Coupled-line and coupled three-line resonators are proposed to design dual-wideband bandpass filters. Compared with the shorted and open stubs shunt at the same locations of the main line, in addition to saving the circuit area, these resonators provide alternative ways to the design of dual-wideband filters, with larger possible bandwidths and different frequency ratio of the two center passbands. The geometric parameters of the coupled-line and the coupled three-line structures are determined by deriving their equivalent circuits to a shunt open stub in parallel connection with a shunt shorted stub. To extend the upper stopband, a cross-shaped admittance inverter is devised to play the role of the 90-degree transmission line section at the center frequency and to create transmission zeros at the spurious passbands, so that the upper stopband of the filter can be extended. It is a quarter-wave section with two open stubs of unequal lengths shunt at its center. For demonstration, two dual-wideband bandpass filters operating at 900/1575 MHz and 900/2000 MHz are fabricated and measured. Measured results of the experimental circuits show good agreement with simulated responses.

An analytical model which predicts the attenuation of ultrawide-band (UWB) signals as they traverse various inhomogeneous tissues is presented. The model provides a computationally efficient method of determining the frequency-dependent losses encountered by electromagnetic radio frequency (RF) signals used to communicate with biomedical implants. Classic transmission line theory is employed to generate an analytical representation which models the inhomogeneous tissue using layers of homogeneous material. The proposed model was verified experimentally with tests of both single and multilayer samples. A realistic abdominal implant scenario was also modeled and the predictions were verified using a commercially available 3D electromagnetic (EM) simulator. The results of this study indicate that for deep implants the higher frequency portion of the UWB spectrum is attenuated much more strongly than the lower end of the band. This implies that for robust communication UWB signals targeting biomedical implants should be limited to the lower portion of the spectrum.

We characterize the pulse propagation on a traveling-wave field-effect transistor (TWFET) with the drain line periodically loaded with Schottky varactors for short pulse amplification. Owing to the coupling between the gate and drain lines, two propagation modes are developed on a TWFET. It is expected that the pulses carried by one of the two modes are uniquely amplified, whereas those carried by the other mode are attenuated. By properly introducing nonlinearity via the loaded varactors, the proposed TWFET succeeds in the amplification of short pulses by compensating for dispersive distortions. This study verifies the design criteria for the amplification of short pulses in TWFETs through the experimental observation of the properties of the linear and nonlinear pulses on a TWFET.

Concentric circular antenna array (CCAA) is synthesized to generate pencil beam with minimum side lobe level (SLL). The comprehensive learning particle swarm optimizer (CLPSO) is used for synthesizing a ten-ring CCAA with central element. This Synthesis is done by finding the optimum current excitation weights and interelement spacing of rings. The computational results show that sidelobe level is reduced to -40.5 dB with narrow beamwith about 4.1^o.

Pipelines are the most common apparatus in industries; therefore, the need for inspection during the manufacturing, construction and the operation stage is inevitable and invaluable. Magnetic Induction Tomography (MIT) is a new type of tomography technique that is sensitive to the electrical conductivity of objects.~It has been shown that the MIT technique is appropriate for imaging materials with high electrical conductivity contrasts; hence, the majority of the MIT systems were designed for detecting metallic objects. In this paper, MIT technique was proposed for pipeline inspection. Structural damages of the outer surface of the pipe were considered in this study. Nonetheless, it is challenging to use the traditional MIT pixel based reconstruction method (PBRM) as a suitable pipelines inspection tool because of the limited resolution. A narrowband pass filtering method (NPFM) of imaging pipe geometry was developed as a suitable image reconstruction method.~The proposed method can overcome the resolution limitations and produce useful information of the pipe structure.~This paper shows the comparative results from the novel NPFM and from traditional PBRM. While the PBRM fails to detect damages in outer structure of the pipe the NPFM successfully indentifies these damages. The method has been verified using experimental data from very challenging test samples. It is well known that using a coil array with an imaging region of 100 mm the PBRM based MIT can retrieve information with accuracy of about 10 mm (about 10%). With proposed NPFM the information on a resolution of 2 mm (which is about 2%) can be detected using the same measurement data.

This paper describes an original approach for determining independent loops needed for mesh-current analysis in order to solve circuit equation system arising in inductive Partial Element Equivalent Circuit (PEEC) approach. Based on the combined used of several simple algorithms, it considerably speed-up the loops search and enables the building of an associated matrix system with an improved condition number. The approach is so well-suited for large degrees of freedom problems, saving significantly memory and decreasing the time of resolution.

Recently, many numerical methods that are developed for the solution of electromagnetic problems have greatly benefited from the hardware accelerated scientific computing capability provided by graphics processing units (GPUs) and orders of magnitude speed-up factors have been reported. Among these methods, the finite-difference frequency-domain (FDFD) method as well can be accelerated substantially by utilizing an efficient algorithm customized for GPU computing. In this contribution, an algorithm is presented that treats iterative solution of the FDFD linear equation system similar to solution of three-dimensional Finite-Difference Time-Domain (FDTD) method, which inherently yields itself to high level parallelization. The presented algorithm uses BICGSTAB iterative solver. Integrated with BICGSTAB, an efficient method of performing matrix-vector products for the linear system of FDFD equations is adapted and implemented in Compute Unified Device Architecture (CUDA). It is shown that FDFD can be solved with a speed-up factor of more than 20 on a GPU compared with the solution on a central processing unit (CPU), while memory usage as well can be reduced substantially with the presented algorithm.

This paper presents the application of unconditionally stable fundamental finite-difference time-domain (FADI-FDTD) method in modeling the interaction of terahertz pulse with healthy skin and basal cell carcinoma (BCC). The healthy skin and BCC are modeled as Debye dispersive media and the model is incorporated into the FADI-FDTD method. Numerical experiments on delineating the BCC margin from healthy skin are demonstrated using the FADI-FDTD method based on reflected terahertz pulse. Hence, the FADI-FDTD method provides further insight on the different response shown by healthy skin and BCC under terahertz pulse radiation. Such understanding of the interaction of terahert pulse radiation with biological tissue such as human skin is an important step towards the advancement of future terahertz technology on biomedical applications.

The frequency difference between signal-under-test and reference signal in phase demodulation will affect the result of the actual phase noise measurement. In order to eliminate the effect, an algorithm for both eliminating the frequency difference and extracting the phase noise of the signal-under-test is presented. Simulation and experiment results show that this algorithm is effective. By using the algorithm in our experiment, the noise floor of the measurement system is improved by 10.1 dB and 9.3 dB, respectively, and the measurement precision is improved from 90.03% to 96.31%. In addition, the use of this algorithm can lower the requirement on the frequency precision of reference source and reduce the cost of measurement system.

Planar waveguide gratings have shown great potential for the application of the wavelength division multiplexing (WDM) functionality in optical communications due to their compactness and high spectral finesse. Planar gratings based on silicon nanowire technology have high light confinements and consequently very high integration density, which is 1--2 orders of magnitude smaller than conventional silica based devices. In the present paper, we will simulate the silicon nanowire based planar grating multiplexer with total-internal-reflection facets using a boundary integral method. The polarization dependent characteristics of the device are analyzed. In addition, the planar grating multiplexer with 1 nm spacing is fabricated and characterized. Compared with measured values, the numerical results show that the sidewall roughness in the grating facets can result in a large insertion loss for the device.

The imaging problem of spotlight synthetic aperture radar (SAR) in the presence of azimuth spectrum folding phenomenon can be resolved by adopting the azimuth deramping-based technique and traditional stripmap SAR imaging algorithm, and this method is the so-called two-step processing approach. However, when the spotlight SAR operates on squinted mode, the echo two-dimensional (2D) spectrum is shifted and skewed due to the squint angle. In such case, the original two-step processing approach is not suitable anymore. This paper presents a novel imaging algorithm using the deramping-based technique and azimuth nonlinear chirp scaling (ANLCS) technique. First, the problem of azimuth spectrum folding phenomenon in squinted spotlight SAR is analyzed. Subsequently, based on the analysis results, the linear range walk correction (LRWC) is applied for removing the squint angle impacts on signal azimuth coarse focusing. At last, a modified azimuth NLCS algorithm is proposed for overcoming the depth of focus (DOF) limitation problem that induced by the LRWC preprocessing. Point targets simulation results are presented to validate the effectiveness of the proposed algorithm to process squinted spotlight SAR data with azimuth spectrum folding phenomenon.

In distributed satellite synthetic aperture radar (DS-SAR), along-track and cross-track baselines couple with each other and change dynamically due to formation flying, which makes it difficult to estimate interferometric baseline accurately. To solve the problem, a novel high-precision baseline estimation approach based on interferometric phase is proposed. By modeling accurate relationship between coupling baselines and two-dimensional (azimuth and range) inteferometric fringe frequency under the ellipsoid earth model, the along-track and cross-track baseline can be estimated separately by interferometric phase decoupling. By selecting several segments from interferometric phase during the whole data-take time and estimating instantaneous baseline of each segment, the dynamic baseline can be obtained via a linear filtering. Besides, to improve the baseline estimation accuracy, Semi-Newton iterative method is applied to acquire high-precision fringe frequency estimation, which can make the baseline estimation achieve centimeter level precision. The simulation validates the approach.

We present a tool to aid the design of periodical structures, such as subwavelength grating (SWG) structures. It is based on the Fourier Eigenmode Expansion Method and includes the Floquet modes theory. Besides, the most interesting implemented functionalities to ease the design of photonic devices are detailed. The tool capabilities are shown using it to analyse and design {three} different SWG devices.

In this work, approximate formulas are presented for computing the magnetic field intensity near electric power transmission lines. Original expressions are given for single circuit lines of any type of arrangement and double circuit lines in both super-bundle and low-reactance conductor phasing. These expressions can be used for assessing directly the Right-of-Way width of power lines related to maximum magnetic field exposure levels which may be efficiently used in environmental impact assessment. The accuracy of approximate formulas is demonstrated by comparison with exact formulas for computing the rms field distribution.

The miniaturized dual-mode dual-band band-pass filters (BPF) using Minkowski-island-based (MIB) fractal patch resonators are proposed in this paper. The BPF is mainly formed by a square patch resonator in which a MIB fractal configuration with 2nd order iteration is embedded in the patch. By perturbation and inter-digital coupling, the wide-band and dual-band responses are obtained respectively. For miniaturized wide-band design, at 2.41 GHz central frequency it has good measured characteristics including the wide bandwidth of 2.26-2.56 GHz (3-dB fractional bandwidth of 12.4%), low insertion loss of 0.72 dB, high rejection level (-52.5/-44.9 dB), and a patch size reduction with 60.6%. For compact dual-band design, the proposed filter covers the required bandwidths for WLAN bands (2.20-2.96 GHz and 4.74-5.85 GHz). The patch size reduction of 78.1% is obtained. Two transmission zeros are placed between the two pass-bands and resulted in good isolation.

Terahertz spectroscopy is a new tool for real time biological analysis. Unfortunately, investigations on aqueous solutions remain difficult and need to work on nanovolumes. Integrated Terahertz instrumentation remains a challenge. We demonstrate that Planar Goubau Line (PGL) technology could bring a real practical solution to reach this goal. This study provides the design, fabrication and test results of passive PGL components like loads and power divider. These PGL components are designed, simulated, fabricated and measured with a Vectorial network analyser (VNA). Simulation and test data support PGL component designs. PGL components operate over a wide frequency range from 0.06 to 0.325 THz.

Stability and dispersion analysis for the three-dimensional (3-D) leapfrog alternate direction implicit finite difference time domain (ADI-FDTD) method is presented in this paper. The leapfrog ADI-FDTD method is reformulated in the form similar to conventional explicit FDTD method by introducing two auxiliary variables. The auxiliary variables serve as perturbations of the main fields variables. The stability of the leapfrog ADI-FDTD method is analyzed using the Fourier method and the eigenvalues of the Fourier amplification matrix are obtained analytically to prove the unconditional stability of the leapfrog ADI-FDTD method. The dispersion relation of the leapfrog ADI-FDTD method is also presented.

A comprehensive facet model for bistatic synthetic aperture radar (Bis-SAR) imagery of dynamic ocean scene is presented in this paper. An efficient facet scattering model is developed to calculate the radar cross section (RCS) of the ocean surface for Bis-SAR firstly. Further more, this facet model is combined with a bistatic velocity bunching ($VB$) modulation of long ocean waves to obtain the Bis-SAR intensity expression in image plane of ocean scene. The displacement of the scatter elements in the image plane and the degradation of radar resolution in azimuth direction are quantificationally analyzed. Finally, Bis-SAR imagery simulations of ocean surface are illustrated, proving the validity and practicability of the presented algorithms.

The design of filter antennas with reconfigurable band stops is proposed. They are meant for employment in ultrawideband cognitive radio (UWB-CR) systems, where unlicensed users communicate using adaptive pulses that have nulls in the bands used by licensed users. Neural networks or circuits implementing the Parks-McClellan algorithm can generate such pulses. With filter antennas, reconfigurable bandstop filters are first designed, to induce adaptive nulls in UWB pulses, and are then integrated in the feed line of a UWB antenna. The advantages of this combination are discussed. The filters are based on split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs). The relationship between the SRR and CSRR parameters and the stop band is also studied.

This study presents new Wilkinson power dividers using compact stepped-impedance structures and capacitive loads to achieve the required power splitting. This approach can produce additional transmission zeros and effectively suppress the desired stopbands because shunt open stubs realize capacitive loads. This study proposes two equal-split dividers and two unequal-split dividers. For the first equal-split case, one shunt open stub forms the needed capacitor in each transmission path, creating one additional transmission zero in each path. To obtain one more transmission zero in each transmission path, the second Wilkinson power divider uses two shunt open stubs in each path to achieve the same capacitor value as the first divider. This study also tests unequal-split dividers with one and two transmission zeros in each path to confirm that compact stepped-impedance transmission lines and shunt to-ground capacitors can be utilized in unequal power division.