Search

Patterns composed of micron‐sized surface structures can abruptly change the properties of an optical wave front, including its phase, amplitude, polarization, and dispersion. Optical components featuring surface micro‐gratings not only possess optical functionalities that can rival or exceed those of traditional bulky components but can also significantly improve the compactness of optical systems. Herein, the design and fabrication process of As2S3 glass‐based micro‐gratings as well as their resulting optical functionality in the infrared regime are reported. The novel two‐step photochemical process consists of spatially controlled direct laser writing and subsequent selective solution etching. The process yields surface micro‐gratings that possess arbitrarily tunable geometries and design patterns on large‐area flat and curved optical surfaces or substrates, offering a potential new avenue for developing aberration‐corrected infrared‐imaging systems. [ABSTRACT FROM AUTHOR]

In this work, an ultra‐wideband double slot Vivaldi antenna (DSVA) loaded with a novel wideband nonresonant metasurface is proposed to enhance the gain. The semi‐elliptical slots are etched on both sides of the ground plane of the DSVA to improve the current distribution. In addition, the nonresonant metasurface composed of WiFi‐shaped unit cells could maintain a stable high refractive index in the operating bandwidth of 1−18 GHz, which could bend the outgoing wave to the end‐fire direction. Both the original antenna and the proposed antenna are simulated, fabricated, and characterized. The measured results are in good accordance with the simulated ones. The return losses of both antennas are less than −10 dB in the frequency range of 2−13.4 GHz, while the gain of the proposed antenna is improved from 13.6 to 16.3 dBi with a maximum gain enhancement of 3.1 dB. [ABSTRACT FROM AUTHOR]

Holography based on optical metasurfaces has attracted a steadily increasing interest. However, most of the optical metasurfaces usually suffer from limited number and fixed viewing angles of multiplexed holography images in one channel. Here, by modifying the Gerchberg–Saxton algorithm, a multiplexed holography at arbitrary‐planes is proposed at two arbitrary microwave frequency bands. As a proof‐of‐concept demonstration, two independent information channels can be established by a single metasurface through dual‐frequency meta‐atoms. The metasurface composed of 35 × 35 meta‐atoms can simultaneously produce four images with 45° and 60° viewing angles at 10 GHz and five images with vertical and horizontal viewing angles at 16 GHz. The experimental results verify the design concept, making it possible to generate multiplexed holography in arbitrary‐planes, and allowing multiplexed functionalities in a variety of applications such as microscopy, display, security, data storage, and information processing. [ABSTRACT FROM AUTHOR]

A novel design of circularly polarized broadband slot antenna with high gain, low profile, and low radar cross‐section (RCS) is proposed by employing polarization conversion metasurface (MS). By introducing sawtooth corner‐truncated square MS with diagonal gaps, a compact circularly polarized antenna composed of 4 × 4 unit cells is presented. It is found that a smaller MS slot antenna can achieve an impedance bandwidth of 42.9% (3.7–5.72 GHz) and a 3‐dB axial ratio (AR) bandwidth of 22.8% (4.55–5.72 GHz). Simultaneously, the MS can realize polarization conversion. The MS and its orthogonal units were arranged in a chessboard‐type pattern and applied as the radiator of a larger MS slot antenna, which was fed by a sequentially rotated feeding network. In addition, owing to the anti‐phase cancellation and scattering, the 5‐dB average RCS reduction can be obtained within the frequency range from 3.8 to 6.9 GHz. For verification, the proposed larger circularly polarized antenna was fabricated and tested. The operating bandwidth was measured as 44% (3.78–5.91 GHz) with a 3‐dB AR bandwidth of 39.6% and a high gain of 10.3 dBic. Furthermore, the larger antenna produces a useful RCS reduction from 3.7 to 6.7 GHz. The simulated and measured results are in good agreement. [ABSTRACT FROM AUTHOR]

Zoom lenses with variable focal lengths and magnification ratios are essential for many optical imaging applications. Conventional zoom lenses are composed of multiple refractive optics, and optical zoom is attained via translational motion of one or more lens elements, which adds to module size, complexity, and cost. In this paper, a zoom lens design based on multi‐functional optical metasurfaces is presented, which achieves large step zoom ratios, minimal distortion, and diffraction‐limited optical quality without requiring mechanical moving parts. Two embodiments of the concept are experimentally demonstrated based on polarization‐multiplexing in the visible and phase change materials in the mid‐infrared, both yielding 10× parfocal zoom in accordance with the design. [ABSTRACT FROM AUTHOR]

Multichannel devices, which can manipulate multiple distinguished wavefronts like a kaleidoscope, are preferably desired for compact systems with higher integration and smaller footprint. Particularly, multiband metasurfaces are one of the intuitive and effective approaches to expand the number of the operation channels in meta‐devices. In this work, a strategy to design four‐channel metasurface based on a novel single‐cell quad‐band meta‐atom is proposed for the kaleidoscopic wavefront manipulations. While illuminating a circularly polarized wave, the independent 2π phase shifts at four distinct frequencies can be obtained by the single‐layered substrate meta‐atom with almost theoretically maximal transmission amplitudes. As a proof‐of‐concept demonstration, a four‐channel metasurface is designed to realize a single‐vortex beam generator, a dual‐vortex beam generator, a meta‐hologram, and a focusing metalens in channels 1, 2, 3, and 4, respectively. The experiment and full‐wave simulation results agree very well with each other, validating the design concept. The proposed strategy has increased the number of operation frequencies for a single‐cell meta‐atom while guaranteeing the electromagnetic performance, and may lead to advances in a variety of multifunctional devices with a compact structure such as ultra‐thin metalenses, beam generators, and holographic displays. [ABSTRACT FROM AUTHOR]

Full‐space metasurfaces have attracted significant interest due to their unprecedented abilities to tailor the electromagnetic wavefronts in both transmission and reflection half‐spaces. However, it remains difficult and challenging to achieve high‐efficiency complex‐amplitude modulation within a single‐substrate‐layer structure for circularly polarized (CP) waves, which can enhance the power distribution regulation. Herein, a universal design strategy for the frequency‐multiplexed full‐space meta‐device is proposed by employing a single‐substrate‐layer meta‐atom with complex‐amplitude modulations. The full‐space metasurface is composed of a subwavelength‐thickness substrate and two discrepant metallic layers, where a modified complementary split‐ring resonator and an electric field coupled resonator are selected to refract and reflect the CP incidences to the cross‐ and co‐polarized components at two distinct frequencies. Based on this emerging meta‐atom, a multifunctional bi‐spectral metasurface is designed and verified by both full‐wave simulations and experiments, which generates the quad‐vortex beam and the hologram in transmission and reflection modes, respectively. The proposed method employs a single‐substrate layer to maintain high efficiency, while incorporating the complex‐amplitude modulation, which has potential applications in imaging and communication systems. [ABSTRACT FROM AUTHOR]

Metasurfaces have provided a novel and promising platform for realizing compact and high‐performance optical devices. The conventional metasurface design approach assumes periodic boundary conditions for each element, which is inaccurate in most cases since near‐field coupling effects between elements will change when the element is surrounded by nonidentical structures. In this paper, a deep learning approach is proposed to predict the actual electromagnetic (EM) responses of each target meta‐atom placed in a large array with near‐field coupling effects taken into account. The predicting neural network takes the physical specifications of the target meta‐atom and its neighbors as input, and calculates its actual phase and amplitude in milliseconds. This approach can be used to optimize metasurfaces' efficiencies when combined with optimization algorithms. To demonstrate the efficacy of this methodology, large improvements in efficiency for a beam deflector and a metalens over the conventional design approach are obtained. Moreover, it is shown that the correlations between a metasurface's performance and its design errors caused by mutual coupling are not bound to certain specifications (materials, shapes, etc.). As such, it is envisioned that this approach can be readily applied to explore the mutual coupling effects and improve the performance of various metasurface designs. [ABSTRACT FROM AUTHOR]

Metasurfaces have enabled precise electromagnetic (EM) wave manipulation with strong potential to obtain unprecedented functionalities and multifunctional behavior in flat optical devices. These advantages in precision and functionality come at the cost of tremendous difficulty in finding individual meta‐atom structures based on specific requirements (commonly formulated in terms of EM responses), which makes the design of multifunctional metasurfaces a key challenge in this field. In this paper, a generative adversarial network that can tackle this problem and generate meta‐atom/metasurface designs to meet multifunctional design goals is presented. Unlike conventional trial‐and‐error or iterative optimization design methods, this new methodology produces on‐demand free‐form structures involving only a single design iteration. More importantly, the network structure and the robust training process are independent of the complexity of design objectives, making this approach ideal for multifunctional device design. Additionally, the ability of the network to generate distinct classes of structures with similar EM responses but different physical features can provide added latitude to accommodate other considerations such as fabrication constraints and tolerances. The network's ability to produce a variety of multifunctional metasurface designs is demonstrated by presenting a bifocal metalens, a polarization‐multiplexed beam deflector, a polarization‐multiplexed metalens, and a polarization‐independent metalens. [ABSTRACT FROM AUTHOR]

A new strategy for designing single‐band and dual‐band balanced bandpass filters (BPFs) based on a circular patch resonator is proposed in this study. By altering the output balanced ports of the balanced BPFs to inhibit or transport the TM31 mode of the circular patch resonator under the differential‐mode (DM) excitation, a single‐band or dual‐band balanced BPF can be realized. As the odd modes could be restrained under the common‐mode (CM) excitation, the balanced BPFs could feature high CM suppression in the DM passbands. Meanwhile, several perturbing tactics are introduced to improve the performance of the balanced BPFs. Specifically, perturbation vias are presented to disturb the electric field distribution to enhance the CM suppression in the DM passbands, and slots are applied on the circular patch resonators to perturb the current distribution to amend the second DM passband of the dual‐band balanced BPF. The proposed single‐band and dual‐band balanced BPFs are fabricated and characterized. Good agreement can be achieved between the simulated and measured results of the fabricated balanced BPFs, which validates the feasibility of the proposed design method. [ABSTRACT FROM AUTHOR]

Meta‐devices have attracted great interest due to the unprecedented capabilities of manipulating wavefronts. Complex‐amplitude hologram can provide high‐quality images that can be free of ghost images and undesired diffraction orders. However, conventional meta‐holograms usually operate at a single band with phase‐only modulation. Here, a reflective 2‐bit meta‐hologram is proposed to operate with independent complex‐amplitude modulations at two frequency bands. The high‐efficiency meta‐atom is composed of a top perforated metallic layer, on which two C‐shape split ring resonators (CSRRs) are located in the centers of a circular hole and an annular slot. By tuning the sizes of the two CSRRs, dual‐band 2‐bit phase modulations can be individually achieved, while the amplitude profile can be continuously tailored at each band by rotating the corresponding CSRR without affecting the phase responses. Based on this emerging meta‐atom, a dual‐band bifocal metalens is demonstrated numerically and a bispectral meta‐hologram is validated both numerically and experimentally at two widely used communication bands. The proposed method features all desirable advantages of the coding metasurfaces with extra degrees of freedom by providing independent frequency control and amplitude modulation, which can provide great opportunities in multifunctional applications with enhanced performance and boosted information capacity. [ABSTRACT FROM AUTHOR]

Metasurface has drawn much attention due to its unprecedented wave‐front manipulation abilities with an ultrathin flat profile. However, the metasurface as a diffractive device usually suffers from chromatic aberrations, which greatly hinders the design freedom at different wavelengths. In this work, it is demonstrated that this limitation can be overcome by a multifunctional metasurface with completely independent phase modulations at three arbitrarily wavelengths. Specifically, a novel single‐layer tri‐spectral meta‐atom composed of three alternatively arranged slot and metallic resonators is proposed to operate at three distinct wavelengths, where 2π geometric phase modulations under the circularly polarized incidence can be achieved independently by rotating the corresponding resonators. As proof of concept demonstrations, a tri‐wavelength vortex beam generator and a meta‐hologram are designed to verify the proposed method. First, a vortex beam generator with arbitrary topological charge numbers at three wavelengths is designed and verified through theoretical calculation and full‐wave simulation. Moreover, a meta‐hologram generated by the computer‐generated holography is designed to display three frequency selective holographic images on the same image plane. The tri‐wavelength meta‐hologram is validated through theoretical calculation, full‐wave simulation, and experiment. The experimental results agree very well with the numerical ones, demonstrating the attractive capabilities of multifunctionalities at three wavelengths. [ABSTRACT FROM AUTHOR]

In this letter, a triple‐mode bandpass filter based on isosceles right‐angled triangular (RAT) resonator with three magnetic walls is proposed. To realize the triple‐mode filter, the RAT resonator is perturbed by two metalized via‐holes around the center. These via‐holes form an LC resonant unit with the patch. Also, the via‐holes make mode shifting of the TM010Z mode while not affecting the TM110Z mode in order to form the passband. The proposed filter is fabricated and measured. The center frequency is 5.51 GHz and the fractional bandwidth is 20%. The minimum in‐band insertion loss and return loss are measured to be 1.26 dB and 20.5 dB. The measurement results show that the filter has featured both compact size and excellent in‐band responses. [ABSTRACT FROM AUTHOR]

Abstract: A miniaturized dual‐band filter using novel triple‐folded substrate‐integrated waveguide (TFSIW) resonators is proposed in this paper. The proposed TFSIW is enabled by specially designed folding structures, which leads to significant size reduction. The 2 lowest resonant modes, namely folded TE102 mode and folded TE101 mode in the TFSIW cavity, are utilized to achieve a dual resonance response with a small frequency ratio. To validate the design concept, a dual‐band filter operating at 1.91 and 2.32 GHz is designed, fabricated and characterized. Good agreement has been achieved between the simulation and measurement results. Moreover, the size of the proposed TFSIW resonator has been reduced for 86% compared with the conventional SIW resonator (assuming the same frequency ratio). [ABSTRACT FROM AUTHOR]

Since its invention, metasurface has been widely utilized to achieve nearly arbitrary wavefront control based on phase only modulation at single wavelength. To achieve better performance or exotic functions, it is desirable to demonstrate metasurfaces capable of realizing both phase and amplitude modulations. Meanwhile, the wavelength-dependent behavior of the metasurface is one of the critical limitations in existing metasurface structures. Specifically, single-layer metasurfaces with the capability to tailor both phase and amplitude at multiple wavelengths have not been reported so far. In this paper, a single-layer meta-atom is proposed which can realize ultrathin metasurfaces with complete phase and amplitude modulations at two THz wavelengths. Several dual-wavelength metalenses and a nondiffractive Airy beam generator operating at two THz wavelengths are numerically demonstrated, the simulated results of which are consistent with the theoretical calculations and design goals. The presented dual-wavelength meta-atom can provide a powerful building block in multiwavelength metasurface designs for controlling electromagnetic waves, including focusing, beam steering, beam generations, hologram, etc. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, we present a dual-band sequential power amplifier (SPA) to provide high efficiency at power back-offs and maximum output power at two separate working frequencies. The proposed SPA, including a carrier amplifier, a peaking amplifier, a power divider, and a combing coupler, is fabricated on Isola I-TeraMTRF boards with 3.45 dielectric constant, 0.0028 loss tangent, and 0.508 mm substrate thickness. The SPA provides 48 and 62% drain efficiency (DE) at 6 dB output back- off (OBO) and maximum output power at 1.1 GHz (first design frequency), and it also provides 52 and 65% DE at 6 dB OBO and maximum output power at 1.5 GHz (second design frequency). The designed SPA achieves above 39 dBm output powers at two working frequencies with about 10 dB gain and ±1.3 dB gain flatness. To the best of the authors' knowledge, it is the first time that a dual-band SPA is reported and demonstrated experimentally. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:99-102, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a dual-band amplifier with flexible frequency ratios. The amplifier features novel Wilkinson power divider/combiner with dual-band property that allows large frequency ratio (2.16-4.9) between its first and second operating bands. The measured combining efficiency on a stand-alone combiner is 97% at 2.25 GHz and 75% at 5.25 GHz. A 2.25/5.5 GHz prototype amplifier is tested to verify dual-band functionality. Measured linear gains are 12.85 dB and 12.07 dB at the first and second frequency bands, respectively. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2242-2247, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, we present a simplified Doherty power amplifier (DPA) architecture for the easy implementation of dual-band operation. The proposed DPA structure eliminates the 35 Ω quarter wavelength impedance inverters used in the conventional DPAs by matching the output impedances of the carrier and peak amplifiers of the DPA to other values (e.g., 100 Ω). The electrical lengths of the offset line and the phase compensation line are carefully chosen to enhance the Doherty effect (high efficiency at back-off power level) at two assigned frequency bands. Broadband matching networks are also designed to increase the operation bandwidths at the two designed bands. To prove the design concept, a dual-band DPA is designed and measured. In the first frequency band (550-650 MHz), the designed DPA provides 60.6-76.3% drain efficiency (DE) at full output power, 46-54.9% DE at 6 dB of output power back-off (OBO); in the second frequency band (950-1050 MHz), the designed DPA provides 51.4-61.2% DE at full output power, 35-38% DE at 6 dB of OBO. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:953-956, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a coupler using Pi-shaped coupled lines for dual-band operations. In this design, two open circuited stubs are tapped at both ends of a coupled line structure to realize the 90° phase changes at two frequencies. The designed structure is used in place of a conventional quarter wavelength transmission line for dual-band application. For verification, a 3-dB branch line coupler with operating frequencies of 0.95 and 1.52 GHz is designed. The simulated and measured results are in good agreement with each other. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:501-504, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, a novel multiband branch-line coupler employing multiband transmission lines is designed to operate at three different frequencies. To realize multiband operations, a Pi-type-based multiband transmission line network with open- and short-ended stubs is employed. Specifically, the Pi-type line is applied to realize the dual-band operation at the first two working frequencies. For the third operating frequency, the open- and short-ended stubs are tapped at the center of the Pi-type line. ABCD-matrix is employed to derive the design formulas for the proposed triband transmission line. To verify the design concept, a planar coupler operating at 1/2.5/4.5GHz is designed and fabricated. The simulation and measurement results show good agreement with the design theory. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2841-2845, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT An eye-opening measurement circuit provides information about the signal quality of the high-speed data through the band-limited channel. Thus this information can be used to evaluate the channel performance, especially when the communication environments are changing constantly. By implementing this as a system-on-a chip, it is possible to realize the reconfigurable system such as an adaptable feed-forward equalizer, which will adapt itself through the changes of the communication channel. Moreover, the highly integrated single-chip eye-opening monitoring block can achieve more efficient and cost-effective communication chip test. In this article, we propose a new eye-opening measurement circuit, which can work up to 10 GHz. Using the fall time and rise time of the signal, which are affected by intersymbol interference, the corresponding characteristic is converted to DC values to assess the channel performance. The proposed eye-opening measurement circuit and tunable delay line are fabricated in 0.18-µm CMOS technology. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2136-2141, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT In this letter, utilizing multimetal layers in the CMOS process, an ultra-slow-wave on-chip coplanar waveguide (CPW) transmission line with interdigital loaded stubs and floating strips is proposed. From the full-wave 3D EM simulation and measurement results, it is found that the proposed on-chip transmission line features smaller size and lower loss comparing to traditional on-chip CPW transmission lines. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:604-606, 2017 [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a novel approach to shrink the size of the conventional phased array antenna fed by Butler matrix. The proposed size reduction of the phased array antenna is obtained by designing the whole system to operate at dual frequency bands. Due to the dual-band operation, an N-element phased array antenna can be used to generate 2N radiation beams, leading to a great size reduction. To verify this design concept, a dual-band feed network is built based on a dual-band 4 × 4 Butler matrix. By integrating this dual-band feed network with a four-element antenna array, eight distinct radiation beams can be realized. An experimental prototype operating at 5 and 8 GHz is designed and fabricated. It can achieve the same function as the conventional phased array antenna system using single-band 8 × 8 Butler matrix, realizing a great size reduction. The simulated and measured results show good agreement with the design theory. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1391-1396, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, a transversal filter with winner-take-all variable gain amplifiers is investigated to improve the performance of a feed-forward equalizer. The proposed equalizer structure with nine gain cells has wide bandwidth and improved voltage headroom, at the same time achieving the low power consumption per gain cell. The proposed equalizer is fabricated in a 0.18 μm CMOS process and shows the successful compensation with 30 and 60 in backplanes with 3 Gbps signal. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2666-2670, 2013 [ABSTRACT FROM AUTHOR]

This article presents the design of a microwave bandpass filter with tunable center frequencies and reconfigurable transmission zeros. The tuning of the center frequencies is realized by loading varactors at the ends of the λ/2 resonator. The reconfiguration of transmission zero is implemented through varactors in combination with tapped λ/4 stubs. The equivalent circuit models of the tunable filters are provided. The transmission zeros can be set to be at the lower side, the upper side, or both sides of the passband. The design concept is demonstrated by measurement results for both one transmission zero case and two transmission zeros case. The tuning frequency ranges are 680-890 MHz and 680-1020 MHz for one zero case and two zeros case, respectively. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1526-1531, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27628 [ABSTRACT FROM AUTHOR]

We propose a dual-band microwave device to detect the dielectric changes in polydimethylsiloxane microfluidic channels. Such a device, which consists of two dual-band Wilkinson power dividers (working at 2 and 5 GHz) and two 90° dual-band microstrip lines (providing 180° phase difference at two operating frequencies), is very sensitive for identifying dielectric material changes. Moreover, by operating at two frequencies simultaneously, it can improve the measurement stability/robustness. Compared with other existing microwave microfluidic sensors, the proposed device features enhanced measurement stability with the same level of measurement sensitivity (up to −80 dB cancellation level). © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2691-2694, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27188 [ABSTRACT FROM AUTHOR]

A parallel-strip line fed antenna with very wide bandwidth is presented in this article. This wideband antenna is designed as a combination of two individual antenna elements that are connected in a way inspired by the log-periodic antenna array technique. To miniaturize the size of the structure, metamaterial-based antennas are used as the basic radiating elements. The proposed antennas are designed on FR4 substrate and measured results show that it has a very wide bandwidth from 0.68 to 120 GHz with a VSWR < 3 for frequency range from 0.68 to 3.2 GHz and VSWR < 2 for the remaining bandwidth, with relative stable radiation characteristics. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2646-2650, 2012; this online at wileyonlinelibrary.com. DOI 10.1002/mop.27150 [ABSTRACT FROM AUTHOR]

This article presents the design of Fermi antenna array with improved gain for radar respiration measurement. A six-element Fermi antenna array working at 5.8 GHz is optimally designed and integrated with the respiration radar system. Specifically, to easily feed the antenna array as well as reduce the total size of the array system, a feeding network based on 0-degree phase shifters is used along with suitable impedance transformers. The whole system is proposed to function as a radar sensor for respiration rate measurement, which is known as a promising noncontact and noninvasive approach for lung cancer radiotherapy. The measurement results verify the improved performance of the proposed system for radar respiration measurement in motion-adaptive lung cancer radiotherapy. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1649-1654, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26871 [ABSTRACT FROM AUTHOR]

A low-profile, compact and easily integrated antenna for RF/microwave applications is presented in this article. The designed antenna works around 430 MHz and can be easily scaled to other frequencies. Metamaterial-inspired slot loop antennas are used as the radiating elements. To shrink the total size of the antenna, periodical structures are loaded to the original slot loop. It is found that with this modification, the total size of the antenna is reduced and the impedance matching of the antenna is improved. To further improve the performance of the proposed antenna, a floating ground plane and a parasitic slot were added, made possible by the multilayered structure of the antenna. As a result, the bandwidth and gain of proposed antenna are increased. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:219-223, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25654 [ABSTRACT FROM AUTHOR]

ABSTRACT A tunable sequential power amplifier (SPA) is presented in this article. The proposed SPA, including a tunable coupler, a carrier amplifier, a peaking amplifier, and a combining coupler is fabricated on Isola I-TeraMTRF boards with 3.45 dielectric constant and 0.508 mm substrate thickness. A conventional SPA (nontunable) is also designed for reference and performance comparison. Measurement results show that the tunable SPA provides about 2 dB higher gain and 1 dB higher power output comparing with the reference design. The measurement results match well with the analysis. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2899-2901, 2015 [ABSTRACT FROM AUTHOR]

A narrow beam monopole antenna is realized by embedding the antenna within a periodic metallic wire array. The 2D wire array is designed to have an effective index of refraction smaller than unity (neff < 1) at the X-band frequencies (8–12 GHz), within which the antenna operates. The narrow beam effect due to the low refractive index of the wire medium is demonstrated in both simulation and experiment. Measured antenna properties including return loss and radiation pattern are in good agreement with simulation results. This simple and straightforward antenna design methodology can be applied at any microwave frequency. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2341–2345, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23653 [ABSTRACT FROM AUTHOR]

A novel ultra‐compact wide‐band microwave cross‐over using lumped components is presented for the first time. The proposed cross‐over is composed by inductors and capacitors, and the explicit design equations are derived based on the even–odd mode method. The size of the proposed cross‐over is 1 × 1 cm2, and the bandwidth is 20–30%. Full‐wave electromagnetic simulations are performed and an experimental prototype is fabricated to demonstrate the novel design concept. The measurement results match well with the theoretical and numerical results. [ABSTRACT FROM AUTHOR]

In this article, a novel balanced wideband filter based on microstrip coupled lines is proposed. It features characteristics such as wide bandwidth, compact size, and good common-mode suppression. The proposed balanced filter was calculated analytically, simulated by full-wave electromagnetic simulator and validated by the measurements. The calculated, simulated, and measured results are in good agreement with each other. The experimental results show that it can allow the differential-mode signal to be transmitted with low insertion loss across a wide frequency band, whereas the common-mode signal will be well suppressed. The fractional bandwidth of the designed filter is 88%. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1139-1141, 2014 [ABSTRACT FROM AUTHOR]

The design and implementation of dual‐band duplexers is presented. The proposed method works well for duplexers with narrow bandwidths and it gives the designers the flexibility to achieve desired return loss levels at different frequency bands. To verify the design concept, dual‐band duplexers based on cavity‐type resonator topologies are designed, fabricated and tested. Good agreement is achieved between the theoretical synthesis results, the simulation results and the measurement results of the duplexer prototype. [ABSTRACT FROM AUTHOR]

Metasurfaces are planar structures that can offer unprecedented freedoms to manipulate electromagnetic wavefronts at deep‐subwavelength scale. The wavelength‐dependent behavior of the metasurface could severely reduce the design freedom. Besides, realizing high‐efficiency metasurfaces with a simple design procedure and easy fabrication is of great interest. Here, a novel approach to design highly efficient meta‐atoms that can achieve full 2π phase coverage at two wavelengths independently in the transmission mode is proposed. More specifically, a bilayer meta‐atom is designed to operate at two wavelengths, the cross‐polarized transmission efficiencies of which reach more than 70% at both wavelengths. The 2π phase modulations at two wavelengths under the circularly polarized incidence can be achieved independently by varying the orientations of the two resonators constructing the meta‐atom based on Pancharatnam–Berry phase principle. As proof‐of‐concept demonstrations, three dual‐wavelength meta‐devices employing the proposed meta‐atom are numerically investigated and experimentally verified, including two metalenses (1D and 2D) with the same focusing length and a vortex beam generator carrying different orbital angular momentum modes at two operation wavelengths. Both the simulation and experimental results satisfy the design goals, which validate the proposed approach. [ABSTRACT FROM AUTHOR]

Information security holds paramount importance in the contemporary information society. Here, a novel cryptography method is proposed based on the multi‐wavelength complex‐amplitude metasurface, which can achieve a high security level by generating a frequency‐selective key as an additional layer of protection. Moreover, the quality of the decrypted holographic images can be significantly improved by employing the complex‐amplitude encoding method and the modified visual secret sharing scheme, which adopts a new superposition operator to prevent fidelity loss. As a proof‐of‐concept demonstration, a prototype metasurface sample is designed, fabricated, and characterized, where the measured results agree very well with the numerical ones and the design goals. The proposed method can reinforce security level and improve fidelity of the decrypted message, rendering it appealing for applications in communication and anti‐counterfeiting. [ABSTRACT FROM AUTHOR]

The Airy beam has attracted considerable interests due to its remarkable non‐diffracting, self‐bending, and self‐healing properties. An auto‐focusing Airy (AFA) beam can be achieved by constructing two counter‐propagation Airy beams, which is a novel method to generate focusing effect. Traditionally, because of the complexity of the generation mechanism, it is hard to realize the Airy beam with complex amplitude modulation. The reported ones usually require bulky optical systems and typically work at one single wavelength. Here, a general scheme is proposed to launch dual‐band Airy and AFA beams based on the single‐layer geometric metasurface, consisting of a newly designed meta‐atom that can realize independent complex amplitude modulations at two arbitrary terahertz wavelengths. Based on the proposed meta‐atom, the aforementioned attractive properties of the Airy beam are demonstrated at two terahertz wavelengths. Besides, the dual‐band AFA beams are illustrated to have the practically important adjustability of the focal length. Furthermore, owing to the self‐healing property, the proposed focusing scheme (i.e., AFA beam) shows a much better capability of circumventing the PEC obstacles compared to the conventional metalens, which could have potential applications in various important scenarios such as biomedical imaging/therapy and nondestructive evaluation with compact size and multiwavelength functionalities. [ABSTRACT FROM AUTHOR]

A novel dual‐band transmission line with flexible phase shifts is presented. To realise dual‐band operations, the proposed transmission line is constructed by series‐connected coupled lines and open‐ended stubs. Using this structure, flexible characteristic impedances and electrical lengths can be designed to operate at two frequencies. Moreover, the proposed dual‐band transmission line features a wide range of realisable frequency ratios and a flexible structure. For practical applications, a planar dual‐band 3 dB branch‐line coupler operating at 2/5.2 GHz is designed using the proposed dual‐band transmission line. The simulation and measurement results agree very well with the design theory. [ABSTRACT FROM AUTHOR]

A novel dual‐band balun is presented. The designed 3‐port balun is based on a 4‐port structure with the fourth port terminated as an open end. Being a 4‐port symmetrical network, even–odd‐mode analysis is used to analyse the balun's performance. Based on the derived explicit design equations, a balun is designed to operate at 1.1 and 2 GHz. Numerical simulations show a low reflection coefficient S11, equal magnitude of −3 dB as well as 180° phase difference at the output ports. To validate the theoretical and numerical simulations, the proposed balun is fabricated on the FR4 Isola printed circuit board and measurement results match well with the design theory. [ABSTRACT FROM AUTHOR]