An efficient quantum mechanical approach is formulated to model electron-photon interactions in nanoscale devices. Based on nonequilibrium Green's function formalism, electron-photon interactions and open boundaries in the nanoscale systems are taken into account in terms of self-energies. By separating different components in the electron-photon interactions, optical absorption and emission processes in the devices can be analyzed, and the method allows studies of different optoelectronic devices. In conjunction with density-functional tight-binding method, photo-induced current and other optical properties of nanoscale devices can be simulated without relying on empirical parameters. To demonstrate our approach, numerical studies of gallium nitride nanowire solar cells of realistic sizes are presented.

An X-band radiator as an open-ended waveguide with a hybrid dielectric insert is proposed. The insert is in the form of a parallelepiped, which fills the entire cross section of the waveguide and constitutes a Teflon matrix with local inhomogeneities in the form of dielectric cylinders with a different permittivity. The design allows for forming various near-field distributions and, hence, the radiator performance by means of definite combinations of the local inhomogeneities can be modified. A number of configurations in the location of air and quartz cylinders are investigted. The calculated and experimental results are in good agreement. The proposed approach to the near-field formation of the aperture antenna is promising, because the variety of possible configurations in the location of local inhomogeneities with different permittivity provides new opportunities in terms of designing both single radiators and antenna arrays.

For wideband common-mode noise suppression in high-speed differential signals, a low-cost compact filter is proposed and designed by etching two coupled C-slotlines on the ground plane. It is found that the bandwidth of the common-mode stopband over -10 dB is from 2.4 GHz to 6.35 GHz with no degradation of the differential-mode insertion loss and group delay within the wide common-mode stopband. In time domain, the differential signal eye diagram is not deteriorated as well. In addition, an equivalent circuit model is developed and provides a quickly prediction of the common-mode stopband. The results show a good consistency between the simulations and measurements.

This work investigates an adaptive, parallel and scalable integral equation solver for very large-scale electromagnetic modeling and simulation. A complicated surface model is decomposed into a collection of components, all of which are discretized independently and concurrently using a discontinuous Galerkin boundary element method. An additive Schwarz domain decomposition method is proposed next for the efficient and robust solution of linear systems resulting from discontinuous Galerkin discretizations. The work leads to a rapidly-convergent integral equation solver that is scalable for large multi-scale objects. Furthermore, it serves as a basis for parallel and scalable computational algorithms to reduce the time complexity via advanced distributed computing systems. Numerical experiments are performed on large computer clusters to characterize the performance of the proposed method. Finally, the capability and benefits of the resulting algorithms are exploited and illustrated through different types of real-world applications on high performance computing systems.

Efficient and accurate computer simulation of wave phenomena plays an important role in invention, development, cost reduction and optimization of many systems ranging from ultra-high-speed electronics to delicate nanoscale optical devices and systems. Understanding the physics of many modern technological applications such as optical nanomaterials calls for the solution of very complex computer models involving hundreds of millions to billions of unknowns. Integral equation (IE) methods are increasingly becoming the method of choice when comes to numerical modeling of wave phenomena for various reasons specifically since the introduction of FMM and MLFMA acceleration that tremendously reduce the computational costs associate with naive implementation of IE methods. In this work, a new acceleration technique specifically designed for the modeling of large, inhomogeneous, finite array problems it introduced. Specifically we use the new method for modelling and design of some metamaterial structures. At last, the presented method is used to study the some of the undesired random effects that occur in metamaterial array fabrication.

This paper presents a compact 2.45 GHz single feed directional circularly polarized (CP) microstrip antenna for radio frequency identification (RFID) applications. The proposed antenna comprises a dodecagonal microstrip patch embedded with an irregular polygonal slot, fabricated on an FR4 substrate. Two antennas, one with right-handed circular polarization (RHCP) and the other with left-handed circular polarization (LHCP), both resonating at a frequency of 2.45 GHz are presented. The measurement results show a 3 dB axial ratio bandwidth of 5.5%, a 10 dB impedance bandwidth of 5.7% for both the antennas, a peak gain of 4.82 dBi for RHCP antenna and 4.67 dBi for LHCP antenna. In addition, the antennas provide symmetrical patterns with 88˚ half-power beam width. The overall size of the antenna is 50 mm × 50 mm × 1.6 mm and offers an area reduction of 21.17%.

A new design of dual-band L1/L2 GPS antenna is proposed. The antenna generates dual-band circularly polarized radiation by exciting a cross-slot and ring-slot of a concentric circular aperture using a proximity-coupled feed. Parametric studies show that the matching and axial ratio bandwidth of L1 (1.575 GHz) and L2 (1.227 GHz) bands can be independently tuned by alternating the ring radius and slot length. The range of frequency ratio and 3 dB center frequency can be highly adjusted by slot's parameters. The size of the antenna is 73 mm × 73 mm × 6.4 mm including the ground, corresponding to 0.29λ × 0.29λ × 0.026λ at 1.227 GHz.

A new compact microstrip UWB bandpass filter with triple band-notched characteristics is presented in this paper. The initial circuit topology and its corresponding electrical parameters of the basic microstrip UWB BPF are desired by a variation of genetic algorithm (GA) technique. Then, triple-notched bands inside the UWB passband are implemented by coupling a novel triple-mode stepped impedance resonator (TMSIR) to the main transmission line of the basic microstrip UWB BPF. The triple-notched bands can be easily generated and set at any desired frequencies by varying the designed parameters of TMSIR. To illustrate the possibilities of the new approach, a microstrip UWB BPF with triple-notched bands respectively centered at frequencies of 5.2 GHz, 6.8 GHz, and 8.0 GHz is designed and fabricated. Measured results agree well with the predicted counterparts.

By using a composite coupling structure for coplanar waveguide (CPW)/microstrip, a new dual-band bandpass filter (DBBPF) stacking inverted Y-shaped CPW resonators and rectangular ring resonators is proposed. Two resonant frequency bands are simultaneously excited by the CPW feed line, However, it can be convenient to tune individually. Several transmission zeros are realized to improve the selectivity of the filter and achieve wide stopband rejection. Good agreement between simulated and measured results demonstrates the validity of this DBBPF.

A broadband Fabry-Perot cavity antenna (FPCA) operates at Ka band with high gain and dual-polarization is reported. The proposed antenna employed a double-sided complementary-circular partially reflective surface (PRS) to enhance the directivity bandwidth. A square patch coupled by two orthogonal slots and fed by two microstrip lines was applied as the primary feed to achieve dual-polarization operation. To further improve the impedance bandwidth and directivity, a series of metal vias were suggested to surround the primary patch. This FPCA design was verified by the measurements. The experimental results show that the common impedance bandwidth of the two ports for the reflection coefficient (S₁₁) below -10 dB is 2.5 GHz from 34 GHz to 36.5 GHz (7.1%), which covers the common 3 dB gain bandwidth of the two ports. At the center frequency of 35 GHz, the measured peak gains at the two orthogonal ports are 16.1 dBi and 15.1 dBi, respectively. The isolation between the two ports is higher than 30 dB within the bandwidth.

To enable the quest for high data rates in telecommunications, wide-band radio designs as well as antennas are required. This paper demonstrates a unique bandwidth enhancement technique for L-probe fed patch antenna. This is a novel technique to enhance patch antenna bandwidth with desired radiation properties. One circular shape main patch and two elliptical shape parasitic patches on PCB give wide-band response by exciting multiple resonances. The designed antenna array gives almost 45%, -10 dB impedance matched relative bandwidth. This is a very simple and inexpensive patch antenna solution for the wide-band wireless application. A two-element array of this antenna has been formed, and wide-band radiation properties of the array are reported.

Compared with traditional monostatic synthetic aperture radar (SAR), bistatic SAR (BiSAR) has stronger advantages in terms of anti-interference and anti-strike abilities. However, the complex system structure of BiSAR brings new difficulties to imaging processing. In order to make the imaging algorithms of traditional monostatic SAR apply to BiSAR imaging as well, this paper proposes an equivalent monostatic model for BiSAR. This model mainly provides two benefits: (1) The equivalent monostatic range history has the form of hyperbolic function; (2) The equivalent monostatic velocity of any scattering point in the observed scene, with respect to the radar platform, is not only the same but also invariant with the equivalent monostatic range. Due to the above benefits, a novel wavenumber domain algorithm (WDA) is further proposed for BiSAR imaging. Finally, the experimental results demonstrate that the proposed algorithm is effective and feasible.

In this paper, the design of a printed circuit antenna based on lotus flower patch of a miniaturized profile is proposed. The antenna consists of three layers including a patch and a ground plane of a thin copper layer separated by a Roger RT/duroid®5880 substrate for high gain-bandwidth product applications including the portable biomedical devices. The patch structure is patterned with triangular defects to provide a fractal structure. Nevertheless, the ground plane is defected with Electromagnetic Band Gap (EBG) structures. The antenna is found to show a first resonant mode around 3 GHz, while the other frequency modes are obtained around 4.2 GHz and 6 GHz which are below -10 dB. Moreover, the antenna operates over the frequency range from 7.8 GHz up to 15 GHz with a bore-sight gain varing from 4 dBi up to 6 dBi when operates in free-space environments. The antenna size is reduced to a 32 mm×28 mm×0.5 mm using shorting plates on the substrate edges. The antenna performance characteristics are examined using CST and HFSS commercial software packages, which are based on the Finite Integration Technique (FIT) and the Finite Element Method (FEM), respectively. Finally, the antenna performance is tested experimentally for both S₁₁ spectrum and radiation patterns to show an excellent matching with the obtained numerical results.

In this paper a broadband radio frequency identification (RFID) tag antenna for the ultrahigh-frequency (UHF) band is designed. The proposed antenna consists of a first-order Hilbert fractal structure and a spiral structure. In order to ensure the conjugate matching between the tag antenna and the electronic chip, a T-matching structure is employed. The interaction between two radiating elements makes the proposed antenna a fractional bandwidth of 20% over the frequency range of 820 MHz-1010 MHz and a small size of 0.2092λ₀×0.099λ₀. Simulated and measured results validate the good performance of the designed tag antenna.

Scattering of light by metal-coated dielectric nanocylinders periodically distributed along a cylindrical surface is investigated both theoretically and numerically. The structure is under the authors' interest because of its practical application in design and fabrication of plasmonic devices such as plasmonic ring resonators, Plasmonic Crystals and THz waveguides. The method is based on the T-matrix approach and the field expansion into the cylindrical Floquet modes. The method is rigorous, straightforward and can be easily applied to various cylindrical configurations with different types and locations of the excitation sources. Scattering cross section and absorption cross section of three and four silver (Ag) coated-dielectric nanocylinders periodically situated along a cylindrical surface are studied. Near field distributions are investigated at particular wavelengths corresponding to the resonance wavelengths in the spectral responses. Special attention is paid to the unique and interesting phenomena characterizing the cylindrical structure composed of the metalcoated nanocylinders such as: a) localization of the field at the outer and inner interfaces of the metal-coated nanocylinders; b) excitement of the field in the gap region between the nanocylinders through the coupled plasmon resonance and c) strong confinement of the field inside the cylindrical structure. Detailed investigations have shown that unique phenomena characterizing the cylindrical configurations of the nanocylinders can be realized using a relatively simple structure composed of three nanocylinders and there is no need to further increase a number of the scatterers (nanocylinders).

The ultra-wide band characteristic basis function method (UCBFM) is an efficient approach for analyzing wide band scattering problems because ultra-wide characteristic basis functions (UCBFs) can be reused for any frequency sample in the range of interest. However, the errors of the radar cross section calculated by using the UCBFM are usually large at low frequency points. To mitigate this problem, an improved UCBFs is presented. Improved UCBFs (IUCBFs) are derived from primary characteristic basis functions and secondary level characteristic basis functions (SCBFs) by applying a singular value decomposition procedure at the highest frequency point. This method fully considers the mutual coupling effects among sub-blocks to obtain the SCBFs. Therefore, the accuracy is improved at lower frequency points because of the higher quantity of current information contained in the IUCBFs. Numerical results demonstrate that the proposed method is accurate and efficient.

This paper mainly deals with the problem of target detection in compound-Gaussian clutter with orthogonal frequency division multiplexing (OFDM) radar. First, the OFDM measurement model is developed to compound-Gaussian clutter by taking advantage of frequency diversity of OFDM radar waveform and we devise a generalized likelihood rate test (GLRT) detector where the target scattering coefficients and clutter covariance matrix are unknown. Then, we propose an adaptive waveform design scheme based on maximizing Mahalanobis distance of the distributions under two hypothesises to improve the detection performance. Finally, the effectiveness of the proposed detector as well as the adaptive waveform design method is demonstrated via numerical examples.

In this paper, a CPW-fed reconfigurable clover-shaped antenna with switchable circular polarization is proposed. This antenna consists of a clover-shaped patch, four p-i-n diodes, and two pairs of quarter-circular-rings. By electrically controlling the four p-i-n diodes to form two orthogonal bow-tie shaped current paths, the proposed antenna can be operated in two modes: the left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) modes. Two pairs of quarter rings are used to improve the bandwidth and AR performance of the antenna. The measured 10-dB reflection coefficient and 3-dB axial-ratio (AR) bandwidth of the prototype antenna is approximately 12.3% and 19%, respectively, which is enough for some wireless applications such as WLAN IEEE 802.11 b/g (4%). Gain and radiation pattern are also presented.

A compact circularly polarized (CP) crossed dipole antenna with chip inductors and square rings loaded for Global Positioning System (GPS) is proposed in this letter. The CP radiation is produced by crossing two dipoles through a 90° phase delay line of a vacant-quarter printed ring. Four chip inductors inserted in the dipole arms and four square rings loaded at the back of the dipole arms are introduced to obtain a compact dipole size. The plane dimension of the proposed antenna is 28 mm×28 mm, which can be widely used for GPS handheld devices. Details of the proposed antenna design and results are presented and discussed.

The PMCHWT-IE-FFT-BURA is applied to the wideband analysis of electromagnetic scattering property of homogeneous targets. Over the broad frequency band, the fast computation is achieved by the Maehly expansion on the basis of the Chebyshev approximation of the electric and magnetic currents. On the Chebyshev sampling points, PMCHWT-IE-FFT greatly reduces the memory requirement by sparsely storing the impedance matrix and decreases the computational time to the greatest degree by block acceleration of the matrix-vector product. Finally, numerical results show that the proposed method can make efficient analysis of wideband property of homogeneous targets without sacrificing accuracy much.