On closely coupled dipoles in a random field

Reception of partially correlated fields by two closely coupled electrical dipoles is discussed as a function of load impedances and open-circuit correlations. Two local maxima of the power may be achieved for two different load impedances, but in those cases the output correlations are high. Choosing the loads to give zero output correlations is possible for almost any real-valued open-circuit correlation with a resulting reduction of received power or gain. However, the excess loss is only of the order 1.5 $dB$ for a spacing as small as 0.05 wavelength

Direction-of-arrival estimation for closely coupled arrays with impedance matching

Conventionally, the spacing between adjacent elements in an antenna array are set at half-a-wavelength in order to obtain maximum spatial resolution while avoiding spurious sidelobes. However, for antenna arrays that are implemented in a compact manner, the spacing between the adjacent elements can be significantly less than half-a- wavelength. The small spacing between the antennas results in strong mutual coupling between the antennas, which has been shown to affect the performance of array algorithms, through modifying the antenna pattern and reducing the antenna efficiency. Recently, impedance matching techniques have been proposed for multiple antenna systems for diversity and MIMO applications, in order to counteract the aforesaid coupling effects. In this paper, we study the impact of different impedance matching conditions on the Cramer-Rao bound performance of direction-of-arrival estimation using closely coupled arrays. We demonstrate that an appropriate matching network can drastically improve the CRB performance with respect to 50 ohm termination or self impedance termination with coupling, and the case of ideal antenna arrays with no coupling. For example, a tenfold reduction in RMSE over the simple matching terminations was obtained with the multiport conjugate match for a two signal scenario and an antenna separation of 0.1 wavelength

Compact multiple antennas in a random world

Recent work on compact multiple antennas in a random environment is reviewed, including extensions of the energy density antenna and the MIMO cube. The performance of handsets with multiple antennas is dependent on many factors due to the close proximity of the antennas. The distribution of scatterers in the environment has an impact on the distributed directivity of the antennas, the powers absorbed in the loads, and the correlation between the open-circuit signals. Matching the antennas is non-trivial, since the matching changes the output correlations and the efficiency. The antennas may be matched for maximum MIMO capacity for a given environment. Basic bandwidth limitations will also be discussed