A new antenna with dual-band circular polarization for the reception of WiMAX and WLAN is presented in this article. The circular polarization is achieved by a symmetrical U-slot together with an L-slot. The width of the signal strip is narrowed at the end of the feed point to widen the 3-dB axial ratio (AR) bandwidth and create a good impedance matching for the proposed antenna. A parametric study is conducted using a commercial simulation software based on the method of moments, and the antenna prototype is constructed and measured for providing the simulation validation. Experimental results show that the measured AR bandwidths are about 16.6% and 16.2% with respect to the center frequency at 3.5GHz and 5.3GHz. The radiation characteristics of the proposed antenna are also presented.

In this paper, a novel approach, namely nonlinear subprofile space (NSS), is proposed for radar target recognition using high-resolution range profile (HRRP). First, the HRRP samples are mapped into a high-dimensional feature space using nonlinear mapping. Second, the nonlinear features, namely nonlinear subprofiles, are extracted by nonlinear discriminant analysis. Then, for each class, the nonlinear subprofile space is formed using all the training nonlinear subprofiles of class. Finally, the minimum hyperplane distance classifier (MHDC) is used for classification. The aim of NSS method is to represent the feature area of target using nonlinear subprofile space, and effectively measure the distance between the test HRRP and feature area via minimum hyperplane distance (MHD) metric. The experimental results of measured data show that the proposed method has better performance of recognition than KPCA and KFDA.

The design and synthesis of quasi-elliptic triple-mode filter with three transmission poles and three transmission zeros are presented in this paper. The transfer and reflection filtering functions are obtained to get the even- and odd-mode admittance. The synthesized admittances give the even- and odd-mode networks, routing structure and coupling matrix of the filter. The microstrip prototype of the quasi-elliptic triple-mode filter is designed and realized to prove the feasibility of the approach. The filter is realized by having a capacitive coupling between the input and the output of a proposed triple mode resonator. The results show an excellent agreement with the theories.

Large electrical systems or facilities can be satisfactorily shielded by using low-cost meshed metallic nets. Here the shielding effectiveness for two such planar meshes is calculated analytically and verified both experimentally by using cascaded reverberation chambers as well as numerically with results computed using a full wave electromagnetic solver. It is shown that all three methods agree and, in addition, that non-square shaped aperture meshes can be handled with an equivalent square area shaped aperture.

This study introduces an extended optimal filtering technique for adaptive-on-transmit radar based on the transmission of pseudorandom noise waveforms as a method to simultaneously achieve low sidelobe level and spectral purity without degrading the main peak of the cross-correlation function. The proposed method is an extended version of the classical optimal filtering technique, resulting in longer codes with three simultaneously improved features that usually work in trade-off: 1) the cross-correlation function (CCF) sidelobe level is reduced in direct proportion to the filter length, K; 2) the out-of-band spectral suppression is at least 40 dB for pseudorandom binary sequences (PRBS); and 3) the frequency spectrum tail presents a decay given by K^-4, offering larger out-of-band frequency suppression. The proposed technique provides skewsymmetry to the input signal and is tested on PRBS, Barker, and Golay pair of complementary codes. The proposed codes are also demonstrated to be Doppler resistant and offer better multipath capability.

The probe correction technique applied to reactive near field characterization is based on a deconvolution process. However, the classical deconvolution based on an inverse Fourier transform has a restrictive limitation. It is based on the use of noiseless measurement data. Consequently, measurement noise makes the result obtained by the classical deconvolution based technique inefficient and requires an extremely low noise measurement facility. In this paper, a method to improve the probe correction stability when using corrupted measurement data is presented. The proposed constrained least squares filtering algorithm (CLSF) uses an inverse filtering approach that takes into account the statistical characteristics of the measurement noise. Computations data with electromagnetic software of two different structures validate this method and illustrate its reliability.

An optimum polarization-space-time joint domain processing (PST-JDP) technique is proposed for clutter suppression which adequately adopts the three-domain information including the polarization, space and Doppler frequency information of the radar echo. The study shows that the polarization information together with the space and Doppler frequency information are effective to significantly enhance the clutter suppression performance for airborne radar. Several new techniques, (i.e., the covariance matrix eigendecomposition, the spectral analysis and the resolution grid method), are utilized for deriving the performance of the optimum PST-JDP. The main factors which affect on the performance of clutter rejection are the clutter degree of polarization, statistical distance of polarization between target and clutter, Doppler frequency of target and input clutter-to-noise ratio. The new optimum PST-JDP method outperforms significantly the traditional optimum space-time processing technology, especially in the case of the slowly or tangentially moving target. The simulation verifies the correctness and efficiency of the model.

A low cost technology based on FR4 and thin flexible Pyralux substrate to develop membrane antennas/array with high efficiency and wide bandwidth for high speed V-band communication systems is proposed in this paper. A new low cost thin Pyralux substrate with a thickness of 75 μm, relative permittivity of εr = 2.4 and tanδ = 0.002 is used. First we developed the known classical aperture coupled antennas based on FR4 and pyralux substrate to validate this technology. The simulated and measured antenna radiation parameters for a single patch, 1x4 array of patches using aperture coupled technology give good results in terms of S11 bandwidth, gain and radiation pattern. But the back radiation is found to be high due to some radiation from the slot and the feeding microstrip line. Measurements of the antennas show approximately 9.7% and 10.8% impedance bandwidth (S11= -10 dB) with a maximum gain of 7.6 dBi and 12.4 dBi around 60 GHz, respectively. In order to reduce the back radiation, we developed slot coupled antennas with substrate integrated waveguide (SIW) technology. Measurements show a 10 % and 7.5 % impedance bandwidth with a maximum antenna gain of 7.9 dBi and 12.7 dBi around 60 GHz for SIW single patch and 1 x 4 array antenna, respectively. The efficiency in this case is found to be very good due to very low back radiation. The measured results are in good agreement with the numerical simulations. The new thin substrate used for making the antenna helps easy integration with millimeter wave components and circuits.

This paper presents a rectifying antenna (rectenna) for the harvesting of the microwave energy associated to UHF (Ultra-High Frequency) Radio Frequency IDentification (RFID) systems. The proposed device uses a capacitively loaded T-shaped monopole with a coplanar waveguide feeding line as receiving antenna and a five-stage voltage multiplier as rectifier. Experimental results demonstrating an RF-to-DC conversion efficiency of about 54% with an input power density of 80 μW/cm² will be presented and discussed.

Air is not the only medium that can spread and can be used to detect speech. In our previous paper, another valuable medium - millimeter wave (MMW) was introduced to develop a new kind of speech acquisition technique [Li et al., Progress In Electromagnetics Research B, 9, 199-214, 2008]. Because of the special features of the MMW radar, this speech acquisition method may provide some exciting possibilities for a wide range of applications. In the proposed study, we have designed a new kind of speech acquisition radar system. The super-heterodyne receiver was used in the new system so that to mitigate the severe DC offset problem and the associated 1/f noise at baseband. Furthermore, in order to decrease the harmonic noise, electro-circuit noise, and ambient noise which were combined in the MMW detected speech, an adaptive wavelet packet entropy algorithm is also proposed in this study, which incorporates the wavelet packet entropy based voice/unvoiced radar speech adaptive detection method and the human ear perception properties in a wavelet packet time-scale adaptation speech enhancement process. The performance of the proposed method is evaluated objectively by signal-to-noise ratio and subjectively by mean-opinion-score. The results confirm that the proposed method offers improved effects over other traditional speech enhancement methods for MMW radar speech.

In this paper, novel Bowtie antennas which cover complete UHF RFID band (860-960MHz), fabricated on various ultra-low-cost substrates using state-of-the-art printing technologies are investigated as an approach that aims to accommodate the antenna during the package printing process whilst faster production on commercially available paper. The proposed antenna structures are evaluated in reference to circuit and field concepts, to exhibit extreme degree of functional versatility. These antennas are developed to cater the variations which appear in electromagnetic properties and thickness of paper substrate due to various environmental effects. Computed (simulated) and well-agreed measurement results confirm a superior performance of the tag modules while stepping towards next generation of ``green'' tags.

A change in the relative proportions of a mixture of rubber tire dust and rice husks will cause a change in the mixture's electrical permittivity and its ability to absorb electromagnetic energy. An open-ended, coaxial probe was used in conjunction with three dielectric mixture equations (the Kraszewski equation, the Landau equation and the Lichtenecker equation) to obtain the dielectric properties of a mixture of rubber tire dust and rice husks (RTDRH) over the frequency range of 7 GHz to 13 GHz. Lichtenecker's equation for dielectrics proved to be a useful practical formulation for determining the effective permittivity of homogeneous dielectric mixtures. The effectiveness of these dielectric mixture equations in determining the effective permittivity of RTDRH was investigated in this study. A newly developed mixture equation was derived based on these dielectric mixture equations, and it and the existing equations were assessed to determine their effectiveness in determining dielectric properties of such mixtures.

This paper deals with the time-domain numerical calculation of electromagnetic (EM) fields in linearly dispersive media described by multipole Debye model. The frequency-dependent finite-difference time-domain (FD²TD) method is applied to solve Debye equations using convolution integrals or by direct integration. Original formulations of FD²TD methods are proposed using different approaches. In the first approach based on the solution of convolution equations, the exponential analytical behavior of the convolution integrand permits an efficient recursive FD²TD solution. In the second approach, derived by circuit theory, the transient equations are directly solved in time domain by the FD²TD method. A comparative analysis of several FD²TD methods in terms of stability, dispersion, computational time and memory is carried out.

PEMC medium is a special type of metamaterial which generalizes the pre-existing concepts of perfect electric conductor (PEC) and perfect magnetic conductor (PMC). PEMC medium is described by a special parameter named as admittance and denoted as M. This admittance parameter acts as a base in order to extract the nature of medium as PEC or PMC. Electromagnetic fields scattered by a PEMC sphere are investigated theoretically. A Hertz dipole as a source of excitation is considered. Co-polarized as well as cross-polarized component of the scattered fields are taken into consideration. A general solution of fields scattered by the PEMC sphere has been sought.

The calculation of electromagnetic (EM) fields and waves inside finite-sized structures comprised of different media can benefit from a diakoptics method such as linear embedding via Green's operators (LEGO). Unlike scattering problems, the excitation of EM waves within the bulk dielectric requires introducing sources inside the structure itself. To handle such occurrence, we have expanded the set of LEGO sub-domains - employed to formulate an EM problem - to deal with the inclusion of elementary sources. The corresponding subdomains (bricks) play the role of ``generators'' in the equivalent model. Moreover, if a source is ``turned off'', as it were, the enclosing brick can be utilized as a numerical ``probe'' to sample the EM field. In this paper, we present the integral equations of LEGO modified so as to accommodate generator/probe bricks. Numerical results are provided which demonstrate the validity and the efficiency of the approach.

Simultaneous exposure to multiple electromagnetic signals with widely differing carrier frequencies is a reality of daily life, but its possible effects on health are unknown. In this study we exposed rats to non-thermal levels of 900 and 2450 MHz TEM-mode radiation, applied individually or simultaneously, and we obtained estimates of 1 g mean SAR (specific absorption rate) in various tissues using a numerical model of the rat and finite-difference time-domain software. The experimental system comprised a GTEM (gigahertz TEM) chamber connected to two vector signal generators, a signal mixer and amplifier, a directional coupler, a spectrum analyzer and a power meter. Tissue sections from rats sacrificed 24 h after exposure, and from negative controls and positive controls exposed to gamma radiation, were stained with haematoxylin-eosin for evaluation of general cell morphology and with DAPI (4',6-diamidino-2-phenylindole) for evaluation of apoptosis. Lesions, tissue destruction and apoptosis were only observed in positive controls. The results for rats exposed to either frequency, or to both simultaneously, were similar to those of unexposed negative controls. It remains to determine whether chronic exposure is similarly innocuous.

The introduction of various wearable textile radiators facilitates the realization of a fully wearable electronic system. However, the human body itself poses a serious fundamental challenge to its realization, mainly due to electromagnetic interaction with radiators placed in its proximity. Thus antenna performance in terms of reflection coefficient, bandwidth, radiation pattern and efficiency is expected to be severely influenced during on-body deployment. Besides addressing the need for a systematic on body evaluation procedure, this work presents an in-depth discussion on the measured degradation relative to free space operation. Considering a practical deployment scenario, the two antenna designs are first optimized in proximity of a human-emulating box using a commercial simulator. ShieldIt textile is chosen to build the antenna's conductive components, and this prototype is then benchmarked against another similarly dimensioned prototype constructed using conductively-homogeneous copper foil. For each material, two dual-band prototypes are fabricated, one resonating at 2.45 GHz and 5.2 GHz, and the other at 2.45 GHz and 5.8 GHz. Two realistic on-body deployment locations are chosen to be investigated, on the chest and back, considering two antenna orientations - one radiating away from the user, and the other radiating along the body. Free space and on-body reflection coefficient, bandwidth and radiation pattern are evaluated for each prototype in an anechoic chamber, while a reverberation chamber is utilized to determine their efficiency. All measurements were carried out using consistently the same human volunteer. Evaluations show that coupling distance and conductivity are the main factors in determining efficiency rather than on-body location, given that evaluations are carried out while the antenna keeps its planar form.

An alternative, field-based formulation of transformation optics is proposed. Field transformations are expressed in the language of boundary conditions for the electromagnetic fields facilitated through the introduction of generalized potential functions. It is shown that the field-based approach is equivalent to the conventional coordinate-transformation approach but is preferable when looking for specific field distribution. A set of example devices such as invisibility cloaks, concentrators, rotators, and transformation optics lenses capable of creating light beams with predetermined field distribution (e.g., Gaussian and sinusoidal) is studied to validate the effectiveness of the field-based formulation. As for the boundary conditions for the cloaked region the absence of the normal component of the Poynting vector is justified. In the frames of the field-based approach the physical reasons behind infinite components (singularities) of the material parameters of transformation optics devices are straightforwardly revealed.

Generation of a wide-band response using partial information from the time domain (TD) data and frequency domain (FD) data has been accomplished in this paper through the use of three different orthogonal functions, such as the continuous Laguerre functions, the Bessel-Chebyshev functions, and the associate Hermite functions. In this hybrid approach, one can generate the early-time response using the method of marching-on-in-time (MOT) and use the method of moment (MOM) to generate the middle-frequency response, as the low-frequency data may be unstable. Since the early-time and the middle-frequency data are mutually complimentary, they can provide the missing low- and high-frequency response and the late-time response, respectively. Even though obtaining middle-frequency response from an object needs more computation time than the low-frequency response, this approach has better performance for the interpolation and extrapolation of a wide-band response.

In this article, a coupled-fed planar printed antenna mounted on the compact no-ground portion of the system circuit board of a mobile phone with a low profile of 10\,mm is proposed and studied. The presented antenna is formed by a double-branch feeding strip, a shorted coupling strip with two open-ended loops of different lengths, and a slotted ground structure consisting of two monopole slots, yet it has a size only 15×50 mm². Two wide operating bandwidths of 698--960\,MHz and 1710-2690 MHz can be achieved by these radiating strips, which provide multiple resonant modes at about 750, 1000, 1750, 2300 and 2900 MHz. In addition, with the presence of the two narrow slots and a chip inductor (L = 1.5 nH), in this study, the printed antenna can lead to much widened bandwidths in both the antenna's lower and upper bands to cover LTE700/GSM850/900 and DCS1800/PCS1900/UMTS2100/LTE2300/2500, respectively. Good radiation efficiency and antenna gain for frequencies over the desired operating bands are obtained. Detailed design considerations of the proposed antenna are described, and both experimental and simulated results are also presented and discussed.