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 compact printed ultra‐wideband multiple‐input multiple‐output prototype with band‐notch ability for WiMAX,LTEband43, and WLAN systems

A compact ultra‐wideband multiple‐input multiple‐output (UWB‐MIMO) antenna with good isolation and multiple band‐notch abilities is developed in this work. It consists of two quadrant shaped monopole antennas backed by ground stubs. A good isolation is achieved due to the two proposed extended curved ground stubs. The frequency rejection for the WLAN system is realized by loading a capacitive loaded loop resonator adjacent to the feed line. The band rejection for the WiMAX and LTE band43 system is achieved by embedding a quadrant shaped CSRR on each radiator's surface. The measured bandwidth of the antenna is 3.06 GHz‐11 GHz (|S₁₁| < ?10 dB and |S₂₁| < ?18 dB) with a band rejection from 3.5 GHz‐4 GHz to 5.1 GHz‐5.85 GHz, respectively. Time domain performances are investigated in terms of group and phase delay characteristics. Diversity characteristics are evaluated in terms of the envelope correlation coefficient, mean effective gain, and channel capacity loss.     

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.     

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.     

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.     

Investigation on decoupling of wide band wearable multiple‐input multiple‐output antenna elements using microstrip neutralization line

An investigation to enhance the decoupling between the elements of a compact wide band multiple‐input multiple‐output (MIMO) antenna is presented in this communication. A microstrip neutralization line (NL) is designed on the top of antenna surface to enhance the port isolation. The geometry is embedded on a jeans material to be apposite for the on‐body wearable applications. The antenna covers the frequency spectra from 3.14 to 9.73 GHz (around 102.4%) and fulfills the bandwidth requirements of WiMAX (3.2‐3.8 GHz), WLAN (5.15‐5.35/5.72‐5.85 GHz), C band downlink‐uplink (3.7‐4.2/5.9‐6.425 GHz), downlink defense (7.2‐7.7 GHz), and ITU (8‐8.5 GHz) bands. The port isolation is found to be more than 32 dB over the whole application bands. The antenna is appraised in a rich scattering environment with very minimal envelope correlation coefficient (ECC < 0.12) and great amount of diversity gain (DG > 9.8). The proposed MIMO antenna system is able to achieve the channel capacity loss (CCL) of less than 0.2 BPS/Hz throughout the whole operating band. The proposed structure is etched on an area of 30 × 50 mm². The simulated and measured performances of the proposed antenna are in well‐matched state.     

Low profile four‐port super‐wideband multiple‐input‐multiple‐output antenna with triple band rejection characteristics

A quad‐port planar multiple‐input‐multiple‐output (MIMO) antenna possessing super‐wideband (SWB) operational features and triple‐band rejection characteristics is designed. The proposed MIMO configuration consists of four modified‐elliptical‐self‐complementary‐antenna (MESCA) elements, which are excited by tapered co‐planar waveguide (TCPW) feed lines. A radiator‐matched complementary slot is present in the ground conductor patch of each MESCA element. The proposed MIMO antenna exhibits a bandwidth ratio of 36:1 (|S₁₁| < ?10 dB; 0.97‐35 GHz). Further, a step‐like slit‐resonator is etched in the radiator to eliminate interferences at 3.5 GHz. A hexagonal shaped complementary split ring resonator (CSRR) is also loaded on the MESCA radiator to remove interferences at 5.5 and 8.5 GHz. The MIMO antenna is fabricated on FR‐4 substrate of size 63 × 63 mm² and experimental results are found in good agreement with the simulated results. The MIMO antenna exhibits inter‐element isolation >17 dB and envelope correlation coefficient (ECC) <0.01 at all the four ports.     

A CPW‐fed UWB MIMO antenna with integrated GSM band and dual band notches

This article presents a coplanar waveguide fed global system for mobile communications band integrated ultra wide band (UWB) multiple input multiple output (MIMO) antenna with single and dual notch band characteristics. The novelty of the antenna lies in its design as all the unit cells of the proposed UWB MIMO antenna structure are orthogonal to each other therefore the additional isolation elements responsible for achieving high isolation are not required consequently making proposed antenna design simple and easy to fabricate. In this context, 2 MIMO systems have been designed. The first MIMO system is consisting of a dual port antenna whereas the second MIMO system is a printed quad port antenna; further single and dual notch band are achieved in the proposed multi‐port MIMO antenna. The antenna shows pattern diversity throughout the impedance bandwidth range. The gain of the antenna varies from 4 to 8.48 dBi. The 2 band notches are achieved at 4.8 and 7.7 GHz in the UWB range. The proposed antenna is fabricated and it is found measured results are in good agreement with simulated results.     

Dielectric resonator based two‐port dual band antenna for MIMO applications

This article investigates a dual band multiple input multiple output (MIMO) cylindrical dielectric resonator antenna (cDRA) for WLAN and WiMAX applications. It consists of two symmetrical orthogonally placed radiators. Each radiator is excited through a narrow rectangular aperture with the help of a microstrip line. For higher mode excitation, the proposed structure uses dual segment DRA which apparently looks like stacked geometry. The aperture fed dielectric resonator works as a feed for upper cDRA to generate higher order mode. The presented radiator covers the band between 3.3‐3.8 GHz and 5‐5.7 GHz. The measured isolation is better than 20 dB in the desired band. The average gain and radiation efficiency achieved for the proposed antenna is 6.0 dBi and 85%, respectively at the operating frequency band. In the proposed geometry, broadside radiation patterns are achieved by exciting HEM_11δ and HEM_12δ modes in a stacked geometry. Different MIMO performance parameters (ECC, DG, MEG, and CCL) are also estimated and analyzed. The prototype of proposed antenna is fabricated and tested. The measured outcomes are in good accord with the simulated one.     

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.     

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.     

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.     

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‐port MIMO dielectric resonator antenna for WLAN applications

A dual‐port multiple‐input multiple‐output (MIMO) dielectric resonator antenna (DRA) for 5 GHz IEEE (802.11a/h/j/n/ac/ax) is discussed in this article. Two prototypes of single feed DRA and dual feed MIMO DRA are fabricated and measured results are compared with the simulated data. The proposed single feed DRA and dual feed MIMO DRA exhibits wide impedance bandwidth (IBW). Antennas have been fabricated on Rogers RT Duroid substrate with Eccostock made DRA placed over the substrate. DRAs are excited by aperture coupled feed to achieve wide bandwidth and high efficiency. The measured IBW of uniport DRA and dual‐port MIMO DRA are 26.6% (4.75‐6.21 GHz) and 27.5% (4.7‐6.2 GHz) respectively. Maximum gain of the antenna is 7.4 dBi. The results of the antennas are in good agreement with simulated data and they are suitable for WLAN applications. These antennas are also compact with area of substrate 32.8 cm².     

A compact UWB‐MIMO with dual grounded CRR for isolation improvement

In this article, a compact half‐hexagonal ultra‐wide band multiple‐input‐multiple‐output (MIMO) antenna is presented. The key feature of the antenna is its novel isolation improvement technique which includes grounded stub along with dual grounded circular ring resonator. The antenna contains two counter facing half‐hexagonal monopoles having hybrid isolation circuit. The antenna has a compact size of 20 × 34 mm², with operating frequency band of 3‐11 GHz where port isolation is better than 20 dB in most of the band. The MIMO performance is ensured by calculating envelop correlation coefficient and mean effective gain ratio for isotropic, indoor, and outdoor environment. The performance of the antenna with multilayer printed circuit board having large dual ground plane and device housing is also studied. Results show that the proposed MIMO antenna is a good candidate for handheld devices for wireless personal‐area networks application.     

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.     

Modified circular common element four‐port multiple‐input‐multiple‐output antenna using diagonal parasitic element

A four‐port multiple input multiple‐output (MIMO) antenna with common radiating element is proposed for 2.4 GHz Wi‐Fi applications. It comprises a modified circular radiator fed by four identical modified feedlines, partial ground planes, and a diagonal parasitic element (DPE). The parasitic element is used to enhance the interport isolation. The antenna has a 2:1 Voltage standing wave ratio (VSWR) impedance band 2.34‐2.56 GHz and nearly omnidirectional radiation patterns. The radiation efficiency is more than 79% and gain is 2 dBi at resonant 2.43 GHz. The isolation in the given frequency band is 10 dB. At the 2.43 GHz, the isolation between adjacent ports (1, 2 and 1, 4) is 14 dB and between opposite ports (1, 3) is 12 dB. The mean effective gain (MEG) ≤ ?2.7 dB and envelope correlation coefficient is <0.01. The ?10 dB total active reflection coefficient bandwidth is 202 MHz. The antenna is designed for a Wi‐Fi device and the effectiveness of antenna has been checked for distance of ½ feet from the human head. The specific absorption rate (SAR) is found to be ≤0.17 W/Kg by CST simulation tool.     

Dual‐functional QM SIW cavity integrating two‐element MIMO antenna and second‐order bandpass filter

A quarter‐mode (QM) substrate‐integrated‐waveguide (SIW) cavity is designed as a dual‐functional component. By etching three slots, four sub‐cavities are formed and then two of them with the same size are individually fed by a coaxial port. Three resonating frequencies are excited in the single QM SIW cavity. One of them can radiate cavity energy input by these ports into free space, implying a two‐element multiple‐input‐multiple‐output (MIMO) antenna, whereas the other two can transmit energy from one port to the other port, indicating a second‐order bandpass filter. Moreover, antenna isolation and filter bandwidth can be adjusted to a certain degree. A prototype with the overall size of 0.40λ₀ × 0.40λ₀ × 0.02λ₀ has been fabricated. The integrated bandpass filter demonstrates the measured center frequency of 3.8 GHz and operating bandwidth of 32 MHz while the integrated MIMO antenna exhibits the frequency of 3.4 GHz, bandwidth of 67 MHz, port isolation of 18.0 dB, radiation gain of 4.0 dBi, and envelope correlation coefficient of 0.25.     

Compact eight‐port MIMO/diversity antenna with band rejection characteristics

A new compact three‐dimensional multiple‐input‐multiple‐output (MIMO) antenna comprised of eight antenna elements is presented. The unit cell of the proposed MIMO/diversity antenna consists of three elliptical rings connected together in the region close to the feed line and a rectangular‐shaped modified ground plane. To achieve polarization diversity with the proposed eight‐port MIMO configuration, four antenna elements are horizontally arranged and the remaining four are vertically oriented. The proposed antenna has an impedance bandwidth (S₁₁ < ?10 dB) of 25.68 GHz (3.1‐28.78 GHz) with a wireless local area network notch‐band at 5.8 GHz (5.2‐6.5 GHz). In addition to polarization diversity, the proposed antenna provides a reliable link with wireless devices. The prototype antenna design is fabricated and measured for diversity performance. Also, the proposed MIMO antenna provides good performance metrics such as apparent diversity gain, channel capacity loss, envelope correlation coefficient, isolation, mean effective gain, multiplexing efficiency, and total active reflection coefficient.     

Bandwidth and gain‐enhanced composite right/left‐handed antenna for ultra‐wideband applications

A coplanar waveguide‐fed metamaterial antenna is presented for ultra‐wideband (UWB) applications. The proposed antenna is designed with single unit‐cell composite right/left‐handed transmission line (CRLH‐TL) loaded with a split‐ring resonator (SRR). The UWB characteristic is obtained by merging the zeroth‐order resonance of CRLH‐TL with two additional resonances due to the ground plane and SRR respectively. Subsequently, a partial reactive impedance surface is embedded on the rear side of the proposed antenna to enhance the realized gain without affecting the UWB response. The overall size of the antenna is 0.241λ_o x 0.267λ_o x 0.013λ_o (28.8 x 32 x 1.6 mm³), where λ_o is the free space wavelength at 2.51 GHz. The measured results indicate –10 dB fractional bandwidth of 139.19% (2.51‐14 GHz) with realized gains of 2.3, 4.6, and 6 dBi at the resonant frequencies 4, 7.84, and 10.29 GHz respectively. The measured peak realized gain is 6.6 dBi at 10.6 GHz. The radiation efficiency is above 63.85% for the entire UWB range with a peak value of 86.84%. A fairly stable group delay with variation within 1 ns is obtained throughout the operating frequency band. A good agreement has been observed between the measured and simulated results.