  Antenna arrays have been used in various applications and have become an
important tool to achieve high spectral efficiency in wireless communications.
Its use brings to the communications system an increase in performance in terms
of capacity and reliability. Recently one of the main communications
architectures that makes use of antenna arrays is the Multiple-Input
Multiple-Output (MIMO) technology. MIMO technology has been applied in antenna
arrays composed of elements in the order of tens to hundreds. In this way, it
is necessary to use the structure of compact antennas that offer all the
necessary robustness to the applied project. In this context, it is important
to revisit the concepts of mutual coupling and impedance matching among antenna
elements in an array. This paper proposes and evaluates three strategies of
joint decoupling and impedance matching networks(DMN) for antenna arrays. The
first method called DMN with Lumped Elements (DMN-LE) performs the decoupling
and impedance matching steps with capacitors and inductors. The second method
is called the Ring Hybrid (DMN-RH). It is utilizes a microstrip line in the
ring form. With this approach is achieved first the decoupling followed by
impedance matching steps. The third method is called Networkless Decoupling and
Matching (NDM). It brings a concept of decoupling without the presence of a
network itself. A comparison of the methods is performed both analytically and
via computer simulations. We conclude that the third method, networkless one,
is an interesting new alternative approach.
