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.     

Compact dual wide‐band four/eight elements MIMO antenna for WLAN applications

A compact four and eight elements multiple‐input‐multiple‐output (MIMO) antenna designed for WLAN applications is presented in this article. The antenna operates in IEEE 802.11b/g WLAN (2.4 GHz), IEEE 802.11 ac/n WLAN (5.2 and 5.8 GHz) and WiMAX (5.8 GHz) bands. The resonated mode of the antenna is achieved by two unequal Reverse‐L shaped, line‐shaped slots on top and parasitic element on the ground layer. The single antenna provides wide bandwidth of about 29% (2.3‐3.1 GHz) in lower and 22% (4.9‐6.1 GHz) in the upper band. The compactness of the single element antenna is found about 95% with respect to the patch and 61% in overall dimension. Thereafter an investigation is carried out to design two, four, and eight elements MIMO antennas. All of the multi‐element structures provide compact configuration and cover entire WLAN frequency ranges (2.4‐2.48 and 5.15‐5.85 GHz). The dimension of the proposed eight element MIMO antenna is 102 × 52 × 1.6 mm³. It covers the frequency (measured) from 2.4 to 3.1 GHz and 5 to 6.1 GHz. The diversity performance of the proposed MIMO antenna is also assessed in terms of the envelope correlation coefficient (ECC), diversity gain (DG), and total active reflection co‐efficient (TARC). The ECC is found <0.5 whereas the DG >9.0 is obtained for the desired bands.     

Dual‐polarized textile‐based two/four element MIMO antenna with improved isolation for dual wideband application

This article presents the designs of dual‐polarized dual wideband textile‐based two and four elements multiple‐input multiple‐output (MIMO) antennas for WLAN (IEEE 802.11a/b/g/c/n) and WiMAX (IEEE 802.16d) applications. These MIMO antennas cover the frequency spectra from 1.5 to 3.8 GHz (87% bandwidth) and 4.1 to 6.1 GHz (40% bandwidth). The characterization of the textile jeans substrate is determined experimentally using a vector network analyzer and dielectric assessment kit. These antennas provide near about 70% radiation efficiency with around 4 dBi peak gain in desired frequency ranges. The diversity performance is improved noticeably by printing meandered line structures on both planes. The proposed MIMO structure has a very low envelop correlation coefficient (ECC) <0.1 and high diversity gain (DG) >9.9. The Medium effective gain (MEG) also lies within a satisfactory value of ±3 dB. The two elements MIMO Antennas provide linear polarization at all desired frequency band while the four‐element antenna provides circular polarization at 2.4 GHz and linear polarization at 5.2 and 5.8 GHz application bands. The antenna also depicts good performance in wearable condition with safe specific absorption rate < 1.6 W/kg in all desired frequencies.     

A low‐profile dual port UWB‐MIMO/diversity antenna with band rejection ability

A band notched ultra‐wideband (UWB) antenna is presented in this article as a good prospect for multiple‐input multiple‐output (MIMO)/diversity application. The proposed MIMO antenna is constituted of two modified rectangle‐shaped patch antenna elements. A stepped stub is extended from the modified ground plane as a decoupling element between the radiators to realize a good isolation level between them. A band rejection response is obtained by connecting an open resonant stub to each of the radiators. The simulated prototype is fabricated and tested for verification. Results reveal that the proposed prototype provides a 10 dB return loss bandwidth from 3.08 to 10.98 GHz with band notch characteristics from 4.98 to 5.96 GHz, and a good port isolation level (S₂₁ ≤ 20). Diversity performances are ensured in terms of total active reflection coefficient, envelope correlation coefficient (<0.013 except notch band), diversity gain (≈9.51 dB), mean effective gain ratio (≈1), and channel capacity loss (≤0.35 bps/HZ except notch band). It evidences that the presented band notched UWB antenna can be a good prospective for MIMO/diversity applications.     

A‐shaped wideband dielectric resonator antenna for wireless communication systems and its MIMO implementation

In this article, a new A‐shaped dielectric resonator antenna (DRA) excited by a conformal strip is proposed for wideband applications. The wide bandwidth is achieved by combining two adjacent modes that is, TM₁₀₁ and TM₁₀₃. The experimental results demonstrate that the proposed DRA offers an impedance bandwidth (for S11?10 dB) of 59.7% (3.24‐6.0 GHz), covering IEEE 802.11 and U‐NII bands. The antenna provides a fairly stable radiation pattern with the gain ranging from 5.29 to 7 dBi across the operating bandwidth. A dual‐element multiple‐input multiple‐output (MIMO) system is also realized using the proposed wideband DRA. The impedance bandwidth of the dual‐element MIMO antenna is 59.2% and 60.9% for Port1 and Port2, respectively and the isolation between the ports is better than 20 dB across the bandwidth. For Port1, the gain of the MIMO antenna ranging from 6.03 to 7.45 dBi is obtained across the bandwidth. Furthermore, the diversity performance of the MIMO antenna is found to be good with envelope correlation coefficient below 0.003 over the operating band. The proposed antenna could be the potential candidate for worldwide interoperability for microwave access (WiMAX), wireless local area network (WLAN) and lower European UWB frequency band (3.4‐5.0 GHz) applications.     

Compact planar frequency reconfigurable multiple‐input‐multiple‐output antenna with pattern and polarization diversity characteristics for WiFi and WiMAX standards

A compact planar frequency reconfigurable dual‐band multiple‐input‐multiple‐output (MIMO) antenna with high isolation and pattern/polarization diversity characteristics is presented in this article for WiFi and WiMAX standards. The MIMO configuration incorporates two symmetrically placed identical antenna elements and covers overall size of 24 mm × 24 mm × 0.762 mm. Reconfiguration of each antenna element is achieved by using a PIN diode which allows antennas to switch from state‐1 (2.3‐2.4 GHz and 4.6‐5.5 GHz) to state‐2 (3.3‐3.5 GHz and 4.6‐5.5 GHz). In state‐1, the configuration offers isolation ≥18 dB and 20 dB in lower band (LB) and upper band (UB) respectively; whereas, in state‐2, isolation ≥21 dB and 20 dB in LB and UB respectively is achieved. The same decoupling circuit provides high isolation in dual‐band of two states, which makes overall size of the proposed design further compact. The antennas are characterized in terms of envelope correlation coefficient, radiation pattern, gain, and efficiency. From measured and simulated results, it is verified that the proposed frequency reconfigurable dual‐band multi‐standard MIMO antenna design shows desirable performance in both operating bands of each state and compact size of the design makes it suitable for small form factor devices used in future wireless communication systems.     

Dual‐band CPW fed MIMO antenna with polarization diversity and improved gain

A dual‐band MIMO slot antenna with polarization diversity and improved gain is proposed in this article. The antenna is composed of two C‐type back‐to‐back connected slot resonators and offers resonances at 3.5 and 5.2 GHz. This antenna element is further used to design a MIMO antenna. By introducing one U‐shaped slot between two antenna elements, isolation between the ports of this MIMO antenna is improved further. Finally, an artificial magnetic conductor (AMC) is placed below the MIMO antenna to enhance its gain. Gain enhancement of 1.5 and 2.2 dB is achieved at lower and upper band, respectively. S‐parameters, radiation patterns, gain, envelope correlation coefficient, and channel capacity loss are investigated to conclude about its performances in MIMO applications. Dual band dual polarization (circular and linear), improved isolation, polarization diversity (right‐hand circular polarization and left‐hand circular polarization), gain enhancement all are presented in a simple design represents the novelty of the proposed MIMO antenna.     

Meander line MIMO antenna for 5.8 GHz WLAN application

A four port compact low profile planar MIMO antenna with meander line radiators and with polarization diversity effect has been proposed to cover 5.8 GHz wireless local area network application. The proposed MIMO antenna has ?10 dB impedance bandwidth of 1.4 GHz (5.3–6.7 GHz) along with the compact size of 38 × 38 mm² and an envelope correlation coefficient (ECC) of less than 4 × 10^?4 in the whole band. The proposed antenna resonates at 5.8 GHz frequency, having return loss of ?43.2 dB. The isolation between diagonal and opposite ports is more than 10 and 12 dB, respectively, in the presented frequency band. The total active reflection coefficient frequency response shows more than 1.0 GHz of bandwidth in the whole band. The antenna gain is more than 4.0 dBi in the operating frequency band. The radiating elements are very close to each other to make the design very compact.     

Implementation of four-port MIMO diversity microstrip antenna with suppressed mutual coupling and cross-polarized radiations

A compact four-element MIMO microstrip antenna is designed, analyzed and proposed for high frequency modern wireless applications. Proposed antenna is compact in size and offers a frequency band of about 6 GHz ranging from 23 to 29 GHz with a peak gain of 7.1 dBi and suppressed mutual coupling and cross-polarization level. Presented antenna possess better diversity with minimum mutual coupling among its all four elements. Diversity is verified in terms of envelope correlation coefficient, directive gain, total active reflection coefficient and ratio of mean effective gain. All the diversity parameters are found within the appropriate limit standardized for a MIMO device. Experimental results of fabricated prototypes verified the proposed results.

     

A WLAN band‐notched compact four element UWB MIMO antenna

A compact four‐element multiple‐input‐multiple‐output (MIMO) antenna for ultra‐wideband (UWB) applications with WLAN band‐notched characteristics is proposed here. The proposed antenna has been designed to operate from 2 to 12 GHz while reject the frequencies between 4.9 to 6.4 GHz. The four antenna elements are placed orthogonal to attain the polarization diversity and high isolation. A thin stub connected to the ground plane is deployed as a LC notch filter to accomplish the rejected WLAN band in each antenna element. The mutual coupling between the adjacent elements is at least 17 dB while it has low indoor and outdoor envelop correlation (<0.45) and high gain with compact size of two boards, each measuring 50 × 25 mm². To validate the concept, the prototype antenna is manufactured and measured. The comparison of the simulation results showed good agreement with the measured results. The low‐profile design and compact size of the proposed MIMO antenna make it a good candidate for diversity applications desired in portable devices operating in the UWB region.     

Dual polarized triple band hybrid MIMO cylindrical dielectric resonator antenna for LTE2500/WLAN/WiMAX applications

In this communication, triple band hybrid multi‐input–multi‐output (MIMO) cylindrical dielectric resonator antenna (CDRA) with high isolation is examined. The proposed MIMO antenna includes two symmetric folded microstrip line feeding structures along with CDRA at two different ends of substrate. Two inverted L‐shaped strips on the ground plane are used to enhance the isolation (S₁₂ < ?15 dB) as well as to generates 2.7 GHz frequency band. Metallic strip on the ground plane act as an electromagnetic reflector and also enhance the isolation between two antennas (S₁₂ < ?20 dB). Archetype of proposed MIMO antenna design has been fabricated and tested to validate the simulated results. The proposed antenna operates at three different frequency bands 2.24–2.38 GHz, 2.5–3.26 GHz, and 4.88–7.0 GHz (S₁₁ < ?6 dB) with the fractional bandwidth 6.06%, 26.4%, and 35.7%, respectively. Folded microstrip lines generate path delay between the electric field lines and originate circular polarization characteristics in the frequency range 5.55–5.75 GHz with the fractional bandwidth of 3.55%. In order to satisfy the different performance requirement of MIMO antenna such as envelop correlation coefficient, mean effective gain, effective diversity gain, peak gain are also examined. The proposed antenna is found suitable for LTE2500, WLAN, and WiMAX applications. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2016.     

A UWB MIMO slot antenna using defected ground structures for high isolation

In this article, a multiple‐input‐multiple‐output (MIMO) antenna with high isolation is proposed for ultrawideband (UWB) applications. The proposed MIMO antenna consists of two symmetric slot antenna elements with quasi F‐shaped radiators and L‐shaped open‐slots to increase impedance bandwidth. To improve isolation at the lower band, a decoupling network, composed of a narrow slot and a fork‐shaped slot, is introduced in the common ground. The measured results show that the proposed antenna provides high isolation of better than 20 dB over the operating band from 3 to 10.9 GHz. The performances of the UWB MIMO antenna in terms of radiation patterns, peak gain, envelope correlation coefficient, mean effective gain, and diversity gain are also studied.     

Carbon fiber‐based deca‐port multiple‐input‐multiple‐output antenna with pattern diversity and high inter‐element isolation

In this article, a deca‐port carbon fiber‐based multiple‐input‐multiple‐output (MIMO) antenna with pattern diversity is presented. The radiating elements of the proposed antenna consist of low cost, light weight, environmental friendly graphite material. The 10 radiating elements of the MIMO antenna are arranged in a group of two (termed as sub‐MIMO structure), in a cubical manner to cover all the propagating directions. Furthermore, the two carbon fiber‐based radiating elements of the sub‐MIMO structure are placed in an orthogonal arrangement to generate different radiation patterns. The antenna exhibits high inter‐element isolation and low envelope correlation coefficient due to orthogonal placement of the radiating elements. The antenna is fabricated and the measured results confirm that the proposed MIMO/diversity antenna may be useful for vehicle‐to‐network applications. The MIMO performance parameters such as diversity gain, total active reflection coefficient, mean effective gain, channel capacity loss are evaluated and found within suitable limits. The three‐dimensional pattern diversity helps to communicate in all directions.     

A frequency reconfigurable MIMO antenna with agile feedline for cognitive radio applications

A novel frequency agile multiple‐input‐multiple‐output (MIMO) patch antenna based on a reconfigurable feedline is proposed. The proposed antenna structure has two hexagonal‐shaped patch antenna elements. A defected ground structure having hexagonal shape is included in the ground plane to make the design compact and improve isolation among antenna elements. Further compactness is achieved using reactive loading. Frequency reconfigurability is realized by employing varactor diodes in the microstrip feedline. The proposed antenna achieves a frequency reconfigurable band with wide tuning range from 1.42 to 2.27 GHz with good gain and efficiency. Furthermore, an envelope correlation coefficient value of less than 0.2 and minimum isolation of 12 dB was achieved, displaying good MIMO performance. The presented antenna has a planar, low profile design with compact size of 100 × 50 mm². Thus, frequency agility, wide range tuning, compactness, and planar structure of the proposed antenna design make it suitable for modern wireless handheld devices particularly in cognitive radio applications.     

Complementary meander‐line‐inspired dielectric resonator multiple‐input‐multiple‐output antenna for dual‐band applications

The communication presents a simple dielectric resonator (DR) multiple‐input‐multiple‐output (MIMO) dual‐band antenna. It utilizes two “I”‐shaped DR elements to construct an “I”‐shaped DR array antenna (IDRAA) for MIMO applications. The ground plane of the antenna is defected by two spiral complementary meander lines and two circular ground slots. In the configuration, two “I”‐shaped DR elements are placed with a separation of 0.098λ. The antenna covers dual‐band frequency spectra from 3.46 to 5.37 GHz (43.26%) and from 5.89 to 6.49 GHz (9.7%). It ensures the C‐band downlink (3.7‐4.2 GHz), uplink (5.925‐6.425 GHz), and WiMAX (5.15‐5.35 GHz) frequency bands. Each DR element is excited with a 50‐Ω microstrip line feed with aperture‐coupling mechanism. The antenna offers very high port isolation of around 18.5 and 20 dB in the lower band and upper band, respectively. The proposed structure is suitable to operate in the MIMO system because of its very nominal envelope correlation coefficient (<0.015) and high diversity gain (>9.8). The MIMO antenna provides very good mean effective gain value (±0.35 dB) and low channel capacity loss (<0.35 bit/s/Hz) throughout the entire operating bands. Simulated and measured results are in good agreement and they approve the suitability of the proposed IDRAA for C‐band uplink and downlink applications and WiMAX band applications.     

A novel compact self‐similar fractal UWB MIMO antenna

A novel compact self‐similar fractal ultra‐wideband (UWB) multiple‐input‐multiple‐output (MIMO) antenna is presented. This fractal geometry is designed by using iterated function system (IFS). Self‐similar fractal geometry is used here to achieve miniaturization and wideband performance. The self‐similarity dimension of proposed fractal geometry is 1.79, which is a fractional dimension. The antenna consists of two novel self‐similar fractal monopole‐antenna elements and their metallic area is minimized by 29.68% at second iteration. A ground stub of T‐shape with vertical slot enhances isolation and impedance bandwidth of proposed MIMO antenna. This antenna has a compact dimension of 24 × 32 mm² and impedance bandwidth (S₁₁ < ?10 dB) of 9.4 GHz ranging from 3.1 to 12.5 GHz with an isolation better than 16 dB. The various diversity performance parameters are also determined. There is good agreement between measured and simulated results, which confirms that the proposed antenna is acceptable for UWB applications.     

A low‐profile quad‐port UWB MIMO antenna using defected ground structure with dual notch‐band behavior

A compact (45 × 45 × 1.6 mm³) ultrawide‐band (UWB), multiple‐input multiple‐output (MIMO) design using microstrip line feeding is presented. The proposed design comprises four elliptical monopoles placed orthogonally on a cost‐effective FR‐4 substrate. In order to improve the impedance bandwidth and lessen the return loss of the MIMO antenna, defects in ground plane are created by etching symmetrical square slots and half‐rings. Moreover, a different method (of unsymmetrical H‐shaped slot with C‐shaped slot) was proposed into the patch to introduce dual‐band rejection performance from UWB at center frequency 5.5 GHz (covering lower WLAN as well as upper WLAN) and 7.5 GHz (X band). In addition, a stub is introduced at the edge of each defected ground structure to obtain isolation >–22 dB covering entire performing band from 2 to 16.8 GHz (where, S₁₁ < –10 dB). The proposed design has miniaturized size, very low envelop correlation coefficient less than 0.1, stable gain (2‐4 dBi except for notch bands). Furthermore, various MIMO performance parameters are within their specifications, such as diversity gain (= 10 dB), total active reflection coefficient (<–5 dB, and channel capacity loss (<0.35 bits/s/Hz). The presented design is optimized using the HFSS software, and fabricated design is tested using vector network analyzer. The experimental results are in good agreement with the simulation results.     

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.     

CSRR‐loaded T‐shaped MIMO antenna for 5G cellular networks and vehicular communications

This article proposes a multiple input multiple output (MIMO) antenna for 5G‐based vehicular communication applications. The designed MIMO antenna consist of two element iterated T‐shape antenna with defected ground structure (DGS) and split ring resonator. The antenna providing reflection coefficient S₁₁ s₁₁ ≤10 dB and bandwidth of 6.3 and 3.96 GHz over the frequency range of 26.83 to 33.13 GHz and 34.17 to 38.13 GHz, respectively. For the suitable future vehicular millimetric wave communications, this antenna achieved resonant frequencies at 28, 33, and 37 GHz. The designed antenna has achieved peak gain of 7.11 dB in operating band. It is fabricated on 12 x 25.4 x 0.8 mm³ Rogers RT duroid 5880 substrate with dielectric constant (ε_r) of 2.2. The antenna is placed on vehicle in virtual environmental using ANSYS SAVANT tool and the simulated results are showing good matching with the measured results of proposed MIMO antenna.     

Design and analysis of a quad‐band substrate‐integrated‐waveguide cavity backed slot antenna for 5G applications

A planar and compact substrate integrated waveguide (SIW) cavity backed antenna and a 2 × 2 multi‐input multi‐output (MIMO) antenna are presented in this study. The proposed antenna is fed by a grounded coplanar waveguide (GCPW) to SIW type transition and planned to be used for millimeter‐wave (mm‐wave) fifth generation (5G) wireless communications that operates at 28, 38, 45, and 60 GHz frequency bands. Moreover, the measured impedance bandwidth (|S₁₁| ≤ ? 10 dB ) of the antenna covers 27.55 to 29.36, 37.41 to 38.5, 44.14 to 46.19, and 57.57 to 62.32 GHz bands and confirms the quad‐band characteristic. Omni‐directional radiation characteristics are observed in the far‐field radiation pattern measurements of the antenna over the entire operating frequency. The reported antenna is compact in size (9.7 × 13.3 × 0.6 mm³) and the gain values at each resonance frequency are measured as 3.26, 3.28, 3.34, and 4.51 dBi, respectively. Furthermore, the MIMO antenna performance is evaluated in terms of isolation, envelope correlation coefficient and diversity gain.