Diversity Gain Research Articles

A DODECAGON SLOTTED CIRCULAR TWO-ELEMENT SUB-6 GHZ FLEXIBLE ANTENNA FOR WEARABLE APPLICATIONS USING MODAL ANALYSIS

The sub-6 GHz 5G band has opened doors for a seamless and high-data-rate communication system connecting multiple devices. Multiple-input/multiple-output (MIMO) antennas are the backbone of such reliable communication systems with enhanced channel capacity. In this paper, a flexible two-element antenna is proposed for wearable applications. The dodecagon-slotted modified circular patch antenna with a defective ground structure gives isolation of 18 dB over the bandwidth. The antenna exhibits a gain of 3.38 dBi at the operating frequency of 4.8 GHz. A characteristic mode analysis was performed to investigate the resonance behavior of the antenna. Furthermore, specific absorption rate analysis was performed and found to be 0.790/0.314 W/kg for 1/10 g of tissue at 4.8 GHz. The MIMO diversity metrics exhibited an envelope correlation coefficient < 0.001, total active reflection coefficient < -10 dB, diversity gain ≈ 10, mean effective gain < -3 dB, channel capacity loss < 0.40 bps/Hz, and multiplexing efficiency < 0 over the operating frequency band.

Mrs HYBRID MUTUAL COUPLING REDUCTION TECHNIQUES IN MULTIPLE INPUT AND MULTIPLE OUTPUT ANTENNA FOR X-BAND APPLICATIONS

In recent years, Multiple Input and Multiple Output antennas (MIMO) used for high-bandwidth communications where it's important to not have interference from microwave or RF systems. The MIMO antenna offers good matching with stable gain and desired radiation patterns but it suffers on mutual coupling effects. The spacing between antenna elements is less than half the wavelength, and then mutual coupling effects are more. This paper provides a review on different mutual coupling reduction techniques in MIMO antenna. In this letter, a hybrid mutual coupling reduction technique such as substrate integrated waveguide (SIW) and defected ground structure (DGS) in MIMO antennas for X-band applications. The developed MIMO antenna has dimensions as 25 x 36 mm over a FR4 1.6 mm substrate. The MIMO antenna has formed by combining two fractal-shaped structures. Here, the antenna element spacing is taken as minimum of 5.62mm. To reduce the mutual coupling effect and enhance gain, hybrid techniques are used. By adding 24 hollow cylindrical SIW is placed in between a MIMO element and six rectangular DGS slots placed at the bottom of the antenna for reducing the mutual coupling and enhance the gain. The proposed antenna operates at resonating frequencies of 10.04 GHz, 11.14 GHz, and 11.69 GHz for measurement. The mutual coupling or isolation loss was observed around <-25 dB. The envelope correlation coefficient (ECC) and diversity gain (DG) of the proposed antenna are 0.0016 and >9 dB, respectively. The gain observed for the proposed design is 5.2 dB. The Ansys high-frequency structure simulator (HFSS) tool is used for antenna simulation.

FRACTAL-BASED UWB-MIMO ANTENNA WITH RECONFIGURABLE BAND-NOTCHING CHARACTERISTICS

A multiple-input-multiple-output (MIMO) antenna-deploying fractal structure is presented for ultra-wide band (UWB) applications. Furthermore, one band notch (WLAN) is introduced on the radiating patch with a PIN diode to achieve reconfigurability. The antenna consists of two planar fractal elements on one side of the substrate along with the microstrip-fed line. The grounds of these elements are connected via a tiny strip on the other side to form a single ground. To reconfigure the notch, the PIN diode acts as a switch. When the diode is turned off, the antenna's impedance bandwidth exceeds 3.1-10.6 GHz, and the WLAN spectrum (5.15-5.725 GHz) is notched. The performance of the antenna is investigated by examining the reflection coefficients of the two ports. There are further measurements of antenna gain, VSWR, envelope correlation coefficients (ECC), and diversity gain (DG).

Fluid Antenna System: New Insights on Outage Probability and Diversity Gain

Fluid Antenna System: New Insights on Outage Probability and Diversity Gain

A closely spaced two-port MIMO antenna with a radiation null for out-of-band suppressions for 5G Sub-6 GHz applications.

This paper presents the design and isolation enhancement of a filtering MIMO antenna with a radiation null for out-of-band suppressions suited for 5G sub-6 GHz communications. The MIMO antenna offers -10 dB impedance bandwidth functionality at the most prominent partial spectrum of the 5G NR n78 band for enabling wireless applications in base stations, ranging from 3.4 GHz to 3.61 GHz. To mitigate the redundancy of an RF filter and to achieve a strong filtering response, a radiation null is produced in the gain with four identical rectangular slots, which results in a significant gain drop of more than 8 dBi at the stopband. The geometrical design also allows 30 percent size reduction of single element. Subsequently, a closely spaced (0.11λ0) two-port MIMO antenna is implemented and with the utilization of the proposed rectangular shaped hollow stub parasitic element, the interelement isolation is significantly improved by more than 8 dB over the operational frequency range while retaining the filtering without any additional RF structure. The design simplification, peak gain of 5.4 dBi, near ideal response of diversity gain, ECC less than 0.03, congruency between simulated and measured results, and stable parameters make it a valuable choice for 3.5 GHz sub-6 GHz communications.

Analysis of Multiuser Diversity Gain Achieved by MIMO Systems Through User Scheduling Based on Limited Feedback in Dense Cellular Networks

Analysis of Multiuser Diversity Gain Achieved by MIMO Systems Through User Scheduling Based on Limited Feedback in Dense Cellular Networks

FOUR-ELEMENT CIRCULAR PATCH MIMO ANTENNA WITH PROTRUDING GROUND STUB FOR 5G COMMUNICATION

A four-element circular patch multiple input multiple output (MIMO) antenna is designed operating at sub-6 GHz frequency for 5G applications. The proposed design of antenna achieves better performance with 85% of measured efficiency and peak antenna gain of 5 dB. Further, an envelope correlation coefficient of 0.00052 with the diversity gain of 9.99 dB is achieved. The MIMO antenna of size 72 × 27 mm which consists of four identical circular patches with a mean effective gain (MEG) < 3 dB. Each patch of the antenna with a circular slot is separated by a stub. It offers better isolation and matching, which helps to achieve wider impedance bandwidth. A shorted T-shaped stub and two I-shaped stubs are created to achieve the isolation of more than 37 dB at 3.8 GHz for 5G applications.

SMALL-SCALE MIMO ANTENNA WITH HIGH ISOLATION FOR 5G COMMUNICATION

This manuscript describes two- and three-element small-scale multiple-input multiple-output (MIMO) antenna configurations for 5G communications ranging from 23.5 to 28.6 GHz. Modern device antennas have two essential features: isolation and a larger bandwidth. In this regard, firstly a single element antenna has been designed using quarter wavelength impedance transformer and semi-circular loaded patch along with defected ground structure. Furthermore, two single-element antennas are placed orthonormal to each other having quarter wavelength distance from the center of the single-element antenna. To increase the bandwidth and isolation, additionally a rectangular patch and strip isolate from ground. This structural change alters the current path, improving the impedance matching and isolation of the two-element MIMO antenna configuration. After that the three-element MIMO configuration was formed by placing two single-element antennas orthogonally at quarter wavelength from the center of the single-element antenna. The total size of two- and three-element MIMO antenna is 15 × 11 × 1.6 mm and 20 × 11 × 1.6 mm, respectively. The proposed MIMO antennas provide isolation of more than 21 dB and gain more than 25 dB throughout the working band. MIMO diversity features function reasonably well, with an envelope correlation coefficient of less than 0.002 and diversity gain of 10. Proposed antennas can be a good candidate for MIMO applications in the 5G communication frequency range 2 (FR2), 28 GHz bands.

Four‐port MIMO Vivaldi antenna for access points

AbstractIn this article, a 4‐port multiple input, multiple output (MIMO) antenna array is presented, based on a Vivaldi design for nonplanar applications like access points above 6 GHz. The antenna is configured with four Vivaldi antennas arranged orthogonally, one to each other, to increase the electromagnetic isolation among elements. The Vivaldi element is fed with a microstrip with an integrated balun in only one arm, and each arm is set in an antipodal position to the other, giving an easy‐to‐design and build prototype, with no complicated feeding techniques. Each antenna plane has dimensions of 90 × 40 mm2. The array presents a bandwidth from 5.3 GHz to beyond 20 GHz, with electromagnetic isolation above 20 dB, an envelope correlation coefficient below 0.001 for the entire bandwidth, giving a diversity gain around 20 dB, and a total active reflection coefficient below −10 dB from 7 to 20 dB, fulfilling the metrics for MIMO applications.

Design And Simulation of a Hexagonal High-Gain MIMO Patch Antenna For 5G Applications

View of the technological evolution and the problems encountered by the world, researchers are obliged to find solutions, particularly researchers in the field of antennas. This article has been devoted to the design and study of a hexagonal dual-band MIMO patch antenna for Satellite and 5G applications. Several parameters have been studied, we can quote among other things the gain, the bandwidth, the radiation diagram, the directivity, and the distribution of the electric field E. To achieve these studies and find optimal solutions, several designs have been made like the design of a simple hexagonal patch antenna, and, in the end, the proposed antenna is a MIMO with a hexagonal shape and 2 feeding ports. The proposed antenna operates at 25 GHz as the central frequency. The obtained ECC (envelope correlation coefficient) value is less than 0.006 for the entire operating bandwidth, which satisfies the standard value criteria of less than 0.5 and indicates minimal isolation between the antenna arrays. The values of the gain and the maximum directivity of the antenna obtained are respectively 8.12 dB and 8.37 dB, which gives us an efficiency of the antenna at 97.01% with high isolation > 25 dB. The results are found to be sufficient for the device to be used for mm-wave 5G MIMO applications. Additional MIMO performance metrics, such as the channel capacity loss (CCL), diversity gain (DG), and total active reflection coefficient (TARC), are evaluated. All this work has been done using HFSS 15 as software.

Space–time labeling diversity for distributed Goppa-coded cooperative networks over Nakagami-[formula omitted] channels

This paper proposes the novel space–time labeling diversity for the distributed Goppa-coded cooperation (STLD-DGCC) scheme over the Nakagami-q fading channel to improve the performance of the short-to-medium information block transmission. Two different Goppa codes with the same information length are deployed in the source and the relay, respectively, with the Goppa code at the relay providing additional redundancy. Meanwhile, two distinct labeling mappers of M-ary quadrature amplitude modulation (M-QAM) are used in the novel space–time labeling diversity (STLD) to achieve the extra diversity gain and decrease the error floor (EF) region in the Goppa coding scheme. To lower the computational complexity of the maximum likelihood (ML) detection, a near-ML reduced-complexity (RC) detection approach that compromises the system performance and the computation complexity is proposed. In addition, two novel joint decoding algorithms based on the critical signal-to-noise ratio (SNR) threshold are presented at the destination, namely the parallel algorithm and serial algorithm, to enhance the overall performance of the proposed STLD-DGCC scheme. In the case of the Nakagami-q fading model, the analytical union bound of the average bit error probability is provided, which tightly matches the Monte Carlo simulated results at high SNR. The simulation results further indicate that the proposed STLD-DGCC scheme significantly outperforms both the corresponding non-cooperative Goppa coding scheme and the DGCC scheme without the STLD technique under identical conditions. Furthermore, the performance of the STLD-DGCC scheme surpasses that of the existing transmission scheme, offering a promising candidate for further small information block communications.

Edge Hole Effect on Isolation of UWB MIMO RDRA for 5G Outdoor Applications

For 5G sub-6 GHz outdoor applications, a highly isolated two-port rectangular dielectric resonator antenna (RDRA) with UWB MIMO is presented in this research. For isolation enhancement purposes at the lower frequency band (2.27 GHz-2.62 GHz), a longitudinal slot is inserted at the ground plane. For isolation enhancement at the higher frequency band (3.9 GHz-5.73 GHz), an edged hole is inserted in the RDRA. Investigations are conducted on the impacts of slotted ground as well as edged hole radius on isolation. The orthogonal feeding scheme of UWB MIMO RDRA considering both edged hole and slotted ground plane effects are investigated. For the edged hole MIMO RDRA with a slotted ground plane, isolation is better than -24.7 dB at a higher frequency band and is better than -15.5 dB at a lower frequency band. This isolation improvement is explained by the surface current density distribution. The use of an edged hole RDRA and an aperture-coupled orthogonal feeding allows UWB bandwidth and good efficiency performances on the 5G operating bands. To justify the MIMO performance, the envelope correlation coefficient (ECC) and diversity gain (DG) are applied.

A reconfigurable wideband MIMO antenna combines RF energy harvesting

SummaryThis article introduces a novel and groundbreaking approach combining multiple‐input‐multiple‐output (MIMO) technology with radio frequency (RF) energy harvesting. The proposed antenna consists of two semi‐circular monopole antenna components, optimized with dimensions of 89 × 51.02 × 1.6 mm3, that share a common ground plane to achieve MIMO characteristics. A series of split‐ring resonators on the ground plane significantly enhances the isolation between the two radiating components. Band‐notched features are performed in the 3.5 GHz WiMAX and 5.5 GHz WLAN bands through modified C‐shaped slots in the radiating patch and two rectangular split‐ring resonators serving as parasitic devices near the feed line. The reconfiguration of band‐notching is made possible by controlling the modes of the embedded PIN diodes. The two antenna elements maintain mutual coupling below −18 dB from 1.5–13 GHz, achieving an impressive 158.62% impedance bandwidth. The antenna's efficiency and gain experience significant drop, indicating effective interference suppression at the center frequencies of the notch bands, and its performance in MIMO systems is assessed through parameters including envelope correlation coefficient, port isolation, radiation patterns, efficiency, gain, and diversity gain. The simulated properties of the designed antenna closely align with the measured outcomes, demonstrating its reliability and consistency. Moreover, the article evaluates the antenna's potential for RF energy harvesting, achieving a maximum harvested energy of 4.88 V. This proposed antenna can be used in multiple applications, like wideband, band‐notching MIMO, and RF energy harvesting. This proposed antenna is an efficient, reconfigurable wideband MIMO antenna with novel RF energy harvesting capability.

Design and analysis of quantized feedback based user-antenna joint scheduling scheme for ongoing 5G and beyond multi-user massive MIMO FDD communication systems

For the efficient user scheduling (US) and interference mitigation, channel state information (CSI) is mandatory at the base station (BS), particularly for the frequency division duplexing (FDD) systems where the users need to provide some CSI back to the BS for performing the scheduling process. As the feedback overhead increases drastically with increase of antennas as well as users, so, US with limited/reduced feedback is essential. Deploying massive multiple-input multiple-output frequency division duplexing (mMIMO FDD) systems remains an open area for research with major difficulties of associated uplink CSI feedback load as the downlink and uplink channels are not reciprocal. Therefore, smart balancing is required between feedback data and achievable throughput while scheduling the users. In order to handle the above mentioned issue, we employed a selective 4-bit quantized CSI feedback based user-antenna paired/joint scheduling scheme for the multi user (MU) FDD mMIMO systems. The key idea involves in this process is that, only a limited set of users qualifying a predefined selection threshold feed back the 4-bit quantized signal-to-interference-plus-noise ratio (SINR) values based on angle-of-departure (AoD) along with the antenna indices for the scheduling process. The BS schedules the users with respective best antenna. Furthermore, using this scheme the multi user diversity gain is also achieved. This dynamic adjustment of antenna/user selection and collision free antenna sharing between the users majorly helps in improving the throughput of the system with this selective 4-bit quantized limited feedback. The mathematical sum rate performance analysis has been demonstrated along with simulation results for different system parameters.

Nested Variational Chain and Its Application in Massive MIMO Detection for High-Order Constellations.

Multiple input multiple output (MIMO) technology necessitates detection methods with high performance and low complexity; however, the detection problem becomes severe when high-order constellations are employed. Variational approximation-based algorithms prove to deal with this problem efficiently, especially for high-order MIMO systems. Two typical algorithms named Gaussian tree approximation (GTA) and expectation consistency (EC) attempt to approximate the true likelihood function under discrete finite-set constraints with a new distribution by minimizing the Kullback-Leibler (KL) divergence. As the KL divergence is not a true distance measure, 'exclusive' and 'inclusive' KL divergences are utilized by GTA and EC, respctively, demonstrating different performances. In this paper, we further combine the two asymmetric KL divergences in a nested way by proposing a generic algorithm framework named nested variational chain. Acting as an initial application, a MIMO detection algorithm named Gaussian tree approximation expectation consistency (GTA-EC) can thus be presented along with its alternative version for better understanding. With less computational burden compared to its counterparts, GTA-EC is able to provide better detection performance and diversity gain, especially for large-scale high-order MIMO systems.

A New Analytical Approximation of the Fluid Antenna System Channel

Fluid antenna systems (FAS) are an emerging technology that promises a significant diversity gain even in the smallest spaces. It consists of a freely moving antenna in a small linear space to pick up the strongest received signal. Previous works in the literature provide a simple yet insightful parameterization of the FAS channel that leads to single-integral expressions of the probability of outage and various insights on the achievable performance. Nevertheless, this channel model may not accurately capture the correlation between the FAS ports, given by Jake’s model. This work builds on the state-of-the-art by incorporating more parameters into the channel model to accurately approximate the FAS channel distribution while maintaining analytical tractability. The approximation is performed in two stages. The first stage approximation considerably reduces the number of multi-fold integrals in the probability of outage expression, while the second stage approximation represents it in a single integral form. Numerical results validate our approximations of the FAS channel model and demonstrate a limited performance gain under a more accurate correlation model. Further, our work opens the door for future research to investigate scenarios in which the FAS provides a performance gain compared to the current multiple antenna solutions.

Dual-polarized 8-port sub 6 GHz 5G MIMO diamond-ring slot antenna for smart phone and portable wireless applications.

This manuscript presents high performance dual polarized eight-element multiple input multiple output (MIMO) fifth generation (5G) smartphone antenna. The design consists of four dual-polarized microstrip diamond-ring slot antennas, positioned at corners of printed circuit board (PCB). Cheap Fr-4 dielectric with permittivity 4.3 and thickness of 1.6mm is used as substrate with overall dimension of 150 × 75 × 1.6 mm3. In mobile system due to limited space mutual coupling between nearby antenna elements is an issue that distort MIMO antenna performance. Defected ground structure is used to control coupling. The defected ground structure has advantages like ease of fabrication, compact size and high efficiency as compare to other techniques. Less than 30dB coupling is achieved for adjacent elements. The -10 dB impedance bandwidth of 700 MHz is achieved for all radiating elements ranging from 3.3 GHz to 4.1 GHz. The value is about 900MHz for -6dB. The proposed antenna offers good results in terms of fundamental antenna parameters like reflection coefficient, transmission coefficient, maximum gain, total efficiency. The antenna achieved average gain more than 3.8dBi and average radiation efficiency more than 80% for single dual polarized element. The antenna provides sufficient radiation coverage in all sides. The MIMO antenna characteristics like diversity gain (DG), envelope correlation coefficient (ECC), total active reflection coefficient (TARC) and channel capacity are calculated and found according to standards. Furthermore, effect of user on antenna performance in data-mode and talk-mode are studied. Proposed design is fabricated and tested in real time. The measured results shows that proposed design can be used in future smartphones applications. The design is compared with some of the existing work and found to be the best one in many parameters and can be used for commercial use.

Compact ACS-fed MIMO antenna with dual-band notch characteristics for UWB applications

Abstract An ultra-wideband (UWB) and compact-size four-port multiple input multiple output (MIMO) antenna with a footprint of 34 mm × 34 mm fed by an asymmetric coplanar strip (ACS) is investigated. The proposed antenna is composed of four orthogonally placed identical modified elliptical-shaped radiators and achieves an impedance bandwidth of 3.4–12.2 GHz. By etching two inverted L-shaped slots in the radiator element, WLAN band and X-band are rejected in the operating communication range. Because of the usage of a meander line decoupler, the isolation enhancement at the 8–12 GHz band is achieved and the isolation is more than 18 dB for most of the UWB range. The performance of the proposed antenna is studied in terms of isolation between each port, radiation pattern, current distribution, gain, envelope correlation coefficient, diversity gain, and total active reflection coefficient. The compact size and reduced complexity make the proposed design highly suitable for portable devices.

Umbrella-Shaped Wideband MIMO Wireless Communication Antenna

A Circular Polarization (CP) Multiple Input Multiple Output (MIMO) system was used in this study with additional components for contemporary communication systems developed. There are 4 elements in the model. On the printed circuit board, each element has a dual-fed with two ports positioned at each of the four corners of smart devices (PCB). A Rogers RO3003 substrate with a dielectric structure size of (64.59 × 64.59) mm2. geometrical shape 50-Ohm microstrip lines are used to feed the antenna ports. To accomplish polarization and variety properties, microstrip feed lines are positioned orthogonally. According to the paradigm results, the operational frequency for each port was 4.25 GHz, and the system's operating frequency was 4.23 GHz while diversity gains (DG) of the MIMO antennas were about 10, the gain was suitable (around 7 dB), and Less than 0.0001 was the envelope correlation coefficient (ECC). Additionally, the outcomes demonstrate that the MIMO system may operate in a sub-6 band that is ideal for smart device applications.

A novel dual-band–high-gain terahertz MIMO antenna

In this study, a terahertz dual-band–high-gain, multi-input–multi-output (MIMO) antenna with two and four input ports was realized, with gain values of up to 7.16[Formula: see text]dBi and 6.44[Formula: see text]dBi, respectively. This represents an increase in gain of 102.4% and 81.8%, respectively, compared to single-input port antennas. By calculating and analyzing the voltage standing wave ratio (VSWR), gain, envelope correlation coefficient (ECC), and diversity gain, the two MIMO antennas achieved perfect impedance matching at their resonance points. Moreover, the interference between the elements of the MIMO antenna was small, and an isolation effect between the units was realized. These MIMO antennas can achieve multiple input signals to regulate the antenna radiation performance and improve signal strength and quality. In addition, they possess good development prospects for achieving high-speed data transmission in the terahertz band and in mobile communication.