Measured Envelope Correlation Research Articles

Frequency reconfigurable two-element MIMO antenna for cognitive radio and 5G new radio sub-6 GHz applications

Abstract 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.

A planar four-element modified L-shaped monopolar multiport antenna for sub-6 GHz applications

This paper presents and implements a four-element modified L-shaped multiport antenna for sub-6 GHz applications. The isolation between the antenna elements is improved by careful engineering in the ground plane. The proposed four-element modified L-shaped MIMO antenna has a footprint of 0.21897 λ02, where, λ0 is the wavelength of the lowest operating frequency. The fractional bandwidth of this antenna is 55.15% while operating between 3.9–6.87 GHz. The inter-element isolation is always above 16 dB in simulation and above 18 dB in measurements, with the simulated peak gain of 2.53 dBi over its operating frequency band. The measured Envelope Correlation Coefficient (ECC) is below 0.008 which makes it a potential candidate for IEEE 802.11a and sub-6 GHz wireless applications requiring compact and low-profile antennas with high inter-element isolation.

Dual-Band Highly Isolated Eight-Element MIMO Antenna for 5G Mobile Phone

Based on the characteristic mode analysis (CMA) theory, a compact dual-band dual antenna pair with high element isolation function for 5G mobile terminal is proposed and designed in this paper. The antenna pair is composed of a pair of symmetrical stacked F-shaped radiators printed on the outside of the side frame, perpendicular to the main board. Based on the proposed decoupled antenna pairs, four pairs of antenna pairs are placed at both ends of two long side plates, and an 8-element MIMO antenna is proposed. High isolation in the operating frequency bands are achieved by using grounding branches and defective ground structure (DGS). All radiation elements are etched on a low-cost FR4 substrate with a total size of 150 × 75 × 6.8 mm3. The prototype of the antenna array is fabricated and measured. The working range of the antenna pair can cover 3.4GHz-3.6GHz,4.8GHz-5GHz 5G frequency bands and 5GHz-6GHz WLAN / WiFi / WiMax frequency bands. Besides, the isolation between any adjacent array elements are also > 15dB and > 16dB respectively, the total efficiency are 52%–75% and 58%–88% respectively, and the measured envelope correlation coefficients (ECC) are <0.16. Furthermore, user’s head effects are investigated and desirable results are obtained. The above results show that this proposed antenna array is a good candidate for MIMO applications in 5G smartphones.

Design of Compact Planar Monopole UWB MIMO Antenna with Four Orthogonal Elements and Tapered Fed Configuration for Wireless Diversity Applications

In this paper, we introduce a four-port self-isolated UWB MIMO antenna for diversity applications. First, we have developed a basic radiating element of the proposed antenna in four stages of design, where patches of geometrically different shapes were added at each stage to arrive at the final radiator form. The antenna was designed on an FR-4 substrate with a compact size of 28 × 28 × 1.6 mm3. A tapered microstrip feeding was employed to enhance the antenna’s impedance matching. An orthogonal arrangement of the four radiators was adopted to mitigate the mutual coupling between them, avoiding the use of a separate isolation structure. A prototype was built and measured with a close agreement between the experimental and simulated results. The MIMO antenna performed well in the entire frequency spectrum of 3.1–10.6 GHz, with an isolation better than 20 dB. The measured envelope correlation coefficient (ECC) was less than 0.001, the diversity gain (DG) was greater than 0.99 dB, and the total active reflection coefficient (TARC) was less than −10 dB. The performance of the proposed antenna design was compared with existing designs. The comparison showed that the proposed quad-element UWB MIMO array is compact, has good isolation and diversity performance compared to existing designs, and is well-suited for wireless diversity applications.

Experimental investigation of super‐wideband 8‐port Multiple‐Input‐Multiple‐Output antenna with high isolation for future wireless applications including Internet of Things

SummaryThe paper reports an experimental investigation of an 8 × 8 MIMO antenna fabricated on a commercially available FR4 substrate. A fractal printed monopole radiator is introduced as a good prospect for super‐wideband (2.85–20.0 GHz) multiple‐input‐multiple‐output (SWB‐MIMO) configuration. The MIMO antenna is printed on both the planes (Plane A and Plane B) where four antennas are printed on Plane A and remaining on Plane B which are fed asymmetric to achieve wider impedance bandwidth. An inverted‐L type strip is embedded in a rectangular elliptical slotted ground to match the impedance. Also, a circular ring is embedded on both planes with a novel stub connected to each antenna ground providing isolation of more than 30 dB. The diversity performance of the antenna is also investigated with measured envelope correlation coefficient (ECC) < 0.025, directive gain (DG) > 9.995 dB, total active reflection coefficient (TARC) < −40 dB, and channel capacity loss (CCL) < 0.30b/s/Hz in the entire operating band.

Dual-Band 6 × 6 MIMO Antenna System for Glasses Applications Compatible with Wi-Fi 6E and 7 Wireless Communication Standards

Multi-user multiple-input and multiple-output (MU-MIMO) systems are the mainstream of current antenna design. This paper proposes a dual-band 6 × 6 MIMO glasses antenna for Wi-Fi 6E and Wi-Fi 7 indoor wireless communication. The six antennas have the same structure, all of which are F-shaped monopole antennas. They are on the left and right temples, at the upper and lower ends of the left and right frames, which effectively uses the space of the glasses. The substrate uses FR4 (εr=4.4, tanδ=0.02). The antenna design is compact (9 mm × 50 mm × 0.8 mm) and the glasses model is made of FR4. The overall model is similar to virtual reality (VR) glasses, which are convenient for a user to wear. The proposed antenna has three working frequency bands, at 2.4 GHz, 5 GHz, and 6 GHz. Through matching and optimization, the reflection coefficient can be lower than −10 dB. In addition, this paper evaluates two usage environments for simulation and measurement on the head and free space. The measurement results show that when the operating frequency band is at 2.45 GHz, the antenna efficiency is 86.1%, and the antenna gain is 1.9 dB. At 5.5 GHz, the antenna efficiency is 86.5%, and the antenna gain is 4.4 dB. At 6.7 GHz, the antenna efficiency is 85.4%, and the antenna gain is 3.7 dB. When the isolation of the MIMO antenna system is optimized, the low-frequency band is better than −10 dB, and the high-frequency band is better than −20 dB. The measured envelope correlation coefficient (ECC) values are all lower than 0.1.

Conjoined Yet Decoupled Wideband Multiantenna MIMO Linear Patch Array

A conjoined yet decoupled wideband multi-antenna MIMO linear patch array (LPA) based on using a wideband patch antenna with dual slanted (±45°) shorting metal walls as a building antenna unit (BAU) is presented. The BAU alone can have a very wide operating band of larger than 4 GHz (about 3.25-7.40 GHz, a fractional bandwidth of about 78%). Owing to the antenna’s dual shorting metal walls, it allows arbitrary antenna units to be directly connected in series into a linear patch array with high port isolation (>20 dB) over the very wide band, with no additional decoupling elements required. A four-antenna LPA constructed by using four BAUs is demonstrated. In addition to the high port isolation, the four-antenna LPA can generate four uncorrelated waves with their measured envelope correlation coefficients (ECCs) less than 0.03 over the very wide band almost same as that of the BAU alone. In addition, the proposed MIMO LPA has an all-metal structure, with no substrate materials required. The obtained results make it promising for MIMO access-point application to cover the 5G band of 3.3-5.0 GHz and the unlicensed or mobile band of 5.925-7.125 GHz. Details of the BAU-based wideband multi-antenna MIMO LPA and the experimental results of the four-antenna LPA are presented.

Design and Performance Analysis of a Compact Quad-Element UWB MIMO Antenna for Automotive Communications

This paper presents the design and analysis of a planar ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna for modern vehicular communication systems. The proposed unit cell antenna structure was designed using modified elliptical radiators on a Rogers RO3003 substrate, has a size of 22 × 22 × 0.76 mm3, and covers an impedance bandwidth (S11 ≤ −10 dB) of 3.14 GHz to 12.24 GHz. The peak gain and efficiency of the unit cell prototype are 5.1 dBi and 81%, respectively. The unit cell was further developed into a MIMO antenna configuration with four elements placed orthogonal to each other in a single plane measuring 50 × 50 × 0.76 mm3. The measured isolation between the antenna elements was greater than 20 dB. The measured envelope correlation coefficient (ECC) of the MIMO antenna was less than 0.004, the diversity gain (DG) was greater than 9.67 dB, the total active reflection coefficient (TARC) was <−10 dB, and the mean effective gain (MEG) ratio was > 0.99. The characteristics of the proposed unit cell and the MIMO antenna were investigated for housing effects in order to validate the consistent performance of the antenna in the presence of conducting bodies. In addition, the radiation characteristics of the antenna when mounted on a vehicle were analyzed using a virtual model of the car. The results show that the proposed quad-element UWB MIMO array is compact, has good performance, and is well-suited for automotive applications.

A multi-slotted 2-element quadband MIMO antenna for 4G and 5G applications

This paper presents design of a multi-slotted quadband 2-element MIMO antenna suitable for 4G and 5G applications. The design is realized on an 18.5 × 56 mm2 (0.154 × 0.467 , where is the wavelength of the lowest resonant frequency of 2.5 GHz) FR4 epoxy substrate having a thickness of 1.6 mm and a relative permittivity of 4.4. The simulated and measured results agree well with each other. A simple de-coupler structure has been incorporated on the bottom side to reduce the mutual coupling at operating frequency bands (2.5, 3.7, 4.3, and 5.5 GHz). Furthermore, it was observed that the measured envelope correlation coefficient of the designed MIMO antenna is considerably lower than 0.05. Also, the design exhibits measured gains of 3.49, 2.97, 2.93, and 2.54 dBi at 2.5, 3.7, 4.3, and 5.5 GHz, respectively.

A high performance UWB MIMO antenna with defected ground structure and U‐shape branches

A binary ultra-wideband multiple-input-multiple-output (MIMO) antenna is proposed and fabricated. In order to increase the impedance bandwidth and resonance frequency, U-shaped branches, defected ground structure, folded stepped impedance stubs, and window-shaped radiation patch slots are analyzed. The total size of the MIMO antenna is 80 mm × 35 mm, and the measured relative impedance bandwidth realizes 131% (2.57-12.2 GHz). Without the addition of a decoupling structure and a metal isolation bar, the isolation measured by this work is less than −15 dB. The measured antenna gain is between 3.064 and 4.669 dBi. The measured envelope correlation coefficient value is less than 0.005, and diversity gain is almost equal to 10 dB. The channel capacity loss obtained in the measurement is less than 0.4 bit/s/Hz in the bandwidth except for 9 to 10 GHz. Excellent properties make it suitable for modern wireless communication applications.

Half‐mode SIW cavity antenna for tri‐band MIMO applications

AbstractA half‐mode (HM) substrate‐integrated‐waveguide (SIW) cavity antenna is designed for tri‐band multiple‐input‐multiple‐output (MIMO) applications. Three cavity edges are shorted by metal posts while one aperture is open to radiate cavity energy into free space. To meet MIMO applications, a T‐shaped slot is etched to split the single HM cavity into two equal SIW subcavities and then they are excited by coaxial feeding ports to realize two antenna elements. To obtain tri‐band operations, four additional rectangle slots are cut, which introduces six quarter modes with different resonating regions. With the cavity size of 0.20λ0 × 0.40λ0, a fabricated prototype exhibits three operating bands with center frequencies of 3.33, 4.09, and 4.72 GHz and peak gain of 4.51, 4.05, and 3.93 dBi. Moreover, the measured port isolation is higher than 18.26 dB and the measured envelope correlation coefficient is below 0.05 within the frequency of interest.

A Compact Building Block With Two Shared-Aperture Antennas for Eight-Antenna MIMO Array in Metal-Rimmed Smartphone

In this paper, a compact building block composed of a slot antenna and a loop antenna is proposed. The slot antenna and the loop antenna share a rectangular clearance, which improves the compactness of the building block effectively. Although the slot and the loop have overlapped completely, the proposed building block exhibits good isolation (better than 19 dB) without any external decoupling structure. Four such building blocks are used to implement a compact eight-port multiple-input multiple-output (MIMO) array operating at 3.5 GHz band (3.4–3.6 GHz) for fifth-generation (5G) metal-rimmed smartphone applications. The proposed eight-antenna MIMO array exhibits good isolation of better than 16 dB across the whole operating band. The measured efficiencies of the proposed MIMO array were between 59% and 73%, and its corresponding measured envelope correlation coefficients (ECCs) were better than 0.05. Furthermore, the calculated channel capacity of the proposed MIMO array with 20 dB signal-to-noise ratio (SNR) was about 38.2–39.8 bps/Hz across the desired bands (3.4–3.6 GHz). The measured results confirm that the proposed MIMO array is a good candidate for 5G terminals.

Multipolarized Wideband Circular Patch Antenna for Fifth-Generation Multi-Input–Multi-Output Access-Point Application

A multipolarized wideband circular patch antenna for multi-input-multi-output operation in the fifth-generation band of 3300-4200 MHz is presented for access-point applications. The circular patch antenna is excited by three probe feeds (Ports 1-3) equally spaced by 120° to generate three different polarized waves in the fundamental (TM11) mode. Each port on the circular patch is surrounded by a printed ring slot to achieve good impedance matching and isolation, thereby achieving good antenna performance in 3300-4200 MHz (measured efficiency better than about 88% and peak antenna gain about 6.6 dBi). Additionally, very low measured envelope correlation coefficients (<;0.05) of the three generated waves are obtained.

A Quad-Antenna System for 4G/5G/GPS Metal Frame Mobile Phones

This letter presents a wideband/multiband quad-antenna system for 4G/5G/GPS metal-frame mobile phones. The quad-antenna system has two kinds of antenna elements and four antenna elements. The merit of the proposed antenna system is that a quad-antenna system is achieved under the condition of metal frame, and without using any decoupling structure, the desired bands for 4G/5G/GPS are covered. A prototype was fabricated and measured. For the first kind of antenna elements (including two antenna elements), the bands of 698–960, 1710–2690, and 3400–3600 MHz are covered, and the LTE700/GSM850/GSM900/GSM1800/GSM1900/LTE2300/LTE2500/3.5 GHz bands all are covered. For the second kind of antenna elements (including two antenna elements), the bands of 1440–2690 and 3400–3600 MHz are covered, and the GPS, GSM1800/GSM1900/LTE2300/LTE2500/3.5 GHz bands are covered. The measured isolations are bigger than 10 dB. The measured efficiencies are bigger than 40% at all the working bands. The measured envelope correlation coefficients are very suitable for multiple-input--multiple-output (MIMO) communication systems.

Slot antenna array for fifth generation metal frame mobile phone applications

An eight-element antenna array based on open/closed slot modes that can cover the 3.5 GHz band (3400-3600 MHz) is proposed and studied. There are two kinds of antenna elements with the slot sizes of 10.8 × 1 mm2 and 28.8 × 1 mm2 for open and closed slot modes, respectively. Both the two kinds of antenna elements are realized with the help of the metal frames with the height of 7 mm at the two long sides of the ground. The proposed antenna array is suitable for 5G metal frame mobile phone applications. A prototype is fabricated and measured. The measured results show that all the eight antenna elements can cover the band of 3400-3600 MHz and the isolations are bigger than 13 dB, the measured efficiencies all are bigger than 42% and the measured envelope correlation coefficients are lower than 0.15.

Structure-Shared Planar UWB MIMO Antenna With High Isolation for Mobile Platform

A two-port structure-shared planar ultrawideband (UWB) antenna with high isolation is presented in this communication. The proposed antenna consists of a planar monopole and two back-to-back tapered slots etched on the monopole. The monopole and the tapered slots are fed by the microstrip line and the differential feeding network, respectively. The differential feeding network of the tapered slots excites the modes, which are orthogonal to those of the monopole. Therefore, high isolation between the two ports can be achieved without additional decoupling structures. The measured results show that the proposed antenna can operate from 3 to 10 GHz with the reflection coefficient of the two ports lower than −10 dB and the isolation higher than 38 dB. The measured realized peak gains are above 2.6 dB, and the measured envelope correlation coefficients are less than $9 \times 10^{-5}$ . The proposed UWB multiple-input-multiple-output (MIMO) antenna can be applied in the MIMO communication systems, especially those requiring high isolation.

Dual-Functional MIMO Antenna Array With High Isolation for 5G/WLAN Applications in Smartphones

A dual-functional antenna array operating in the long term evolution (LTE) band 42 (3.4-3.6 GHz) and 5.8-GHz wireless wide area network (WLAN) band (5.725-5.875 GHz) for multiple-input multiple-output (MIMO) applications in 5G smartphones is proposed. The proposed 8-antenna array is composed of two different antenna elements, namely, the folded L-shaped antenna and couple-fed U-shaped antenna. It can be applied in the 8 × 8 (by using 8 antenna elements) and 4 × 4 (by using 4 antenna elements) MIMO system across the LTE band 42 and 5.8-GHz WLAN band, respectively. The quasi-orthogonal polarization, balanced mode excitation and pattern diversity are properly used to achieve high isolation within the operation bands. A prototype of the proposed antenna array was fabricated and measured. The measured isolations in the LTE band 42 (6-dB impedance matching) and 5.8-GHz WLAN band (10-dB impedance matching) are better than 17.1 dB and 34.6 dB, respectively. The total efficiencies are 45%-62% and 52%-59% in the two operation bands, respectively. Besides, the measured envelope correlation coefficients (ECCs) are less than 0.045 and 0.0001, the calculated peak ergodic channel capacities are 37.9 bps/Hz and 19.3 bps/Hz in the 8 × 8 or 4 × 4 MIMO system across the operation bands. Furthermore, user's hand and head effects are investigated and desirable results are obtained. The above results show that this proposed antenna array is a good candidate for MIMO applications in smartphones.

Dual-Band Eight-Antenna Array Design for MIMO Applications in 5G Mobile Terminals

This paper proposes a dual-band eight-antenna array for multiple-input and multiple-output (MIMO) applications in 5G mobile terminals. The designed MIMO antenna array comprises eight L-shaped slot antennas based on stepped impedance resonators (SIRs). The required dual-resonance can be obtained by adjusting the impedance ratio of the SIR, and good impedance matching can be ensured for each antenna element by tuning the position of the microstrip feed line. The experimental results show that a measured return loss of higher than 10 dB and a measured inter-element isolation of greater than 11.2 dB have been obtained for each antenna element with a simulated total efficiency of larger than 51% across the long term evolution (LTE) band 42 (3400-3600 MHz) and LTE band 46 (5150-5925 MHz). In addition, the measured envelope correlation coefficient (ECC) is lower than 0.1 between arbitrary two antenna elements, and the proposed MIMO antenna array realizes a simulated channel capacity of higher than 36.9 bps/Hz within both operation bands. Furthermore, the MIMO antenna array can maintain acceptable radiation and MIMO performance in the presence of specific anthropomorphic mannequin (SAM) head and human hands.

Compact 5G MIMO Mobile Phone Antennas With Tightly Arranged Orthogonal-Mode Pairs

In this communication, the novel compact tightly arranged pairs are employed to form a $4 \times 4$ multiple-input-multiple-output (MIMO) system and an $8 \times 8$ MIMO system operating at 3.4–3.6 GHz for fifth-generation (5G) mobile phones. Each tightly arranged pair is composed of a bent monopole and an edge-fed dipole with a compact size of $7 \times 12$ mm2. The orthogonal-mode method is presented to mitigate the mutual coupling of the tightly arranged pairs without any external decoupling structure. With the help of the orthogonal mode, isolation performances across the desired band of the $4 \times 4$ MIMO system and the $8 \times 8$ MIMO system are better than 20 and 17 dB, respectively, with the elements closely spaced. The measured efficiencies are 51.7%–84.5%/49%–72.9%, and the measured envelope correlation coefficients are less than 0.06/0.07 for the $4 \times 4/ 8 \times 8$ MIMO system. The proposed MIMO systems provide a promising solution to compact 5G MIMO mobile phone antennas with good isolation and diversity performance.

Highly miniaturised semi‐loop meandered dual‐band MIMO antenna system

A novel dual-band two-element directional multiple-input-multiple-output (MIMO) antenna system is presented with 68% miniaturisation, which is achieved using a semi-loop meandered driven element and a small ground plane. The centre frequency of operation is 2 GHz. The antenna system covers two bands: the telemetry L-band 1.27-1.43 GHz and the global system for mobile communications/long-term evolution band 1.8-2.133 GHz. The simulation and measurement results are in good agreement. The proposed antenna system mimics the quasi-Yagi antenna configuration with a measured front-to-back ratio of around 15 dB at 1.35 GHz and 17 dB at 2 GHz, which is achieved without using a large ground plane, extra metallic structures, multiple reflector elements, or any complex technique. A gain of more than 5 dBi is measured for the single element with a total radiation efficiency of around 85% in both bands. The measured isolation of the proposed MIMO antenna is more than 15 dB with <;0.0785 measured envelope correlation coefficient values in both bands.