A Research Of Ultra-Wideband And High Isolation MIMO Antenna

The technology for multiple input multiple output（MIMO）systems in recent years has become one of the key driving forces toward more efficient spectrum usage,faster transmission rate,and higher space efficiency for the 5G and future wireless communica-tion systems.As the MIMO antennas are certainly one of the crucial components for the transmission and reception of signals in modern communication systems,developing var-ious MIMO antennas in a variety of wireless communication environment becomes more important.These days MIMO antennas are designed towards ultra-wideband,miniatur-ization,and high isolation.However,there is a trade-off between miniaturization and high isolation.To relieve this problem,this thesis addresses various decoupling methods,and aims to design ultra-wideband and high isolation antennas.Based on the decoupling meth-ods been discussed,in this thesis,three types of wideband,high isolation MIMO antennas are designed.The main contributions includes:Firstly,this thesis discusses a novel decoupling network for high isolation.By an-alyzing and optimizing a narrowband decoupling network in terms of its scattering and admittance matrices,a wideband decoupling network is designed.The proposed wide-band decoupling network consists of two transmission lines and a second order circuit.The transmission lines are used to make the parameter S₂₁purely imaginary,and the sec-ond order circuit,a parallel connection of a capacitor and an inductor,is used to cancel the imaginary part of the mutual coupling.As a result,the mutual coupling parameter S₂₁decreases to zero.As a design example,Chapter 3 discusses a T-shaped MIMO an-tenna with reduced mutual coupling.The antenna in simulation results exhibits isolation of larger than 20 d B over the operating frequency range of 1.6_-2.1 GHz with a relative bandwidth 25%.Measurement results of antenna is almost the same as simulation results.Secondly,this thesis discusses and exploits the advantageous effects of defected ground structure（DGS）for decreasing mutual coupling.The DGS enhances the isolation by introducing extra inductance and capacitance and changing the current distribution on the ground of antennas.Based on the theoretical characteristics of the DGS,Chapter 4 de-signs an antenna with a dimension of 44_×26 mm²,in which a high isolation is achieved via a polygon slot.The antenna so designed has an operating frequency range of 3.8_-11GHz,over which the parameter S₂₁is mostly smaller than_-15 d B.Finally,this thesis addresses and utilizes the effects of parasitic elements.In addition to a traditional parasitic element which neutralizes the coupling current,Chapter 5 intro-duces a parasitic element operating like a reflector into the antenna.Employing the two types of parasitic elements,the isolation of the proposed pair of two unit antennas placed orthogonally provides enhanced isolation.With the decoupling,the antenna is shown to operate over the frequency range of 3.6_-9.3 GHz with the parameter S₂₁samller than-20 dB.