Effect of on-air-combining on the signal quality in distributed transmitter systems

In this paper the effect of on-air-combining on the signal quality in distributed transmitter systems like active antennas is described. Active antennas containing a multitude of parallel, independent transmitter chains are emerging in the mobile communication base station market. Due to the independent transmitter chains, each signal is subject to different distortions by the various transmitter components like D/A-converters, filters, amplifiers, noise sources etc. These multiple signals are then radiated by individual antenna elements, which, according to their phase and amplitude offsets, then combine on air; forming the required beam pattern. In this paper the effect of the combining process is described; a system simulation tool in Matlab and Simulink is described and the measured verification-results of an implemented test system are presented.