A new defected ground structure (DGS) with tunable working frequency and reconfigurable bandwidth is proposed in this paper. The prototype combines the conventional DGS with T-shaped patch featuring narrow bandwidth and two such units located symmetrically featuring wide bandwidth. The proposed structure is designed, simulated and measured. By embedding two reversely-set PIN diodes and four varactors, the proposed structure achieves a narrow bandwidth with a tuning range of 21.1% and a wide bandwidth with a tuning range of 24.6%. In comparison, the bandwidth (-10 dB) is about 13.6% for the narrowband state and 49.2% for the broadband state, where an approximately 4-times extension is obtained.

In [1], Hacivelioglu and co-authors criticize my paper, named ``Fringe waves in an impedance half-plane" [2]. Unfortunately, the general scenario of the criticisms is based on misconceptions and lack of basic knowledge in the diffraction theory. Below we give our detailed rebuttals on their comments.

This paper (i.e., [1]) extends PTD to an impedance half-plane problem.

A passive DC magnetic concentrator is designed with transformation optics (TO) and realized by meta-materials. The passive DC magnetic concentrator, based on space compression transformation, can greatly enhance the magnetic field in a free space region, which can be used for e.g. improving the sensitivity of magnetic sensors and increasing the efficiency of wireless energy transmission. The magnetic property of the medium obtained by TO is extremely anisotropic. To solve this, we use magnetic meta-materials made of alternated high-permeability ferromagnetic (HPF) materials and high-temperature superconductor (HTS) materials. We optimize our structure by conducting simulations using the finite element method (FEM), and experimentally demonstrate a strong, 4.74-time enhancement of the DC magnetic field by our meta-material magnetic concentrator. We also demonstrate that a simplified structure with only HPF materials working at room temperature could still give 3.84-time enhancement of the DC magnetic field. The experimental results are in good agreement with the numerical simulations based on FEM.

High-Q inductors are realized on a 3-8 Ω•cm silicon substrate in the buildup of BCB/Cu. Anisotropic wet etching is utilized to remove the silicon in the cavities underneath the spirals from the backside. Examples of 3.5-turn spiral inductors with and without cavity are compared, and their parameter extractions are accomplished with an equivalent circuit model. Compared to the inductor without cavity, the measured peak quality factor of a 8.19-nH inductor with cavity increases from 24 at 0.8 GHz to 39 at 2.5 GHz by 67%, and the inductor with cavity has a wider bandwidth using the same equivalent model. The inductors utilizing this technique have a potential wide application in hand-held RF modules either as part of an off-chip device or as an integrated passive in a silicon interposer.

A novel 180˚ out-of-phase power divider based on stepped-impedance slotline is presented in this article. This power divider employs one T-junction formed by microstrip line and slotline to obtain two out-of-phase dividing signals. Stepped-impedance slotline and lumped resistor are introduced to improve the isolation between output ports. The experimental data show that the proposed power divider has good performance on insertion loss, return losses, isolation, phase balance, as well as group delay over the wide band 5 GHz-10 GHz.

In this paper, a compact tri-band bandpass filter (BPF) using multi-stub-loaded resonator with controllable frequencies is presented. The multi-stub-loaded resonator consists of a main transmission line, two open stubs and a short stub. Characterized by using even- and odd-mode analysis, it is found that the resonator consists three modes, and the modes can be controlled individually, which enables convenient designs of tri-band BPFs. To demonstrate the proposed idea, a tri-band BPF with operating frequencies of 2.45, 3.8 and 5.15 GHz is implemented. Five transmission zeros are generated near the passband edges, resulting in high skirt selectivity. The total size of the filter is 0.19λ_g × 0.13λ_g, featuring compact size. The comparisons of the measured and simulated results are presented to validate the theoretical predications.

Excitation of electrostatic ion cyclotron waves (EICW) in a magnetized dusty plasma by an ion beam is studied taking into account the effect of dust particle size, dust particle charge and dust particle number density variations. The presence of dust grain charge fluctuations modifies the dispersion relation for ion cyclotron waves in dusty plasma. It is shown that in the absence of ion beam, the ion cyclotron mode damps due to dust charge fluctuations and an additional damping dust charge fluctuation mode is induced in plasma. The ion beam propagating parallel to the magnetic field drives ion cyclotron waves to instability via Cerenkov interaction. Using the analytical and numerical results the influence of the relative density of negatively charged dust particles on growth rate of ion cyclotron waves is studied. The dust grain size distribution has also significant contributions on the growth rate of ion cyclotron waves.

A new approach to classify synthetic aperture radar (SAR) targets is presented based on high range resolution (HRR) profiles time-frequency matrix non-negative sparse coding (NNSC). Firstly, SAR target images have been converted into HRR profiles. And the non-negative time-frequency matrix for each of the profiles is obtained by using an adaptive Gaussian representation (AGR). Secondly, NNSC is applied to learn target time-frequency basis of the training set. Feature vectors are constructed by projecting each HRR profile time-frequency matrix to low dimensional time-frequency basis space. Finally, the target classification decision is found with support vector machine and nearest neighbor algorithm respectively. To demonstrate the performance of the proposed approach, experiments are performed with Moving and Stationary Target Acquisition and Recognition (MSTAR) public release SAR database. The experimental results support the effectiveness of the proposed technique for SAR target classification.

A model of solar cell embedding quantum dots in the intrinsic layer of a p-i-n solar cell has been presented. With proper selection of material, size and fractional volume, quantum dots can provide an intermediate band between the valence and conduction bands of the matrix material, which will absorb photons with energy lower than the original bandgap to absorb more incident photons in the otherwise unused spectral irradiance. The design approach to acquire the highest efficiency of the conventional p-i-n solar cell is presented as a benchmark. Quantum dots are then embedded in the intrinsic region of the reference solar cell to improve its efficiency. InAs is chosen to implement the quantum dots, to be embedded in the p-i-n solar cell made of GaAs. With a more packed arrangement of QD's from that in the literatures, the simulation results shows that the efficiency of the conventional GaAs p-i-n solar cell can be increased by 1.05%.

In this paper, a novel and compact dual-band filter with enhanced upper stop characteristics has been presented. Dual band pass filter characteristics are achieved by introducing transmission zero (TZ) in pass band of band pass filter (BPF). The wide band pass filter (BPF) is implemented by combining low pass filter characteristics (i.e. stepped impedance resonator) and high pass filter characteristics (i.e. short stubs). Closed rectangular ring resonator (CRRR) and open loop rectangular ring (OLRR) combination is used to produce two transmission zeros (TZs). One TZ is placed on the pass band of BPF such that resultant filter characteristic consists of two pass bands. However, the second TZ is placed at edge of the pass band in BPF to improve skirt selectivity. The two pass bands are designed to cover two popular wireless bands namely WiMAX (center frequency f₁ (3.5 GHz) and WLAN (center frequency f₂ (5.7 GHz)) bands i.e. 3.35-3.65 GHz and 5.5-5.85 GHz respectively. Equi-ripple low pass stepped impedance resonator (SIR) filter response is responsible for improved and spurious free upper stop band (>20 GHz i.e. >6f₁) and also provides sharp skirt attenuation at upper stop band. The proposed filter is implemented on an RT/Duroid 5880 (ε_r=2.2) substrate with thickness of 0.785 mm and surface area of 19 × 12 sq. mm. Good agreement between simulated and measured results ensures that the proposed filter is a suitable candidate for modern dual band communications.

A compact multiple-input-multiple-output (MIMO) antenna that covers the WLAN (2.4 GHz) and UWB (3.1-10.6 GHz) bands for wireless device applications is presented. The proposed antenna consists of two open L-shaped slot (LS) antenna elements and a narrow slot on the ground plane. The antenna elements are placed perpendicularly to each other to obtain a high isolation, and the narrow slot is added to reduce the mutual coupling between antenna elements at the WLAN band (2.4 GHz). The presented MIMO antenna has a small size of 40×40mm², and the prototypes of antenna is fabricated and measured. The measured results show that the antenna has an impedance bandwidth of larger than 2.4-10.6 GHz with the mutual coupling less than 20 dB in WLAN band and 18dB in 3.1-10.6GHz, making the antenna a good candidate for portable applications.

Based on the Minimum Variance Distortionless Response-Sample Matrix Inversion (MVDR-SMI) method, we propose a novel Adaptive Covariance Estimator (MVDR-ACE) beamformer for adaptation to multiple interference environments. The MVDR-ACE beamformer iteratively determines a minimum number of data samples required while maintaining its average signal-to-interference-noise to be within 3dB from the performance of a theoretical optimum MVDR beamformer and meeting an instantaneous interference cancellation requirement. Finally, based on numerical simulations, we analyze and validate the performance of the MVDR-ACE beamformer. We also compare its performance to the conventional MVDR-SMI beamformer that uses a fixed data sample in its covariance estimator.

An efficient wide-band analysis that combines modified integral equation-physical optics (IE-PO) hybrid formulation with the best uniform approximation is proposed for antennas around an electrically large platform in this paper. The modified single-level Fast Fourier Transform (FFT) algorithm which is based on the subdomain FFT acceleration is employed by interpolating the Green's function and introducing the concept of the empty groups. Furthermore, the correction of the near-interaction is avoided. On the other hand, the best uniform approximation technique is applied to analyze wide-band properties of antennas. Due to the above modifications, the hybrid method needs fewer unknowns and memory requirements than the conventional one.

Mixed near-field and far-field sources localization problem has received significant attention recently in some practical applications, such as speaker localization using microphone arrays and guidance systems, etc. This paper presents a novel space-time matrix method to localize mixed near-field and far-field sources. Using the proposed method, both the direction-of-arrival (DOA) and range of a source can be estimated by the same eigen-pair of a defined spacetime matrix. Therefore, the pairing of the estimated angles and ranges is automatically determined. Compared with the previous work, the presented method offers a number of advantages over other recently proposed algorithms. For example, it can avoid not only parameters matching problem but also aperture loss problem. It has lower computational complexity since the proposed method does not require the high-order statistics or any parameter search. Simulation results show the performance of the proposed algorithm.

In this paper, we investigate electromagnetic problems for nanoscale antennas by using a boundary integral equation method with fast inverse Laplace transform. The antennas are designed for realizing ultrafast and high-density magnetic recording. Characteristics of nanoscale antennas are discussed in terms of eigenmodes and time domain responses of electric fields. Our computational method is highly efficient and the computational cost can be reduced by selecting coarse time step size and performing parallel computation.

A tunable electromagnetic-bangap (EBG) structure based on a double layer slotline using plasma is proposed. The plasma permittivity can be tuned by the electron density. The idea of integrating periodical plasma elements inside the slot to tune the stopband is investigated. An electron density and an electron collision frequency equal to 1.75 10¹³ cm^-3 and 10¹⁰ s^-1 respectively, are the plasma parameters selected in this study. The simulations reveal a shift rate of the second stopband equal to 6%. A new configuration of the structure is also proposed to adapt it better to the experimental requirements. Based on the simulation results, adding the plasma elements to the modified configuration shifts the stopband 4% and reduces its bandwidth by 43% (at -20 dB).

Bistatic forward-looking SAR (BF.SAR) has many potential applications, such as self-landing in bad weather and military detection. Therefore, BFSAR receives considerable attention recently. The imaging algorithms for BFSAR are the difficulties of the study. The original Loffeld's Bistatic Formula (LBF) can handle most general bistatic SAR configurations well. But in some complex bistatic geometries, such as high squint or forward-looking cases, the performance of LBF is degenerated. Some extended LBF (ELBF) methods have been developed, which improve the performance of LBF in some special geometries, but still not the forward-looking configuration. In this paper, we modify the LBF method and try to solve the instantaneous azimuth frequencies of transmitter and receiver directly. Then, we can obtain a bistatic point target reference spectrum (BPTRS), which is accurate enough for forward-looking configuration. A range Doppler algorithm (RDA) based on this BPTRS is derived. Finally, simulations validate the accuracy of the modified Loffeld's Bistatic Formula (MLBF) and effectiveness of imaging algorithm.

This paper presents a new approach for localizing mobile phone users using the promising technique of stratospheric platform (SP) flying at altitudes 17-22 km high and a suitable Direction-of-Arrival technique (DOA). The proposed technique provides information about accurate locations for mobile stations - through high resolution DOA technique - which is very important for traffic control and rescue operations at emergency situations. The DOA estimation in this technique defines the user location using MUSIC algorithm which provides good accuracy comparable to the Global Positioning System (GPS) techniques but without the need for GPS receivers. Several scenarios for users' locations determination are tested and examined to define the robustness of the proposed technique.

In this paper, a novel near zero refractive index metamaterial is designed and used as a superstrate of a microstrip antenna. In order to decrease the return loss, particle swarm optimization (PSO) is used to optimize the metamaterial structure. One of the important factors in the antenna designing, which influences the radiation efficiency, is to determine the accurate position of the feed, and PSO is used to find a precise location of the feed with minimum return loss. The simulation and fabrication of the microstrip antenna using the optimized metamaterial structure is also presented. The performance of the antenna is improved, and the gain is increased up to 4.5 dB. The directivity and radiation efficiency are significantly enhanced. Moreover, a very good agreement is observed between simulation and measurement results.