On the Mutual Coupling in an Active Highly Integrated TX Phased Array over Wide-Angle Scanning

Communication at mmWave frequencies is currently being developed to achieve higher data-transfer capacity combined with a larger coverage in an energy-efficient way. Highly integrated TX phased array antennas have recently been proposed to improve the performance of such systems. The high-density integration results in an ultra-compact array system in which the knowledge of an accurate port-to-port mutual coupling and the associated power-transfer under operation is essential. The impact of the mutual coupling determines the quality of the overall system performance. This includes areas such as operation linearity, system efficiency, total output power, and the stability of the system. The investigated case has a non-standard impedance at each port of the antenna where an amplifier is directly integrated into the antenna elements in the array (direct-integration). Thus as a difference to passive antennas [1], a full multi-port electromagnetic-circuit co-simulation is required to characterize the system. Note that all ports need to be included, e.g. all the ports of the power amplifier, biasing, antenna for each element in the array. This increases the complexity of the system simulations due to the following facts: 1. the unit-cell consists of multi-ports with often unequal complex termination impedance, 2. active components are non-linear and their behavior depends on both the input power and the considered frequency. 3. although the transferred power to each port through mutual coupling is essential, the particular ports, like the input port of the amplifier, are more sensitive. 4. The transferred power depends on the scan angle of the array. This effect is similar to that of a passive antenna where the active-reflection coefficient depends on the scan-angle.