Improving the performance of strongly coupled antennas using a compensating transmission line network

In MIMO systems the capacity of a wireless link in a rich scattering environment is increased by using multiple antennas on both transmitter and receiver sites. It is desirable to receive different uncorrelated replicas of the signal, but for closely spaced antennas the channel responses will be correlated. Moreover the strong mutual coupling reduces the antenna efficiency. In this thesis the performance of two 0.08 wavelengths separated monopole antennas in the 700 MHz band is evaluated and improved by connecting a compensating network to the antenna ports. It is shown through measurements that the network improves the efficiency with 0.9 dB, diversity gain with 1.3 dB and reduces the envelope correlation coefficient from 0.59 to 0.20. The simulated 2 x 2 MIMO Shannon capacity is increased with 17 %. Finally the concept is implemented into a dual-antenna mock up with the size of a mobile phone. Acknowledgements First we wish to thank Ericsson and specially Antenna Research Center for this great opportunity. Furthermore we want to thank our supervisors Anders Derneryd and Anders Stjernman for their excellent guidance and encouragement. They were always there and willing to help us and assist, always with calm and patience. Special thanks go to Lars Manholm for his assistance with layouts and practical issues, and Jonas Friden and Patrik Persson for the help with Matlab. We are very grateful to Lars Torstensson and Hakan Karlsson for their help and patience with Bluetest measurements. In addition, we would like to thank Sony Ericsson Mobile Communications at Lund for the opportunity to use their anechoic chamber for the measurements