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This research investigates the MIMO antenna by using the Theory of Characteristics Mode (TCM) where 10 modes are subjected in designing. Also, 5 modes are the significant mode and 2 modes correspond to non-significant which defines the operating bandwidth and notched bands. The proposed 2 × 2 MIMO antenna configuration is designed for wideband applications with a size of 0.44 × 0.68 mm2. The two isolated 12-sided polygons radiating patches placed adjacent to each other share a common ground which is printed on an FR4 substrate. The measured impedance bandwidth covers bandwidth 3.11–11.98 GHz with two bands rejecting capability: Wireless Local Area Network (WLAN) and Downlink-Uplink Satellite (DUS) system. These two interfering bands are mitigated by etching a C-type slot on the radiating patch and an inverted U-type slot in the microstrip feed. The simulated and measured results are also compared in the far-field region (Normalized Radiation Efficiency (NRE), Peak Gain (PG), and 2-D/3-D radiation pattern). Proposed MIMO antenna also offers good diversity performance with ECC2×2 < 0.00001, DG2×2 > 9.999 dB, TARC2×2 < −15.0 dB, CCL2×2 < 0.001 b/s/Hz and MEG2×2 ≅ −3.0 dB.

The aim of this paper is to present an analytical study for the investigation of the reciprocal metamaterial gyro-bianisotropy effects on the input impedance of a dipole antenna. This study is based on the numerical resolution, using the spectral method of moments (SMoM), of the integral equation developed through the mathematical derivation of the appropriate spectral Green’s functions of the studied dipole configuration. The original obtained results are discussed and showed good agreements with the isotropic studied cases available in published literature. It is found that the imaginary valued magnetoelectric elements (chiral medium) exhibit an inverse effect on the resonant length compared to purely real elements (Tellegen medium), while negative elements decrease the input impedance. Combination of the two cases has led to more general complex media with further inspiring features.

A novel compact fractal loaded two- and eight-element multiple input multiple output (MIMO) with strong diversity is designed for 5G Sub 6 GHz and WLAN applications. The suggested antenna is designed and manufactured on inexpensive FR4 dielectric material with small size of 72 mm × 72 mm × 1.6 mm (0.792λ × 0.792λ × 0.0176λ, where λ is calculated at a lower operating frequency). The proposed layout features a partially grounded, protruding T-shaped stub on the underside of the substrate and a set of fractally loaded circular patch antenna elements on the top. Four triangular slots on the substrate and a T-shaped stub on the ground are employed to produce good isolation over the intended bands. The proposed antenna has a frequency range of (3.3–6.0) GHz, making it compatible with the 5G sub-6 GHz bands and the WLAN band thanks to its high isolation of above 15 dB and good impedance matching characteristics. Good agreement is observed between the antenna results and the theory of characteristic mode analysis approach. The designed antenna is well suited for 5G sub-6 GHz and WLAN communication applications due to its low ECC (0.005), total active reflection coefficient (TARC) (−10 dB), mean effective gain (MEG) (−3 dB), and diversity gain (DG) (−10 dB), channel capacity losses (CCL) (0.05), peak gain (>2.5 dBi), radiation efficiency (>95%), and stable boresight radiation patterns.

In the present work, characteristic mode analysis (CMA) is utilized for analyzing and designing a novel ultra-wideband (UWB) antenna having a pentagon-shaped structure. The designed antenna gives the impedance bandwidth in the range of 3.1-12.7 GHz, covering the whole UWB range. The developed antenna has compact dimensions 35 × 30 × 1.6 mm with good directional radiation properties and gain characteristics. The antenna is analyzed using the latest analytical tool known as CMA. The parameters like modal significance, modal surface current distribution, and modal patterns are generated and studied in arriving at the operational behavior of the proposed antenna structure.

A Compact Multiple-Input Multiple-Output (MIMO) antenna of size 16 × 26 mm2 (0.144 λ0 × 0.234 λ0) with improved isolation is presented in this paper. It covers the bandwidth of 2.7–14.9 GHz (FBW is 138.2%), which includes the entire UWB, X band, and Ku band applications. The elements in the structure are placed at a distance of 0.018 λ0 (2 mm). Optimized values of two parallel strips are placed between the elements for isolation, giving│S21│ > 15 dB in most of the band. For further enhancement, four small rectangular strips with different dimensions are protruded to the ground plane, resulting in improved isolation│S21│ > 20 dB in most of the band. The radiation efficiency and peak gain values are 86–96% and 0.8–6.6 dBi respectively. Diversity performance is evaluated with the Envelope Correlation Coefficient (ECC 9.975 dB) and Total Active Reflection Coefficient (TARC

The Theory of Characteristic Modes (TCM) enables for the systematic design of conducting radiators. TCM gives a deep insight into the device physics of the conductor so that its radiation mechanism and resonant frequencies can be estimated in a systematic manner, when the conductor is used in antennas. In the proposed work, the resonant behavior and radiation properties of curved conducting planes of different radii of curvature are studied. The important Characteristic Mode parameters like characteristic angle, modal significance and surface currents are obtained and analyzed for the flat and curved conducting plane. This analysis is very helpful in the design of conformal antennas, where antenna shape is required to be bent.

Multiple-input multiple-output (MIMO) antennas with four and eight elements having connected grounds are designed for ultra-wideband applications. Careful optimization of the lines connecting the grounds leads to reduced mutual coupling amongst the radiating patches. The proposed antenna has a modified substrate geometry and comprises a circular arc-shaped conductive element on the top with the modified ground plane geometry. Polarization diversity and isolation are achieved by replicating the elements orthogonally forming a plus shape antenna structure. The modified ground plane consists of an inverted L strip and semi ellipse slot over the partial ground that helps the antenna in achieving effective wide bandwidth spanning from (117.91%) 2.84–11 GHz. Both 4/8-port antenna achieves a size of 0.61 λ × 0.61 λ mm2 (lowest frequency) where 4-port antenna is printed on FR4 substrate. The 4-port UWB MIMO antenna attains wide impedance bandwidth, Omni-directional pattern, isolation &gt, 15 dB, ECC &lt, 0.015, and average gain &gt, 4.5 dB making the MIMO antenna suitable for portable UWB applications. Four element antenna structure is further extended to 8-element configuration with the connected ground where the decent value of IBW, isolation, and ECC is achieved.

A compact 2 × 2 MIMO diversity antenna of size 32 × 32 × 1.6 mm3 is presented in this paper for portable devices. The proposed structure uses polarization and pattern diversities for isolation enhancement. The orthogonal arrangement of radiating elements, pattern diversity, and defected ground structure is achieved isolation. The whole configuration is designed and fabricated over the FR4 substrate with er 4.4, and fed by a 50Ω microstrip line. The proposed structure operates from 7.9 GHz to 13 GHz, and it resonates at 9 GHz, 12.3 GHz. The isolation between orthogonal elements is above 20 dB and the anti-parallel element is above 15 dB. The radiation efficiency and peak gain values are above 86% and 3.1–5.2 dB, respectively. The diversity metric value of ECC is less than 0.07, DG is above 9.985 dB, and TARC is below −10 dB for the entire desired band. Simulated and measured values are in good concord.

A novel compact structure of wrench-shaped MIMO antenna for ultra-wideband applications is presented in this paper. The acceptable return loss ( $\mathrm{S}11 \leq -10$ dB) values of the proposed layout ranging from 3.18 GHz to 11.15 GHz. Half circular slotted T shaped stub is used for isolation enhancement. The isolation ( $\vert \mathrm{S}21\vert$ ) between elements is higher than the 15 dB for the entire operating band and it is above 20 dB in mystifying the band The realized peak gain and efficiency values are 1.97-5.61 dB and 85-95% respectively. MIMO performance metrics checked with MEG (Mean effective gain), MEG ratio (MEG1/MEG2), ECC (Envelope correlation coefficient), DG (Diversity gain) and TARC (Total active reflection coefficient) values. The structure is designed and simulated on a low-cost FR4 substrate of size 24 × 32 × 1.6 mm3, constant 4.4 (€r) with loss tangent of 0.002.

A very compact and closely spaced circular-shaped UWB – MIMO antenna with slotted T-shaped stubs and protruded strips for high isolation is discussed in the present paper. The fractional bandwidth of the proposed model reaches 134.68% from 2.82 GHz to 14.45 GHz with S11