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A two-port symmetrical, reciprocal, U-shaped mutually coupled hybrid ring resonator for ISM, L-band, and S-band applications is presented. The designed resonator is novel with a hybrid ring which comprises a square ring, a circular ring, and two U-shaped couplers for effective mutual coupling between rings and microstrip feeds. The proposed resonator serves as a bandpass filter with a passband ranging from 1.31 GHz to 2.68 GHz. This design offers superior performance compared to conventional ring resonators. The equivalent circuit model of the hybrid ring resonator validated the behavior of the filtering action. The resonator is validated using the measurement of reflection and transmission coefficients. The comparisons of measured values of the prototyped resonator model with CST-designed and HFSS-designed simulated values are found in good agreement in terms of design frequency 2.45 GHz, reflection and transmission coefficient values, and −10 dB bandwidth values. The equivalent circuit model is validated using ADS software. The designed circuit parameter values are found to be in excellent match with manually evaluated circuit parameters with tolerances under ±20%. Selectivity of the ring resonator is investigated for applicability of proposed resonator filter for practical applications. The hybrid resonator is good for the measurement of dielectric permittivity and loss tangent estimations at any frequency without the need for a calculator. The effective parameters are evaluated for characterizations of dielectric properties and their behavior as metamaterials. These attributes make the proposed hybrid ring resonator a highly versatile and efficient solution for next generation communication devices and applications.

In this article, a dual-port single-element coaxial probe-fed cylindrical dielectric resonator MIMO antenna is designed and investigated. The high-permittivity dielectric ( ${\varepsilon }_{\mathrm {r}}=15$ ) is composed of barium-titanate-doped polydimethylsiloxane (PDMS) silicone polymer. The orthogonal excited antenna generates orthogonal modes ( $\mathrm {H}\mathrm {E}_{11\delta }^{\mathrm {x}}$ and $\mathrm {H}\mathrm {E}_{11\delta }^{\mathrm {y}}$ ) with high port-to-port self-isolation ( $\lt -21$ dB) without additional mutual coupling reduction structures. The antenna achieved bandwidths are 5.65–5.96 GHz (gain: 8.91 dBi) and 5.62–5.92 GHz (gain: 8.97 dBi) for Port1 and Port2, respectively. It has an axial ratio >26.5 dB, ensuring orthogonal linear polarization characteristics and improved isolation. The antenna attains excellent MIMO parameters; TARC $\lt -10$ dB, VSWR-MIMO $\sim ~10$ dB, CCL $\lt \pm 3$ dB in operating bandwidth. The HFSS simulated and investigated performance parameters of the MIMO antenna are found to be in excellent agreement with experimental data, this validates the antenna’s MIMO functionality. The antenna is modeled as a parallel RLC equivalent circuit in ADS using a novel technique based on complex-valued impedance parameters (Zij). This approach demonstrates improved accuracy, validated by both simulations and measurements. The antenna is suitable for ISM (5.725–5.85 GHz), WLAN 5.8 GHz, C-band (5.0–6.0 GHz).

Four miniaturized four-element multiple-input multiple-output (MIMO) antenna designs are proposed, designed, and fabricated with dimensions of 26 mm x 26 mm x 0.8 mm each. The first MIMO design operates at 3.5 GHz, while the second operates at 5.2 GHz. The first and second designs are combined into a third design that can be reconfigured to operate at either 3.5 GHz or 5.2 GHz. A new concept of balance is introduced to address the issue of small ground faced by the previous designs. This concept is applied to the third antenna design, resulting in a fourth design of reconfigurable MIMO operating at 5.2 GHz or 3.5 GHz. The antenna demonstrates good impedance matching at both operating frequencies, with isolation levels of approximately 25 dB and 21 dB, envelope correlation coefficients (ECC) less than 0.0001, diversity gain (DG) of around 10 dB at both frequencies, and peak realized gains of 3.5 dBi at 3.5 GHz and 4 dBi at 5.2 GHz. The radiation efficiency of the fourth compact antenna design is approximately 88% at 3.5 GHz and 91% at 5.2 GHz. The measured results show excellent agreement with the simulated results for all four antenna designs.

A compact, dual polarized, multiband four-port flexible Multiple Input Multiple Output (MIMO) antennae with the connected ground and high isolation is designed with computation and experimental measurement studies. All four monopole radiators are embedded decagon-shaped flexible FR-4 substrate with an outer radius of 10 mm in order to accomplish circularly polarized (CP) radiations, bandwidth enhancement, and compact size of only $45\times 38\times 0.2$ mm3 ( $0.375\lambda \times 0.316\lambda \times 0.0016\lambda $ , at lowest resonating frequency 2.5GHz). The interconnected ground structure is loaded with an Interlaced Lozenge Structure (ILS) to suppress the surface wave radiations resulting in low mutual coupling between the radiators. The proposed MIMO antenna demonstrates measured 10-dB impedance bandwidths of 9.63% (2.37–2.61 GHz), 28.79% (3.30–4.41 GHz), and 16.91% (4.98–5.90 GHz) in the LTE 38/40, Sub-6 GHz 5G NR n77/n78, WLAN and Wi-Fi bands, respectively. Furthermore, broad 3-dB Axial Ratio Bandwidth (ARBW) of 28.79% (3.30–4.41 GHz) with gain greater than 4 dBi and efficiency above 80% are achieved. Finally, the bending analysis of the proposed flexible MIMO antenna along the X- and Y- directions shows good performances in terms of scattering parameters, 3 dB ARBW, and MIMO diversity parameters.

The main objective of this work is to investigate the combinatory effects of both uniaxial magnetic and electrical anisotropies on the input impedance, resonant length and the mutual coupling between two dipoles printed on an anisotropic grounded substrate. Three different configurations: broadside, collinear and echelon are considered for the coupling investigation. The study is based on the numerical solution of the integral equation using the method of moments through the mathematical derivation of the appropriate Green’s functions in the spectral domain. In order to validate the computing method and evaluated MatlabⓇ calculation code, numerical results are compared with available literature treating particular cases of uniaxial electrical anisotropy; good agreements are observed. New results of dipole structures printed on uniaxial magnetic anisotropic substrates are presented and discussed, with the investigation of the combined electrical and magnetic anisotropies effect on the input impedance and mutual coupling for different geometrical configurations. The combined uniaxial (electric and magnetic) anisotropies provide additional degrees of freedom for the input impedance control and coupling reduction.

In this paper a metamaterial-inspired T-matching network is directly imbedded inside the feedline of a microstrip antenna to realize optimum power transfer between the front-end of an RF wireless transceiver and the antenna. The proposed T-matching network, which is composed of an arrangement of series capacitor, shunt inductor, series capacitor, exhibits left-handed metamaterial characteristics. The matching network is first theoretically modelled to gain insight of its limitations. It was then implemented directly in the 50- $\Omega $ feedline to a standard circular patch antenna, which is an unconventional methodology. The antenna’s performance was verified through measurements. With the proposed technique there is 2.7 dBi improvement in the antenna’s radiation gain and 12% increase in the efficiency at the center frequency, and this is achieved over a significantly wider frequency range by a factor of approximately twenty. Moreover, there is good correlation between the theoretical model, method of moments simulation, and the measurement results.

A new compact Cylindrical Dielectric Resonator Antenna (CDRA) with a defected ground for ultra-wideband applications is presented. The structure is based on two cylindrical dielectric resonators asymmetrically located with respect to the center of an offset rectangular coupling aperture, with consideration of three and four Dielectric Resonators (DR). The resonant modes generated by the defected ground are studied and investigated. A parametric optimization study of the antenna design has been carried out to determine the optimal dimensions of the defected ground plane, resulting in an impedance bandwidth of over 133% that covers the frequency band from 3.6 GHz to 18.0 GHz. A power gain of about 7.9 dBi has been achieved. Design details and measured and simulated results are presented and discussed.