A polarization-dependent mutiband radar absorbing material (PDM-RAM) composed of polarization-dependent multiband AMC (PDMAMC) and perfect electric conductor (PEC) cells is proposed. The PDMAMC is realized by etching a complementary split ring resonator (CSRR) on the patch of a conventional AMC. Around the two/three operational frequencies of the PDMAMC-elements for different electric field polarizations, the reflections of the PDMAMC and PEC have opposite phases, so for any normal incident plane wave the reflections cancel out. The basic principle is discussed, and a sample is measured. The results show that the proposed method is feasible and effective for the polarization-dependent multiband radar cross section (RCS) reduction.

This paper proposes a 10:1 unequal Gysel power divider using a capacitive loaded transmission line (CLTL). For obtaining a high dividing ratio of divider, the CLTL is proposed to realize a low characteristic impedance line below 10 Ω. A design method using a CLTL which consists of a small transmission line with shunt open stub at periodic intervals is newly suggested for power divider with the high power division ratio. For the validation of the CLTL power divider, the high dividing ratio of the fabricated Gysel divider is measured at a center frequency of 1 GHz. The measured performances are in good agreements with simulation results.

A novel miniaturized microstrip dual-mode filter using a half wavelength resonator with centrally loaded open stub and quasi-L shaped feed-lines is proposed. The advantage of using such a resonator is inherently generating a transmission zero by itself. To further improve the selectivity, quasi-L shaped feed-lines are introduced to create additional transmission zeros. Theoretical and simulated analyses of this filter are performed. A demonstration filter centered at 2.33 GHz with a fractional bandwidth of 4.7% is designed, fabricated and measured to validate the design methodology.

Principle component analysis based through wall image enhancement is proposed which is capable of discriminating target, noise and clutter signals. The overlapping boundaries of clutter, noise and target signals are separated using fuzzy logic. Fuzzy inference engine is used to assign weights to principle components. The proposed scheme works well significantly for extracting multiple targets having different range profiles in heavy cluttered through wall images. Simulation results are compared on the basis of mean square error, peak signal to noise ratio and visual inspection.

The research about the so-called \emph{complex beams}, localized solutions of the Helmholtz wave equation, lead to the problem of finding the sources of such solutions, which may be formally expressed as a Dirac delta function of a complex argument. To investigate about the meaning of the Dirac delta distribution of complex argument, the Green's function of the 3D Poisson problem with a point source localized at an imaginary position in free space is considered. The main physical features of the potential created by that source are described. The inverse problem consists in looking for the real source distribution which causes that potential. The sources appear on a disk in the real space. Their physical interpretation requires a regularization process based on including the border of the disk.

The adoption of microwave imaging as a tool for non-invasive monitoring of brain stroke has recently gained increasing attention. In this respect, the paper aims at providing a twofold contribution. First, we introduce a simple design tool to devise guidelines to properly set the working frequency as well as to choose the optimum matching medium needed to facilitate the penetration of the probing wave into the head. Second, we propose an imaging strategy based on a modified formulation of the linear sampling method, which allows a quasi real time monitoring of the disease's evolution. The accuracy of the design guidelines and performance of the imaging strategy are assessed trough numerical examples dealing with 2D anthropomorphic phantoms.

A 16-way radial waveguide power divider with the characteristics of low insertion loss and high power handling capacity is investigated. Its design theory and basic structure are proposed at first; a power divider with the center frequency of 4.0GHz is designed, fabricated, and measured. Good agreement between the simulated and measured results is found for the proposed power divider. The measured 15-dB return loss bandwidth is demonstrated to be 440MHz and the measured 0.5-dB insertion loss bandwidth is demonstrated to be 540MHz. The power handling capacity of the proposed power divider is analyzed through simulation, and the results prove its usability in high power applications.

A reconfigurable stacked patch antenna is introduced for wireless power reception and data telemetry application in sensors. The proposed antenna operates at 5.8 GHz with 9.4 dBi gain and 7.6% bandwidth. At a lower frequency 2.45 GHz the antenna operates as a planar inverted-F antenna (PIFA) with 3.3 dBi gain and 2% bandwidth. Switching between the two regimes of operation is achieved using PIN diodes. It is proposed that the antenna can be used for wireless power reception in sensors at 5.8 GHz and for data telemetry in between a sensor and a control station at 2.45 GHz. The wireless power reception ability of this antenna was tested and verified by developing a high efficiency schottky diode rectifying circuit. The RF-to-DC conversion efficiency was 85% for an input power density level of 1 mW/cm².

In this paper, we introduce a new technique for an electronic beam scanning/directivity reconfigurable which can be carried out by using a joint array of Metallic Electromagnetic Band Gap (M-EBG) sectoral antennas. This study opens new avenues of research on M-EBG sectoral antennas by combining multiple radiating elements in an array. Usually M-EBG structures are designed in passive configurations to radiate fixed/shaped beams thanks to a specific radiating aperture at the surface of the M-EBG antenna. However by opting this new technique, we are able to control the radiating aperture, and therefore provide a tunable directivity/beam pattern. The objective of the paper is to propose a solution for M-EBG antennas in order to achieve Beam Scanning and Directivity reconfigurability. The main advantage of the proposed technique is that the array have negligible mutual coupling between the radiating elements, simplifying therefore the conception of the beam-forming network and the problems of constrained beam scanning. Another objective of the paper is to be able to achieve wide angle beam scanning -/+58 degrees. This method makes it possible to obtain in a simple way an agile M-EBG antenna without the need of the expensive active electronic components. Several results show the effectiveness and the capabilities of the proposed technique.

A low frequency (50 Hz) dielectric barrier discharge (DBD) system with a single dielectric cover on copper coil anode is designed to generate and sustain the microdischarge plasma which is very practical for material processing applications. The DBD system is powered by a high tension ac source consisting of a conventional step up transformer and variac. The dielectric barriers (quartz and glass) between the conducting electrodes appreciably influences the discharge plasma characterized by optical emission spectroscopy technique. Using intensity ratio method, the electron temperature and electron number density are determined from recorded spectra as function of ac input voltage, type and thickness of dielectric barrier and inter-electrode gap. It is observed that both the electron temperature and electron number density increase with the increase in ac input voltage and ε_r/d ratio, while a decreasing trend is observed with increase in inter-electrode gap.

The 35GHz and 96GHz electromagnetic wave propagation characteristics in plasma are studied theoretically and experimentally in this paper. The variations of the incident electromagnetic wave attenuation along with the plasma density, collision frequency and electromagnetic wave frequency are acquired based on the physical model. The electromagnetic wave propagation properties in plasma are studied experimentally with the shock tube, and the experimental results match well with the theoretical ones. The theoretical and experimental results show that increasing the electromagnetic wave frequency is an alternative and effective method to solve the reentry blackout problems.

Network fade countermeasures for link budget can be better implemented based on the knowledge of seasonal variability of rainfall attenuation in a locality. Therefore, in this study, a seasonal approach is applied to estimate the effects of spatial rainfall attenuation in Durban (29^o52'S, 30^o58'E), South Africa using two-year rainfall data obtained from the RD-80 Joss-Waldvogel (J-W) distrometer. An analysis is undertaken for different seasons to obtain the rainfall rate exceedences at 0.001%, 0.01%, 0.1% and 1% of time. Consequently, rainfall drop-size distribution (DSD) models are developed for the control site at different seasons for the same period. The probability density analysis for each model indicates that the lognormal distribution best fits the summer and autumn season with percentage root-mean-square errors (RMS) of 30% and 26% respectively; gamma distribution fits winter season with RMS error of 16% and Weibull distribution fits spring season with RMS error of 26%. The results from the rainfall rate and rainfall DSD are combined to estimate the rainfall specific attenuation, by applying spherical droplet assumption for Mie scattering techniques, between 2 GHz and 1000 GHz. With this, the seasonal k and α coefficients for specific attenuation are derived from the best rainfall DSD models, using regression technique at 2.5 GHz, 25 GHz, 40 GHz and 100 GHz. At these frequencies, the results show that the predicted specific attenuation coefficients for all seasonal rainfall rates at the control site are lower, when compared to those from ITU-R models. It is concluded that specific attenuation levels may be similar and more intense in summer and autumn seasons, while, lower and less intense in autumn and winter seasons at similar rainfall rates.

This investigation is one of the first steps towards the realization of low-cost, mass producible, miniaturized antenna solutions utilizing screen printed magnetic thick films of cobalt nanoparticle ink. The ink has a curing temperature lower than 125°C, feasible printing characteristics and metal loading higher than 85 wt.%. The properties are achieved by using an oxidatively polymerising natural fatty acid, linoleic acid, both as a surfactant and a binder. DSC-TGA-MS-analysis, TEM and SEM microscopies were utilized to investigate ink composition, nanoparticle coating and print quality. The resonant frequency of a microstrip patch antenna was tuned by screen printing of cobalt nanoparticle ink with different layer thicknesses on top of the antenna element. The influence of magnetic layers on resonance frequency, return loss, total efficiency and radiation pattern was measured and compared with a reference antenna without the magnetic films. For example, five layers of magnetic film (52 μm total thickness) tuned the resonance frequency (2.49 GHz) of the patch antenna by 68 MHz. The radiation efficiency of the patch antenna was increased from 39% to 43% by the loading of a 52 μm thick magnetic film compared to the reference antenna. The radiation patterns remained essentially unchanged, despite the presence of the magnetic thick films.

The time-domain studies of the modal fields in a lossy waveguide are executed. The waveguide has a perfectly conducting surface. Its cross section domain is bounded by a singly-connected contour of rather arbitrary but enough smooth form. Possible waveguide losses are modeled by a conductive medium which fills the waveguide volume. Standard formulation of the boundary-value problem for the system of Maxwell's equations with time derivative is given and rearranged to the transverse-longitudinal decompositions. Hilbert space of the real-valued functions of coordinates and time is chosen as a space of solutions. Complete set of the TE-time-domain modal waves is established and studied in detail. A continuity equation for the conserved energetic quantities for the time-domain modal waves propagating in the lossy waveguide is established. Instant velocity of transportation of the modal flux energy is found out as a function of time for any waveguide cross section. Fundamental solution to the problem is obtained in accordance with the causality principle. Exact explicit solutions are obtained and illustrated by graphical examples.

The reflection and transmission of electromagnetic waves obliquely incident on a uniaxial chiral slab with the optical axis perpendicular to the interface have been investigated. Firstly, the formulas of the reflection and transmission are derived. Then numerical results for four cases of the uniaxial chiral media are presented and different chiral parameters are considered. Finally, the Brewster's angles and total transmission are discussed.

A novel extremely wide band dipole antenna with omni-directional radiation patterns is investigated experimentally and numerically. The proposed antenna comprises two groups of crossing semicircular discs. The shape of each disc is modified to broaden the working bandwidth. Measured results demonstrate that the novel antenna possesses good impedance match from 0.45 to 38.9 GHz for S₁₁ lower than -10 dB, in good agreement with simulated results. Omni-directional radiation patterns keep stable within the operating band. The proposed antenna is highly suitable for various wide band systems.

Traditional optimization methods are not well suited for thinning large arrays to obtain a low sidelobe level (SLL). The chaotic binary particle swarm optimization (CBPSO) algorithm is presented as a useful alternative in the synthesis of thinned arrays. The proposed algorithm is improved by nonlinear inertia weight with chaotic mutation to increase the diversity of particles. Two examples have been proposed and solved. Simulation results compared with published results illustrate the effectiveness of the proposed method for both linear and planar arrays.

Although a Coherent Transponder (CT) is widely utilized in the field of Synthetic Aperture Radar (SAR), its Digital Elevation Model (DEM) has yet not been well studied for Interferometry SAR (InSAR). Based on the fact that the interferometry phase is a constant for CT with single transmit antenna, this paper mainly focuses on InSAR DEM induced by CT. The decorrelation effect in the intersection region of CT and nature terrain is researched in detail to support the analysis of CT's phase-unwrapping. The most important property, which makes DEM of CT being unique, is found to be the "slope" effect. The incline angel of "main slope" of DEM is verified to be determined only by the depression angle of InSAR system, whereas the incline angles of the "subordinate slopes" are affected by all the geometric parameters of InSAR baseline. Finally, all the incline angels are independent of CT' s waveform modulations, since the modulations have no contribution to the interferometry phase.

Multiple signal classification (MUSIC) algorithm has been applied to localize small scatterers for super-resolution imaging. A problem associated with this application is the estimation of the number of scatterers in presence of noise and multiple scattering between targets. In this paper, we show that the mathematical model behind the scattering from the small objects is well compatible with the minimum description length (MDL) model. This leads us to use the MDL so as to estimate the number of scatterers before application of the MUSIC algorithm. As the MDL assumes the sources are independent, the nearby wave sources are grouped together to improve the independency criterion. The application of MDL to synthetic and experimental data verifies accurate estimation of the target number with low complexity, even if the data embodies significant noise and multiple scattering.

A high performance balun bandpass filter (BPF) with very simple structure is proposed in this letter, this structure realizes superior performance in bandpass filtering meanwhile with good differential performance of the balun. The proper balanced outputs and BPF characteristic by the symmetric feeding and skew-symmetric feeding have been obtained, and the theory of this simple structure for unbalanced input to balanced outputs has been studied. The center frequency of the fabricated balun-BPF was operated at 2.4 GHz with 5.8% fractional bandwidth (FBW), and this frequency is used for Bluetooth and some other communication systems. The differences between the two outputs are 180° ± 5° in phase and within 0.39 dB in magnitude. At f₀, the amplitude imbalanced and phase difference are within 0.37 dB and 179.2°, respectively. The measured frequency responses agree well with the simulated ones. With the theoretical analyses and practical results, it is shown that the proposed one has the advantages of simple structure, convenient analysis and good performance of both BPF and balun.