Multiband multiple‐input multiple‐output antenna with high isolation for future 5G smartphone applications

A multiband high‐isolation multiple‐input multiple‐output (MIMO) antenna using balanced mode and coupled neutralization line (NL) is presented in this article. The balanced modes of dipole and loop antennas, which leads to good isolation intrinsically are used for the 8 × 8 MIMO in the LTE bands 42 (3400‐3600 MHz)/Chinese 5G band (3300‐3400 and 3400‐3600 MHz). The unbalanced mode of loop antennas, which optimized by decoupling structure are designed for the 4 × 4 MIMO in the LTE band 40 (2300‐2400 MHz). Therefore, the eight‐antenna array is formed by four dipole elements and four loop elements. The simulated and measured results show that the proposed antenna can cover 2300 to 2400 and 3300 to 3600 MHz, with reflection coefficient better than ?6 dB and isolation higher than 15 dB. Good radiation performance and low envelope correlation coefficient can also be obtained. Specific absorption rate of user's hand is also discussed in this article.     

A compact multi‐band multi‐input multi‐output antenna for 4G/5G and IoT devices using theory of characteristic modes

A compact four element multi‐band multi‐input multi‐output (MIMO) antenna system for 4G/5G and IoT applications is presented in this paper. The proposed antenna is developed using the theory of characteristic modes helping in systematic design of MIMO antenna system. It consists of four L‐shaped planar inverted‐F antenna (PIFA) elements each operating at 3.5, 12.5, and 17 GHz bands with the bandwidth of 359 MHz, 1 GHz, and more than 3.7 GHz, respectively. The proposed antenna system is suitable for both 4G/5G and internet of things devices as it shows the satisfactory MIMO system performance. Good isolation characteristics are observed by implementing complimentary Metamaterial structure on the ground plane resulting in isolation level lower than ?21 dB between the antenna elements. The proposed antenna is fabricated and experimental results are also presented and discussed.     

A dual‐band eight‐antenna multi‐input multi‐output array for 5G metal‐framed smartphones

A dual‐band eight‐antenna array operating in the long‐term evolution (LTE) band 41 (2.496‐2.69 GHz) and 3.5‐GHz band (3.3‐3.7 GHz) for fifth‐generation (5G) metal‐framed smartphone is presented. The proposed dual‐band antenna array is composed of four identical dual‐antenna building blocks (DABBs). Each DABB consists of two identical antenna elements with a neutralization line between them. The antenna array is simulated, fabricated, and measured. The isolations are better than 10.5 dB and 11.0 dB in the low band (LB; LTE band 41) and high band (HB; 3.5‐GHz band). The total efficiencies are 41% to 54% and 46% to 64% in the two operation bands, respectively. In addition, the measured envelope correlation coefficients are less than 0.11 and 0.06, the calculated channel capacities are better than 34.5 and 36.3 bps/Hz in the LB and HB, respectively. Furthermore, four hand‐grip scenarios are investigated, and results show that proposed antenna array can maintain excellent multiple‐input multiple‐output performances in all scenarios.     

Dual‐mode and triple‐band 10‐antenna handset array and its multiple‐input multiple‐output performance evaluation in 5G

A 10‐element multiple‐input multiple‐output (MIMO) handset antenna array with triple‐band operation in the long‐term evolution band 42 (3400‐3600 MHz), band 43 (3600‐3800 MHz), and band 46 (5150‐5925 MHz) is studied in this article. Acceptable antenna performances are obtained by using polarization and pattern diversity techniques. To assess the multiplexing performances of the handset array in 5G, an 8‐element base station array covering 3.4‐7.1 GHz is presented and studied. An 8 × 10 MIMO system incorporating 8 transmit antennas, propagation scenario and 10 receive antennas is successfully reported, and its multiplexing performances are evaluated. The computed channel capacities in the low and high bands can be as high as 43.3 bps/Hz and 41.6 bps/Hz, which are promising for multi‐gigabit‐per‐second (multi‐Gbps) data transmission in 5G. The effects of user's hand and low MIMO order on the channel capacities are also investigated. Results show the robust performances of the proposed antenna system.     

Ultra‐compact 4‐port DR antenna for multi‐input multi‐output standards

Here, an ultra‐compact Multi‐Input‐Multi‐Output (MIMO) antenna system is presented for Wireless Local Area Network (WLAN) applications. The proposed antenna compactness approach is based on using Cylindrical‐Dielectric‐Resonator‐Antenna (CDRA) symmetry with the help of image theory to achieve the best size reduction of the resonators and maintain the resonance frequency of the original CDRA. The electric/magnetic walls approach is utilized to miniaturize the size by exploring the symmetry and antisymmetry of the resonant mode. First, a CDRA for MIMO system is designed and tested in terms of return loss and radiation efficiency. Then, two configurations of MIMO‐Antennas (two and four ports) are examined by using the same substrate size. The 2‐port‐MIMO antenna is built from two half‐CDRs (HCDRs) facing each other. Similarly, four‐quarter‐CDRs (QCDRs) are created to form a 4‐port MIMO antenna system. As a result, a 75% size reduction is achieved (size of 30 × 30 × 7.62 mm³). The measured impedance bandwidth for the 4‐port MIMO antenna is 5.4% (5.4‐5.7 GHz), with more than 15 dB isolation levels. Proper levels of Envelope Correlation Coefficients (ECCs) are also achieved (1 × 10^?2‐4 × 10^?2), with a channel capacity loss (CCL) of 0.04 bits/S/Hz. The proposed MIMO antennas are suitable for compact wireless communication systems.     

Dual‐band and enhanced‐isolation MIMO antenna with L‐shaped meta‐rim extended ground stubs for 5G mobile handsets

A novel compact planar dual‐band multiple input multiple output (MIMO) antenna with four radiating elements for 5G mobile communication is proposed. Each radiating element has a planar folded monopole, which is surrounded by L‐shaped meta‐rim extended ground stubs. The compact folded arms act as the main radiating elements, while combined with the L‐shaped meta‐rim stubs, the proposed antenna forms multiple resonances so as to achieve dual‐band coverage. The simulated and measured results show that the proposed antenna has two wide bands of ?6 dB return loss, consisting of 1.6 to 3.6 and 4.1 to 6.1 GHz, respectively. Without any additional isolation structure between the elements, the isolation for the proposed 2 × 2 MIMO antenna in both desired bands can be achieved better than 12 dB. The measured results show that the proposed MIMO antenna with good performance, that is, stable radiation patterns, high efficiencies, low specific absorption ratio (SAR) to human tissues, is suitable for WLAN/LTE, 4G and future 5G mobile phone applications.     

Compact thirteen‐band antenna for 4G/5G/WLAN metal frame mobile phones

An antenna which can cover 13 bands for 4G/5G/WLAN mobile phones including metal frames and has the size of 70 mm × 7 mm × 7 mm is proposed and studied. It comprises four ground branches and a coupled line. The merit of the antenna proposed in this article is that it can cover 13 bands under the condition of a metal frame environment and a 7 mm ground clearance. The prototype of the proposed antenna is fabricated and tested. The measured impedance bandwidths (reflection coefficient less than ?6 dB) are 315 MHz (0.680‐0.995 GHz), 1.1 GHz (1.67‐2.77 GHz), 0.65 GHz (3.25‐3.9 GHz), and 1.35 GHz (4.55‐5.9 GHz). The LTE700, LTE2300, LTE2500, UMTS, GSM850, GSM900, GSM1800, and GSM1900 bands for 4G/3G/2G systems, the 3.5 GHz and 4.8 GHz bands for 5G system, and the 2.4 GHz, 5.2 GHz and 5.8 GHz bands for the WLAN system are covered. The measured efficiencies and patterns are also presented.     

Isolation enhancement of 5G multiple‐input multiple‐output microstrip patch antenna using metamaterials and the theory of characteristic modes

This paper presents a compact 5G multiple‐input multiple‐output (MIMO) microstrip antenna with isolation enhancement based on a slotted complementary split‐ring resonator (SCSRR) and the theory of characteristic modes (TCMs). The metamaterial unit consists of three CSRR connected by extra slots. These added slots improve significantly the rejection response in terms of bandwidth and suppression. The dispersion diagram analysis is introduced to show the filtering characteristics of the band‐gap structure before and after adding these additional slots. The TCM is employed to investigate the behavior of this 5G MIMO antenna before and after adding the slotted CSRR. The TCM is also applied to the MIMO antenna system to build up a precise methodology that can foresee whether the isolation can be upgraded further or not. The slotted CSRR is inserted meticulously in specific locations to block the coupling modes and almost does not affect the results of the noncoupling modes to improve the isolation remarkably. With this slotted CSRR, a 27‐dB reduction in the mutual coupling between the two patch antennas is achieved. The whole design has been simulated utilizing the Microwave Studio CST ver. 18 simulator. The antenna being proposed is highly efficient and suitable for 5G wireless communication.     

A wideband stacked dielectric resonator antenna for 5G applications

A wideband stacked dielectric resonator antenna with stable patterns is proposed for fifth‐generation of mobile technology in this paper. With the help of inserted air gaps to reduce the radiation Q factor, the stacked structure with two thin high permittivity sheets and two hollow low permittivity slabs can provide four adjacent resonant modes to form a wide bandwidth. Measured results demonstrate that the antenna obtains an impedance bandwidth of 54% for |S₁₁| < ?10 dB and a peak gain of 9.2 dBi. The radiation patterns remain stable and symmetrical over the entire operating band.     

Compact slot‐loaded ultra‐wideband multiple‐input multiple‐output antenna with fractal‐inspired isolator

In this paper, a compact multielement ultra‐wideband (UWB) multiple‐input multiple‐output (MIMO) antenna is presented. The proposed antenna is designed by integrating novel technique of stub‐loaded slot, split square ring (SSR), and fractal‐inspired isolator. The antenna size is effectively miniaturized by implementing three‐sided symmetrical stub‐loaded Koch slot and square split ring. The impedance bandwidth is broadened by using small notched partial ground plane. The mutual coupling between the element is impressively reduced by isolating the structure with a Sierpinski fractal. As a result, the proposed antenna achieves a UWB response with a very broad impedance bandwidth of 3.1 to 19 GHz. Moreover, the proposed antenna obtains high peak stable gain and diversity gain of up to 10 dBi, lower group delay (<1 ns), and lower envelop correlation coefficient of <.01. The proposed antenna has electrically small dimensions of 35 × 53 × 0.8 mm. With this low‐profile configuration, the proposed antenna is especially a good candidate for portable UWB‐MIMO wireless communication system.     

Multi‐standard,multi‐band planar multiple input multiple output antenna with diversity effects for wireless applications

Wireless generations require the miniaturized radiating elements for the portable devices. This research article presents a miniaturized multiple input multiple output (MIMO) antenna for IEEE 802.11 (WLAN) and IEEE 802.16 (WiMAX) wireless standards. The multi‐standard, multi‐band MIMO with 1 × 2 diversity arms is impedance matched with 50 Ω microstrip line on FR‐4 dielectric substrate having dielectric constant 4.4 and 1.524 mm thickness. The simple low profile design covers16.46% (2.23‐2.64 GHz) and 12.37% (3.26‐3.70 GHz) microwave frequency bands, with voltage standing wave ratio (VSWR) ≤ 2 achieves more than 12.5 dB of isolation between radiating ports. The proposed MIMO with inverted L shaped slot exhibits more than 73% efficiency, and more than 4 dBi gain at resonant frequencies. The presented MIMO is designed on FR‐4 dielectric substrate of size 45.1 × 90.2 mm². The compact size of the radiating element is 6.7 × 6.7 mm². The effect of radiations on the body has been evaluated using specific absorption rate (SAR) and found to be in safety limit.     

Compact sub‐6 GHz 5G‐multiple‐input‐multiple‐output antenna system with enhanced isolation

A compact two‐element multiple‐input‐multiple‐output (MIMO) antenna system with improved impedance matching and isolation is presented for future sub‐6 GHz 5G applications. The two identical tapered microstrip line fed modified rhombus‐shaped radiating elements are placed in the same orientation at a compact substrate area of 0.24λ₀ × 0.42λ₀ (where, λ₀ at 3.6 GHz) on a shared rectangular ground. A remodeled T‐shaped ground stub is placed between a pair of radiating element to achieve improved impedance bandwidth and isolation. Further, a split U‐shaped stub connected to center of each radiating element to achieve the desired resonant frequency of 3.6 GHz. The proposed antenna covers a ?10 dB operating band of 3.34 to 3.87 GHz (530 MHz) with more than 20 dB isolation between a pair of elements. MIMO performances are also analyzed and experimentally validated. The measured performances of a prototype are found in good agreement with simulated performances. Further, the simulation study is carried out to see the effect of housing and extended ground plane on two‐element MIMO antenna for practical application. An idea of realization of 12‐element MIMO is also studied using the proposed two‐element MIMO antenna.     

Design and packaging of ultra‐wideband multiple‐input‐multiple‐output/diversity antenna for wireless applications

In this article, a new compact eight‐element three‐dimensional (3D) design of ultra‐wideband (UWB) multiple‐input‐multiple‐output (MIMO) antenna is proposed. For realizing polarization diversity, four elements of the MIMO antenna are oriented horizontally and four elements are arranged vertically. In the horizontal arrangement, the antenna resonating elements are placed orthogonally to each other, which reduces interelement coupling and offers a consistent link with the wireless systems/devices. The proposed antenna shows a bandwidth (S₁₁ ≤ ?10 dB) of 17.99 GHz (2.83‐20.82 GHz) and isolation larger than 15 dB in the resonating band. The proposed MIMO/diversity antenna performance parameters such as envelope correlation coefficient, diversity gain, and total active reflection coefficient are evaluated and presented. Furthermore, the unit cell of the MIMO system is simulated for the packaged environment and it is observed that the antenna housing does not affect the antenna performance.     

Dual‐band circularly polarized multiple‐input multiple‐output antenna for GSM and lower LTE applications

A circularly polarized multiple‐input multiple‐output (MIMO) antenna is presented for global system for mobile (GSM) (710 MHz) and lower long term evolution (LTE) (900 MHz) frequency bands. The antenna consists of four ports with four impedance transformers on the bottom substrate and elliptical rings on the upper substrates. Impedance transformers include open stub and irregular microstrip lines in order to control impedance matching and resonant frequencies. Two upper substrates that contain orthogonal elliptical rings cause the circular polarization property of the proposed antenna. The results of measurement for the presented antenna show its performance with S‐parameters of less than ?10 dB in the frequency ranges of 699‐750 MHz for GSM and 880‐1115 MHz for lower LTE applications. Also, the gain and radiation efficiency are higher than 5dBi and 70%, respectively.     

Three‐dimensional cylindrical design multiple‐input‐multiple‐output/diversity antenna with high isolation for wireless communication applications

In this article, a three‐port nonplanar multiple‐input‐multiple‐output/diversity antenna with very high isolation between the radiating elements is presented. To realize diversity from the proposed three‐dimensional (3‐D) antenna configuration, three monopole radiating elements are arranged at an angle of 120°. The isolation between the radiators is enhanced by using a multilayered cylindrical decoupling structure and defected ground structure (DGS). The DGS reduces the coupling due to surface waves while the cylindrical decoupling structure reduces the coupling due to space waves. The proposed antenna offers consistent pervasive connectivity in the wireless communication environment due to its 3‐D geometry with multiple radiating elements and good diversity performance. The prototype is fabricated and measured result shows that more than 42 dB isolation is obtained at the center frequency 1.45 GHz. An increment of 1.2 dBi in the antenna gain is also achieved by using DGS and decoupling structure arrangement. The proposed antenna can be easily placed inside the cylindrical housing or it can be integrated with the existing electronics chip, thus nullifying the requirement for dedicated location in the system.     

Compact nine‐band antenna for 4G/5G smartphones

This article presents a nine‐band antenna whose size is 70 mm × 7 mm × 5.8 mm for 4G/5G smartphones. The proposed antenna consists of a T‐shape coupled line and two ground branches. The T‐shape coupled line is used to produce the resonances at about 925 and 2900 MHz respectively. One ground branch along with the T‐shape coupled line is used to cover the lower band (698‐960 MHz), and the other ground branch is used to cover the 3.6 GHz band (3400‐3800 MHz). By using the higher order modes of the T‐shape coupled line and the ground branches, the higher band (1710‐2690 MHz) is covered. The advantage of the proposed antenna is that a nine‐band antenna can be realized with an only 7 mm ground clearance and without using any lumped element. A prototype is manufactured and measured. According to the measured results, at the bands of 0.693‐0.98 GHz, 1.69‐2.94 GHz, and 3.05‐4 GHz, the S11 are smaller than ?6 dB. The ?6 dB impedance operating frequency band of the proposed antenna can cover the LTE700, GSM850, GSM900, DCS, PCS, UMTS, LTE2300, LTE2500, and 3.6 GHz bands. The simulated and measured results of the radiation performance also are presented.     

Compact C‐shaped MIMO diversity antenna for quad band applications with hexagonal stub for isolation improvement

A compact MIMO antenna was proposed in this article. The designed antenna is compact in size with dimensions of 20 × 34 × 1.6 mm. In this proposed antenna model the patch consisting of two counter facing C‐shaped elements facing each other in which a hexagonal ring attached to a strip line which is placed in between the two C‐shaped patch acts as the stub. The novelty of the antenna elements lies isolation improvement by using the ground stub with the use of circular ring resonator. The proposed antenna operates in four bands in which 2.66 to 3.60 GHz (Wi‐Max, Wi‐Fi), 4.52 to 5.78 GHz (WLAN), 6.59 to 7.40 GHz (satellite communication), and 9.55 to 10.91 GHz and having bandwidth of 0.94, 1.26, 0.81, and 1.36 GHz at four bands. The envelope correlation coefficient is ECC ≤ 0.3 and diversity gain > 9.8 dB for the operating bands of antenna proposed. This antenna can work in the bands of Wi‐Max, Wi‐Fi, WLAN, satellite communication in X‐band and for radio location, and astronomy applications.     

Small‐size four‐element antenna system for 2 × 2 LTE LB and 4 × 4 LTE M/HB MIMO operations in 5G mobile terminals

A small‐size four‐element antenna system for 2 × 2 LTE low band (LB, 698‐960 MHz) and 4 × 4 LTE middle/high band (M/HB, 1710‐2690 MHz) multiple‐input multiple‐output (MIMO) operations in 5G (fifth‐generation) mobile terminals is presented. The proposed antenna system is formed by two identical tunable loop antennas and two identical coupled‐fed IFA (Inverted‐F Antenna) antennas. By loading a RF switch with four output states as tunable component, the proposed loop antenna can not only operate in the M/HB, but also achieve improved bandwidth coverage in the LB. Each coupled‐fed IFA element operating in the M/HB with compact volume. The four antennas are placed on the both short side‐edge of the mobile terminal with small ground clearance of 4.2 mm. The simulated S‐parameters show that the proposed MIMO system can cover 698 to 960 MHz and 1710 to 2690 MHz with reflection coefficients less than ?6 dB and isolations are all more than 12 dB. Good MIMO performances such as radiation efficiencies, envelope correlation coefficient (less than 0.4 within the entire operation bands) and channel capacity are also obtained. The effects of user's hand(s) on performances for the proposed antenna system are also discussed. This four‐element antenna system prototype is fabricated and measured.     

Planar antenna beam deflection using low‐loss metamaterial for future 5G applications

A method to tilt the beam of a planar antenna in the E‐plane is demonstrated by implementing a metamaterial (MM) structure onto the antenna substrate at the fifth‐generation (5G) band of 3.5 GHz. The beam tilting is achieved due to the phase change that occurs when the electromagnetic (EM) wave traverses through two media with different refractive indices. A new adjacent square‐shaped resonator (ASSR) structure is proposed to achieve the beam tilting in a dipole antenna. This structure provides a very low loss of ?0.2 dB at 3.17 GHz. The simulation and measurement results illustrate that the radiation beam of the dipole antenna is tilted by +25° and ?24° depending on the position of the ASSR array onto the dipole antenna substrate. In addition, no degradation in the gain is observed as in the conventional beam‐tilting methods; in fact, gain enhancement values of 3 dB (positive deflection) and 2.7 dB (negative deflection) are obtained compared with that of a dipole antenna with no ASSR array. The reflection coefficient of the dipole antenna with ASSR array has a good agreement with that of the dipole antenna with no ASSR array. The measured results agree well with the simulated ones.     

Design of a compact multiband circularly polarized antenna for global navigation satellite systems and 5G/B5G applications

Design of a multiband circularly polarized antenna is proposed in this article. The antenna has a simple and compact form factor by employing single‐feed stacked patch structure. It exhibits good performance at the global navigation satellite system (GNSS) frequency bands of L1, L2, and L5 and cellular communications frequency band of 2.3 GHz. The antenna has a 3‐dB axial ratio bandwidth of 1.1%, 1.0%, 4.1%, and 1.5% at the four operating bands of L1 (1.575 GHz), L2 (1.227 GHz), L5 (1.176 GHz), and 2.3 GHz. The antenna also achieves a gain of more than 2.2 dBiC and efficiency of more than 70% at the four frequencies. A detailed parametric study is carried out to investigate the importance of different structural elements on the antenna performance. Results are verified through close agreement of simulations and experimental measurements of the fabricated prototype. Good impedance matching, axial ratio bandwidth, and radiation characteristics at the four operating bands along with small profile and mechanically stable structure make this antenna a good candidate for current and future GNSS devices, mobile terminals, and small satellites for 5G/Beyond 5G (5G/B5G) applications.