In this letter, a compact branch-line coupler using a new type of uniplanar composite right/left-handed transmission line (CRLH-TL) is proposed. The transmission line is obtained by etching spiral structure and series meandered capacitive gaps at both ends on the host line. With the aid of lumped element equivalent circuit model and dispersion relations, the CRLH property of the line is studied. By using the proposed structures, the 90-degree phase shift 35.35 ohm and 50 ohm transmission lines are designed for a compact branch-line coupler operating at 1 GHz. It's occupied size is only 32.5% of that of the conventional one. Its uniplanar prototype makes it very useful for wireless communication systems requiring high encapsulation quality.

In this work we present a new physics-based approach for formulating MoM problems based on the use of dipole moments (DMs) --- as opposed to the conventional Green's functions. The proposed technique is valid over the entire frequency range without any need for special treatments and is also free of singularities associated with the Green's function. The DM approach can be used equally well to both PEC and Dielectric objects. We also introduce certain refinements to the DM method to improve its computational efficiency like the use of higher-order basis functions, combining the DM with the Characteristic Basis Function Method (CBFM), the use of closed-form expressions for the calculation of interaction matrix elements and employing Fast Matrix Generation (FMG) for electrically large problems. We also demonstrate ways to incorporate lumped loads, capture sharp resonances even at low frequencies, calculate the input impedance of small antennas, calculate fields from irregular geometries; from faceted surfaces; from geometries with slot and slit; and also demonstrate the capability to model microstrip line type of geometries with fine features.

In order to reduce the higher harmonic component of the magnetic field in magnetically levitated permanent-magnet planar motors (PMPMs), a sinusoidal index for 2-dimensional (2D) wave is proposed and verified by calculating the average total harmonic distortion (THD) of the discrete waveform. Based on this, a novel optimal design method using THD for 2-dimensional wave (THD2D) and fundamental amplitude is proposed for PMPMs. The finite element analysis and experimental results show that the higher harmonic component of magnetic field is reduced with average fundamental amplitude invariant, and the back-EMF is better. So the optimal design method can improve the electromagnetic performance of magnetically levitated PMPMs.

To avoid the spatial variation of scattering characteristic effect, a three-dimensional synthetic aperture radar (3-D SAR) imaging based radar cross section (RCS) extraction technique with fixed transmitter is developed. The 3-D SAR image is used to extract targets' RCS, so it can spatially distinguish different parts of a complex object, or the targets' RCS from environment. With the abilities of outdoor measurement, it can greatly reduce the cost of measurement. Two simulations of three squares and a 3-D complex-shaped electric-large flight model demonstrate the accurate prediction of RCS.

Biomedical imaging has played an important role in identifying and monitoring the effectiveness of the current state of the art treatments for many diseases. The authors recently proposed a novel single-transmitter-multiple-receiver holographic microwave imaging (HMI) technique for imaging small inclusion embedded in a dielectric object which has potential application in medical diagnostics. HMI image quality depends highly on the antenna baseline difference, in order words, the antenna array configuration. Different antenna arrays produce different quality of dielectric images by using HMI imaging algorithm. This paper investigates the antenna array configurations effect on image quality by using HMI imaging approach. Three configurations including spiral, random and regularly spaced arrays are presented in this paper. Both simulated and experimental results are obtained and compared to fully demonstrate the effectiveness of antenna arrays to the HMI technique. The results show that the proposed spiral and random array configurations have an ability to produce high-resolution images at significantly lower costs than regularly spaced arrays.

In this paper, angular glint characteristics of a two-dimension (2-D) perfect electric conductor (PEC) target above a PEC rough surface are investigated. The induced surface currents on the target and on the rough surface are obtained by employing the method of moments com-bining UV matrix decomposition technique (MOM-UV). Based on electromagnetic (EM) theory and the phase-front distortion concept of angular glint, the formulae of angular glint for 2-D target are proposed, and angular glint is calculated precisely by using phase gradient method (PGM). The analysis of the result is implemented by means of numerical extraction of the coupling currents and relationship between the phase front and angular glint, thus revealing the effects of the coupling on the angular glint.

Advances in micro robots in non-invasive medicine have enabled physicians to perform diagnostic and therapeutic procedures with higher resolution and lower risk than before. However, navigation and precise localisation of such micro robots inside human body still remains a challenge. This is mostly due to the 1) lack of precise communication channel models, 2) inhomogeneity of the propagation medium and 3) non-geometric boundaries of the tissues morphometric parameters. In this study, we derive novel intra-body path loss channel models for wave propagation in wireless capsule endoscopy, i.e., propagation through the gastrointestinal tract and the abdominal wall. We formulate an adaptive attenuation parameter as a function of permittivity, conductivity and the thickness of various layers between the transmitter and the receiver. The standard deviation of modelling error of the path loss using our adaptive channel model is smaller than 50% of that of existing channel models. We further analyse the sensitivity of the path loss model to the variations of thickness of different abdominal wall layers. We finally show that the thickness of the fat layer has the greatest influence on the total attenuation parameter of the path loss model and therefore, we modify our adaptive model accordingly.

A right-angled waveguide bend using conformal transformation optics is proposed which guides the input electromagnetic wave smoothly through the waveguide, reduces the reflections and broadens the bandwidth of the device significantly. The isotropic material parameters are obtained through solving Laplace's equations with Dirichlet and Neumann boundary conditions. It is shown that the performance of the proposed bend is mainly determined by refractive indices lower than one. Utilizing this, the approximated resulting medium is implemented by drilling hole arrays in a dielectric background. In order to take advantage of planar technology, it can be implemented in a substrate integrated waveguide.

Active Magnetic Bearings (AMBs) are advantageous due to their active control on rotor position, but are disadvantageous due to their high initial as well running costs. The running cost of AMB can be reduced by improving design of electromagnet so that the same magnetic field can be generated with reduced supply of electric current. In the present paper, analyses of various arrangements of electromagnets using 2D finite element (FE) have been presented. To validate the results of magnetic flux density obtained from theoretical study, experiments were performed, and comparisons have been presented. The electromagnet using Halbach winding arrangement provides the best results.

Statistical Maxwell's Electromagnetic Theories have been developed over many years and applied to a wide range of practical problems in remote sensing of geographical media, imaging in biological media, medical optics, ultrasound imaging, and object detection and imaging and communications in clutter environment. This paper gives a review of recent advances, development and applications of statistical wave theory. Many important problems on imaging in geophysical and biological media have been treated often as separate problems. This paper attempts to present unified theoretical work and viewpoints under the statistical theories which may help further advance and understanding of theories and applications. The statistical electromagnetic theories encompass most advanced mathematical and theoretical work and most practical applications. This includes time-reversal imaging through multiple scattering media, super resolution, communication channel capacity in clutter, space-time vector radiative transfer, bio-electromagnetics and ultrasound in tissues, coherence in multiple scattering, memory effects, the use of transformation electromagnetics, seismic coda, and the fundamental multiple scattering theories. Statistical Electromagnetics Theories are one of the most challenging theoretical problems today involving many applications in geographical and biological media.

A novel miniaturized combined-element frequency selective surface (CEFSS) with simple design process is proposed for multiband applications. In this article, complementary meandered structures and complementary grid structures are combined to realize controllable tri-band characteristics, which allow the designed FSS to transmit different frequency signals at 3.3, 4.5 and 5.4 GHz while reflecting signals at 4.0 and 4.9 GHz. The miniaturized combined-element FSS in this paper has the advantage of smaller size comparing to traditional tri-band FSSs due to the use of meandered structures, which contributes to its independence of both angle and polarization. The associated equivalent circuit is provided to analyze its transmission characteristics. Furthermore, the performances of the proposed structure are evaluated by simulation and measurement, and they agree well.

A planar ultra-wideband (UWB) antenna with triple-notched bands based on square ring short stub loaded resonator (SRSSLR) is presented in this paper. By coupling a SRSSLR beside the microstrip feedline, band-rejected filtering properties around the C-band satellite communication band, 5.8 GHz WLAN band, and 6.8 GHz RFID band are generated. The notched frequencies can be adjusted according to specification by altering the SRSSLR. The results indicate that proposed planar antenna not only retains an ultra wide bandwidth, but also owns triple band-rejections capability. The UWB antenna demonstrates omnidirectional radiation patterns across nearly whole operating bandwidth that is suitable for UWB communications.

In this paper the propagation of electromagnetic waves in a medium with non zero conductivity is discussed, analyzing the dielectric properties of the sea water, in order to accurately characterize a wireless communication channel. Mathematical models for sea water dielectric constant, wavelength, propagation speed and path loss when an electromagnetic wave at 2.4 GHz propagates through sea water are presented. A Bow-Tie microstrip antenna that is required to overcome the high path loss and bandwidth requirements in sea water is studied. A dual-band antenna, with arc-shaped circular slots, operating for IEEE802.11 b/g/n standards, at 2.4 GHz and 5.1 GHz for WLAN communications, with dimensions 1.4 cm² is implemented. Return loss, input impedance and gain have been extracted in order to characterize antennas' performance in a conductive medium.

A novel coupled-defected ground structure (C-DGS) with inductors inserted between the adjacent defected ground structure (DGS) cells is presented in this paper. In comparison to conventional C-DGS structure, the proposed C-DGS exhibits a larger coupling-coefficient, resulting in a wider stop-band. Moreover, the stopband can be adjusted flexibly without modification since the coupling-coefficient varies with the change of the inductance of the inserted inductor. Based on this new C-DGS, a low-pass filter (LPF) using cascaded C-DGS is constructed. The proposed structure is experimentally verified through the demonstration of a low-pass filter design.

In this article, a matching pursuit algorithm is developed to improve the performance of a passive multiplexing technique based on compressed sensing. This deconvolution technique is applied to RADAR imaging in the microwave range, starting from previous studies based on a compact coding device and L₁-norm regularizations. This study demonstrates that in this context, the quality of the reconstructed RADAR images can be improved using an algorithm close to Hogbom's Clean, and based on a dictionary built with Tikhonov pseudo-inversions. The theoretical principle of this new algorithm is developed, followed by a parameters study. Finally, an experimental validation is presented to demonstrate the efficiency of this iterative algorithm.

Novel compact ultra-wideband (UWB) rectangular stacked dielectric resonator antennas (DRAs) with band-notched characteristics are proposed. The DRAs are designed to cover the FCC band (3.1-10.6 GHz) and have very compact sizes, due to the shorting conductor. Printed dipoles that are placed on one side of the dielectric resonator will resonate and generate band notches within the ultra-wide operating band. Simulations and measurements confirm the validation of the design principle.

A loop antenna is designed and fabricated for ultra-high frequency (UHF) near-field radio frequency identification (RFID) readers. The artificial mu-negative transmission line (MNG-TL) structure has been applied to the antenna design, which will help the current distribution along the loop to keep in phase even with the perimeter of the loop more than two operating wavelengths. Thus a strong and uniform magnetic field distribution in the near field of the antenna can be generated. The simulated and measured results indicate that a relatively large impedance bandwidth from 762 MHz to 1048 MHz has been obtained. The overall size of the antenna is 216 mm×216 mm×0.4 mm, and a large interrogation zone with uniform and strong magnetic field distribution of up to 187.2 mm×187.2 mm has been achieved.

Permanent-magnets (PMs) with tangential and parallel magnetization directions are combined in the Halbach PM (HPM) machine, which can offer high performances. However, the existing lumped parameter magnetic circuit (LPMC) model can only calculate one PM magnetization direction, namely either tangential direction or parallel direction. The key of this paper is to propose a method to divide and establish equivalent magnetic motive force (MMF) for HPM machine with both tangential and parallel magnetizations. Then, a LPMC model, using equivalent MMF, is developed to predict the electromagnetic performances for a four-phase HPM machine. In order to verify the effectiveness of the proposed LPMC model, a 6-pole/8-slot 15 kW HPM prototype is built. The comparative results of the proposed LPMC model, finite-element results and the experiments verify the effectiveness of the proposed LPMC model.

It is generally believed that antenna correlations of up to 0.5 in magnitude have negligible effects on the performance of multi-antenna systems, and that antenna correlation only affects the system performance via its magnitude. In this paper, we show that antenna correlations of 0.5 in magnitude that has negligible effect in capacity (i.e., theoretically maximum data rate) can cause noticeable degradation on the throughput (i.e., actual achievable data rate); and that, when the number of antennas is larger than two, the phase of the correlation also has an impact on the performance of multi-antenna system. We demonstrated these via simulations and measurements in a reverberation chamber.

In this paper, a SPICE model representative for the mode conversion occurring in differential lines affected by imbalance either of the line cross-section and the terminal networks is developed. The model is based on the assumption of weak imbalance and allows approximate prediction of modal quantities, through separate modeling of the contributions due to line and termination imbalance by controlled sources with (possibly) frequency dependent gain. The proposed SPICE model is used to perform worst-case prediction of undesired modal voltages induced at line terminals by mode conversion.