Port balance, efficiency and correlation impact evaluation for MIMO compact multiantenna systems

The diversity gain and efficiency of two multiantenna prototypes have been evaluated with the reverberation chamber, which represents an advantageous measurement method due to its low time consumption and its high accuracy. The relation between port balance, efficiency, correlation and diversity gain has been analysed for the two compact multiantenna prototypes: Q-dime and 4-square, following a procedure according to Figure 1. Taking into account the good behaviour of both antennas regarding correlation (rho lower than 0.1), it can be said that the apparent DG difference of 0.8 dB between both prototypes is due to the amplitude unbalanced ports: since there is a branch much worse than the other three in case of 4-square patch, only the 3 good elements will be used in the selection combining, becoming a 3times3 system. The effective DG difference between the two structures is approximately 2 dB of which 0.8 dB is due the contribution of the port unbalance. The additional 1.2 dB increase is caused by the higher losses in the antenna elements, which is in accordance with the efficiency measurements.