Recent development of mimo antennas and their evaluation for small mobile terminals

This paper discusses the antenna configurations in small mobile terminals for MIMO (multiple-in-multiple-out) systems. It is very challenging to fit several antennas with low correlation, high efficiency and adequate bandwidth, as required in MIMO communications systems, into such devices, whose length is typically about 100 mm. Moreover, in the future MIMO techniques may be utilised at several frequency ranges starting probably from as low as 500 MHz like in UHF handheld TV receivers and ranging to over 5 GHz like in multiband OFDM based UWB systems. The paper presents some visions how all these antenna configurations might be realized in the very limited space available in the mobile terminal. As in such cases the performance of the antennas is far from ideal, it is also very important to be able to estimate the behaviour of the antenna configurations in realistic usage conditions already at the design phase of the antennas and systems. In this paper we describe the Measurement Based Antenna Test-bed (MEBAT) for the evaluation of mobile terminal antennas for MIMO systems. The method combines data from a measured directional channel library and the radiation patterns of antennas under test. The patterns can be either simulated or measured e.g. with the Rapid Antenna Measurement System (RAMS). The RAMS system enables to define the radiation properties of mobile terminal antenna systems in very short time also in the case, when a real test person is used in the measurement. Examples of performance evaluations with the MEBAT system are given for realistic MIMO antenna configurations for mobile terminals.