuming free-space propagation show that high throughput is maintained over a wide transmission range even if radii of UCAs at transmitting and receiving sides are fixed.