We report on the design, simulation and characterization of a solid-state W-band in-phase power-combined frequency tripler. In order to increase the output power of the frequency tripler without sacrificing efficiency and bandwidth, two mirror-image tripler circuits with four UMS^® Schottky varistor diode chips are designed and mounted in a waveguide block, which includes a compact double-probe power divider at the input waveguide and a Y-junction power combiner at the output waveguide, respectively. Each circuit chip features four anodes on a 50 mil thick Rogers RT/duroid 5880 substrate. The tripler has 1.2~3.8 % conversion efficiency measured across the 75~110 GHz band when driven with 24 dBm of input power at room temperature. With the input power of 27 dBm, 5.5~11 dBm of saturated output power is produced over 75~110 GHz. Suppression of undesired harmonics is greater than 17 dB.

Magnetic antennas are suitable in short range medical in-body applications because they are less perturbed in the presence of the human tissues comparing to electrical antennas. After a preliminary study on magnetic antennas designed separately at 40 MHz with a matching system, a link budget between a spiral coil ingestible capsule transmitter antenna and a square coil onbody receiver antenna has been established in the presence of the human body. The efficiency (ratio of received power to transmitted power) of the magnetic induction link through a homogeneous human body (muscle) is equal to 0.6 % when the TX (transmitter) capsule is in front of the RX (receiver) antenna. If the transmission channel is a three-layered human body (muscle / fat / skin) the performances of the inductive link can be enhanced and the efficiency reaches 0.8 %. These performances can be improved (up to 1 %) when the dimensions of the receiver antenna increase. Consequently, the power consumption can be reduced and hence the battery life of the wireless capsule increases. Additionally, when the TX antenna is located randomly at an arbitrary orientation and position, the efficiency of the magnetic induction link can be improved by orienting the RX antenna parallel and perpendicularly to the human body surface.

Behavioral modeling technique provides an efficient and convenient way to analyze and predict the performance of the RF power amplifiers (PAs) in system-level, and thus helps to constructe a suitable predistorter to linearize the PA system. To accurately describe the nonlinear dynamic characteristics of PAs, an orthonormal Hermite polynomial basis neural network (OHPBNN) is utilized to represent the PAs behavioral model, which outperforms, mainly in respect of modeling accuracy, the classic feedforward neural network using sigmoid activation functions. In addition, we apply an adaptive algorithm to determine the appropriate memory depth of PA behavioral model. Simulation results show that the proposed model provides more accurate prediction of the PAs output signal compared with classic neural network models.

An 8 mm-band two-dimensional Synthetic Aperture Interferometric Radiometer (SAIR) called BHU-2D has been developed by Electromagnetics Engineering Laboratory of Beihang University. The radiometer could obtain images in realtime benefiting from the adoption of a 1bit/2level FPGA-based correlator array. The correlator array requires a group of Power Measurement Units (PMUs) to denormalize the correlation coefficients into visibility function samples. The design and implementation of the PMU in BHU-2D is presented in this paper. The PMU adopts a novel method based on probability statistics. The principle and quantitative error analysis of this power measurement method is presented. In order to verify the principle of the design, a sample board is manufactured and a series of validation experiments have been conducted. Measurement results have proved that the performance of the PMU could meet the requirements of SAIR systems. The PMU has been applied to BHU-2D and the result is satisfactory.

We show that a metal can be turned into a broadband and omnidirectional absorber by coating a purely-dielectric thin layer of grating. An optimal design for such an absorber is proposed by putting a dielectric slot waveguide grating (SWG) on the metallic substrate. The SWG consists of two germanium nanowires (Ge NWs) separated by a sub-100 nm slot in each period. Average absorption reaches 90% when the incident angle varies between 0° and 80° over a broad wavelength range from 300 nm to 1400 nm. Multiple optical mechanisms/effects, namely, diffraction, waveguiding in the high-index Ge NWs and low-index air slot, Fabry-Perot resonances as well as surface plasmon polaritons (SPPs), are identified to govern the absorption characteristics of the present absorber. The designed absorber with such a dielectric grating is easier to fabricate as compared with other absorbers with metallic structures, and has potential applications in e.g. solar cells and photodetectors.

A hierarchical interpolative decomposition multilevel fast multipole algorithm (ID-MLFMA) is proposed to handle multiscale, dynamic electromagnetic problems. The hierarchical scheme to conduct the ID skeletonization and to implement the matrix vector multiplication is discussed. A strategy to improve the efficiency of ID skeletonization is developed. The hierarchical ID-MLFMA are investigated by numerical experiments on complex targets, demonstrating the capability of the hierarchical ID-MLFMA.

The conventional integrated lens antennas (ILAs) for beam steering suffer from internal reflections that deteriorate the scanning properties. The internal reflections are known to affect side lobes, cross-polarisation level, input impedance of the feed, and mutual coupling. In this paper, ILAs are designed to exhibit very low reflection loss, i.e., to minimize the internal reflections. Wide ranges of realistic relative permittivities of the lens and of the feed element directivities are considered. It is shown that with any permittivity and with any feed directivity it is possible to design the lens shape in such a way that the reflection loss is low, for moderate beam-steering angles, without resorting to a complicated matching layer. The gain, directivity, beam-width, and the resulting distance between the feed elements are compared for all the designed lenses.

A new broadband microstrip branch-line quadrature hybrid with very flat phase response is presented. The device is made by cascading four branch-line couplers with arbitrary power division. The novel design is based on the microstrip transposition of a broadband waveguide polariser [4]. Across a 32% bandwidth centred at 9.3 GHz, the RL and the IL are respectively -15 dB and -3 dB/-4 dB; the phase difference is very flat, i.e. 90°±1.5°.

The particle swarm optimization (PSO) algorithm, a global optimization technique based on cooperative swarming strategy, has been used to solve inverse scattering problem for red flood cells (RBCs) and detect possible anomalies. The inverse scattering problem is recast as an iterative optimization one by definiing a suitable cost function.With this method is possible to estimate the morphological parameters of a red blood cell and to distinguish healthy RBCs from diseased ones. This work lays the basis for a new approach to make diagnosis. Preliminary numerical experiments show the potential effectiveness and the reliability of the proposed method as diagnostic tools.

A novel microstrip grid array antenna that is simultaneously high in gain and wide in bandwidth is proposed. To enhance its bandwidth, the antenna adopts elliptically shaped and variably dimensioned radiation elements as well as a linearly tapered ground plane, and is optimized by a parallel genetic algorithm (GA) on a cluster system. A prototype antenna was fabricated and tested. Results of simulation and measurement agree well and show the antenna exhibits encouraging properties, e.g., a maximum gain of approximately tely 15.1 dBi at 5.8 GHz; the |S₁₁| ≤ 10 dB bandwidth and the 3dB gain-drop bandwidth are 25.6% (from 5.03 GHz to 6.51 GHz) and 27.6% (from 5.0 GHz to 6.6 GHz), respectively, of the center frequency, both of which are much wider than that of conventional microstrip grid array antennas. Moreover, the overlap between the antenna's impedance bandwidth and the gain bandwidth results in a wide effective operating frequency bandwidth of 25.6%, which is the largest so far achieved for microstrip grid-array antennas.

Most of the current imaging methods in microwave induced thermoacoustic tomography (MITAT) system assume that the heterogeneous sound velocity (SV) and density distribution are given or subject to Gaussian distribution. These situations generally are not satisfied. To improve multi-targets thermoacoustic sources imaging quality in a heterogeneous tissue, an iterative TR adjoint imaging method is proposed. The proposed iterative TR adjoint method can reconstruct thermoacoustic sources from the measured data even if the prior heterogeneous information of the tissue is unknown. This method estimates misfit between synthesized and observed measured signals, and iteratively updates supposed model parameters which give the heterogeneous tissue structure. In this iterative procedure, error kernels of SV, density and the approximate point source position information can be obtained independently. After the time of flight (TOF) convergence criterion is reached, a regular time reversal (TR) method with updated model will give out the final imaging result. The proposed TR adjoint imaging method is based on strictly theoretical derivation, and some simulations are presented to validate the method.

A new printed monopole antenna configuration, asymmetric inverted cone ring monopole antenna, is proposed. The proposed antenna which has the size of 23.6 mm x 40 mm, is fabricated on a low-cost FR4 substrate that has the relative permittivity (ε_r) of 4.4 and substrate thickness of 1.6 mm to operate in the UWB band (3.1 GHz to 10.6 GHz) released by Federal Communications Commission (FCC) in 2002. It gives an ultra-wide impedance bandwidth of VSWR ≤ 2 from 2.9 GHz to 35 GHz (169.4%) for numerical result and from 3.1 GHz to 31.1 GHz (163.74%) for experimental result. Moreover, it exhibits omni-directional radiation patterns with acceptable gain across the whole operation band, which meets the requirements of UWB applications. The parameters which affect the performance of the antenna characteristics are investigated in this paper. The simulated results have a good agreement with the measured ones, and the proposed antenna shows that it is a very good candidate for UWB operations.

We present an accurate, efficient numerical analysis for vector modes of dielectric optical waveguide structures with an arbitrary refractive index profile using a quadratic spline collocation method (QSCM). The unknown weights of the polynomials are determined by forcing the errors at the collocation points to be zero. Consequently, the original second order differential equation is converted to a set of algebraic equations which can be solved by matrix techniques. The proposed QSCM method demonstrates better performance than the standard finite-difference method of the same convergence rate in terms of grid size with the same degree of computational complexity.

This paper presents a generalized volume-surface integral equation (GVSIE) to solve electromagnetic (EM) scattering of high contrast inhomogeneous materials. Then the method of moments (MoM) is employed to solve the GVSIE. The GVSIE technique where the domain is represented by a corresponding uniform background medium coupled with a variation, together representing the overall inhomogeneity, is solve by the method of moments (MoM) using Schaubert-Wilton-Glisson (SWG) and Rao-Wilton-Glisson (RWG) basis functions. The adaptive cross approximation (ACA) algorithm combined with the equivalent dipole-moment (EDM) method are extended to reduce memory and CPU time. A highly effective preconditioning strategy is presented to solve the system of equations without any increase in the computational complexity. Experiments on several problems representative of scattering simulations are given to illustrate the potential of the above proposed techniques for solving EM scattering involving high contrast applications.

The paper demonstrates a novel antenna which can achieve a broad impedance bandwidth and circularly polarized bandwidth with a suspended corner-truncated square patch and a new probe-fed rectangular strip. By incorporating a probe-fed rectangular strip inside a high substantial cavity (~ 0.144λ₀), a broad impedance bandwidth (VSWR < 2.0) of 770 MHz (31.43%) is achieved. To obtain a good circularly polarized (CP) bandwidth overlap with the impedance bandwidth, two stubs with optimized lengths are loaded with the non-radiating edges of the corner-truncated square patch symmetrically. Measured results show that the CP antenna features a wide operating bandwidth of 10% ranging from 2.41 GHz to 2.66 GHz (VSWR < 1.5 and axial ratio < 3 dB) and that of 22.45% ranging from 2.31 GHz to 2.86 GHz (VSWR < 2 and axial ratio < 6 dB) and good radiation patterns with cross-polarization level (LHCP) lower than the co-polarization level (RHCP) by more than 20 dB at the broadside direction. The average gain of this antenna is recorded as about 8.16 dBi across the operating bandwidth.

We carried out measurements of optical transmission through a Frequency Selective Surface (FSS) on a silicon substrate perforated periodically with square cavities of 1 mm². The substrate is covered on one side with a thin film (1 μm thick) of silicon-nitride, thus forming a membrane for each cavity. The measurements were taken using a Martin-Puplett Interferometer over a spectral range from 100 to 650 GHz, providing a maximum transmission value of around 40% at 480 GHz. Analytical and computed results are also presented for comparison purposes.

The paper introduces the use of Non-Uniform Fast Fourier Transform (NUFFT) routines in ``complex'' (i.e., amplitude and phase) and phaseless Near-Field/Far-Field transformations. The use of those routines results computationally very convenient when non-regular field sampling prevents the use of standard FFTs. The attention is focused on a plane-polar acquisition geometry. Numerical and experimental results show the effectiveness of the developed algorithms.

In order to perfectly match arbitrary frequency-dependent complex load impedances at two uncorrelated frequencies, a novel coupled-line impedance transformer without transmission-line stubs is proposed in this paper. This transformer mainly features small size, wide bandwidth, simple analytical design method, and easy planar implementation. The transformer simply consists of a coupled-line section and an additional transmission-line section. Due to the usage of a coupled-line section, the theoretical synthesis of the proposed transformer becomes very simple when compared with previous transformers and the total size of the planar circuit without deterioration of operating bandwidth becomes small. Furthermore, several numerical examples are presented to demonstrate the flexible dual-frequency matching performance. Finally, the profile of matching frequency-dependent complex load impedance at two arbitrary frequencies has been examined by simulation and measurement of two microstrip generalized T-junction power dividers. Good agreement between the calculated results and measured ones justifies this proposed transformer and the design theory.

Statistical modeling of Synthetic Aperture Radar (SAR) images is of great importance for speckle noise filtering, target detection and classification, etc. Moreover, it can provide a comprehensive understanding of terrain electromagnetics scattering mechanism. Over the past three decades, many sophisticated models have been developed for SAR images, such as Rayleigh, Gamma, K and G, etc. The G° distribution is a special form of the G model, which can model the speckle fluctuations of many classes of objects like homogeneous, heterogeneous and extremely heterogeneous ones, and is widely used in SAR images interpretation. However, as many improvements have been performed on SAR sensors, the traditional parameter estimation methods of the G° distribution may be not sufficient, notably in high resolution SAR images. They cannot arrive at a solution frequently when modeling regions in high resolution SAR images, especially the extremely homogeneous regions. In order to deal with this problem, this paper proposes an improved parameter estimation scheme of the G° distribution, which combines the classical moment estimation with the mellin transform. To quantitatively assess the fitting precision of the proposed method, we adopt the Kullback-Leibler (KL) distance, Kolmogorov-Smirnov (KS) test and Mean Square Error (MSE) as similarity measurements. The advantage of this proposed parameter estimation method becomes evident through the analysis of a variety of areas (ground, vegetation, trees and buildings) in two high resolution SAR images.

When particle swarm optimization(PSO) technique is used for the inverse scattering problems, it will take unbearably long time for the final solution, especially when the PSO algorithm traps into the premature convergence. To overcome this problem, a hybrid multi-phased particle swarm optimization algorithm (HMPPSO) is proposed. By adopting the small swarm size strategy and the idea of ``sub swarms'' working cooperatively and alternatively with ``optimal swarm'' into the MPPSO, the HMPPSO can converge quickly with much less fitness function evaluation times, thus will reduce the reconstruction time. After the HMPPSO is validated by the numerical simulations on benchmark functions, the wall parameters (permittivity, conductivity, and thickness) together with target shape parameters (approximated by the trigonometric serials) with 20 dB additive Gaussian white noise are successfully reconstructed by HMPPSO using multi-frequency, multi-view/single-illumination scattering fields calculated by MOM.