Showing papers on "Metamaterial antenna published in 2020"

Review of Metasurface Antennas for Computational Microwave Imaging

Abstract: This article covers recent advances in the fusion of metasurface antenna design and computational imaging (CI) concepts for the realization of imaging systems that are planar, fast, and low cost. We start by explaining the operation of metamaterial antennas which can generate diverse radiation patterns. Their advantages and distinctions from previous antennas are elucidated. We then provide an intuitive overview of the CI framework and argue that metamaterial antennas are a near ideal platform for implementing such schemes at microwave frequencies. We describe two metamaterial antenna implementations: frequency diverse and electronically reconfigurable. The tradeoffs governing the design and operation of each architecture are examined. We conclude by examining the outlook of metamaterial antennas for microwave imaging and propose various future directions.

Broadband and Low-Profile Penta-Polarization Reconfigurable Metamaterial Antenna

Abstract: In this paper, a penta-polarization reconfigurable antenna with mushroom-type metamaterial loading is proposed, which can operate in $x$ -direction linear polarization ( $x$ -LP), $y$ -LP, 45°-LP, left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). In order to realize polarization reconfigurability, a dual-port dual LP mushroom antenna excited by crossed H-shape slot is designed by characteristic mode analysis (CMA). Through shifting the states of PIN diodes on the reconfigurable feeding network, the amplitude and phase distributions of two ports of the dual LP antenna can be dynamically controlled and the five polarization modes can be achieved. A prototype with a profile of $0.06\lambda _{0}$ at 5.2 GHz ( $\lambda _{0}$ is the operated wavelength in free space) is simulated and measured. The measurement results exhibit a wide impedance bandwidth over 33.2% for LPs and over 38.7% for CPs. In addition, the measured axial ratio bandwidths are 28.0% for LHCP and 30.3% for RHCP, and the maximum measured boresight gains of all modes are higher than 8.2 dBi. The simulated and measured results verify that the proposed antenna can achieve a balance between low-profile and broadband on the basis of penta-polarization reconfigurability. The proposed antenna can be applied to polarization diversity and C band satellite communication.

Design of Metamaterial Antenna for 2.4 GHz WiFi Applications

Abstract: In this paper, Antenna is an evergreen field of research because of its never-ending demand in the modern communication era. In this paper metamaterial antenna is presented. “Meta” a Greek word defines “beyond” the materials provide properties beyond conventional materials. In this paper the metamaterial and micro patch antenna concepts are combined to improve the performance of the ordinary patch antenna. This metamaterial antenna is designed in FR4 Epoxy substrate with dielectric permittivity of 4.4, height of the substrate is 1.6 mm and loss tangent tan δ = 0.02 with a simple shape of rectangular patch of dimension 40 mm length and 30 mm width. This antenna is simulated in an integral based solver simulation software called CST Microwave studio v2018 and yielded best results such as return loss − 46.58 dB, VSWR 1.009 and bandwidth of 574 MHz, directivity is 3.379 dBi, gain is 3.23 dBi for the resonant frequency(fr) of 2.4 GHz. The feeding network is also designed for better integration in real time applications. This antenna is further fabricated and tested for the validation and obtained, VSWR 1.3, Return loss − 26 dB and Bandwidth of 200 MHz. This metamaterial antenna is suitable for 2.4 GHz WiFi applications.

Miniaturized RFID Reader Antennas Based on CRLH Negative Order Resonance

Abstract: This article presents a type of miniaturized high-efficiency patch antennas for UHF radio frequency identification (RFID) reader applications based on the composite right-/left-handed (CRLH) negative order resonance. Miniaturization is achieved by using the first negative order resonance (−1st mode). These proposed CRLH resonators are realized by etching gap on the patch surface, which acts as a series left-handed (LH) capacitor as well as an effective radiator, and using metallic screws on the corner as steadying posts while also providing an LH inductor. Different from the traditional mushroom structures, these screws are placed on the two sides or corner of the unit cells allowing unobstructed current and field flowing inside the cavity. This enhances the quality factor and radiation efficiency. In addition, only metallic sheets, screws, and one thin substrate are used in the design, therefore dielectric loss is basically eliminated. Overall, these proposed antennas achieve a miniaturized size, as well as a high gain and radiation efficiency. The radiation characteristics of these RFID antennas are similar to the conventional patch antennas due to the −1st-order operation. Four antennas, including linearly polarized, circularly polarized (CP), frequency-tunable, and polarization/frequency-reconfigurable antennas, are carefully designed, investigated, and experimentally verified. Remarkable agreement has been observed between simulation and measurement. These antennas well cover 902–928 MHz UHF band. RF range tests are carried out for application verification. They demonstrate a compact size, low-cost, low-loss, and high efficiency with easy implementation. The CP antennas exhibit a good bandwidth and an excellent axial ratio in the whole upper semisphere. They have been selected for mass production, which illustrates a good engineering application example of CRLH metamaterial antennas.

Metamaterial Antenna Designs for a 5.8-GHz Doppler Radar

Abstract: The aim of this paper is to investigate applicability and the effectiveness of the metamaterial-based antennas for a 5.8-GHz Doppler radar. Thus, a double negative index metamaterial structure is designed as a transmitter antenna and a near-zero index medium is integrated with a patch antenna for the receiver. Significant improvements in bandwidth for the transmitter, slight improvements in gain and in directivity for the receiver, and typically size reduction for both antennas are obtained. It is shown that return loss, radiation pattern, and gain measurement results of the newly designed antennas agree well with the simulations for a desired frequency band. The last part of the study is devoted to express the adaptation of the antennas for a low-power radar system whose aim is to reconstruct the velocity of the human, indoor as well as behind the wall, from the shift in the received frequency. The accuracy of the velocity measurements and field test results of the radar with the metamaterial antennas are reported.

Broadband omnidirectional patch antenna with horizontal gain enhanced by near‐zero‐index metamaterial cover

Abstract: Enhancing the horizontal gain of the omnidirectional patch antenna is always a problem with great difficulty. Inspired by near-zero-index metamaterial (NZIM) cover that can improve the vertical gain of a directional patch antenna, the authors designed two kinds of NZIMs that are placed above the broadband omnidirectional antenna to enhance the horizontal gain. Simulated and measured results indicate that both covers can increase the values of horizontal gain >50% (1 dBi) at various frequencies in all directions, which provides a new approach to improve the horizontal gain of the broadband omnidirectional patch antenna.

Mutual coupling reduction using near-zero ε and μ metamaterial-based superstrate for an MIMO application

Abstract: Here, a near-zero permittivity (e) and permeability (μ) metamaterial superstrate is presented as a decoupling structure for a multiple-input–multiple-output (MIMO) antenna. The proposed design offers peak isolation of 41 dB with reduced edge separation of 0.042λ o at the resonating frequency. To verify the simulation results, the prototype of the proposed superstrate and antenna is fabricated and tested. The two-element MIMO antenna has −10 dB impedance band of 5.5–5.92 GHz with a peak measured gain of 7.41 dBi and efficiency above 78%. The measurement results ensure an isolation enhancement of 30 dB with a correlation coefficient of <0.26 within the operating band. The proposed method offers a good design technique for high gain and a closely packed MIMO antenna system for WLAN applications.

Small New Wearable Metamaterials Antennas for IOT, Medical and 5G Applications

Abstract: Efficient small antennas are crucial in the development of wearable wireless communications and medical systems. Low efficiency is the major disadvantage of small antennas. Meta materials technology and active components are used to improve the efficiency of small antennas. Moreover, the dynamic range and the efficiency of communication system may be improved by using active wearable antennas. Amplifiers may be connected to the wearable antenna feed line to increase the system dynamic range. Novel wideband passive and active efficient wearable metamaterial antennas for IOT, BAN and 5G applications are presented in this paper. The gain and directivity of antennas with Split-ring resonators, SRR, is higher by 2.5dB than the antennas without SRR. The resonant frequency of the antennas with SRR is lower by 4% to 11% than the antennas without SRR. The resonant frequency of the antenna with SRR on human body is shifted by 3% to 5%. Active small wearable antennas may be used in receiving or transmitting communication systems. For example, the active metamaterial antenna gain is 13+3dB for frequencies from 0.1GHz to 0.8GHz. The active antenna Noise Figure is 0.5+0.3dB for frequencies from 0.1GHz to 0.8GHz.

Split ring resonator inspired THz antenna for breast cancer detection

Abstract: A circular split ring resonator inspired (THz) antenna for breast cancer detection is proposed in this paper. The proposed metamaterial antenna is made from a simple rectangular patch antenna loaded with a Circular Split Ring Resonator (CSRR) structure in the ground plane. The design equations for the CSRR along with its equivalent circuit and permittivity calculations are also discussed in this paper. The experimental technique for detection of tumor in human breast model are also offered in this paper. The proposed circular split ring resonator inspired antenna operates at 1.5 THz resonant frequency with the VSWR ≤ 1.5 along with 24.2 dBi of gain and 90% of efficiency. The proposed circular split ring resonator inspired (THz) antenna could be a suitable candidate for a breast cancer detection application.

Gain-enhancement technique for wearable patch antenna using grounded metamaterial

Abstract: In this study, a metamaterial (MTM)-based high-gain compact-wearable antenna for 2.45 GHz industrial, scientific and medical radio band application has been proposed. To achieve the flexibility of the antenna, textile material felt fabric has been chosen as the substrate of the antenna as well as MTM. An omega (Ω) like structure has been taken as MTM unit cell design. High value of permeability is utilised for the gain enhancement of the antenna. In addition, very low specific absorption rate (SAR) is obtained using the MTM which makes the proposed antenna suitable for the biomedical application. The proposed antenna has achieved about 3 dB gain enhancement along with SAR value of 0.405 W/kg (1 g tissue). The design has been optimised and the prototype with the optimised parameter has been fabricated and tested over the semi-solid phantom and human body. Further, the proposed antenna over different type of textile material has also been validated.

Binary meta-hologram for a reconfigurable holographic metamaterial antenna

Abstract: This research reports a design method for synthesizing the binary meta-hologram pattern implemented in a leaky waveguide that can radiate the feeding signal toward a prescribed direction. In fact, the obtained pattern is not always a uniform array; it is an almost-periodic one. Statistical analysis of the radiation pattern for imperfect array is then conducted to demonstrate that radiating main-beam angle (ensemble average) is dominated by the average period of a non-uniform array subject to a small perturbation. Additionally,the leaky wave of higher-order space harmonic in a periodic structure is employed to accurately predict the directional radiation including main beam as well as grating lobes.

Low-profile and wideband gain enhanced Fabry–Perot cavity antenna using gradient PRS and AMC

Abstract: Low-profile and wideband gain enhancement Fabry–Perot cavity antennas (FPCA) is proposed using gradient Partially Reflective Surface (PRS) and gradient Artificial Magnetic Conductor (AMC). A wideband source antenna is designed with a −10 dB impedance bandwidth of 58.1% (6.1–11.1 GHz). The PRS is constructed by a complementary frequency-Selective Surfaces (FSS) with a square hole and four small patches in a unit, which realizes phase increasing with frequency. The PRS and the AMC are gradient alone x-direction to achieve wideband phase compensation. While they are uniform in y-direction to realize better gain enhancement. Compared with the source antenna, the gain enhancement of the proposed FPCA is about 4–7 dBi. Moreover, the simulated and measured 3-dB gain bandwidths are 7.26–10.33 GHz (34.8%) and 6.8–10.8 GHz (46%), respectively. The gain enhanced bandwidth is about 52.3% (6.5–11.1 GHz). The impedance bandwidth is 6–11.1 GHz (59.65%). By using the gradient size AMC, the profile of the FPCA is reduced from 0.5λ 0 to 0.2λ 0, where λ 0 is the wavelength of 8.5 GHz. The proposed FPCA has the characteristics of wide impedance bandwidth, wide 3-dB gain bandwidth, wide gain enhanced bandwidth and low-profile.

Random Forest Regression for Predicting Metamaterial Antenna Parameters

Abstract: Metamaterial is an artificial substance that has unique properties such as negative refractive index and negative permittivity that do not exist naturally in the universe. Metamaterial has been extensively used in antenna applications because of its numerous advantages. In antenna applications, the Split Ring Resonator (SRR) structure in the metamaterial antenna can improve antenna performance. In this paper, we use random forest regression which is part of machine learning algorithm to predict antenna parameters, such as gain, Voltage Standing Wave Ratio (VSWR), bandwidth, and return loss. Based on prediction result, number of estimator that resulted in lowest MAE for gain is 3 while for MSE is 2. For VSWR the lowest MAE and MSE is reached when the number of estimator is 8. For bandwidth, lowest MAE is achieved when the number of estimator is 1 while for MSE is 8. Return loss reaches the lowest MAE and MSE when the number of estimator is 24.

Low-Profile Slotted Metamaterial Antenna Based on Bi Slot Microstrip Patch for 5G Application.

Abstract: A low-profile high-directivity, and double-negative (DNG) metamaterial-loaded antenna with a slotted patch is proposed for the 5G application. The radiated slotted arm as a V shape has been extended to provide a low-profile feature with a two-isometric view square patch structure, which accelerates the electromagnetic (EM) resonance. Besides, the tapered patch with two vertically split parabolic horns and the unit cell metamaterial expedite achieve more directive radiation. Two adjacent splits with meta units enhance the surface current to modify the actual electric current, which is induced by a substrate-isolated EM field. As a result, the slotted antenna shows a 7.14 dBi realized gain with 80% radiation efficiency, which is quite significant. The operation bandwidth is 4.27-4.40 GHz, and characteristic impedance approximately remains the same (50 Ω) to give a VSWR (voltage Standing wave ratio) of less than 2, which is ideal for the expected application field. The overall size of the antenna is 60 × 40 × 1.52 mm. Hence, it has potential for future 5G applications, like Internet of Things (IoT), healthcare systems, smart homes, etc.

Further investigation on solant–rectenna-based flexible Hilbert-shaped metamaterials

Abstract: This study discusses the design of a low-profile metamaterial-based antenna consisting of a 3 × 5 array of Hilbert shaped unit cells organised as a rectangular patch. The antenna is backed by with a partial ground plane loaded with square electromagnetic band gap defects for energy harvesting applications in the context of ultra-wideband self-powered wearable wireless devices. The antenna is mounted on a 28 × 32 mm FR4 substrate, with a thickness of 0.394 mm, a relative permittivity of 4.2 and a loss tangent of 0.02. The antenna is also printed on a flexible solar panel for self-powered devices through solant-rectenna output terminals. The proposed solant-rectenna is found to cover the frequency range from 0.8 up to 10 GHz. The I-V characteristics of the solar panel are measured with and without the antenna structure to realize low shadowing effects. After that, the solant radiofrequency (RF) port is connected to a rectifier circuit to create a rectenna port that collects the RF energy and converts it to an output DC voltage at 0.915 GHz. It is found that the proposed rectenna provides an output DC voltage of 1.42 V with a conversion efficiency of 90%.

Compact quasi-Yagi antenna with enhanced bandwidth and stable high gain

Abstract: A compact double-dipole driver is constructed for designing quasi-Yagi antenna with enhanced bandwidth and stable high gain. It is composed of a magnetic dipole and a folded electric dipole, realised by cylinder dielectric resonator and split-ring resonator. The two dipoles operate at two close frequencies, leading to bandwidth enhancement. Meanwhile, the gains of the two dipoles are also close so that the stable gain in the operating band is obtained, which can be entirely enhanced by the zero-index metamaterial in front of the dual-dipole driver. For demonstration, an antenna prototype centred at about 9.6 GHz is implemented and measured. The simulated and measured results are given, showing good agreement.

Dual-band reconfigurable metasurface-assisted Fabry–Pérot antenna with high-gain radiation and low scattering

Abstract: The authors have proposed a dual-band reconfigurable Fabry–Perot (F-P) cavity antenna with high gain and meanwhile small radar cross-sections (RCSs) in wideband. Different from the traditional F-P antennas, they used a dynamic metasurface reflective plane (DMRP) as the lower superstrate to realise reconfigurable functions and a digital coding metasurface as the upper superstrate to achieve wideband RCS reduction. To investigate the dual-band reconfigurability, a wideband rectangular waveguide is used to feed the F-P antenna. By varying the bias voltage applied to varactors embedded in the elements of DMRP, the reflection phase of DMRP is changed and the two operating frequencies can be tuned electronically. To realise RCS reduction, they adopted a meticulous arrangement of the coding elements on partially reflecting surface. The designed metasurface-assisted F-P antenna has good radiation performance with high gain, high aperture efficiency, and high radiation efficiency. In the experiments, a prototype was fabricated via printed circuit board technology, and measured results agree well with numerical simulations. The measured peak gain reaches 17.52 dBi and the maximum aperture efficiency is 56.97%. The two reconfigurable bandwidths cover 5.10–5.40 and 6.60–6.93 GHz, respectively; and 7 dB RCS reduction is achieved from 9.40 to 13.7 GHz for arbitrary polarisation

Stored energy of arbitrary metamaterial inclusions

Abstract: Electromagnetic metamaterials are generally defined and classified in terms of their effective parameters. They are evaluated in the far-field which limits the evaluation of its near field interaction in some applications such as metamaterial inspired design. An alternative approach proposed in this paper is based on the modal stored energy of metamaterial inclusion. This approach is based on the surface current distribution which would address the challenge of metamaterial near-field application. This paper describes a method for quantifying the modal stored energy of arbitrary-shaped metamaterial inclusions based on the theory of characteristic modes. The theory of characteristic modes is independent of excitation, gives good physical insight into the behaviour of an inclusion and would be helpful for near-field application of metamaterials. The modal stored energy approach is also compared with the common effective parameter approach. It shows similarity in terms of the physical and qualitative analysis when far-field assumptions are accounted for. The broadside-coupled split-ring resonator and the S-shaped inclusion are considered. The physical and qualitative analysis based on the modal stored energy approach shows a good agreement with the effective parameter approach.

New Compact Wearable Metamaterials Circular Patch Antennas for IoT, Medical and 5G Applications

Abstract: The development of compact passive and active wearable circular patch metamaterials antennas for communication, Internet of Things (IoT) and biomedical systems is presented in this paper. Development of compact efficient low-cost wearable antennas are one of the most significant challenges in development of wearable communication, IoT and medical systems. Moreover, the advantage of an integrated compact low-cost feed network is attained by integrating the antenna feed network with the antennas on the same printed board. The efficiency of communication systems may be increased by using efficient passive and active antennas. The system dynamic range may be improved by connecting amplifiers to the printed antenna feed line. Design, design considerations, computed and measured results of wearable circular patch meta-materials antennas with high efficiency for 5G, IoT and biomedical applications are presented in this paper. The circular patch antennas electrical parameters on the human body were analyzed by using commercial full-wave software. The circular patch metamaterial wearable antennas are compact and flexible. The directivity and gain of the antennas with Circular Split-Ring Resonators (CSRR) is higher by 2.5dB to 3dB than the antennas without CSRR. The resonant frequency of the antennas without CSRR is higher by 6% to 9% than the antennas with CSRR. The computed and measured bandwidth of the stacked circular patch wearable antenna with CSRR for IoT and medical applications is around 12%, for S11 lover than −6dB. The gain of the circular patch wearable antenna with CSRR is around 8dBi.

Multi-functional sandwich structure with metamaterial antenna lattice cores: protection, radiation and absorption

Abstract: In this study, a multi-functional sandwich structure is proposed with mechanical support, electromagnetic radiation and absorption by radome-integrated design of metamaterial antenna array. The pyramid metamaterial absorber (PMA) is used as the radiator of the antenna element, with a fibre-reinforced resin composite radome attached on the top. To enhance mechanical strength of the radome and meanwhile to reduce radar cross-section (RCS) of the antenna, the PMA is used as the lattice core of sandwich structure. By engineering the dispersion, the PMA structure is used as low-loss antenna in-band radiator and broadband out-of-band absorber simultaneously. For instance, an antenna working in the C-band and with RCS reduction in the X-band was designed, manufactured and measured. Radiation performances of the antenna are verified. A 5 × 5 antenna array and a 2 × 2 array were also fabricated to evaluate the absorption and mechanical properties, respectively. Measured results of the 5 × 5 array present that the RCS reduction is more than 20 dB in the X-band. Quasi-static out-of-plane compression tests on the 2 × 2 antenna array verify the good mechanical performances. The sandwich structure can achieve high mechanical strength, good radiation performance and low RCS, which provides a new paradigm of antenna–radome-integrated design for practical applications.

A Survey on applications of Metamaterials in Antenna Design

Abstract: Recent advancements in telecommunication sector focuses on developing miniaturized devices with the integration of multiple functions as per the customers need. Mobile systems, smart portable equipment, communication receivers, wireless networks require antennas which are compact and condensed in size, one that possesses good gain and has multiband functionalities. To enhance these antenna parameters novel artificial materials are known as metamaterials are incorporated in antenna designs. Broad classification of metamaterials is presented in this paper with emphasis on their functionality in antenna design. Applications of such artificial structures in enhancing antenna gain, in miniaturization of antenna size, to get multi-band characteristics are discussed extensively. A comparative survey is presented to highlight the advantages of using the metamaterial antennas as against the conventional antennas to the above-mentioned parameters. The purpose of this paper is to analyze the best structure for specific applications and testify the significant improvements obtained because of the meta structures.

Wideband frequency reconfigurable metamaterial antenna design with double H slots

Abstract: This paper presents the design of wideband frequency reconfigurable metamaterial antenna with double H slots. The design is based on the idea of composite right/left-handed transmission line (CRLH-TL) technique. Bandwidth enhancement was achieved by utilizing series left-handed capacitor CL transmission line parameter. The design has several outstanding advantages which include efficient bandwidth to cover many lower Application bands with multi frequency operation characteristics. A comprehensive analysis and simulation were done by using computer simulation technology (CST) software to determine the performance and efficiency of the proposed antenna. From the result obtained, the antenna aquired bandwidth range which covered (2.3-5.2) GHz which is equivalent to 77% fractional bandwidth. The wideband antenna was reconfigured by using frequency reconfiguration technique. From the reconfiguration results, the antenna can be switch from wideband to two single bands which resonate at 2.4 GHz and 4.2 GHz and to dual band which resonate at 2.4 GHz and 4.2 GHz. The realized peak gain at 2.4 GHz is 2.28 dBi and 2.58 dBi for E and H field respectively. The maximum efficiency of 96% was obtained. The antenna can be use for WLAN, proposed lower 5G band and cognitive radio system for frequency sencing.

Low-loss ultra-wideband beam switching metasurface antenna in X-band

Abstract: This study proposes an ultra-wideband (UWB) metasurface-based beam-switching antenna system. A coplanar (CP) waveguide fed slot antenna (with 49% operating bandwidth) is coupled with a hexagonal metallic aperture to generate CP beam in the 10.2–10.8 GHz band. An octagonal split ring inclusion-based meta-element is designed to achieve 2π transmission phase variation with near-unity magnitude. The principle of the Pancharatnam–Berry metasurface is used to design an offset metasurface superstrate for tilting the main beam of the UWB antenna for the CP band. Measured results (S 11, axial ratio, and radiation pattern) agree well with full-wave simulations. The fabricated X-band UWB aperture coupled antenna system uses the metasurface superstrate to achieve a broadside beam for the lower band and tilted beam for the upper band. This antenna system holds promise for next-generation vehicular and satellite communication applications.

Tripole type wideband bandpass frequency selective surface for X-band applications

Abstract: The study presents a novel single dielectric layer wideband bandpass frequency selective surface (FSS) topology. The structure is designed using a kind of the tripole type FSS which has been analysed for its behaviour. Next, the operating bandwidth has been increased by using the meander lines in the middle of the unit-cell. The proposed FSS structure covers the X-band (45.03% fractional bandwidth) of the electromagnetic (EM) spectrum with a −3 dB transmission bandwidth. Its −1 dB bandwidth extends from 7.93 to 11.93 GHz. The wide operating bandwidth with a single dielectric layered structure makes it suitable for the hybrid radome applications. For the normally incident EM wave, adjacent to the lower and upper cut-off frequencies, the structure offers better than 18 dB attenuation which increases the out of the band rejection. Finally, the proposed structure is fabricated and experimentally verified for the dual polarisation and angle stability up to 45°. Eventually, to prove the novelty in terms of the operating bandwidth and the fabrication simplicity, an exhaustive state-of-the-art comparison is also presented.

Double-layer metasurface-based low profile broadband X-band microstrip antenna

Abstract: In this paper, a novel technology based on double-layer metasurfaces is proposed in order to broaden the bandwidth of microstrip antennas, which has been verified in X-band linearly polarised and circularly polarised antennas. Referring to the conventional metasurface antenna that employs slot-coupled feeding, these designs add an extra metasurface between the radiation patch and the ground plane so as to establish dual resonance modes, TM10 and TM20. Following the adoption of the composite right/left-handed transmission lines principle, this technique aims to adjust the propagation constant in the right-hand region by introducing parallel inductors and capacitors to widen the dual resonant frequencies' interval, thereby realising a broadband antenna. In addition, the interlayer metasurface may also be utilised as a director to balance the E-field of the radiation patch. A linearly polarised double-layer metasurface antenna with a size of 0.8 0.8 0.058 (wavelength in free space at the centre frequency) is filled with F4B substrate with a dielectric constant of 2.2. It finally realises an impedance matching bandwidth (VSWR 2) from 8.41 to 11.67 GHz, occupying about 32.47 of the centre frequency. This circularly polarised antenna attains both an impedance matching bandwidth of 32.44 (i.e. 8.29–11.5 GHz) and an axial-ratio bandwidth of 19.72 (i.e. 9.6–11.7 GHz).

Increasing the transparency of compact flexible antennas using defected ground structure for unobtrusive wearable technologies

Abstract: In this paper, new designs of optically transparent wearable antennas have been presented. The explored antennas have the excellent features of high flexibility, small size, low specific absorption rate (SAR) and high optical transparency. The proposed antennas are realised by utilising highly flexible, optically transparent and low-cost materials. For achieving compactness in antenna dimension and for improved transparency, square-ring-shaped radiator is used in the antenna design. To improve the efficiency and gain of the square-ring patch antennas, a new technique is proposed in this paper. The proposed technique utilises a strip line that connects the middle of the two opposite sides of the ring. Full ground plane is used in antenna design to reduce the back radiation. However, full ground plane reduces optical transparency. To elevate optical transparency without affecting antenna's back radiation significantly, a new technique of defected ground structure is investigated in this study. With this defected ground structure, the optical transparency is improved by about 6% without significantly compromising the SAR. The compatibility of the proposed antennas for wearable applications are investigated by examining the performances on flat and bent phantoms. Moreover, the robustness of the antennas are studied by subjecting the prototypes to multiple bending operations.

Miniaturised tri-band rhombus-shaped metamaterial-inspired antenna with gain enhancement using complementary closed ring resonators

Abstract: In this study, a rhombus-shaped patch antenna is proposed using metamaterial transmission line. The motivation of this work is to overcome the problem of low gain while designing miniaturised antennas. The proposed design is based on coplanar waveguide feeding technique. A rhombus-shaped patch is chosen in this structure in which striplines are provided to connect the ground planes and to obtain the shunt inductance. Asymmetric meandered line inductors are integrated with the striplines for miniaturising the electrical size of the antenna. Further to improve the gain of the antenna in the lower bands, asymmetric ground plane and complementary closed ring resonator have been employed in the proposed structure. The electrical size of the proposed antenna is 0.168 λ 0 × 0.151 λ 0 corresponding to the physical size of 25 mm × 22.5 mm, where λ 0 = free space wavelength at 2.02 GHz. Considering below -10 dB input reflection coefficient, this antenna operates in three bands covering 1.96-2.07, 4.06-4.72, and 6.43-7.79 GHz. In addition, the proposed antenna exhibits gain of 1.49, 2.68, 2.19, and 4.31 dB at 2.02, 4.48, 6.72, and 7.43 GHz, respectively, in the maximum direction of radiation.

A Fractal Metamaterial Antenna for Bluetooth, WLAN, WiMAX and X-band Applications

Abstract: A novel multiband fractal wide slot meta material antenna is designed for Bluetooth/WIMAX/WLAN and X band downlink applications. In order to generate the WLAN (2.4/5.8GHz) and X-band (7.5 GHz) spectrums, the antenna slot structure is now in the form of a new fractal-like geometry on the first iteration. The Bluetooth (2.45 GHz) and WIMAX (3.5 GHz) bands are excited when the antenna is loaded respectively by a loop resonator and meandered shaped meta materials. The proposed antenna was simulated using both (CST MWS) and (HFSS) to verify against the obtained simulation results. This antenna has successfully demonstrated multiband and broadband characteristics. Simulation results show that the antenna gives an acceptable antenna gains over the resonant frequency signals. In addition, influence dimensions on the electromagnetic performance for the meandered-shaped and resonator and fractal circular slot for this structure are performed and implemented in detail this paper.

Frequency Reconfigurable Antenna Inspired by Tri-SRR Metamaterial

Abstract: A frequency reconfigurable metamaterial-based microstrip antenna is presented in this paper. The proposed antenna consists of three split-ring resonators (SRR) and a tapered feeder placed on the top layer of a 30 × 25 × 1.6 mm3 substrate. Nine PIN-Diode switches are distributed around the three rings, each ring contains 3 switches with 120-degree spacing. Reconfigurability is achieved by varying the condition of these switches. The suggested antenna is simulated using Ansys Electronics Desktop simulator (HFSS), and MATLAB software is used to analyze the characteristics of the metamaterial unit-cell. Single and dual bands are produced at 2.8, 3.025, (2.45 and 4.75) and (2.93 and 4.85) GHz. Radiation patterns, gain, input impedance and radiation efficiency are simulated to have a better observation of the performance of the antenna.