compact loop antenna system
K. V. Anikin, V. B. Belyansky
The signal from the transmitter to the receiver is transmitted in any certain plane but under restrained urban conditions because of a large number of obstacles, such as buildings, trees, cars etc., the zero line of sight situation arises very often between the subscriber equipment and the base station antennas. Thus, there are many signal re-reflections, deviations from the pre-determined plane, the part of which energy is absorbed by the obstacles. As a result several copies of the original signal with different polarization are received by the radio signal receiver. The principle of polarization diversity is used to collect the original signal energy from various planes. This type of diversity is realized by receiving elements location approach inside the receiving antenna at right angle to each other. This paper presents several modifications of compact loop antenna system with polarization diversity, the dimensions of which are 10 х 10 х 5 mm, consisting of two orthogonal loop system or single loops.
At present the interest in small-sized antennas appeared that is due to the rapid development of systems of mobile communication imposing strict dimensioning specification requirements to the antenna units. In the same direction it should be noted the development of individual communication systems, the occurrence of portable and even pocket radio communication devices. At the same time the small dimension equipment functionality should not be impaired, so the need for the development of compact antenna devices with acceptable electrical specifications was approved. The implementation of said requirements to the antenna device not only on the theoretical but also on practical level is rather difficult problem. It is obvious that the determination of limiting characteristics of small-sized antenna devices, wherein the MIMO technology – the principle of diversity reception – is used, is intimately connected with solving the problem of interaction between the antenna elements and achieving of weak correlation between the adjacent antennas.
To reduce the mutual coupling between two closely spaced loop systems (single loops) the method of their screening by the magnetic walls with μr > 1 is used. Further was demonstrated that there is an optimal ratio between the wall thickness and the magnetic permeability μr of the material from which they are made. The relative bandwidth of antenna considered in this paper is 19%.