Anders Stjernman

Antenna mutual coupling effects on correlation, efficiency and Shannon capacity

MIMO (multiple-input-multiple-output) systems make use of multiple antennas at both ends of a communication link to exploit the spatial dimension for increasing the capacity. Correlation of the antenna signals has an affect on the capacity of a MIMO implementation. High correlation levels occur mainly for compact antenna realizations, where the separation of the antenna elements is small and the mutual coupling is strong. The antenna mutual coupling distorts the antenna radiation patterns and the input impedances, and therefore affects the correlation level and the efficiency. The correlation level is decreased by coupling, which would improve the Shannon capacity, but the effiency of the antenna system is also decreased, which leaves the Shannon capacity nearly unchanged as compared to the case when neglecting coupling effects. The Shannon capacity is increased in a interference limited receiving situation and can also be increased in a transmitting situation in a narrow frequency band by using a decoupling network.

MIMO Performance of Realistic UE Antennas in LTE Scenarios at 750 MHz

Multiple-input-multiple-output (MIMO) is a technique to achieve high data rates in mobile communication networks. Simulations are performed at both the antenna level and Long-Term Evolution (LTE) system level to assess the performance of realistic handheld devices with dual antennas at 750 MHz. It is shown that MIMO works very well and gives substantial performance gain in user devices with a quarter-wavelength antenna separation.

Practical multi-antenna terminals in LTE system performance simulations

In cellular radio network simulations the modeling of terminal antennas is often extremely simplified. In this paper the results from a study on the impact of using realistic terminal antennas in LTE system simulations are presented. Results from downlink simulations using measured radiation patterns of a number of typical multi-antenna terminals have been compared with results using an ideal antenna model. The results showed that the impact was weak in a scenario with high intercell interference while a substantial performance degradation could be observed in a scenario with low interference. Cell-edge throughput was found to be the most sensitive performance metric which in the worst case suffered a 53% throughput reduction compared to the ideal model. An analysis of the relation between antenna properties and system performance is also presented. It was observed that the geometric mean of the eigenvalues of the pattern covariance matrix has a distinct connection to system performance. It was also found that efficiency is important for cell-edge throughput and that the pattern correlation has impact on peak throughput.

Multi-objective optimization of MIMO antennas for dual-band user devices

This paper presents the use of multi-objective optimization when designing a dual-antenna system for MIMO application. As a study case, a user device is selected operating within two separate frequency bands, namely 750–800 MHz and 2.5–2.7 GHz. The MIMO performance of such an antenna system depends strongly on the antenna efficiency in a noise-limited environment but also on the correlation between the antenna branch signals. The antennas also share space with other components in a user device, which puts restrictions on the occupied area. This leads to conflicting requirements that are handled with a multi-objective optimization procedure.

MIMO performance of closely spaced antennas in the 700 MHz band

Performance of two 0.3 wavelengths separated antennas in the 700 MHz band are evaluated and improved by connecting a matching and decoupling network to the antenna ports. It is shown through simulations that the network improves efficiency, diversity gain, MIMO Shannon capacity, and reduces the correlation coefficient. The concept is implemented and validated in two dual-antenna mock-ups with slightly different ground plane sizes.

Performance improvement of closely spaced antennas incorporating a compensating network

This study implements a concept to reduce the effects of antenna coupling on efficiency, correlation, diversity gain, and Shannon capacity of two closely spaced antennas. Antenna system performance without and with different matching and compensating networks is presented. Improved performance is demonstrated in the upper 700 MHz band for an antenna element separation of 0.08 wavelengths.