Applications of localized surface plasmon resonance (LSPR) such as surface enhanced Raman scattering (SERS) devices, biosensors, and nano-optics are growing. Investigating and understanding of the parameters that affect the LSPR spectrum is important for the design and fabrication of LSPR devices. This paper studies different parameters, including geometrical structures and light attributes, which affect the LSPR spectrum properties such as plasmon wavelength and enhancement factor. The paper also proposes a number of rules that should be considered in the design and fabrication of LSPR devices.

This paper focuses on the electromagnetic compatibility domain, coupling in microwave circuits and wideband (WB) impedance matching in time domain using a purely temporal method, such as the centered-points Finite Difference Time Domain (FDTD). The paper here presents a new approach of WB impedance matching in transient regime and coupling context, of active circuits such as multiple complex nonlinear components (represented here by metal semiconductor field-effect transistors (MESFETs)), using Nonuniform Multiconductor Transmission Lines (NMTL) with frequency dependent losses and FDTD as modeling method. The FDTD method has several positive aspects such as the ease to introduce nonlinear components in the algorithm, the ease to use NMTL and the gain in simulation time and memory space. Also the FDTD method allows the study of WB impedance matching in time domain without recourse to the frequency domain. Systematic comparisons of the results of this method with those obtained by PSpice are done to validate this study. These comparisons show a good agreement between the method presented here and PSpice. The technique presented in this paper shows higher efficiency and ease to implement when compared to PSpice in regard to the treatment of frequency dependent losses, or shapes of transmission lines.

The observation data obtained from 4-D synthetic aperture radar system is sparse and non-uniform in the baseline-time plane. Hence, the imaging results acquired by traditional Fourier-based methods are limited by high sidelobes. Considering the sparse structure of actual target space in high frequency radar application, a novel 4-D imaging scheme based on compressive sensing is proposed in this paper. Firstly, the azimuth-slant range image is acquired by traditional pulse compression. Then, the basis matrix and the measurement matrix are constructed based on the sparse distribution of the radar positions and the signal form after the azimuth-slant range compression. Moreover, a weighted matrix related to the supporting field of the target is introduced to the cost function. Finally, the elevation-velocity image is reconstructed with this new cost function. Simulation results confirm the effectiveness of the proposed method.

The main purpose of this paper is to separately estimate the important surface parameters (soil moisture and roughness) by using full polarimetric bistatic measurements. The results provide a basis for new satellite application of future bistatic measurement systems such as the TanDEM-X satellite mission. Initially, bistatic X-band measurements, which have been recorded in the Bistatic Measurement Facility (BMF) at the DLR Oberpfaffenhofen, Microwaves and Radar Institute, will be presented. The bistatic measurement sets are composed of soils with different well-known statistical roughness scales and different moistures. The BMF has been calibrated using the Isolated Antenna Calibration Technique (IACT). The validation of the calibration was achieved by measuring the reflectivity of fresh water. In the second part, the assessment of the surface parameters (soil moisture and surface roughness) using the well calibrated data introduced in the former related part, will be detailed. The validation of the specular algorithm by estimating the soil moisture of two surfaces with different roughness scales will be reported. Additionally, a new technique using the coherent term of the Integral Equation Method (IEM) to estimate the soil roughness will be presented, as well as the sensitivity of phase and reflectivity with regard to moisture variation and therefore the penetration depth was evaluated. Current results demonstrate a non-linear relationship between the signal phase and the soil moisture, as expected, confirming the possibility of using DInSAR to measure variations in soil moisture.

A four-layer metallization Cr-Cu-NiP-Au with amorphous and nonmagnetic NiP as a barrier layer is one of the promising candidates for use in microwave integrated circuits. Multi-section Wilkinson broadband 1:2 power divider circuits are delineated photolithographically on alumina substrates metallized by Cr, TiW, Ni, NiP, copper and gold using different metallization processes. The adhesion and dc resistivity are compared for different metallization scheme. Testing and evaluation have been carried out for multi-section Wilkinson broadband 1:2 power divider in the 10 MHz-6 GHz frequency range for Cr-Cu-Au, TiW-Ni-Au and Cr-Cu-NiP-Au to see the effect of NiP. Insertion loss, return loss and isolation are measured and compared. The microwave properties do not show any appreciable differences due to the various metallizations.

A low profile CPW fed millimeter wave rectangular slot antenna operating with a wideband; centered at 94 GHz has been designed, fabricated and tested on a 10 μm silicon diaphragm. To improve the bandwidth of the conventional slot antenna a C-shaped tuning stub has been incorporated. Measurement results show that the antenna operates from 75 to 105 GHz with a reflection coefficient better than -10 dB. At its resonant frequency the fabricated slot antennas have a reflection co-efficient ranging from -25 dB to -35 dB. The bandwidth of the antenna with a tuning stub was found to be over 30% at -10 dB. By using the slot antenna with a C-shaped tuning stub the bandwidth has been shown to improve, which could be used for several Millimeter wave applications.

Using a new combined approach, the effect of the uniaxial anisotropic dielectrics on the resonant frequency and radiation field of an equitriangular patch antenna is presented in this paper. The problem is analysed in the spectral domain using the moment method and an electric field integral equation combined with a mathematical approach. However, the dyadic Green's functions corresponding to the proposed structure are separately developed and the Fourier transform of the basis current components are calculated mathematically using ``the reference element" method. Numerical results show that the change in the resonant frequency and the radiation patterns of the antenna is due primarily to a small disturbance of the substrate's nature. Then the effect of the uniaxial anisotropic materials is a significant parameter and most essential on the microstrip antenna characterization.

The Sources Reconstruction Method (SRM) is a non-invasive technique for, among other applications, antenna characterization. The SRM is based on obtaining a distribution of equivalent currents that radiate the same field as the antenna under test. The computation of these currents requires solving a linear system, usually ill-posed, that may be very computationally demanding for commercial antennas. Graphics Processing Units (GPUs) are an interesting hardware choice for solving compute-bound problems that are prone to parallelism. In this paper, we present an implementation on GPUs of the SRM applied to antenna characterization that is based on a compute-bound algorithm with a high degree of parallelism. The GPU implementation introduced in this work provides a dramatic reduction on the time cost compared to our CPU implementation and, in addition, keeps the low-memory footprint of the latter. For the sake of illustration, the equivalent currents are obtained on a base station antenna array and a helix antenna working at practical frequencies. Quasi real-time results are obtained on a desktop workstation.

In this paper, a hybrid method combining equivalence principle algorithm with physical optics is proposed to solve the radiation problem of antenna mounted on electrically large platform. It is based on domain decomposition method which is a scheme for multi-scale problems. Equivalence principle algorithm can simulate antenna accurately, and physical optics is an asymptotical method to obtain current distribution on the electrically large platform. Continuity of currents is considered when the conductor on the platform is decomposed into two parts by the equivalence surface. In addition, a preconditioning for the hybridization of equivalence principle algorithm and physical optics is discussed. Numerical results demonstrate the feasibility of the hybrid method.

In the previous works, based on winding function theory, the calculation of reluctance machine inductances is carried out using numerical integration or inexact analytical equations based on approximated Fourier series expansions of the inverse air gap function. In this paper, development in Fourier series of the inverse air gap function has not been used, but a closed form analytical equation is developed for inductances calculation. This leads to a very precise computation of the inductances of the faulted machine and more accurate results. Moreover, all space harmonics ignored by the Fourier series expansions of the inverse air gap function will be included in the model. Derived comprehensive equation allows calculating time varying inductances of reluctance machines with different static, dynamic and mixed eccentricities in the frame of a single program. Inductances obtained by the proposed method are compared to those obtained from FE results. A satisfactory match was found between them.

In this paper, we use the concept of stub loadings of planar microstrip antennas to convert a single band antenna into a dual-band antenna used for WLAN. We load a planar triangular monopole (PTM) antenna by combline stubs attached to the edges of patch in order to obtain a second resonance frequency. The simple PTM antenna is first designed to produce the lower resonance frequency and the geometry of combline stubs is then optimally designed to generate the higher resonance frequency to realize a dual-band or a wideband antenna. Three prototype models of PTM antennas are designed, fabricated and measured. Their performances verify the concept of inductive loadings of planar antennas by combline stubs for the realization of dual-band and wideband performance for WLAN.

A planar folded dipole antenna with triple-band operation for WLAN and WiMAX applications is proposed. It comprises a pair of symmetrical branch arms, which occupy a compact size of 35(L)x4(W) mm² to be easily embedded inside a portable device as an internal antenna. By properly designing the branch radiating strips, three operating bands covering 2.39-2.5 GHz, 3.3-3.94 GHz, and 5.06-6.06 GHz can be acquired with the antenna. Moreover, the antenna's resonance can be appropriately adjusted to optimize the radiation performance for actual application. A fabricated prototype of the proposed antenna is tested and analyzed. Experiments show that good omnidirectional coverage and stable gain variation to enhance communication quality for WLAN/WiMAX operations can be obtained with the antenna.

Despite its popularity, the conventional Vivaldi antenna has long suffered from some design problems, such as tilted beam, low or inconsistent directivity and gain, complicated design and fabrication methods, and limited size reduction. These setbacks make its progress lag on the fast track of technological demand. Thus, the antenna overall performance is anticipated to improve by incorporating negative index metamaterial (NIM) into the design method, plus, it is also tunable. In this study, the design uses linearly-tapered shape-loading structure, as its projected performance crucially depends on the space in between the antenna arms, a prerequisite to further boost its performance when combined with NIM technology. A unique slitting approach synchronizes the integration between the Vivaldi antenna and NIM where a single layer NIM piece is simply snugged into the slit perpendicular to the middle antenna substrate. The major improvement in the spotlight is the capability of NIM to focus the entire beam so that it can radiate to the targeted direction. The measurement results are similar to the simulations in terms of high gain, where the gain and directivity of the antenna are increased up to 4 dB. The contrast of overall performance between the plain modified Vivaldi antenna and the ones with NIM evidently asserts the expected contribution of snug and boost method applied and attests its significant potentials for a broad range of ultra-wideband applications.

Analytic expressions for the scattered magnetic vector potential from an infinitely long DB circular cylinder are presented. An arbitrarily oriented electric dipole is considered as a source of excitation that induces surface currents on the DB circular cylinder. Approximate far field expressions for magnetic vector potential are also derived in this setting. Numerical results of the scattering from the DB cylinder are also presented and compared with those of the PEC cylinder.

In this paper, linearly polarized transmitarray is investigated as to avoid the usage of multilayers for improving the bandwidth of transmitarray. The transmitarray is formed from a single dielectric sheet by perforating selected areas of the material. A perforated dielectric layer is divided into square cell elements. Each cell has four holes with the same diameters. Holes with different diameters in the cell elements are used to allow continuous tuning of the transmitted signal's phase over 360^o range with a maximum loss of 3.6 dB at 10 GHz. The transmission coefficient versus the diameter of the holes is calculated by using the finite integration technique. The results are compared with those calculated with transmission line method for verification. The focal-to-diameter ratio of the transmitarray is optimized for lower side lobe level and highest transmitarray gain. A comparison between the transmitarray and the reflectarray with the same aperture area is illustrated.

Recent trends in propagation modeling indicate the study of mobile radio propagation modeling with the help of electromagnetic formulations which traditionally has been explained with empirical methods. These empirical methods were preferred by the cellular operators in their radio planning tools due to their ease of implementation and less time consumption. In the present study, AWAS electromagnetic code and conventional prediction methods have been employed to explain the observed results of ten base stations mainly in the near field zones of GSM 900 MHz band situated in the urban and suburban regions around Delhi in India. The suitability of the above models in terms of prediction errors and standard deviations are presented. Path loss exponents deduced from the observed data have been explained by Sommerfeld's formulations. Recent trends indicate the study of mobile radio propagation modeling with the help of electromagnetic formulations which traditionally has been explained with empirical methods. These empirical methods were preferred by the cellular operators in their radio planning tools due to their ease of implementation and less time consumption. In the present study AWAS electromagnetic code and conventional prediction methods have been employed to explain the observed results of ten base stations mainly in the near field zones of GSM 900 MHz band situated in the urban and suburban regions around Delhi in India. The suitability of the above models in terms of prediction errors and standard deviations are presented. Path loss exponents deduced from the observed data have been explained by Sommerfeld's formulations.

In this work, the linearity of a high gain Harmonic Self Oscillating Mixer (HSOM) is analyzed. In order to obtain high conversion gain, the working point of the HSOM is established close to a Hopf bifurcation point. The traditional figures of merit used to characterize the linearity of conventional mixers cannot be directly applied to characterize the behavior of autonomous circuits, because of the influence of the input RF signal power on the autonomous signal parameters. The 1\,dB compression point and the third order distortion will be analyzed as a function of the harmonic content and maximum gain of the circuit. From the collected data, the optimum harmonic content and the maximum conversion gain of the HSOM can be selected, for a particular application, in order to minimize the output IF signal distortion.

In this paper, linear lightning diffusion into a Faraday cage is studied. The high-altitude Electromagnetic Pulse (HEMP) and nearby lightning are used as examples for a uniform field drive and the direct-strike lightning adjacent to the enclosure is used as a worst-case configuration of a line source excitation. The time-derivative of the magnetic field (HDOT) inside the enclosure for a uniform field drive with a decaying exponential waveform is analyzed and numerically determined. The physically relevant time-derivative of the magnetic field and voltage characterizations of an optimum coupling loop inside the enclosure for a decaying exponential waveform in a worst-case line source coupling configuration are numerically determined. First, the impulse and the unit step response peaks are shown to bound the decaying exponential peaks. Next, a simple fit function for a decaying exponential peak HDOT or a voltage bound for a single-turn loop inside the Faraday cage is constructed from peak responses of the unit step and impulse limiting cases. Excitations used are from (1) a uniform field drive of HEMP or nearby lightning and (2) a line source of direct-strike lightning. Comparisons of HDOT and voltage bounds of the fit function and actual numerical evaluations are given in Table 3.

A novel peer-to-peer (P2P) interconnection architecture in a 60-GHz millimeter-wave (mm-wave) radio-over-fiber (RoF) access network is proposed for the first time. In this scheme, the beating of the lightwaves for downlink and P2P transmissions at the photodiode (PD) can provide signal up-conversion for both signals. Phase noise and frequency instability between the two independent lightwaves can be eliminated by a self-heterodyned radio frequency (RF) receiver (envelope detector) located on the user terminal, which can also down-convert simultaneously the two mm-wave signals to their associated intermediate frequencies. No high-frequency clock sources or other high bandwidth devices are required for signal up/down-conversions. A proof-of-concept experimental demonstration has also been carried out. Error-free transmission of the 1-Gb/ signals is achieved over 50-km fiber (downlink) or 25-km fiber (P2P) plus 4-m air link.

This paper presents lumped dual-frequency impedance transformers for frequency-dependent complex loads. According to different dual-frequency allocations of a complex load in Smith chart, three types of impedance matching networks are presented respectively. Several kinds of lumped circuit blocks are used as basic element for constructing these transformers with design formula deduced. Various examples are given for describing the design procedures.~Good features such as big frequency ratio and big matching bandwidths are demonstrated. These lumped dual-frequency impedance transformers have advantage of much compacter dimensions compared to distributive solutions.