The proposed microstrip antenna is based on fractal techniques and designed for wireless applications. The radiating element is an A-shaped triangle on which fractal concept is applied. Fractal concept is applied on the proposed A-Shaped Fractal Microstrip Antenna (ASFM-Antenna), similar to English alphabet letter A. Further the analysis and verification of result is achieved by testing the fabricated antenna and also comparison of simulated and experimental results. Von Koch's snowflake concept is used in which a single line is divided into four new lines, and it is done at each side of the triangle. This step is repeated. In this paper, a two-iteration Koch generator is used, thus the proposed antenna is designed. Simulations are carried out using commercially available HFSS (High Frequency Structure Simulator) based on finite element method. The antenna is simulated and fabricated, and results are recorded. It is found that simulated and experimental results are in close agreement with each other. The antenna resonates at 11.44 GHz, 13.178 GHz, 15.482 GHz, 19.902 GHz and 23.529 GHz. Hence, X-band [8.2-12.4 GHz], Ku-band [12.4-18 GHz] and K-band [18-26.5 GHz] are the frequencies of operating bands under consideration.

In this paper, we report the formulation to account for dielectrics in a first principles multipole-based cable braid electromagnetic penetration model. To validate our first principles model, we consider a one-dimensional array of wires, which can be modeled analytically with a multipole-conformal mapping expansion for the wire charges; however, the first principles model can be readily applied to realistic cable geometries. We compare the elastance (i.e. the inverse of the capacitance) results from the first principles cable braid electromagnetic penetration model to those obtained using the analytical model. The results are found in good agreement up to a radius to half spacing ratio of 0.5-0.6, depending on the permittivity of the dielectric used, within the characteristics of many commercial cables. We observe that for typical relative permittivities encountered in braided cables, the transfer elastance values are essentially the same as those of free space; the self-elastance values are also approximated by the free space solution as long as the dielectric discontinuity is taken into account for the planar mode.

A synthesis problem of a 2D array of thin linear vibrators, whose geometric centers are located at the nodes of a flat rectangular grid with double periodicity solved. The problem can be formulated as follows. A 2D antenna array radiates monochromatic electromagnetic waves into free space. Suppose that the array radiation pattern (RP) can be scanned in space by varying complex surface impedances of separate vibrators. Then, it is necessary to determine vibrator surface impedances to control the direction of the RP maximum. The analytical solution of the impedance synthesis problem, as an alternative to a numerical solution of a two-dimensional equation system, was obtained under two assumptions: the vibrators are excited by electric currents of equal amplitudes, and the RP of each radiator does not differ from that of an isolated radiator. Verification of theoretical formulas will be done by comparing them with relations known for one-dimensional equidistant arrays.

A self-consistent time-domain travelling-wave model for the simulation of self-assembled quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) is developed. The 1-D time-domain travelling-wave model takes into consideration of time-varying QD optical susceptibility, refractive index variation resulting from intersubband free-carrier absorption, homogeneous and inhomogeneous broadening, and QD spontaneous emission noise source. Carrier concentration rate equations are considered simultaneously with the travelling wave model. Effects of temperature on optical susceptibility and carrier density in the active region are taken into account. The model is used to analyze the characteristics of 1.3-μm oxide-confined QD InAs-GaAs VCSEL. The field distribution resulting from time-domain travelling-wave equations, in both the active region and distributed Bragg reflectors, is obtained and used in finding the device characteristics including light-current static characteristics considering the thermal effect. Furthermore, the dynamic characteristics and modulation frequency response are obtained in terms of inhomogeneous broadening.

An annular-ring element for building a miniaturized bandstop frequency selective surface (FSS) structure which possesses a superior performance with respect to electromagnetic wave polarizations and incident angles is introduced in this paper. The proposed element has prominent miniaturization characteristics with a unit dimension of 0.061λ×0.061λ, where λ represents the free-space wavelength corresponding to resonant frequency. Miniaturization of the proposed FSS element is achieved by constructing special meandered strips in geometry and arranging lumped components between the elements. The advantage of this method lies in its great simplicity in tuning the resonant frequency of FSS by adjusting values of the printed capacitors rather than rebuilding the geometry. The obtained FSS also exhibits a stable performance in terms of angle stability and polarization insensitivity. Prototypes of the proposed FSS are fabricated and measured to verify design method. Measurements are well in line with simulation results.

In this paper, a broadband transition structure from microstrip line to slotline with band-notched characteristic is proposed. To match the 50 Ω microstrip line, 4 Chebyshev impedance transformations are used in the transition structure, and its bandwidth is widened. There is a fan-shaped radial line at the microstrip terminal. A U-shaped slot is etched on the microstrip line with stepped impedance matching to achieve band-notch characteristic. By changing the length of the slot, the band notch is realized at different frequencies. Simulation and optimization of the transition structure are made by using the high frequency simulation software HFSS in this paper to achieve the band-notch function at 3.37-3.84 GHz and 10.67-11.14 GHz. In the rest of the band, return loss S₁₁ is less than -15 dB, and voltage standing wave ratio (VSWR) is less than 1.5.

This paper proposes a two-dimensional (2-D) inverse synthetic aperture radar (ISAR) imaging method with nonuniformly obtained angle samples. A one-dimensional (1-D) radar image, a range profile, is obtained using frequency samples within a given bandwidth. 2-D ISAR images are then obtained by acquiring the Doppler spectrum using range profiles obtained from multiple observation angles having a constant interval. However, when ISAR images are obtained by applying the range-Doppler imaging method for a target scattered signal with nonuniform angle samples, a clear image cannot be obtained. In this paper, we propose a method to generate a covariance matrix from a nonuniform angle sample and obtain an ISAR image based on the multiple signal characterization (MUSIC) technique. The proposed method can be applied to the target scattering signal using a search radar, which observes target with nonuniform aspect angles. We present a scattering signal model of a target for the search radar and provide ISAR images obtained by applying the proposed method to simulated and measured data, respectively. Results reveal that the proposed method improves image quality and reduces computation time compared to the conventional method.

The aim of this paper is to present a compact coplanar waveguide (CPW) fed switchable UWB antenna as an antenna filter with adjustable notched frequency bands. Novel miniaturized tunable resonators are also presented to achieve notched bands. The antenna is made tunable in notched frequency bands without any modification in the basic structure. These stopbands are made tunable just by varying values of the capacitors according to our desired applications. The antenna structure is very compact having overall dimensions of 24×30.5 mm² with partial ground plane.The proposed small size, variable, low cost and low weight antenna with good propagation characteristics will pave the way for UWB wireless communication applications.

Ultrablack materials play an essential role in astronomical observation and many thermal applications. Many material systems such as vertically aligned carbon nanotubes have produced extraordinarily high absorption, but require complicated fabrication. Here we report a single step self-masked etching process performed on compressed-coal graphite plates on a silicon substrate, which produces an ultrablack material with 0.7% hemispherical reflectance in the visible region and specular reflectance below 0.7% between 850 nm and 10 μm. Nanoscopic pieces of silicon are ripped off the substrate and deposit on the graphite resulting in carbon nanoneedle structures, which grow linearly with etching time reaching a height of 5.7 μm after 60 minutes.

A wideband circularly polarized magnetoelectric dipole antenna fed by a Γ-shaped structure is investigated. In the design, a pair of vertical plates connected to ground work as a magnetic dipole, while a pair of rotationally symmetric horizontal plates with strips bent downward work as an electric dipole. And four metallic plates are vertically added on edges of the ground, forming a cavity reflector with four gaps to improve the axial ratio (AR) bandwidth. Measurements show that the antenna has a wide impedance bandwidth of 102% from 1.35 GHz to 4.2 GHz for voltage standing wave ratio (VSWR) ≤ 2 and a 3-dB AR bandwidth of 79.7% from 1.6 GHz to 3.72 GHz, over which the antenna gain varies from 5.4 dBic to 10.6 dBic. Furthermore, the antenna exhibits right-hand circular polarization and has good unidirectional radiation characteristic. The proposed antenna can be applied to wideband wireless applications.

An implantable magneto-electric antenna (IMEA) aiming for operation at ultra-wideband (UWB: 3.1-10.6 GHz) frequency spectrum is presented for biotelemetry usages for the first time. The IMEA is composed of a horizontal planar bowtie radiator, from whose middle the antenna is excited, and a vertically inclined rectangular radiator. The two radiators are complementary and correspond to electric and magnetic dipoles, respectively. The radiators are built over a square dielectric material (ε_r = 6, σ =0.0005) with a cavity for embedding suitable accompanying circuitry system. The IMEA with its biocompatible insulator (PEEK: ε_r = 3.2, tan δ = 0.01) measures 1456 mm³ in volume. HFSS software was used to carry out numerical optimization of the IMEA with a simple multilayered model of body tissue (Skin, Fat and Muscle) as the host environment. The simulated result of the proposed IMEA shows over 90% impedance bandwidth (S₁₁<-10 dB) and records a remarkable high gain of 2 dBi within 70% bandwidth. The radiation efficiency is around 50%, and a unidirectional radiation pattern with little back lobe is observed.

An LED array with 2N-1 lines and N rows is designed, which consists of red, blue, and far-red LEDs. The red and blue LEDs with N lines and N rows are uniformly and intervally arranged. The central distance between adjacent red and blue LEDs is d. The far-red LEDs are filled in-between every two lines of red and blue LEDs, which results in an array of far-red LEDs with N-1 lines and N rows. The central distance of adjacent far-red LEDs is also d. By using the imperfect Lambertian model, the irradiance distribution of the LED array with N being even and odd is derived in the reference plane, respectively. Also, solving equation of the optimal distance d is presented. Numerical results show that irradiance distributions of the three mixed-color, red, blue, and far-red lights of the LED array are uniform in the reference plane. Ratios of R/B and R/Fr are both relatively uniform in the reference plane. The ratio of R/B in the case of N being even is more uniform than that in the case of N being odd. However, the ratio of R/Fr is opposite.

In this paper, a compact metamaterial quad-band antenna is presented. The antenna is designed from a unit cell of asymmetric extended-composite right/left handed transmission line (E-CRLH TL) as the main resonator part and a 50 Ω coplanar waveguide (CPW) as the feeding part. The design concept and resonant frequencies are analyzed and discussed. The results show that the proposed antenna exhibits four frequency bands covering GSM810, WLAN 2.45/5.5 GHz and WiMAX 3.5 GHz bands. The overall size of the fabricated antenna is only 57.2 mm×31.2 mm×1.6 mm and is very small compared with other proposed quad-band antennas. In addition, a good agreement can be seen among the estimated resonant frequencies, HFSS simulated and measured results.

A dual-frequency InSAR imaging technique is proposed to estimate the position and motion parameters of a moving target, including velocity and cross-track acceleration. By applying a dual-frequency technique, phase ambiguity is effectively removed to obtain accurate estimation of motion parameters.

An alternative formulation of the Small Perturbation Method (SPM) in solving electromagnetic scattering from multi-layer random rough surfaces to resolve singularities in spectral integrals is presented. Non-monotonic permittivity changes will allow a multi-layer structure with flat interfaces to support guided modes. The presence of these guided modes translates to poles in the zeroth order Green's function of the media for the surface fields. The poles appear in the first and second order perturbation solutions based on a iterative procedure. Thus, evaluating the spectral integrals to obtain the spatial fields becomes problematic. The Sommerfeld integration path instead of real line integrals is introduced by analytic continuation of the integrand into complex spectral space. It is verified that this alternative spectral integration method is valid for both monotonic and non-monotonic cases.

To improve stability of time-domain integral equation, a stable implicit scheme is proposed to solve the transverse-magnetic (TM) electromagnetic scattering from 2D conducting objects. The time-domain electric-field integral equation (TD-EFIE) was adopted and expressed using second-order derivative of the magnetic vector potential. To reduce numerical error, the magnetic vector potential was approximated by second-order central finite difference. TM transient scattering from 2D conducting objects was calculated by an implicit marching-on-in-time (MOT) scheme. To obtain stable numerical results, the TD-EFIE MOT implicit scheme was firstly combined with the time-averaging technique. The accuracy and stability of the scheme were demonstrated by comparison with the results from inverse discrete Fourier transform technique.

A Frequency Selective Surface (FSS) reflector with wideband response for 4G/X-band/Ku-band is proposed. The wideband FSS reflector consists of cascaded dual-layer patch FSS which is etched on separate layers of FR4 substrate. The targeted frequency range is 5-16 GHz. A wide stopband of 10.4 GHz (100% percent bandwidth) is obtained with two layers in cascade. The Equivalent Circuit (EC) method is used to approximate the simulated results. An extensive parametric study is also carried out to understand the effect of various combinations of FSS layers and their disposition. A panel of final FSS is fabricated where measured and simulated results agree well.

A compact ultra-wideband (UWB) top-loaded antenna for multiservice wireless applications is presented. It consists of a metal cone radiator, a small ground plane, four shorting poles and a top-cross plate, among which the top-cross plate with two slots shorted to the ground planet is important to broaden the low frequency bandwidth. The measured result shows that an improved impedance bandwidth of 185% from 1.17 to 30 GHz is achieved. The omnidirectional stable radiation pattern in the horizontal plane is also obtained. The volume of proposed design is approximately 0.0173λ³ at 1.17 GHz. With the small volume and UWB characteristic, the design of the proposed antenna is very suitable for many wireless standards such as Softbank (1427-1500 MHz), DCS1800, PCS1900, UMTS, IMT2000, Wi-Fi (2.4 GHz), WiMAX (2.2-5.5 GHz), UWB (3.1-10.6 GHz), and satellite communication (X band, Ku band and Ka band).

In this paper linear and nonlinear properties of graphene at millimeter wave frequency band are investigated. The nonlinear properties of the graphene are utilized to design frequency multiplier and mixer for millimeter wave applications. A patch of graphene is deposited on the dielectric image guide that will generate higher order harmonics. The amplitude of harmonics is optimized based on the dimensions of the graphene patch on top of the dielectric image guide. A frequency multiplier and mixer are designed, which utilize the second harmonics generated through graphene. The nonlinear behavior of the proposed designs has been simulated in the 50-75 GHz input signal frequency range. A conversion efficiency of -23 dB is obtained for the second harmonic for the frequency doubler. The frequency mixer is designed to mix two frequencies in V-band using dielectric image guide as the waveguide. A -28 dB conversion efficiency is simulated on a dielectric image-guide platform.

In this paper, we present a compact tri-band bandpass filter (BPF) using two stub-loaded dual mode resonators (SLDMRs) combined with intra-coupled internal resonators. The designed filter operates at 1.575, 2.4, and 3.45 GHz, corresponding to the GNSS, WLAN, and WiMAX applications, respectively. The passbands of the filter are determined by odd- and even-mode frequencies created by the SLDMR and the internal open loop resonator inside of it. The corresponding even-mode frequency can be adequately tuned by adjusting the length of the stub while the odd-mode frequency is fixed. Two transmission zeros (TZs) are introduced on each side of the passband to improve the selectivity of the implemented filter. Five TZs around the edges of three passbands make the passbands highly isolated, and these transmission zeros can be placed according to the desired choice. The proposed tri-band BPF was designed, fabricated and measured, and the simulated and measured results corresponded very well.