This paper investigates the use of double concentric circular ring elements arranged in a sub-wavelength grid on a single layer of substrate, in an effort to enhance the beam-scanning capability of reflectarrays. The work is done at 10 GHz on a 405 mm×405 mm aperture. In addition to a broad gain bandwidth, the reflectarray with a sub-wavelength grid exhibits a superior beam-scanning performance compared to the one with λ/2 grid. The measured results show that the reflectarray with 0.3λ grid spacing achieves a 1-dB gain bandwidth of 22% with an aperture efficiency of 56.6%. With the reflectarray fixed, this paper studies the possibility of beam scanning by displacing the feed horn laterally. The results show that beam scanning of ±15º is possible while preserving the broadband characteristics. It is also observed that a 1-dB gain bandwidth of 28% is achieved for the 0.3λ array when the feed is displaced laterally with an angle of 30º.

With the advancement of wireless networks and cloud computing, people are becoming increasingly surrounded by a variety of displays - rich electronic devices: TV, Phone, Pad, Notebook and other portable or wearable devices. These electronic products put high demands on the quality of the visual interface. Paper-like displays are reflective and do not require a backlight. They have received much attention after electrophoretic-based electronic paper displays were commercialized in 2004. Paper-like displays combine excellent reading experience with ultra-low power consumption. In particular, their outdoor readability is superior to transmissive liquid crystal displays (LCDs) and organic light emitting devices (OLEDs). In this paper, we give an overview onvarious paper-like display technologies with emphasis of the status and future development of electrophoretic display and electro-fluidic display principles. We focus on both technologies because electrophoretic displays have been commercialized successfully, and electro-fluidic display has high potential to deliver video and full color.

In this paper, a compact asymmetric coplanar strip (ACS)-fed printed monopole antenna for tri-band WLAN/WiMAX applications is presented. The proposed antenna is composed of a circular-arc-shaped stepped monopole with dual operating frequencies at 2.4/5.7 GHz and a simple circular-arc-shaped strip with the third operating frequency at 3.5 GHz. The three resonant frequencies of the antenna can be controlled by adjusting the geometries and the sizes of the stepped monopole, the strip and the ground plane. The antenna occupies a very compact size of 22.1×12 mm² including the ground plane, has nearly omnidirectional radiation characteristics and reasonable gain in the operating bands. The simple feeding structure, compactness and uniplanar design make it easy to be integrated within the portable device for wireless communications.

Equilateral-triangular slot antennas with modified edges for wideband circular polarization are proposed in this paper. Circular polarization was firstly obtained by adding two asymmetric perturbations to two edges of triangular slot. Then fractal-like boundaries were adopted in the antenna design for size reduction and broadband operation. Two antenna prototypes for RFID readers were fabricated to cover RFID UHF band and ISM 2.4 GHz band, respectively. Measured results show that the presented antennas obtain fairly wide 3-dB axial ratio bandwidths of 15.7% (820-960 MHz) and 19.8% (2.18-2.66 GHz).

An analytical expression of AC resistance of a single-layer air-core Helmholtz coil is presented. Proximity effects between both bundles and strands of litz-wire as well as skin effect are considered. To obtain an accurate analytical expression of proximity effect on bundle level and strand level, a precise distribution of magnetic field is discussed. The analytical expression of AC resistance and quality factor is verified with the experimental results, and the theoretical predictions are in agreement with the measured results.

A novel dual-band filter based on substrate integrated waveguide (SIW) is presented in this paper. The proposed filter is composed of two filters with different center frequencies and bandwidths, where they share the input and output ports with source-load coupling using rectangular SIW cavity structure. Muliti-transmission zeros have been obtained through electrical coupling between the source and load, which improves the frequency-selective characteristics of the filter greatly. Finally, a Ku-band substrate integrated waveguide dual-band filter with bandwidths of 220 MHz and 120 MHz was finally designed, fabricated, and measured. The measurement results are found to be in good agreement with the simulation results.

In this paper, a number of different application fields of inorganic luminescent materials are being discussed. In a tutorial manner, it will be shown how device requirements are being translated into properties the luminescent materials need to have. To this end many different material properties that have a strong influence on the device performance are discussed, such as the shape, the spectral position of the absorption- and emission bands and the decay time of the emission. The light yield under excitation with ionizing radiation, the energy resolution and the occurrence of afterglow are being treated as well. Subsequently, strategies are shown how to optimize these properties. Examples are given for light sources (fluorescent lamps and LEDs), radiation sources used for disinfection purposes and also for devices used in medical imaging and in horticultural applications.

A broadband printed quadrifilar helical antenna (BPQHA) integrated with a broadband feeding network for satellite communications is proposed. Using a multiple arm technique, satisfactory antenna characteristics over a wide bandwidth are realized. To feed the antenna, a novel compact broadband feeding network composed of a frequency independent 180° out-of-phase power divider, two Wilkinson power dividers and two broadband 90° phase shifters is designed. The measured boresight gain remains positive with a reflection coefficient lower than -11 dB over a bandwidth of approximately 26%. The axial ratio is below 1.7 dB and the half-power beamwidth is more than 120° over the same bandwidth. Details of the proposed antenna design are provided and discussed, as well as the experimental results.

A novel design of miniaturized dual-bandantenna based on mushroom cell and interdigital capacitor is presented in this paper. Four transmission line (TL) elements are loaded in a microstrip antenna, and each one is composed ofamushroom cell and interdigital capacitors. The interdigital capacitors contribute to the series capacitance and metallicvia-hole of mushroom structuresresult in the shunt inductance in the equivalent circuit model. The antenna works as a zeroth-order (f₀= 2.51 GHz) and first-order (f₁ = 3.78 GHz) resonant antenna with varied radiation patterns. Omnidirectionalradiation pattern and unidirectional radiation pattern are obtained at 2.51 GHz and 3.78 GHz, respectively.The overall size of the antenna is only 0.25×0.25×0.017λ₀³ (at f₀= 2.51 GHz). The proposed antenna features compact structure, low profile and easy fabrication. Good agreement between the simulated and measured results is also achieved, validating our design concept.

A new metamaterial-inspired polarization reconfigurable microstrip antenna is presented in this paper, in which a square slot is etched on the ground plane and two PIN diodes are mounted across the slot for polarization reconfigurability. A complementary split ring resonator (CSRR) can be formed by integrating the square slot with two diodes. By controlling the working states of two diodes, we can change the gap position of CSRR which will alter the polarization of the microstrip antenna. Therefore, the polarization of the microstrip antenna can be switched among linear polarization (LP), left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), respectively. The planar electromagnetic bandgap (EBG) structure is further introduced to extend the bandwidth of the 3dB axial ratio. In addition, the proposed metamaterial-inspired antenna with agile polarization reconfiguration can be feasibly controlled by using a simple biasing circuit. The simulations and experiments are given to verify the effectiveness and correctness of the proposed reconfigurable antenna design.

A novel ultra wideband (UWB) multiple-input-multiple-output (MIMO) antenna with different polarizations and band-notch characteristics is proposed in this letter. The antenna consists of two monopole antenna radiating elements with gradual change structure, which are placed perpendicularly to each other and printed on each side of the substrate to achieve a wide bandwidth and different polarizations. Band-rejected filtering property in the WLAN band is achieved by etching a H-shaped slot and employing a resonant L-shaped strip on two antenna elements. The proposed antenna has a small size of 27×37×1 mm³ with a bandwidth of 128.6% (2.35-10.82 GHz). Within the required band, the isolation for the two ports exceeds 18 dB. The envelope correlation coefficient is also measured.

Circularly polarized graphene based transmitarray for terahertz applications is proposed. The characteristics of the graphene material is explained. The cell element of the transmitarray is made of square Quartz cell. Dual circular graphene rings are printed on both sides of the Quartz substrate. The graphene ring radius is varied to change the transmission coefficient phase and magnitude. The effect of the graphene chemical potential on the transmission coefficient is demonstrated. Transmitarray is composed of 9×9 unit cell elements. A circularly polarized circular horn is used to feed the transmitarray at f=6 THz. The left- and right-hand field components in the E- and H-plane are determined. The variation of the gain and the axial-ratio with the frequency are explained. The peak gain is 18.63 dB and 1-dB gain bandwidth is 6.8%. The transmitarray produces a circular polarization from 5.5 THz to 6.5 THz.

The recent extension of the orbital angular momentum (OAM) concept from optical to microwave frequencies has led some researchers to explore how well established antenna techniques can be used to radiate a non-zero OAM electromagnetic field. In this frame, the aim of the present paper is to propose a new approach to generate a non-zero OAM field through a single patch antenna. Using the cavity model, we first analyze the radiated field by a standard circular patch and show that a circular polarized (CP) TM_nm mode excited by using two coaxial cables generates an electromagnetic field with an OAM of order ±(n-1). Then, in order to obtain a simpler structure with a single feed, we design an elliptical patch antenna working on the right-handed (RH) CP TM₂₁ mode. Using full-wave simulations and experiments on a fabricated prototype, we show that the proposed antenna effectively radiates an electromagnetic field with a first order OAM. Such results prove that properly designed patch antennas can be used as compact and low-cost generators of electromagnetic fields carrying OAM.

This paper presents a new method for antenna pattern retrieval from reflection coefficient measurements. A reflective load with known reflective properties is placed close to the aperture of the antenna under test. The reflection coefficient of the antenna is measured at the antenna feed with multiple different reflective loads. The antenna pattern is then solved from the measurements with an inversion method. This paper derives and verifies the analytical foundations needed to implement the method, and demonstrates the method both by simulations and experiments for a pyramidal horn antenna at 30 GHz.

In this paper, a new approach for the radar cross section (RCS) reduction of patch array antenna is proposed. Complementary split-ring resonators (CSRRs) are etched on the ground of the proposed patch antenna array. A conventional 1 × 4 patch antenna array is designed with the central frequency of 5.0 GHz. The monostatic RCS of the patch antenna array with CSRRs can be reduced as much as 14 dB compared to that of the conventional array while maintaining almost the same radiation characters. For the case of φ-polarized incident wave, the RCS has been reduced in the angular range of -90° ≤ θ≤+90° in xoz-plane and this angular range is usually less than ±45° when using conventional methods of RCS reduction.

Due to the traditional recognition researches prevalently fastening on HRRP's amplitudes while almost completely neglecting the phases, this paper attempts to directly prove the discriminant availability of HRRP's phases via two proposed fusion recognition strategies. The first strategy includes three sub-processes, respectively, based on phase cosine, phase sine and their fusion. The second strategy also includes three sub-processes, respectively, based on phases, amplitudes and their fusion. Additionally, a trigonometric function couple (TFC) method is used to reduce the phase sensitivity. Several measured experimental results indicate as follows. Firstly, employing TFC can perform much better. Secondly, the two fusion recognition sub-processes apparently outperform the corresponding subprocesses constructing them. Finally, phase information usually has a better noise immunity compared with amplitude information, and fusing phase information into amplitudes may improve the traditional recognition performance. Therefore, the availabilities of HRRP's phases and the two fusion strategies have been experimentally proven.

The analysis of the scattering by a tilted perfectly conducting strip buried in a lossy half-space at oblique incidence is formulated as an electric field integral equation (EFIE) in the spectral domain and discretized by means of Galerkin's method with Chebyshev polynomials basis functions weighted with the edge behaviour of the surface current density on the strip. In this way, a convergence of exponential type is achieved. Moreover, a new analytical technique is introduced to rapidly evaluate the slowly converging integrals of the scattering matrix coefficients consisting of algebraic manipulations and a suitable integration procedure in the complex plane.

A compact coplanar waveguide (CPW) fed asymmetric slot antenna with dual operating bands is proposed. The slot is modified rectangular in shape and asymmetrically cut in the ground plane. A hexagonal patch fed by a two-step CPW is used to excite the slot. The feed itself is slightly asymmetric (shifted, with unequal ground planes). The asymmetric cuts on the slot together with the feed line asymmetry have helped in obtaining ultra wideband impedance matching. An extra resonance at 2.4 GHz for Bluetooth applications is obtained by cutting an additional meandered narrow rectangular shape slit in the ground plane. The prototype of the proposed antenna has been fabricated and tested. The measured 10 dB return loss bandwidth of the proposed antenna is 200 MHz (2.3-2.5 GHz) for the first band and 12.1 GHz (2.9-15.0 GHz) for the second band. The radiation patterns of the proposed antenna are obtained and found to be Omni-directional in H-plane and bi-directional in E-Plane. The measured and simulated results are in good agreement.

The design of a dual-frequency single-layer circularly polarized reflectarray with frequency selective surface (FSS) backing is presented in this paper. The proposed reflectarray consists of rotated cross dipole elements etched on an FSS-backed substrate. Compared with the conventional design, the FSS layer reduces the mutual effect between the elements of two bands between the elements of two frequencies. The technique of element rotation ensures the proposed reflectarray obtain excellent performance of circular polarization. A dual-frequency circularly polarized reflectarray with FSS backing is fabricated and tested. All the simulated and measured results demonstrate these advantages.

A miniaturized Gysel power divider/combiner(PDC) based on planar artificial transmission line (ATL) is presented in this paper. This planar ATL is composed of microstrip quasi-lumped elements and their discontinuities, and the ATL is capable of synthesizing microstrip line with various characteristic impedances and electrical lengths. For demonstration, the simulated and experimental results of the proposed PDC @1 GHz implemented on microstrip are given. Experimental results of the designed PDC agree well with the theoretical predictions. The proposed Gysel PDC circuit not only demonstrates low insertion loss at the fundamental frequency with compact size and high frequency suppression features, but also maintains Gysel PDC's high power-handling advantage. The occupied sizes of the proposed Gysel PDC are merely about 40% of the conventional Gysel PDC.