Axial permanent magnetic couplings are composed of two discs with a small air-gap in-between. Each disc consists of several segments in the shape of slices of cakes. The segments are polarized in axial direction with alternating polarity. In this work the homogeneous magnetization in the segments is replaced by equivalent currents on the surface of the segments (Amperean model). In a simplified model we consider only radial currents whereas azimuthal currents along the perimeter of the discs are discarded. This corresponds to the arrangement where one of the discs has much larger diameter than the other disc. Compared to the case of two equal discs it leads to a notable error in the magnetic field near the perimeter, yet it has only a small effect on the torque, especially for the case of optimum couplings. This trick allows for summing up the fields of all segments in closed form. A concise double integral over the radial magnetic field component describes the torque. An investigation of this integral reveals many properties of axial magnetic couplings: A diagram is introduced and areas in this diagram are identified where the torque shows overshoot, rectangular pulse shape or sinusoidal dependence versus twist angle between bothdiscs. The diagram contains also a curve for maximum torque and one point on this curve is of considerable economic significance: It denotes the global maximum of torque over magnet mass.

An ultra-wideband (UWB) printed monopole antenna with dual band-notched characteristics is proposed. Two spiral electromagnetic-bandgap (EBG) structures placed on the front and back side of the substrate are employed to create two notch bands at 5.2 and 5.8 GHz for the lower and upper bands of the wireless local-area network (WLAN), respectively. The notch-frequency can be tuned, and the band width is narrow and adjustable. Furthermore, the spiral EBG structure used in this design are more compact than conventional mushroom-type EBG. Equivalent circuit model is extracted and discussed to explain the operating mechanism of this structure. The proposed antenna has been simulated and measured, good agreement between calculated and experimental results has been achieved.

A technique that expands dynamic range (DR) of frequency down-converters in the C band frequency is presented. Primary characteristics of down-converter are evaluated to confirm that it can be used in microwave receivers. The C band down-converter is carried out by the combination of RF mixers, band pass interdigital filter, and X band combline filter which are designed entirely for this project. Attainment of the perfect receiver is the final purpose of this paper, and a method that causes 72 dB dynamic range, high tangential signal sensitivity and fine gain flatness is used for achieving the mentioned purpose. These efforts improve the dynamic range about 19 dB and gain flatness about 3.07 dB.

A double-layer radial line helical array antenna with rectangular aperture is proposed. With rectangular aperture, the antenna can be assembled to form high gain antennas. The use of double-layer feed system ensures an equal-amplitude in-phase feed for all elements in an expected frequency band, which can improve antenna gain and aperture efficiency. This paper presents its design concept, derives pertinent design and performance, and a 16-element array antenna is simulated and measured. The experimental results show that in the range of 3.8 GHz to 4.2 GHz, the antenna gain is over 17.7 dB, aperture efficiency over 82%, antenna sidelobe level below -12.0dB, antenna axial ratio below 3.2 dB, and antenna VSWR below 1.52.

This paper presents a design methodology of wide-band bandpass filters based on short-circuited multi-conductor transmission lines with bonding wires between alternated strips. General design guidelines, based on analytical equations, are derived and a left-handed behaviour of the multiconductor structure is inferred and studied. Analytical equations are assessed by means of full-wave electromagnetic simulations and experimental work. A very good agreement between theoretical results and measurements is achieved, that allows both the design and performance analysis of filters without the need for costly electromagnetic simulations. In addition, the equations presented yield a compact design of the filter with a left-handed behavior.

To reduce the size and improve the performance, a 4th-order miniaturized dual-mode microstrip bandpass filter (BPF) is developed. A meander shorted stub loaded resonator is used, and much compact size is obtained. Theoretical model is set up, and the odd and even modes of the BPF are analyzed based on a symmetrical structure. Full wave simulation validates the design method. To verify the design, a fabricated BPF sample has been tested. Experiment result demonstrates that the designed BPF has wider stopband and better selectivity. Its fractional bandwidth and a center frequency are available.

A dual wideband CPW-fed slotted Koch snowflake fractal monopole, which is suitable for WLAN/WiMAX applications, is presented. The proposed antenna has been analyzed and designed with Ansoft HFSSTM v.11. Then an experimental prototype is fabricated and measured. It is compact with a total size of 41.5 mm × 27 mm × 1 mm (L×W×T). Results of simulation and measurement indicate that the proposed fractal monopole with a U-shaped slot has dual impedance bandwidths 2.35-4.25 GHz and 4.8-5.95 GHz, which covers WLAN bands (2.4/5.2/5.8GHz) and the WiMAX bands (2.5/3.5/5.5 GHz) respectively. In addition, good radiation performances such as omnidirectional and doughnut-shaped directivity and goodish gain over the operating bands have been obtained.

This paper presents a new composite material, which is developed by mixing calcium alginate spheres with commercially available epoxies Stycas 2850 FT (s2850) and Stycast W19 (W19). The resulting composite material is examined in terms of transmission and reflection coefficients in microwave frequencies (26 to 40 GHz, 70 to 110 GHz and 300 to 320 GHz). The study reveals that the new material exhibits reflection coefficients much lower than some commercial CR absorbers from the Eccosorb group. The experimental results justify the use of the new composite material as absorber at microwave frequencies.

A problem of electromagnetic waves scattering and radiation by a structure, consisting of a narrow transverse slot in broad wall of rectangular waveguide and a vibrator with variable surface impedance, located inside the waveguide and interacting with one another, is solved. A solution of integral equations for electric current on the vibrator and equivalent magnetic current in the slot is derived by the generalized method of induced electro-magneto-motive forces. Conditions necessary for achievement of maximal slot radiation coefficient are defined. Effectiveness of impedance vibrators application to ensure required level of radiation by vibrator-slot structure in low profile rectangular waveguides is shown. Calculated and experimental plots of energy characteristics of the vibrator-slot structure for different vibrator placement relative to the slot and for various surface impedance dependencies upon the vibrator length are presented.

In this paper, a new plasma antenna of beam-forming is investigated based upon the interaction of plasma elements due to the electromagnetic wave. It presents a study of the multiple scattering from argon plasma cylinders rigorously applying boundary value method, grounded on the properties of electromagnetic wave transmitted in the argon plasma. Approximate expressions for the total radiation of plasma antenna in the far field are derived briefly. Also presented is a study that this new antenna of beam-forming exhibits interesting performance in terms of radiation efficiency, beam-forming and beam-scanning. Valid results are brought forth to demonstrate the capabilities of such antenna of two scales. Comparisons are given in detail as well.

In this work, a detailed investigation on the effective plasma frequency f_p,eff for one-dimensional binary and ternary plasma-dielectric photonic crystals is made. We extract and then analyze the effective plasma frequency from the calculated photonic band structures at distinct conditions. In the binary photonic crystal, it is found that f_p,eff in a photonic crystal is usually smaller than the plasma frequency f_p of a bulk plasma system. f_p,eff will increase when the electron concentration in the plasma layer increases. It also increases as the thickness of the plasma layer increases, but decreases with the increase in the thickness of dielectric layer. In the ternary photonic crystal, f_p,eff is shown to be decreased compared to that of in the binary one. Our results are compared with the analytical expression for f_p,eff derived from the concept of effective medium. Fairly good consistence has been obtained for both results. Additionally, a discussion on the effect of loss on f_p,eff is also given. The study is limited to the case of normal incidence.

Finite element hp-adaptivity is a technology that allows for very accurate numerical solutions. When applied to open region problems such as radar cross section prediction or antenna analysis, a mesh truncation method needs to be used. This paper compares the following mesh truncation methods in the context of hp-adaptive methods: Infinite Elements, Perfectly Matched Layers and an iterative boundary element based methodology. These methods have been selected because they are exact at the continuous level (a desirable feature required by the extreme accuracy delivered by the hp-adaptive strategy) and they are easy to integrate with the logic of hp-adaptivity. The comparison is mainly based on the number of degrees of freedom needed for each method to achieve a given level of accuracy. Computational times are also included. Two-dimensional examples are used, but the conclusions directly extrapolated to the three dimensional case.

This paper present a fast algorithm for synthetic aperture radar (SAR) image segmentation based on the augmented Lagrangian method (ALM). The proposed approach considers the segmentation of SAR images as an energy minimization problem in a variational framework. The energy functional is formulated based on the statistical characteristic of SAR images. The total variation regularization is used to impose the smoothness constraint of the segmentation result. To solve the optimization problem efficiently, the energy functional is firstly modified to be convex and differentiable by using convex relaxing and variable splitting techniques, and then the constrained optimization problem is converted to an unconstrained one by using the ALM. Finally the energy is minimized with an iterative minimization algorithm. The effectiveness of the proposed algorithm is validated by experiments on both synthetic and real SAR images.

A novel dual-band circularly-polarized slot antenna fed by a coplanar waveguide (CPW) is presented for digital multimedia broadcasting (2.6 GHz) and Worldwide Interoperability for Microwave Access (3.5 GHz) application. The circular polarization in the lower band is achieved by the slots loaded in two opposite corners, and corner truncation of the square slot can offer a current path for the upper band. Experimental results show that the measured impedance bandwidths (VSWR ≤ 2) are 18.5% for the lower band and 19.1% for the upper band, and the measured 3 dB axial-ratio bandwidths are 22.3% and 18.3%, with respect to 2.6 GHz and 3.5 GHz, respectively.

This paper presents the extension of the Maxwell Garnett effective medium model accounting for an arbitrary orientation of ellipsoidal inclusions. The proposed model is shown to be asymptotically convergent to the Maxwell Garnett mixing rule for a homogenous distribution of inclusions. Subsequently, a special case of a thin composite layer with a two-dimensional distribution of inclusions is considered and a simplified Maxwell Garnett formula is formally derived. The proposed model is validated against the alternative theoretical calculations and measurements data.

An adaptive approach to minimize acquisition time in planar near-field antenna measurements is described. In contrast to the traditional planar near-field scanning, the presented technique acquires the near-field in form of rectangular rings and skips sampling points in smoothly varying near-field regions. Abrupt changes in the near-field are detected by comparing extrapolated and measured near-field values at coarser sampling points. A decision function based on the signal-to-noise ratio (SNR) of the measured value is used to determine the threshold difference between the measured and the extrapolated near-field values for skipping the sampling point. Near-field data thus collected on the resultant irregular grid is processed using the multilevel plane wave based near-field far-field transformation algorithm. The multilevel transformation algorithm is computationally efficient and capable of handling data collected on irregular grids. A rigorous analysis of the adaptive data acquisition approach is then performed in terms of transformed far-field accuracy, decision factor, and test time reduction. Several test cases covering a variety of antennas are shown using synthetic as well as measured data for realistic results. Afterwards the acquisition time for the worst case scenario is compared with the traditional planar near-field measurement technique.

In this paper, a novel idea of reducing numerical complexity of finite difference method using multiple macromodels is presented. The efficiency of the macromodeling technique depends on the number of ports of a model. To enhance the efficiency of the algorithm the field samples at the boundary of the macromodel are replaced with amplitudes of discretized Legendre polynomials. Redefining the problem in such manner results in significant reduction of the analysis time. The validity and efficiency of the proposed procedure are demonstrated by performing the analysis of two microwave filters requiring a high density mesh.

Based upon the standard IEEE 1309, a new calibration method for electromagnetic (EM) probes is proposed. The aforementioned method compares the electric field strength measured with the EM probe subject to calibration with the E-field intensity calculated through a linear interpolation of the corrected measurement using a reference EM probe. The corrected measurement results are computed by means of the calibration factors stated in the calibration certificate of the reference EM probe. The conditions and criteria under which it is possible to calibrate EM probes inside semi-anechoic chambers in the frequency range of 80 MHz to 1 GHz, are presented. The results shows that the calibration method proposed in this paper is characterized by deviations of less than 1 dB in almost all the frequencies considered, verifying the reliability of the method. The proposed approach is very useful for registering the measurement drift of EM probes used in EMC testing laboratories.

Remote sensing approaches based on both optical and microwave region of EM spectra have been widely adapted for large scale crop monitoring and condition assessment. Visible, infrared and microwave wavelengths are sensitive to different crop characteristics, thus data from optical and radar sensors are complementary. Synthetic Aperture Radar (SAR) responds to the large scale crop structure (size, shape and orientation of leaves, stalks, and fruits) and the dielectric properties of the crop canopy. Research is needed to assess the saturation effects of SAR data and to investigate the synergy between the optical and SAR imagery for exploring various dimensions of crop growth which is not possible with any one of them singly with higher degree of accuracy. An attempt has been made to study the potential of SAR and optical data individually and by fusing them to separate various landcover classes. Two-date and three-date SAR data could distinguish jute and tea crop with 70-85% accuracy, while cloud free optical data (green, red and infrared bands) resulted in accuracy 80-85%. On fusing the optical and SAR single date data of May, 29 2010 using Brovey method, an accuracy of 85{\%} was obtained. PCA and HSV with munsell based approaches resulted in similar accuracies but HSV performed the best among these. This emphasizes on the synergistic effect of SAR and optical data. Also the fused data could be used to delineate the crop condition and age by inputs like NDVI from optical and XPR (Cross polarization ratio) from SAR data. The co- and cross polarization ratios along with various indices viz. Biomass Index (BMI), Volume Scattering Index (VSI) and canopy structural index (CSI) were used to discriminate tea from jute. Due to differences in structural component of tea and jute at early season as manifested by the indices, there is clear separability as observed from the mean values. Among the dual polarization combinations, HV/VV performed the best (70%) followed by HV/HH (62%) and lastly HH/VV (42%). Among the single best indices for discrimination BMI performed the best. Combination of Co, Cross-polarization and BMI yields around 80% classification accuracy. BMI and VSI combination yielded the best classification accuracy of 84%. This level of accuracy obtained was much superior to that of multidate HH polarization SAR data.

In this work, we propose a method based on Genetic algorithm hybridized with Pattern Search for joint estimation of Amplitude and Direction of Arrival, azimuth as well as elevation angles using L-type array. Four other schemes i.e., the Genetic algorithm, Pattern Search, Simulated Annealing and Simulated Annealing hybridized with Pattern Search are also discussed and compared with Genetic algorithm hybridized with Pattern Search. Multiple sources are taken in the far field of sensors array and Mean Square Error is taken as a fitness function. This fitness function is optimal in nature and requires only a single snapshot. It avoids any ambiguity or required permutation as in some other methods to link it with angles found in the previous snapshot. The reliability and effectiveness of the proposed scheme is tested on the basis of Monte- Carlo simulations and its statistical analysis.