This article focuses on reducing mutual coupling between the ports of dielectric resonator antenna (DRA) using defected ground structures (DGSs). The antenna has the dimension of 50 mm × 50 mm × 8.5 mm. The resonating element in the proposed two-port radiator consists of a cylindrical structure of alumina ceramic (ɛr = 9.8). The rectangular-shaped aperture is utilized to excite both of the resonating elements. The resonating ceramic elements acting as radiators are offset-fed to enhance the antenna’s coupling. Combining interdigital-shaped and semicircular arc-shaped DGSs improves isolation between two resonating elements, embodying the structural novelty. The measured operating frequency range of Port-1 and Port-2 is 5.19–6.7 and 5.15–6.68 GHz, resonating at 5.58 and 5.56 GHz, respectively. The measured mutual coupling between the two ports is −35.5 dB. The measured gain for Port-1 is depicted to be 5.5 dB. The presented multiple-input–multiple-output (MIMO) radiator in this article is an appropriate candidate for WLAN (5.25–5.35, 5.47–5.725, 5.725–5.85, 5.850–5.925 GHz) and WiMAX(5.5 GHz) applications. All the simulated and experimentally observed MIMO parameters of the radiator are discovered to be within optimal bounds.

This research article proposes a dual-sense dual-port wideband circularly polarized (CP) multi-input multi-output (MIMO) antenna designed for Wi-Fi 6E applications. The main novelty lies in achieving CP for both ports using a truncated rectangular-shaped aperture. By incorporating design and spatial diversity and defective ground structure between the two radiators, the design improves isolation and enables the antenna to generate Left-Hand Circular Polarization (LHCP)depending on the selected feed port. The proposed MIMO rectangular dielectric resonator antenna demonstrates an impressive impedance-matching bandwidth (IBW)from 5.5 to 8.0 GHz (37.10%) as well as an axial ratio bandwidth (ARBW) covering from 6.0 to 6.55 GHz (12.20%). Additionally, the dual-port wideband CP MIMO antenna exhibits satisfactory diversity performance parameters. To validate the simulated results, a physical prototype is fabricated and subjected to experimental testing. The measured outcomes of the fabricated model align closely with the simulated results, confirming the accuracy of the design. With both MIMO and CP capabilities and improved isolation, this proposed model proves beneficial in reducing latency and minimizing the impact of multipath fading. Therefore, it stands as an excellent choice for future devices utilizing the Wi-Fi 6E band due to its broad IBW and overlappingAR.

In this paper, a compact two-element reconfigurable multiple-input multiple-output (MIMO) antenna for 5G new radio sub-6 GHz is presented and discussed. The proposed MIMO antenna has four frequency operating modes: a wideband operating mode (2.41–6 GHz), a wideband operating mode with a notching band at 3.5 GHz (3.2–3.66 GHz), a low-pass filter mode that filters the higher frequencies with a wide operating band from 2.41 GHz to 4.7 GHz, and a dual-band mode with two operating narrow bands (2.41–3.16 GHz and 3.64–4.7 GHz). To improve the isolation over the entire operating band, a strip line connecting the two ground planes of the two antenna elements has been used. To validate the proposed approach, different prototypes have been fabricated and measured. The simulation results are in good agreement with the measurement results. The proposed antenna has good MIMO diversity performance with a maximum gain of 4.64 dBi. The minimum isolation is 18 dB for the four operating modes, while a measured envelope correlation coefficient of less than 0.008 is achieved. The diversity gain is near 10 dB for various operating modes. The antenna is suitable for cognitive radio and 5G sub-6 GHz applications.

This paper proposes a wideband four-element multiple-input multiple-output (MIMO) antenna operating in the millimeter-wave frequency band for 5G communications from 24.37–39.44 and 45.09–50.62 GHz. The antenna design has been realized using Rogers 5880 substrate and consists of a T-shaped strip that is attached to the top of a 50 Ω feeding line. Two microstrip lines are affixed at the terminal points of T-shaped strip and bent toward the feeding structure. These bent strip lines are then extended by joining two additional L-shaped microstrip lines. On the back, there is a partial defective ground plane featuring a rectangular slot and a thin strip line located at its center. The dimensions of the proposed single element and MIMO antenna are 0.933λ × 0.933λ × 0.024λ and 1.865λ × 1.865λ × 0.024λ, respectively (at 28 GHz), while the edge-to-edge distance between the radiation elements of the MIMO antenna is 4.0 mm. The design incorporates an efficient passive fan-shaped decoupling structure to decrease coupling between antenna elements. Simulations and experimental results show good agreement with each other. For all resonant frequencies the measured peak gain is greater than 4.85 dBi, radiation efficiency is over 90%, diversity gain is greater than 9.5, ECC is less than 0.025, TARC is less than -10 dB and CCL is below 0.4 bits/s/Hz. The proposed MIMO antenna, with its wide bandwidth, high gain, high inter-port isolation, and high efficiency characteristics, can be used for 5G wireless communication applications.

This paper describes the experimental investigation of orthogonal time-frequency space (OTFS) modulation using a 28 GHz multi-user distributed multiple-input multiple-output (D-MIMO) testbed in over-the-air (OTA) and mobility environments to enhance cell throughput in a millimeter-wave band. We build the D-MIMO testbed having newly developed OTFS modulator and demodulator, and measured OTFS signals and orthogonal frequency-division multiplexing (OFDM) signals with up to four user simultaneous connections on an actual office floor. Additionally, the Doppler effect on OTFS signals is mathematically analyzed and is confirmed in the measurements. OTFS indicates higher robustness in time-variant channels than OFDM. The error vector magnitude (EVM) and system throughput of OTFS are −22 dB and 1.9 Gbps with 100 MHz signal bandwidth, respectively. To our knowledge, this is a first paper describing the OTA measurements of EVM, throughput, and spectral efficiency using OTFS modulation on the 28 GHz coherent beamforming system.

The main interest in using synthetic aperture radar (SAR) technology in automotive scenarios is that arbitrarily long arrays can be synthesized by exploiting the natural motion of the ego vehicle, enabling finer azimuth resolution and improved detection. All of this is achieved without increasing the hardware complexity in terms of the number of physical antennas. In this paper, we start by discussing the application of SAR imaging in the automotive environment from both theoretical and experimental perspectives. We proceed by describing an efficient processing workflow and we derive the rough number of operations required to focus an image proving the real-time imaging capability of the system. The experimental results are based on open road data acquired using an eight-channel radar at 77 GHz, considering side-looking SAR and forward SAR. The results confirm the idea that SAR imaging can be successfully and routinely used for high-resolution mapping of urban environments in the near future.

A 2 × 2 dual band MIMO flexible antenna with a low profile and CPW feeding is designed for Internet of Things (IoT) domains, operating in 5G (3.3–3.6/4.8–5.0 GHz), WiMAX (5.25–5.85 GHz) and WLAN (5.15–5.35/5.725–5.825 GHz) bands. Two resonant frequencies are generated by L-shaped branches and a rectangular monopole. The mentioned MIMO antenna comprises four elements arranged vertically. With the addition of an orthogonal branch, significant isolation is attained, which exceeds 21 dB in the entire bands. The four-element MIMO antenna is fabricated and experimented to analyze the performance. According to the measurement, the antenna can operate bandwidth covering 3.156–3.84 GHz (19.55%) and 4.638–6.348 GHz (31.13%). Furthermore, the provided four-element MIMO antenna possesses a number of advantageous properties, such as ECC, DG, and TARC, indicating its suitability for 5G/WiMAX/WLAN applications. In accordance with the results of bending measurement and human body influence, it is evident that the presented liquid crystal polymer antenna could be an ideal candidate for integrating into wearable 5G/WiMAX/WLAN devices.

A two-element low-profile closely coupled dual-band MIMO antenna is demonstrated for WiMAX applications. Based on the principle of metasurface (MTS) decoupling, a double-layer MTS consisting of pairs of elliptic patches with two different sizes is proposed. The MTS is loaded above a coupled dual-band MIMO antenna, and the mutual coupling in the lower and upper band is reduced by the larger and smaller elliptic patches, respectively. The edge-to-edge distance of antenna elements is only 0.01λ0 (λ0 is the free-space wavelength at 2.6 GHz). The measured results show that the working bandwidths of the MIMO antenna are 2.5–2.69 and 3.4–3.69 GHz. The −10 dB impedance bandwidths in two bands are 8.83% (2.49–2.72 GHz) and 8.50% (3.38–3.68 GHz), and the isolation between antenna elements is enhanced by 13.5 and 18.4 dB in two bands, respectively. Moreover, broadside radiation performances in two bands are obtained.

This paper presents results for active and passive measurements using a novel method based on multiple compact antenna test range (CATR) reflectors to perform simultaneous multiple angle measurements in order to characterize the beam-forming characteristics in a real environment of the 5G devices operating in the millimeter wave frequency band: 24–44 GHz. The over-the-air (OTA) system generates four planar wavefronts with different incidence angles, realizing up to five pairs of angular spreads or four switched/simultaneous angles of arrival. The initial target application is radio resource management (RRM) testing, where the execution of mobility procedures and radio link monitoring of a 5G millimeter wave device are evaluated. The applicability of the multi-reflector approach to RRM testing is measured with commercial 5G handsets, through three test scenarios. The paper demonstrates that baseband (non OTA) testing is not sufficient for RRM FR2, as the results are influenced by the direction of arrival of the signal. It is further shown that OTA testing in a multi-reflector CATR system and a careful selection of a representative set of test directions is critical for full characterization of the performance of a wireless device operating in the millimeter wave bands.

A printed ultra-wideband (UWB) multiple input multiple output antenna with isolation enhancement and pattern diversity is presented, which is based on characteristic modes (CM) for upcoming wireless mobile platforms. The presented antenna is composed of dual UWB antenna elements (AEs) – an antipodal Vivaldi and a circular-shaped monopole positioned on the two opposite edges of the antenna's rectangular-shaped ground surface. The two AEs are capable to stimulate distinct modes in the ground surface and therefore obtaining the required distinct radiation (far-field) patterns and highly isolated AEs without introducing any decoupling structure (DS). The measured results demonstrate that both AEs are UWB with an operating frequency from 2.6 to 11 GHz. The measured isolation is more than 30.1 dB with a maximum value of 55 dB in UWB. The peak realized gain is over 0.83 dBi. The radiation efficiency is greater than 75%. The Envelope Correlation Coefficient is <0.08.

This paper presents the prototype demonstration where an integrated transmitter circuit drives a mobile handset terminal antenna in order to provide frequency tunability and multiple input multiple output (MIMO) operation across the 0.5–4.5 GHz frequency range. The transmitter implementation incorporates on-chip weighted signal generation, i.e. amplitude and phase scaling to provide sufficient MIMO performance in the low band (700–960 MHz) and in the high band (1.5–4.5 GHz). In the transmitter, two antenna elements are used for MIMO operation in the low band and another two in the high band. The transmitter integrated circuit (IC) is fabricated in a 28 nm bulk CMOS technology with an active on-chip area of 0.2 mm$^2$. A custom antenna measurement procedure is proposed here in order to support and verify active antenna measurements with transmitter IC. A measurement procedure for the transmitter system comprising the transmitter IC and four antenna clusters is developed and discussed in comparison with traditional passive antenna measurements. The measurement results demonstrate that the transmitter IC driving the antenna clusters provides total antenna efficiency of $-6.5$ dB to $-1.5$ dB, and envelope correlation coefficient below 0.4 across the designated frequency bands. The results indicate that the implemented transmitter IC successfully tunes frequency response of the antenna clusters, and enhances the MIMO operation of such mobile antennas.

A dual-band 10-port multiple input multiple output (MIMO) antenna array for 5G smartphone is proposed. Each antenna in the MIMO system can work from 3.4 to 3.6 GHz and 5 to 6 GHz with 10 dB (2:1 VSWR) impedance bandwidth. Nevertheless, for a 3:1 VSWR, the antenna operates from 3.3 to 3.8 GHz and 4.67 to 6.24 GHz. The MIMO system is formed by making 10 seven-shaped coupled fed slot antenna elements excited at two different resonant modes and integrated into the system circuit board. By implementing the spatial and polarization diversity techniques, high isolation better than 28 dB between any pair of antenna elements is achieved. The proposed 10-port MIMO antenna array is fabricated and measured. Significant radiation efficiency is obtained, ranging from 65 to 82% for both bands. The antenna gain in the required operating band is substantial, around 3–3.8 dBi. Further, the MIMO parameters such as envelope correlation co-efficient, channel capacity, and total active reflection co-efficient are calculated. The antenna's robustness is estimated by analyzing the user hand effects and specific absorption rate (SAR). The measured results are well agreed with the simulated results.

In this paper, a coplanar waveguide-fed ultra-wideband-multiple-input and multiple-output (UWB-MIMO) antenna with a novel stub for isolation has been presented. The dimensions of the proposed antenna are 18 × 22 × 1.6 mm3. The proposed antenna is design on an FR4 substrate and simulated in CST studio. The |S11| of the presented MIMO antenna is less than −10 dB between 2.8 and 13 GHz with an impedance bandwidth of 10.2 GHz. The envelope correlation coefficient (ECC) is less than 0.007 and diversity gain (DG) is greater than 9.97 dB. The proposed UWB-MIMO antenna is analyzed in terms of isolation, reflection coefficient, current distribution, ECC, DG, peak gain, multiplexing efficiency, and radiation pattern.

A low-profile, wideband dual-polarized 1 × 2 multiple-input-multiple-output (MIMO) antenna with frequency selective surface (FSS) decoupling technique is presented. Low profile is realized with two different artificial magnetic conductor (AMC) cells out of which one operates at 3.5 GHz and other with dual band at 3.1 and 4.5 GHz. The proposed antenna height is maintained at 0.125λ0 which is significantly reduced when compared with the conventional perfect electric conductor (PEC) ground plane. Wideband dual polarization is enabled by two pairs of bow-tie antenna elements surrounded by a square ring placed in the orthogonal orientation. To mitigate the near-field coupling in 1 × 2 MIMO an FSS wall is constructed with wide band stop characteristics from 2.85 to 4.75 GHz. Measured results show by inserting FSS wall vertically, coupling reduction is improved by 27 dB over the existing coupling and the antenna exhibits a bandwidth of 57.14% (2.95–4.95 GHz) for VSWR<2 with port isolation of more than 25 dB for entire band of operation.

This study presents a novel configuration of a cuboidal quad-port ultra-wideband multiple-input and multiple-output antenna with WLAN rejection characteristics. The designed antenna consists of four F-shaped elements backed by a partial ground plane. A 50 Ω microstrip line is used to feed the proposed structure. The geometry of the suggested antenna exhibits an overall size of 23 × 23 × 19 mm3, and the antenna produces an operational bandwidth of 7.6 GHz (3.1–10.7 GHz). The notched band characteristic at 5.4 GHz is accomplished by loading a pair of spiral electromagnetic bandgap structures over the ground plane. Besides this, other diversity features such as envelope correlation coefficient, and diversity gain are also evaluated. Furthermore, the proposed antenna system provides an isolation of −15 dB without using any decoupling structure. Therefore, to validate the reported design, a prototype is fabricated and characterized. The overall simulated performance is observed in very close agreement with it's measured counterpart.

In this paper, a low profile 4 × 4 multiple input and multiple output (MIMO) antenna is proposed and designed for wireless local area network (WLAN) application using a square split-ring resonator. Initially, a single square-patch antenna is designed with square-shaped split-ring slot. Subsequently, the two-element MIMO antenna is designed and it is extended to four-element MIMO antenna. Finally, the defected ground structure (DGS) is implemented in order to enhance antenna performance. The antenna elements are placed opposite to each other. The mutual coupling between the antennas elements is reduced by DGS. The proposed single, two and four-element antennas operate at 5.8 GHz for WLAN. The overall performance is measured in terms of S parameter, radiation pattern, and envelope correlation coefficient. The simulated results are verified through measurements. The simulated and measured results demonstrate that the proposed 4 × 4 MIMO antenna is the most suitable for WLAN applications.

In this research article, a compact wideband stack patch antenna array integrated with compact stack electromagnetic band gap (EBG) structure for multiple input multiple output (MIMO) application is proposed. The wide resonance bandwidth is achieved at 2.45 GHz band by stack arrangement of compact meander line slot driven and parasitic patch elements. The isolation bandwidth is matched with resonance bandwidth with the design of a compact stack L slot EBG structure. The polarization diversity and three-layer EBG structure ensure an enhancement in isolation level. To validate the performance of the proposed stack antenna array, a prototype was fabricated and tested for different MIMO parameters. The measured result confirms the effectiveness of the proposed antenna array in a diverse MIMO environment.