Design and fabrication of a new high gain multilayer negative refractive index metamaterial antenna for X‐band applications

This article presents the design of a planar high gain and wideband antenna using a negative refractive index multilayer superstrate in the X‐band. This meta‐antenna is composed of a four‐layer superstrate placed on a conventional patch antenna. The structure resonates at a frequency of 9.4 GHz. Each layer of the metamaterial superstrate consists of a 7 × 7 array of electric‐field‐coupled resonators, with a negative refractive index of 8.66 to 11.83 GHz. The number of layers and the separation of superstrate layers are simulated and optimized. This metamaterial lens has significantly increased the gain of the patch antenna to 17.1 dBi. Measurements and simulation results proved about 10 dB improvement of the gain.     

Gain enhancement of the ultra‐wideband tapered slot antenna using broadband gradient refractive index metamaterial

In this article, a broadband gradient refractive index (GRIN) metamaterial is designed and used to enhance the gain of the tapered slot antenna (TSA). The proposed GRIN is implemented using nonresonant parallel‐line unit cell with different refractive index values. GRIN lens are placed in front of the tapered slot direction in the direction of x‐axis. The designed GRIN metamaterials have broad bandwidth (2‐12 GHz) characteristics due to the nonresonant parallel‐line elements which is suitable for the ultra‐wideband frequency band. The measurement results indicates that the radiated beam becomes more directive with narrow beam width. The measured reflection coefficient is below ?10 dB over the frequency bandwidth of 3‐11 GHz. The peak gain of TSA is obtained up to 14 dB at 10 GHz using GRIN lens.     

CPW fed miniaturized dual‐band short‐ended metamaterial antenna using modified split‐ring resonator for wireless application

A miniaturized dual‐band metamaterial (MTM) antenna has been designed in this article. The designed coplanar waveguide fed antenna has composed of inner split‐ring resonator and an outer open ring resonator with rectangular stub. The series parameter of the antenna is used to determine the zeroth order resonance frequency due to short‐ended boundary condition. The whole size of proposed structure is 20 × 25.5 mm². This MTM antenna exhibits dual‐band operation at 3.17 GHz (3.1–3.22 GHz) and 5.39 GHz (5.27–5.47 GHz). The proposed MTM structure achieves measured peak gain of 0.71 and 1.89 dB at 3.17 and 5.39 GHz, respectively. The proposed antenna can be used for recent radio communication in form of S‐band application and Wi‐MAX.     

Mutual coupling reduction by SIW ZOR elements on broadside high gain CP beam steering array

In this article, a new circularly polarized (CP) beam steering array antenna based on substrate‐integrated‐waveguide (SIW) is proposed for mm‐wave applications. To generate a wider half power beamwidth (HPBW) and reduce mutual coupling effect a radiation element relying on zeroth order resonance (ZOR) technique has been used which has a treatment such as electromagnetic band gap (EBG) structure to have a specific structure. The antenna element can operate in a bandwidth from 33.82 to 36.37 GHz and AR bandwidth from 34.32 to 35.94 GHz. Besides, the propose element has a HPBW wider than 103°, and a maximum gain of antenna is of 9.2 dBic. A 4 × 4 Butler matrix feed network based on SIW feeding technique is then designed. This feed network includes novel techniques in designing cross‐over and broadband phase shifter. The synthesis of proposed Butler matrix and ZOR elements lead to a four‐beam array antenna with circular polarization can cover a beam switching angles range more than 44° with a gain of 17.6 dBic.     

A novel miniaturized metamaterial lens antenna

This article develops a flat, miniaturized lens based on metamaterial for antenna gain improvement. The overall size of the lens is 1.9λ₀ × 1.9λ₀ × 0.05λ₀ . The distance between the metamaterial lens and the antenna is only about 0.4λ₀ . The prototype lens antenna is fabricated and the measured results are in agreement with the simulated results. It shows that the proposed lens provides significant gain enhancement by 2 to 3.5 dB between 1.3 and 1.45 GHz, which effectively demonstrate a high directivity, miniaturized, and compact metamaterial lens antenna.     

A compact energy harvesting multiband rectenna based on metamaterial complementary split ring resonator antenna and modified hybrid junction ring rectifier

This article presents an improved wireless energy harvesting multiband rectifying antenna. The proposed design is based on an original optimized bidirectional complimentary split ring resonator (CSRR) metamaterial multiband antenna and a modified hybrid junction ring rectifier with four rectifying branches. It harvests the ambient radiofrequency radiations at GSM, 1.8 GHz; UMTS, 2.1 GHz; WiFi, 2.45 GHz; and 4G‐2.6 GHz GSM bands. The created prototypes are printed on a 1.57‐mm‐thickness FR4 substrate and achieve the needed dimensional optimization in both antenna and rectifier. The CSRR antenna accomplished a maximum harvesting realized gain of 2.41, 2.26, 1.58, and 2.69 dB on the aforementioned frequency bands, respectively, 63.75% of antenna size reduction, and 23.62% rectifier size reduction regarding the conventional designs. The hybrid ring junction is used to independently match the subrectifiers at each frequency band. The realized rectenna has been accurately tested in both controlled and outdoor environments, achieving a 67.6% peak efficiency at 1.8 GHz frequency band for an input power level of 10 dBm. It powered up a digital batteryless watch in the outdoor experiment.     

Wideband bow‐tie antenna with increased gain and directivity by using high impedance surface

Metamaterial surfaces offer a wide range of advantages in terms of antenna design. One such metamaterial is designed to capture the benefits of both high‐impedance surfaces as well as artificial magnetic surfaces. The confluence of both these properties delivers an added advantage to planar antennas by delivering high gain and directivity simultaneously. Bidirectional radiation pattern has been transformed to a directional radiation pattern by placing the metamaterial as substrate beneath the antipodal bowtie antenna. In addition, zero separation between the antenna and metasurface ensures low profile. The proposed design has been verified both by simulation and measurement which have shown an improvement on gain of 3.2 dBi with an almost steady gain response inside the resonating band of the antenna which lies between 12 and 16 GHz.     

Single‐layer high‐gain flat lens antenna based on the focusing gradient metasurface

A single‐layer transmitting focusing gradient metasurface (F‐GMS) has been proposed that can realize high gain increment at 10 GHz. The unit of F‐GMS is composed of two identical structures placed on the top and bottom of one dielectric layer, which can have high transmitting efficiencies that over 0.8 and achieve [0, 2π] phase range in X‐band. The F‐GMS can convert the spherical waves into plane waves. A patch antenna working at 10 GHz is positioned as the focus of the proposed F‐GMS as the feed source to develop an ultrathin flat lens antenna system. It achieves a simulated gain of 19.6 dBi which is 12.9 dB greater than that of the single patch antenna at 10 GHz. Lastly, the F‐GMS and the patch antenna are manufactured and then measured in an anechoic chamber. A good agreement was demonstrated between experimental and simulated results.     

Implementation of hybrid fractal metamaterial inspired frequency band reconfigurable multiband antenna for wireless applications

In the present paper authors propose the design and analysis of a hepta band metamaterial inspired octagonal shape antenna using hybrid fractals for wireless applications. Multiband characteristics in the designed antenna is accomplished by introducing of slotted octagonal shape radiating part with hybrid fractal form of Moore curve and Koch curve and two SRR cells. The frequency band reconfigurability is obtained with aid of PIN diodes placed inside the strips connected between Moore curve (fused with centered Koch curve) and feedline. During ON mode of PIN diode antenna operates at seven microwave frequency S‐band WiMAX (3.4~3.69 GHz—IEEE 802.16e)/Lower C‐band terrestrial fixed and mobile broadband application (4.25~4.76 GHz)/C‐band WLAN (5.15~5.35/5.75~5.825 GHz—IEEE 802.11a] (5.4~5.9 GHz)/Lower X‐band Earth exploration‐satellite service ITU region 2 (7.9~8.4 GHz)/Upper X‐band Amateur satellite operating band (10.45~10.50 GHz)/Lower Ku‐band Radar communication application (13.25~13.75 GHz)/Middle Ku‐band Geostationary satellite service (14.2~14.5 GHz) covering various wireless applications. Proposed design exhibit hexa/hepta band features during OFF/ON mode of PIN diode. An acceptable gain, stable radiation characteristics, and good impedance matching are observed at all the resonant frequencies of the proposed structure.     

Gain enhancement and mutual coupling reduction of multiple‐intput multiple‐output antenna for millimeter‐wave applications using two types of novel metamaterial structures

A method to significantly increase the gain and reduce the mutual coupling of microstrip multiple‐intput multiple‐output (MIMO) antenna based on metamaterial concept is presented. The μ‐negative and ε‐negative features of the proposed modified peace‐logo planar metamaterial (MPLPM) and two‐sided MPLPM (TSMPLPM) structures are calculated. The antenna structure consists of eight MPLPM slabs and two TSMPLPM, which are embedded in azimuth plane of a MIMO antenna vertically. The dimensions of MIMO antenna are 28 × 16 × 6.3 mm³ at 40 GHz. As a result, a compact MIMO antenna is simulated in comparison with primary microstrip structures. The corresponding return‐loss of the antenna is better than 10 dB over 34.5 to 45.5 GHz for Ka‐band applications. Good consent between the measured and simulated result is tacked. The maximum simulated gain of the structure is 15.5 dB at 40 GHz, creating a maximum gain improvement of 11.5 dB in comparison with a MIMO antenna without any metamaterial combinations. The value of the insertion‐loss (isolation) is 33 dB, which has improved by more than 25 dB compared to the conventional sample.     

Miniaturized 1D beam switching and 2D printed Yagi-Uda antenna arrays

This article presents a multi-board arrangement of printed Yagi-Uda antennas that can be configured into 1D and 2D arrays. First, a 1 × 4 collinear array is designed and fed with a metamaterial Butler matrix (BM) network to provide beam switching at four azimuthal directions. Slow-wave concept is used in designing the hybrid, crossover and delay sections of BM to achieve a footprint reduction of 67%. The 1 × 4 collinear array with the feed network achieves 8.42–11.7 dBi gain and 21.7–25.7 degrees half power beam width (HPBW) in horizontal plane for the four switched beam patterns at 5.8 GHz in simulations. Second, measurement results of the fabricated 1 × 4 collinear array with its miniaturized feed network confirm a range of 22–27 degrees in HPBW in the horizontal plane. Finally, parasitic structures are designed to reduce antenna coupling and a 3-shelf holder is proposed to stack the 1 × 2 printed Yagi antenna subarray boards in compact 2D planar array configurations. Simulations of the 2 × 4-array demonstrate achieving 13.09 dBi peak gain at 5.8 GHz along with reduction of the HPBW by 24.7 degrees in horizontal plane in comparison with the 1 × 4-array prototype.     

Design of a dual‐band MIMO dielectric resonator antenna with high port isolation for WiMAX and WLAN applications

A novel dual‐band MIMO dielectric resonator antenna with high port isolation for WiMAX and WLAN applications is designed and investigated. The proposed antenna operates at 3.5 and 5.25 GHz bands. High port isolation is achieved using hybrid feeding mechanism that excites two orthogonal modes at each frequency bands. The measured impedance bandwidth of the proposed antenna covers the entire WiMAX (3.4–3.7) GHz and WLAN (5.15–5.35) GHz bands. The scalable behavior along with the frequency ratio of the antenna has also been investigated in this work. The measured isolation between antenna ports is ?52 dB at the lower band and ?46 dB at the upper band, respectively. Envelope correlation coefficient, diversity gain and mean effective gain have also been investigated. Moreover, measured results are in good agreement with the simulated ones.     

High‐gain compact rectangular dielectric resonator antenna using metamaterial as superstrate

A compact high‐gain rectangular dielectric resonator antenna (RDRA) using metamaterial (MTM) as superstrate for C‐band applications is proposed in this article. The proposed antenna consists of coaxial‐fed RDRA with 50 unit cells of MTM arranged in 5 × 10 layout as superstrate. Each unit cell is constructed of two parallel eight‐shaped copper strips printed over both faces of a dielectric substrate to provide negative refractive index from 7.3 to 8.1 GHz covering the maximum bandwidth of RDRA. The extracted lumped equivalent circuit model of unit cell of MTM shows concurrence with electromagnetic simulations. The use of MTM superstrate increases the peak gain of the antenna by 89% through simulation and 86% experimentally. The measured results show that the proposed antenna achieves an impedance bandwidth of 16.1% over a band of 7.18‐8.44 GHz, with a peak gain of 14 dBi at 7.8 GHz.     

Pattern diversity of path loss compensated antennas for 5G base stations

In this article, a tapered slot antenna (TSA) operating from 27 to 29.8 GHz with an endfire gain of 9 dBi and high pattern integrity is presented. The gain specifications for path loss compensation on ground for a ceiling mounted millimeter wave base station is computed and the gain of the antenna elements with beam angled at ±45° was found to be 12 dBi. To enhance gain with minimal physical footprint, a combination of dielectric loading and electrical resonator metamaterial unit cells were integrated to the proposed TSA to achieve the expected gain enhancement of 3 dB across the band, operating in the same frequency band with aperture efficiency greater than 73% and a 1 dB gain bandwidth of 20.7%. A compact stacking topology for pattern diversity of all three antenna elements for path loss compensation is also investigated. The base station has a coverage of ±60° with uniform illumination and mutual coupling lesser than 35 dB. The detailed simulated and measured results are presented.     

Millimeter‐wave antenna with wide‐scan angle radiation characteristics for MIMO applications

A three‐element quasi Yagi‐Uda antenna array with printed metamaterial surface generated from the array of uniplanar capacitively loaded loop (CLL) unit‐cells printed on the substrate operating in the band 25‐30 GHz is proposed. The metamaterial surface is configured to provide a high‐refractive index to tilt the electromagnetic (EM) beam from the two dipole antennas placed opposite to each other. The metamaterial region focuses the rays from the dipole antenna and hence increases the gain of the individual antennas by about 5 dBi. The antenna elements are printed on a 10 mil substrate with a center to center separation of about 0.5 λ ₀ at 28 GHz. The three‐element antenna covers 25‐30 GHz band with measured return loss of 10 dB and isolation greater than 15 dB between all the three ports. The measured gain of about 11 dBi is achieved for all the antenna elements. The three antenna elements radiate in three different directions and cover a radiation scan angle of 64°.     

Design of high gain/directional ultra‐wideband antenna for radar imaging systems

A compact size of 40 × 40 mm² ( λ₀ × λ₀ ) semi‐elliptical slotted ground structure (SESGS) directional ultra‐wideband (UWB) antenna is proposed for radar imaging applications. A vertical semi‐elliptical slot is inserted into ground and subsequently, an axis of semi‐ellipse is rotated diagonally (with 45°) in direction of the substrate. Axes of semi‐ellipse are optimized symmetrically around the circular patch to work antenna as a reflector. Furthermore, semi‐elliptical slot is rotated horizontally (with 90°) again to improve the impedance bandwidth. Proposed antenna achieves fractional bandwidth around 83% covering the UWB frequency range from 4.40 to 10.60 GHz (S₁₁ < ?10 dB) having 4.5/6/7/8/9.3/10.2 GHz resonant frequencies. Also, antenna is capable to send low‐distortion Gaussian pulses with fidelity factor more than 95% in time‐domain. Measured gain and half power beam width (HPBW) are 6.1‐9.1 dBi and 44°‐29° in 4.40‐10.60 GHz band, respectively, which show an improvement of 1‐3 dBi in gain and half power beam‐width is reduced by 5°‐10° when compared with previously designed antennas. Experimental results show good agreement with CST simulation.     

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 metamaterial hepta‐band antenna for wireless applications with specific absorption rate reduction

Present article embodies the design and analysis of slotted circular shape metamaterial loaded multiband antenna for wireless applications with declination of SAR. The electrical dimension is 0.260 λ × 0.253 λ × 0.0059 λ (35 × 34 × 0.8 mm³) of proposed design, at lower frequency of 2.23 GHz. The antenna consists of circular shape rectangular slot as the radiation element loaded with metamaterial split ring resonator (SRR) and two parallel rectangular stubs, etched rectangular single complementary split‐ring resonator (CSRR) and reclined T‐shaped slot as ground plane. Antenna achieves hepta bands for wireless standards WLAN (2.4/5.0/5.8 GHz), WiMAX (3.5 GHz), radio frequency identification (RFID) services (3.0 GHz), Upper X band (11.8 GHz—for space communication) and Lower K_U band (13.1 GHz—for satellite communication systems operating band). Stable radiation patterns are observed for the operating bands with low cross polarization. The SRR is responsible for creating an additional resonating mode for wireless application as well as provide the declination in SAR about 13.3%. Experimental characteristic of antenna shows close agreement with those obtained by simulation of the proposed antenna.     

Dual‐band beam scanning filtering antenna using dual‐eighth mode substrate integrated waveguide‐based metamaterial structure

In this article, a dual‐band beam scanning antenna with filtering capability is proposed by using novel dual‐eighth mode substrate integrated waveguide‐based dual‐band metamaterial (DB‐MTM) structure. The novel DB‐MTM structure consists of two interconnected modified eighth mode substrate integrated waveguide (EMSIW) structures, which is designed by etching four interdigital fingers on the upper ground, and has two balanced composite right/left‐handed (CRLH) passbands. Taking advantage of the continuous phase constant changing from negative to positive values within the two CRLH passbands of the DB‐MTM structure, a beam scanning antenna, which is composed of 11 dB‐MTM unit cells, is designed to achieve continuous beam scanning from backward to forward directions within dual operating frequency bands. For verification, the proposed dual‐band antenna is fabricated and measured. According to the measurements, the fabricated antenna can scan its main beam from ?72° to +57° and ?70° to +38° over the two operating frequency bands of 3.40‐4.95 GHz and 5.85‐6.80 GHz, respectively; and exhibits very sharp transitions at the band edges over the two operating frequency bands. Besides, the measured peak gains in the two operating bands are 14.0 dB at 4.5 GHz and 14.5 dB at 6.4 GHz. Moreover, the measurements show good agreement with the simulations, proving the validity of the design method, and further expanding the applications of EMSIW.     

Design of multi band triangular microstrip patch antenna with triangular split ring resonator for S band,C band and X band applications

With the rapid advancement in multi-functional communication devices, devices capable of operating for more than one frequency bands emerged. Such applications demand for multiband antennas. Wide band antennas are capable of resonating over larger frequency bands, but it limits the impedance bandwidth and gain. So, the solution of this could be compact multi band antennas. A quad band Triangular Microstrip antenna designed for IEEE 802.16e Wi-MAX, IEEE 802.11a WLAN, C band downlink communication and x band radar applications is suggested in this work. The proposed antenna has triangular patch with triangular split ring resonator. The conservativeness and data transfer capacity are the preferred possessions of the suggested antenna. The proposed antenna yields better return and gain by resonating in 3.5 GHz, 4.1 GHz, 5.6 GHz and 9.7 GHz.