This paper presents an orbital angular momentum (OAM) multiplexing communication system employing active uniform circular arrays (UCAs) to achieve simultaneous five-mode transmission. At 28 GHz, dual-loop UCAs are implemented in the transceiver, in which four UCAs comprising multiple 4×4 microstrip subarrays are placed concentrically. The next stage of each channel is an active transmitter and receiver (T/R) module, which is composed of a beamformer integrated circuit (IC) and a feed network. Additionally, a central antenna with the ability to transmit mode 0 is integrated. Similar to the active phased array system, both the receiving and transmitting modes are reconfigurable by adjusting the phase shifter. According to specific requirements, the modes of different UCAs can be assigned arbitrarily, and the receiving and transmitting states of each UCA can be configured independently. In this study, a 6-m OAM link with data transmission rate of 3 Gbit/s has been successfully implemented.