Antenna Theory And Design

In recent years, multiple-input-multiple-output (MIMO) antennas with the ability to radiate waves in more than one pattern and polarization play a great role in modern telecommunication systems. This paper provides a theoretical review of different mutual coupling reduction techniques in MIMO antenna systems. The increase in the mutual coupling can affect the antenna characteristics drastically and therefore degrades the performance of the MIMO systems. It is possible to improve the performance partially by calibrating the mutual coupling in the digital domain. However, the simple and effective approach is to use the techniques, such as defected ground structure, parasitic or slot element, complementary split ring resonator, and decoupling networks which can overcome the mutual coupling effects by means of physical implementation. An extensive discussion on the basis of different mutual coupling reduction techniques, their examples, and comparative study is still rare in the literature. Therefore, in this paper, different MIMO antenna design techniques and all of their mutual coupling reduction techniques through various structures and mechanisms are presented with multiple examples and characteristics comparison.

/pdf/study-on-mutual-coupling-reduction-technique-for-mimo-529ha50g6v.pdf

Study on Mutual Coupling Reduction Technique for MIMO Antennas

A compact planar quad-element ultrawideband (UWB) antenna with a band-notch and low coupling for multiple-input multiple-output (MIMO) system is proposed in this paper. The antenna consists of four circular monopoles with modified defected ground plane and a periodic electromagnetic band gap (EBG) structures. The proposed EBG structures are modified from the traditional mushroom-like ones, comprised of patterns of grids on the top patch, the metallic ground plane, and several vias that connect the top and bottom plane. It is printed at the center of the dielectric substrate to lower electromagnetic coupling between the parallel elements. Besides, by etching four crescent ring-shaped resonant slots on the radiators, a sharp band-notched characteristic is achieved. From the experimental results, the −10 dB bandwidth of the antenna is extended covers from 3.0 to 16.2 GHz, with a sharp notched band at 4.6 GHz. And the isolation is greater than 17.5 dB between its elements, with a peak gain of 8.4 dB and a peak efficiency of 91.2%. Moreover, it has a compact size of at 3 GHz and could be a good candidate for portable devices.

/pdf/a-quad-element-uwb-mimo-antenna-with-band-notch-and-reduced-127ajvnotn.pdf

A Quad-Element UWB-MIMO Antenna with Band-Notch and Reduced Mutual Coupling Based on EBG Structures

A compact single-polarized filtering dielectric resonator (DR) antenna (DRA) with high selectivity is investigated. The DRA is fed by hybrid microstrip line/conformal strip, excited in its fundamental TE $_{1\delta 1}^{y} $ mode. Owing to different loading effects of the microstrip stub and conformal strip, the resonance frequency of TE $_{1\delta 1}^{y}$ mode excited by the two feed lines is slightly different. Such stepping resonances yield a wide bandwidth of 21.9% and a very flat gain of 5.1 dBi. The hybrid-feeding scheme also establishes a cross-coupled structure in the DRA, which introduces two radiation nulls right near the band edges. A compact wideband filtering DRA (FDRA) with quasi-elliptic bandpass response is, therefore, obtained without requiring any specific filtering circuit. This single-polarized design is also modified to realize a dual-polarized FDRA by adding another orthogonal port with the same feeding scheme. To reduce mutual coupling between the two ports, the microstrip stubs are folded to L shape, and four additional metal posts are inserted into the DR. As a result, the isolation is improved by 14 dB, from 7.2 to 21.2 dB.

Compact Single-/Dual-Polarized Filtering Dielectric Resonator Antennas

A DGS monopole antenna loaded with U‐shape stub for UWB MIMO applications

Dielectric resonator based circularly polarized MIMO antenna with polarization diversity

Design approach for dual element hybrid MIMO antenna arrangement for wideband applications

This Letter presents a dielectric resonator (DR)-based multiple-input-multiple-output (MIMO) antenna with bi-directional pattern diversity. The back-to-back arrangement of cylindrical DR antennas DRAs (cDRAs) is one of the unique features of the proposed design. The cDRAs are placed on an FR4 substrate with a common ground plane. Each cDRA element is excited by two ports to establish a four-port MIMO antenna system. At ports 1 and 2, the top cDRA is excited via co-planar waveguide (CPW) fed conformal strip lines. In case of ports 3 and 4, the bottom cDRA is excited by microstrip line fed conformal strip lines. Isolation between all ports is improved (better than 18 dB) by generating orthogonal modes in the cDRAs and use of opposite excitations. Measured results confirm that the proposed four-port MIMO antenna system is useful for the frequency ranges between 5.4 and 6.0 GHz for WLAN applications.

Compact back-to-back DRA-based four-port MIMO antenna system with bi-directional diversity

In this communication, triple band hybrid multi-input-multi-output MIMO cylindrical dielectric resonator antenna CDRA with high isolation is examined. The proposed MIMO antenna includes two symmetric folded microstrip line feeding structures along with CDRA at two different ends of substrate. Two inverted L-shaped strips on the ground plane are used to enhance the isolation S12<-15 dB as well as to generates 2.7 GHz frequency band. Metallic strip on the ground plane act as an electromagnetic reflector and also enhance the isolation between two antennas S12<-20 dB. Archetype of proposed MIMO antenna design has been fabricated and tested to validate the simulated results. The proposed antenna operates at three different frequency bands 2.24-2.38 GHz, 2.5-3.26 GHz, and 4.88-7.0 GHz S11<-6 dB with the fractional bandwidth 6.06%, 26.4%, and 35.7%, respectively. Folded microstrip lines generate λ4 path delay between the electric field lines and originate circular polarization characteristics in the frequency range 5.55-5.75 GHz with the fractional bandwidth of 3.55%. In order to satisfy the different performance requirement of MIMO antenna such as envelop correlation coefficient, mean effective gain, effective diversity gain, peak gain are also examined. The proposed antenna is found suitable for LTE2500, WLAN, and WiMAX applications. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2016.

Gourab Das

Papers

Dielectric resonator based circularly polarized MIMO antenna with polarization diversity

Design approach for dual element hybrid MIMO antenna arrangement for wideband applications

Compact back-to-back DRA-based four-port MIMO antenna system with bi-directional diversity

Dual polarized triple band hybrid MIMO cylindrical dielectric resonator antenna for LTE2500/WLAN/WiMAX applications

Dual port aperture coupled MIMO cylindrical dielectric resonator antenna with high isolation for WiMAX application