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An efficient multifunctional metasurface for cross and circular polarization conversion is presented in this letter. The metasurface acts not only as an efficient polarization converter for linearly polarized wave over frequency bands of 5.3–5.4, 7.2–8, and 12.3–13.76 GHz but also perfectly converts linearly polarized wave into circularly polarized wave over multiple bands of 5.1–5.2, 5.6–6.85, 8.8–11.2, and 14.9–20.2 GHz. The behavior of the metasurface is quite stable under oblique incidence for certain bands up to 75°. The broadband circular- polarization conversion, compactness, angular stability, and multiple functionality make it a strong candidate for many applications in the strategic C -, X -, Ku -, and K -bands.

An impedance matched metasurface can efficiently channel the electromagnetic fields for maximum power transfer. The thin film based impedance matching techniques often utilize highly dissipative materials and destructive interference of reflection components from multiple subwavelength layers. Here, we propose a novel method to achieve anti reflection characteristics through destructive interference of antiparallel electromagnetic scattering emerging from chiral metasurface. The supercell structure of metasurface consists of four adjacent multi split-rings on FR-4 substrate. The split-rings are arranged to induce anti-parallel surface currents leading to destructive interference for scattered fields. The antireflection characteristics results in near perfect broadband absorption at dual frequency bands. A broadband absorption of 983 MHz is achieved between 12.687 and 13.669 GHz. Similarly, a narrow band absorption of 108 MHz is achieved in frequency range of 15.307–15.415 GHz. The impedance matched with unique symmetric design of supercell results in identical absorption for both x- and y-polarized incident fields. The numerical and experimental results verify broadband absorption characteristics at Ku band frequencies. The proposed metasurface absorber can be used for microwave energy harvesting applications.

A dual-band UHF/industrial, scientific and medical (ISM) compact rectenna with wideband UHF matching (855–935 MHz) covering all, EU, U.S., and Chinese UHF radio frequency identification (RFID), standards is presented. The proposed design consists of a compact single-port, dual-band antenna, a three-port dual-branch matching network, and two voltage doubler rectifiers implemented with Schottky diodes and terminated with a common 10 $\text{k}\Omega $ load. For each band, the measured RF-to-dc efficiency is around 60% for a −5 dBm unmodulated signal. The wideband behavior of the rectenna supports harvesting of multitone signals. The use of a six-tone signal increases the maximum RF-to-dc efficiency of the dual-band rectifier, from approximately 60% for a single-tone UHF signal (890 MHz) to 80% for a six-tone signal for a received RF power of −5 dBm in both cases. A signal generator is used to generate a six-tone signal of equally weighted and equally spaced (10 MHz separation) monochromatic tones, with a total bandwidth of 50 MHz. The measurement results demonstrate that the dc voltages rectified from the two separate RF signals are effectively superimposed on the load, providing a clear advantage compared to single-band rectennas. The single-layer, compact design with a size of $80\times45$ mm2, with a high RF-to-dc efficiency, is an excellent candidate for wirelessly powered RFID tags.

A circularly polarized monopole antenna fed by coplanar waveguide is presented in this research. The antenna operates in wireless local area network and worldwide interoperability for microwave acc...

A 32-bit chipless RFID tag operating in the 4.5–10.9 GHz band is presented in this paper. The tag has a unique multiple-arc-type shape consisting of closely packed 0.2 mm wide arcs of different radii and lengths. The specific tag geometry provides multiple resonances in frequency domain of an RCS plot. A frequency domain coding technique has also been proposed to encode the tag’s RCS signature into a 32-bit digital identification code. The tag has an overall dimension of 17.9 × 17.9 mm2, resulting in a high code density of 9.98 bits/cm2 and spectral efficiency of 5 bits/GHz. The proposed tag is built on a low loss substrate bearing a very small footprint, thereby making it extremely suitable for large-scale product identification purposes in future chipless RFID tag systems.

This work presents the design of a low profile Fabry-Perot (FP) cavity-based multiple-input-multiple-output (MIMO) antenna with low correlation coefficient. The fields of closely placed antenna elements are tilted by using a phase-gradient partially reflective surface (PRS), thereby decreasing the correlation coefficient. The PRS is designed in such a way that its reflection phase is complementary to that of the ground plane. The PRS decorrelates the fields of the two radiating elements when placed at a height of λ/10 above them resulting in a reduction of the correlation coefficient by almost 95% for an isotropic environment. This height is considerably less than λ/4, which has been reported previously.

This paper presents a novel methodology for designing high-capacity frequency domain chipless RFID tags based on the backscattering principle. The tag consists of multiple square open-loop resonators loaded with a varying number of square metallic patches to form a mesh structure. Thus, in contrast to conventional designs, the overall physical size of each resonator remains fixed and does not change with respect to its operating resonant frequency. The RCS response of the proposed tag can be easily manipulated by varying the loading factor of each resonator. The tag size is further miniaturized by placing resonators on both sides of the substrate used. The tag configuration with resonators arranged in the form of a single row (4 × 1) printed on both sides of the substrate is finally chosen for maximum robustness and efficiency. The frequency shift coding (FSC) technique is used to encode more than one bit per resonator by using segments within sub-bands. The proposed tag encodes 16-bit data in a frequency band from 5.9 to 10.5 GHz and has a very high code density of 23.51 bits/cm2 and a spectral efficiency of 3.47 bits/GHz. The design methodology is novel and leads to a very efficient chipless RFID tag that can be used in a variety of high-data-capacity applications.

This work presents the design of a low profile Fabry-Perot cavity-based multiple-input-multiple-output antenna with low correlation coefficient. The fields of closely placed antenna elements are tilted by using a phase-gradient partially reflective surface (PRS), thereby decreasing the correlation coefficient. The PRS is designed in such a way that its reflection phase is complementary to that of the ground plane. The PRS decorrelates the fields of the two radiating elements when placed at a height of λ/10 above them resulting in a reduction of the correlation coefficient by almost 95% for an isotropic environment. This height is considerably less than λ/4, which has been reported previously.

In this article, a single-layer metasurface based reflector design is proposed for linear-to-linear cross-polarization conversion in microwave frequency range. The unit-cell of the proposed design consists of triple-arrow resonant design printed on a grounded FR4 substrate. Excellent cross-conversion is achieved over a broad frequency range (8.0–18.50 GHz) with polarization conversion efficiency higher than 90%. The proposed design has a large fractional bandwidth (FBW) of 80% due to three resonances occurring in the band. The polarization response is angularly stable with respect to oblique incidences with incidence angles up to 45°. The proposed design has been fabricated and experimentally validated. The measurement results are in good agreement with the simulation results.

This paper presents a unique geometry of a chipless radio frequency identification (RFID) tag for encoding a large number of bits in a very small form factor. The tag geometry consists of semi-octagonal copper strips, sequentially laid on a single side of an ultra-thin substrate. A unique and robust encoding mechanism for the tag identification (ID) is proposed. The operating frequency spectrum of the tag ranges from 3.1 to 10.5 GHz. The tag is compact, having an overall size of 14.5 × 28 mm2. The proposed tag exhibits very high code density of 9.85 bits/cm2 and spectral efficiency of 5.4 bits/GHz. The unique geometric configuration of the proposed tag allows it to encode up to 40 bits of data as an RCS signature. This chipless RFID tag seems to be a potential candidate for a wide range of modern RFID applications.

A wideband snowflake antenna for 28 GHz millimeter-wave communications is proposed. The antenna has a size of 8×5 mm2, fabricated on ultra-thin 0.254 mm substrate. The antenna consists of four small hexagons surrounding a bigger hexagon in order to attain broadband characteristics. Bandwidth response of the antenna is between 25.28-29.04 GHz (13.43% @ 28 GHz), having 3.12 dBi gain and more than 80% of radiation as well as total efficiency. The antenna specific structure is designed such that it gives dual beam over its entire bandwidth without a noticeable shift in its beam directions. For enhanced gain performance, its 4-element array (of size 32×12 mm2) has been fabricated separately to increase its gain upto 10.12 dBi at 28 GHz. The proposed dual-beam antenna and its array has been modelled on thin Rogers substrate to show that its application in millimeter-wave communication equipment is viable.

A wideband antenna with a high gain and narrow beam-width for future 5G communication systems is presented in this research. The antenna operates in 28 GHz 5G band with a large 35.53% bandwidth ranging from 23.41-33.92 GHz. The array has 4-elements arranged in a linear fashion to attain a high gain of 10.7 dBi. It radiates along its end-fire direction and provides a very narrow beam-width of 14.6° in its H-plane. A corporate feed network specifically designed for thin substrates was used in order to excite the array elements. It is built upon thin 0.254 mm Rogers substrate to minimize transmission losses and attain high radiation efficiencies of more than 90% throughout its operating frequency range. It has a compact structure bearing low cost and is easy to fabricate. This antenna fulfills necessary requirements of 5G communication and is therefore a good candidate to be used in the millimeter-wave range.

A double-rhomboid bowtie-slot on-chip antenna aided by a back-to-back E-shaped electromagnetic bandgap (EBG) surface for gain enhancement at W-band is presented. The specific structure of both the antenna and the EBG surface is being reported for the first time in an on-chip implementation. The antenna is analyzed independently as well as backed by different electromagnetic bandgap reflective surfaces using standard 0.13 $\mu$ m BiCMOS process. The proposed EBG surface provides a measured gain enhancement of 2 and 8 dB when used as a frequency selective surface and as an artificial magnetic conductor, respectively. With an overall chip size of 1 $ {}\times {\text{1 mm}}^{2}$ , the on-chip antenna demonstrates a $-$ 6 dB impedance bandwidth from 75–100 GHz and an effective gain bandwidth from 80–90 GHz with a peak measured gain of $-$ 0.58 dBi at 84 GHz. The antenna has the smallest reported size and the highest gain in W-band with artificial magnetic conductor as reflective surface.

This paper presents a very low profile and simple antenna design for dual beam and dual-band operation to be employed in future 5G mobile phones operating in the millimeter-wave bands of 26.75–30.31 and 35.83–41.22 GHz. The two distinct resonances at 28 and 38 GHz are achieved using a meta-material-based structure consisting of a closed-ring resonator (CRR) and a split-ring resonator (SRR) by co-centrically combining two planar hexagonal rings; i.e., an inner split-ring resonator (SRR) and an outer closed-ring resonator (CRR). The antenna has a high gain of 4.5 dBi. The antenna also exhibits a dual-beam radiation pattern in one of its planes. The overall antenna size is 6 × 8 mm2 and is manufactured using a low-cost PCB fabrication process. The antenna’s dual-beam operation, broadband characteristics, high gain, and low profile makes it a potential candidate for future millimeter-wave mobile phones, especially in applications where space diversity is required.

Two-dimensional metamaterials, consisting of an array of ultrathin building blocks, offer a versatile and compact platform for tailoring the properties of the electromagnetic waves. Such flat metasurfaces provide a unique solution to circumvent the limitations imposed by their three-dimensional counterparts. Albeit several successful demonstrations of metasurfaces have been presented in the visible, infrared, and terahertz regimes, etc., there is hardly any demonstration for ultraviolet wavelengths due to the unavailability of the appropriate lossless materials. Here, we present diamond as an ultra-low loss material for the near and deep ultraviolet (UV) light and engineer diamond step-index nanowaveguides (DSINs) to achieve full control over the phase and amplitude of the incident wave. A comprehensive analytical solution of step-index nanowaveguides (supported by the numerical study) is provided to describe the underlying mechanism of such controlled wavefront shaping. Due to the ultra-low loss nature of diamond in near and deep UV regimes, our DSINs and metasurfaces designed (from them) exhibit a decent efficiency of ≈ 84% over the entire spectrum of interest. To verify this high efficiency and absolute control over wavefront, we have designed polarization-insensitive meta-holograms through optimized DSINs for operational wavelength λ = 250 nm.

This paper presents a new beam shaping technique for a linear array. The technique is based on discretization of the desired array factor at specified discrete locations. At each location, a weighted pencil beam is placed which is obtained through Taylor synthesis, whereas the weight of the pencil beam depends upon the desired array factor. Superposition of weighted pencil beams approximates the desired pattern. The method gives a better compromise between shaped beam and sidelobe level (SLL). Two beam shapes are realized using the proposed method to verify its effectiveness. A comparison with similar beam shaping methods shows that the proposed method results in accurate beam shape with low SLLs.

A frequency reconfigurable MIMO antenna is presented for tablet computers. The antenna comprises of two branch strips, a folded monopole strip loaded with a pin diode, and an inductively coupled branch strip. Reconfigurability is achieved using pin diode, which electronically controls the effective length of driven monopole strip. In the ON state, antenna covers the GSM850/900, GPS/GLONASS, and LTE2300/2500/3400 whereas in the OFF state, it supports the DCS/PCS/UMTS frequency bands thus covering nine bands in total.

A millimeter-wave antenna working in 28 GHz band is presented here. It has an asymmetric meandered line path radiator, laid down in a semi-circular region. The antenna’s impedance bandwidth is improved via the use of hexagonal parasitic patches placed at its back side. The meandered line radiating element is fed by a microstrip line connected through a smooth tapered line. The antenna has an overall dimension of 6×4 mm2, and has an ultra-thin 0.254 mm substrate platform. It has a 6.3% bandwidth at 28 GHz, ranging from 27.13-28.90 GHz. The antenna possess very high radiation efficiency of more than 90% and a gain of 2.25 dBi. The antennas compact structure, simple planar design, low loss and large bandwidth will be of considerable interest for 5G system developer.

In this paper a fully passive, compact and polarization independent chipless RFID tag with high bit capacity is presented. The proposed tag is constructed using L-shaped open loop resonators of variable lengths. It is modeled upon a thin 0.8 mm substrate with an area of 1.7 × 1.7 cm2. The tag can encode 16-bits in a frequency range 4.5-8 GHz with a very high bit density of 5.5 bits/cm2. It also has an improved spectral bit efficiency of 4.57 bits/GHz. RCS response of the tag is also independent of incident wave polarization. The tag’s attractive features such as compact size, orientation independence, high code density and large spectral efficiency make it a good candidate for various product identification scenarios.

A compact design of ultra-wide band (UWB) log-periodic dipole array (LPDA) antenna printed on FR-4 substrate is presented. The proposed design consists of array of printed dipoles fed by a coaxial cable. The dimensions of the printed dipoles and the spacing between the array elements are optimized by parametric simulations using full wave simulator. The size of the fabricated LPDA antenna is 0.9 $\lambda \times 0.33 \lambda (135 \times 50 mm^{2})$. The antenna has a fractional bandwidth of 133% and covers the band from 2.2 GHz to 11 GHz. The antenna exhibits a consistent end-fire radiation patterns over the whole operating band of 2.2-11 GHz with a maximum operating gain of 8.6 dBi.

This paper presents a planar wideband antenna for future 5G millimeter-wave communication. The antenna structure consists of a Tri-Cell network of hexagonal rings backed up by pseudo-pyramidal patches for improved impedance bandwidth. It operates in 26.677-29.601 GHz spectrum that covers the most famous 28 GHz 5G band. The antenna has an excellent radiation efficiency performance of more than 90% throughout its operating band. It has a good gain of 4.81 dBi suitable for millimeter-wave propagation. It has simple planar structure which is easy to fabricate and demands low cost. Its attractive features such as wide band, high gain, low profile and simple construct makes it quite suitable for use in the upcoming future 5G communication systems.

A wide band antenna working in the 28 GHz 5G designated band has been presented in this paper. It has a semicircular structure backed up by a network of small hexagonal parasitic patch on the backside. It is fed through a coplanar waveguide (CPW) and has a small footprint of $9\times 7.38 \ \mathrm{mm}^{2}$ . It has 3.75 GHz of bandwidth ranging from 27 to 30.76 GHz. It is low loss with radiation efficiencies exceeding 95%. It also exhibits a large gain performance of 5.67 dBi at 28 GHz. The antenna has attractive features that will interest 5G system developers due to its small form factor, low cost, wideband and high gain performance.

In this paper, we present the implementation of two rectennas, on the same planar module, one in the UHF frequency band and the second one in the ISM frequency band. The two MIMO antennas were designed considering the expected mutual coupling effect and based on good design practices the mutual coupling was suppressed. The presented radiation patterns and the estimated antenna gains indicate the good isolation between the two radiators. Two voltage coupler topologies were implemented, one for each radiator and their integration with the MIMO antennas resulted in the two rectennas which divert the rectified voltage on two different loads. The presented rectennas can be used for MIMO energy harvesting systems or Simultaneous Wireless Information and Power Transfer Systems - SWIPT.

This paper presents a Chip-Less RFID tag working in 2–14 GHz. The tag consists of a hexagonal patch surrounded by multiple closed loop hexagonal rings. The tag generates 5 low-point RCS signatures within the operating band resulting in a 12-bit sequence code. Complementary bits are separated by 25 dB RCS transitions indicating a satisfactory code resolution capability. The overall tag dimension is $2.5\times 2.5\mathrm{cm}^{2}$ and a code density of 1.76 bits/cm2. Due to the tag's ability to store a long bit-sequence code, it can be a good candidate for use in various different RFID applications.

This paper presents a compact and cost effective chip-less RFID tag (CRFID) to be operated in 4–14 GHz band. The tag has circular and diagonal closed loop rings for generating multiple resonances to encode a 12-bit sequence. It has a size of $\mathbf{1.4}\times\mathbf{1.4\ cm}^{\mathbf{2}}$ and code density of 6.122 bits/cm2. The proposed tag is modeled upon low cost FR4 substrate and has a planar construct. Due to its attractive features such as long bit-encoding capability, compact size and ease of fabrication, this CRFID is deemed quite suitable to be used in various RFID application scenarios in Internet of Things.

A monopole antenna inspired from Rotman Lens is presented in this paper. It is designed to operate in the unlicensed 60 GHz millimeter-wave band from 54.318-64.477 GHz. It also has a high gain of 5.25 dBi, suitable for millimeter-wave communication. It has more than 90% of radiation efficiency due to the use of Rogers 5880 low loss substrate. It has dual beam radiation pattern in azimuth plan and back radiations are less than −10 dB. The antennas overall dimensions are $5\times 4.5\ \text{mm}^{4}$ , ensuring small form factor. It has a planar structure and along with its other attractive features such as high gain, large bandwidth and dual beam, is deemed quite suitable for future 5G, millimeter-wave communication in the unlicensed 60 GHz band as well as indoor communications.

We demonstrate transmission-based all-dielectric, highly efficient (≈73.4%) and polarization-insensitive meta-axicons (for the visible wavelength of 633 nm) to generate zero and higher order Bessel beams without using additional components. The Bessel beams, owing to their diverse applications and non-diffractive properties, attract great interest from the scientific community. It is shown that the propagation length can be increased through a lower numerical aperture (∼2600 λ for NA = 0.1) whereas a higher full width at half maximum (

A reflective metasurface exhibiting both cross-polarization conversion (CPC) and linear-to-circular polarization (LP-to-CP) conversion is presented in this paper. The proposed metasurface is composed of 45° tilted T-shaped unit cell having a circular ring at its center. The proposed metasurface converts linearly-polarized wave into its orthogonal counterpart over two frequency bands; 6.2-9.7 GHz, and 15.5-16.5 GHz with more than 90% CPC efficiency. The metasurface also transformed linearly-polarized wave into circularly-polarized wave at frequency bands; 5.6-5.8 GHz and 11.5-14.5 GHz. The metasurface is insensitive to incident angles up to 30° for both CPC and LP-to-CP conversion.

This paper presents design of an hp-shaped reconfigurable antenna printed on a 1.6 mm thicker FR-4 substrate. The antenna works in four distinct modes frequency modes, contingent on the status of the two switches. Six resonant bands are obtained by the antenna, i.e. 1.8 GHz (GSM1800), 2.10 (3G LTE-advanced), 3.15 GHz (Radiolocation), 3.50 GHz (WiMAX), 3.88 GHz (Fixed satellite services) and 5.56 GHz (WLAN). The antenna gives optimum performance in terms of gain (1.84–3.22 dB), bandwidth (180–1020 MHz) and radiation efficiency (91–95%) in these six frequency bands. The antenna is properly matched in all these bands (VSWR

This paper presents a dual-band coplanar waveguide (CPW) fed printed antenna with rectangular shape design blocks having ultrawideband characteristics, proposed and implemented on an FR4 substrate. The size of the proposed antenna is just 25 mm × 35 mm. A novel rounded corners technique is used to enhance not only the impedance bandwidth but also the gain of the antenna. The proposed antenna design covers two ultrawide bands which include 1.1–2.7 GHz and 3.15–3.65 GHz, thus covering 2.4 GHz Bluetooth/Wi-Fi band and most of the bands of 3G, 4G, and a future expected 5G band, that is, 3.4–3.6 GHz. Being a very low-profile antenna makes it very suitable for the future 5G Internet of Things (IoT) portable applications. A step-by-step design process is carried out to obtain an optimized design for good impedance matching in the two bands. The current densities and the reflection coefficients at different stages of the design process are plotted and discussed to get a good insight into the final proposed antenna design. This antenna exhibits stable radiation patterns on both planes, having low cross polarization and low back lobes with a maximum gain of 8.9 dB. The measurements are found to be in good accordance with the simulated results.

Metasurfaces, two dimensional (2D) metamaterials comprised of subwavelength features, can be used to tailor the amplitude, phase and polarisation of an incident electromagnetic wave propagating at an interface. Though many novel metasurfaces have been explored, the hunt for cost-effective, highly efficient, low-loss and polarisation insensitive applications is ongoing. In this work, we utilise an efficient and cost-effective dielectric material, hydrogenated amorphous silicon (a-Si:H), to create a ultra-thin transmissive surface that simultaneously controls phase. This material exhibits significantly lower absorption in the visible regime compared to standard amorphous silicon, making it an ideal candidate for various on-chip applications. Our proposed design, which works on the principle of index waveguiding, integrates two distinct phase profiles, that of a lens and of a helical beam, and is versatile due to its polarisation-insensitivity. We show how this metasurface can lead to highly concentrated optical vortices in the visible domain, whose focused ring-shaped profiles carry orbital angular momentum at the miniaturised scale.

In this paper two triple-band monopole antennas are proposed for portable wireless applications such as WiFi, WiMAX and WLAN. Two different geometrical structures are used for the radiating elements of these antennas, each printed on a low cost FR-4 substrate. Truncated metallic copper ground is used to attain optimum radiation pattern and better radiation efficiency. The frequency of the antennas is reconfigured using a lumped-element switch. The proposed antennas covers three frequency bands 2.45, 3.50 and 5.20 GHz depending upon the switching conditions. Both antennas works with an optimum gain (1.7–3.4 dB), bandwidth (6–35%), VSWR (

Recent surge in the development of wireless communication has increased the need of the antennas that can operate at more than one frequency band. To meet the requirements, reconfigurable antennas are used. This paper presents design and analysis of a low profile, planar and, frequency reconfigurable E-shape patch antenna, using a 1.6 mm thicker FR-4 substrate. The antenna operates in two single-band and two dual-band modes, depending on the status of the two switches. The proposed antenna works efficiently (>90%) with an adequate gain (>2 dBi) and bandwidth (430 MHz–1 GHz) in the desired frequency bands {WiFi (2.45 GHz), WiMAX (3.59 GHz), WLAN (5.2 GHz), Military/NATO (4.5 GHz), C-Band (6.22 and 6.27 GHz)}. The antenna is optimally matched (VSWR < 1.45) in all these six frequency bands. The proposed antenna is compact in size (40 × 35 mm2) and can be used in portable electronic devices to support multiple wireless services. The antenna is analysed in computer simulation technology, microwave stud...