A compact triple-band monopole antenna with two different slots for WLAN and WiMAX applications is proposed and experimentally studied. The proposed antenna with a size of 30mm×25mm×1mm is excited by a 50Ω microstrip feed line. The designed antenna obtains three frequency bands through loading an inverted E-shaped slot and an inverted C-shaped slot which incise the surface current and change the path of the current on the rectangle patch. The obtained results show that the designed antenna has impedance bandwidths of 2.4 GHz, 5.8 GHz for WLAN and 3.5 GHz for WiMAX. The return loss, radiation patterns and peak antenna gains are presented using computer simulations and measurements.

We experimentally quantify the radiation of a small Ultra-Wideband (UWB) antenna placed on a human body. The measurements are performed for different antenna locations on the body, namely the head, torso and belt. First the antenna is measured in free space as reference, and then the influences of the body are investigated for different frequencies and antenna polarizations. We observe minimal signal blockage when the antenna is located on the head. It is around 5d B-10 dB loss for all polarizations. For the belt and torso, the blockage is 10 dB to 35 dB, for both polarizations.

The plane-wave synthesis is brought to the CATR. The feed scans in the focal plane and antenna pattern is measured several times in different feed positions. The corrected antenna pattern is obtained by weighting the measured patterns. The weight is obtained by the least squares method for the electric fields in the aperture plane of the test antenna. The fashion, number and spacing of feed scanning are investigated. By the plane-wave synthesis in the CATR, a larger antenna can be tested, and higher test accuracy can be obtained than that of the CATR. Lower test number and less test time are needed than the conventional plane-wave synthesis. The technique proposed in this paper is numerically investigated in an offset single paraboloid CATR and verified experimentally in a Cassegrain CATR at 100 GHz.

Target localization is one challenge in passive coherent location (PCL) radar system, and the time delay is the most important parameter in the location. The difficulty of time delay estimate (TDE) in PCL system is that the target signal is completely buried in direct path signal, multipath and clutter (DMC). The conventional clutter cancellation algorithms in matched filter (MF) are time consuming. In this paper, we propose a time delay estimate method based on blind source extraction (BSE) which directly extract the target signal from the mixed signals, thus a new passive coherent location system is built. In this model, the reference antenna is not needed any more. For low signal to interference plus noise ratio (SINR) and frequency overlapped signals in passive coherent location, we introduce the cyclostationarity to enhance the target signal. The experiments on FM broadcast signals show that the computational burden of the proposed algorithm is extremely small and the improved SNR satisfies the location requirements of PCL system.

This paper presents a novel tri-band unequal Wilkinson power divider. The proposed structure is derived from the conventional unequal Wilkinson power divider by replacing the quarter-wavelength branch lines and quarter-wavelength transformers with the extended T-shaped short stubs and three-section transformers respectively. The first and third operating frequencies of the proposed Wilkinson power divider can be flexibly controlled, while the second frequency is equal to the mean value of the other two frequencies. Both of the closed-form equations and design procedure are given. For verification, a tri-band unequal power divider with the power dividing ratio of 2:1 and operating frequencies of 1.3, 3.0 and 4.7 GHz is designed, fabricated and measured. The measurement results are in good agreement with the simulation ones. It is shown that the proposed power divider has simple topology and good performances in terms of insertion loss, port matching and isolation at all three operating frequency bands.

In this paper, a deterministic strategy to generate the aperiodicity, based on three geometric taper distributions is studied and validated. The method is applied to study arrays with average inter-elements spacing larger than a wavelength, exhibiting a reduction of the grating lobe level and requiring lower aperture size against a periodic structure with same directivity. Finally, a microstrip patch aperiodic array has been designed, manufactured and measured for an experimental validation of the concept, obtaining good agreement between simulated and measured radiation patterns. This manufactured antenna demonstrates experimentally the reduction of the grating lobes with a similar level to the side lobe.

In this paper, a rectifying antenna (rectenna) for energy scavenging applications is presented. The proposed device uses a modified bowtie antenna to collect the electromagnetic energy coming from UHF RFID systems, and RF Schottky diodes to convert it into DC power. Experimental results at 866 MHz demonstrating an RF-to-DC conversion efficiency of about 65% with an input power density of 60 μW/cm² will be presented and discussed.

A transient quasi-analytic method is improved to analyze the offset reflector for impulse radiating antenna (IRA) applications. Physical optic (PO) approximation and analytic time transform (ATT) are utilized to investigate the time domain (TD) radiating characteristics of the offset reflector. With the appropriate coordinate transformation, the TD far-field integral problem can be simplified to one dimensional angular integral which is independent of the reflector's size. In addition, the Fast Fourier Transform (FFT) of impulse responses is compared to the direct frequency domain result, and good agreement is obtained.

This work presents a novel approach in building a multidimensional approximator which is used as a linear operator for mapping the vector of detuned filter characteristic to the vector of deviations of tuning elements. This has been done for the purpose of using it in postproduction filter tuning algorithm. With the use of collected sets of deviations of tuning elements and filter characteristics corresponding to them, the least squares method (LSM) is applied to determine the matrix which realizes the linear mapping between these vectors. The matrix found in this method approximates the vectors of both spaces (filter characteristics and corresponding deviations of tuning elements). In tuning process this matrix is used to determine the vector of tuning element deviations for a given detuned filter characteristic read from Vector Network Analyzer. To increase the ``quality'' of linear operator filter characteristics are transformed with the use of Karhunen-Loeve transform (Principal Component Analysis). In contrast to non-linear artificial intelligence approximators used in filter tuning and published to-date, this method does not require a time-consuming training process. Filter tuning experiments have been performed and proved the correctness of the presented approach.

The composite backscattering of the ship model on sea surface is investigated with the spilling breaking waves and ship bow waves. The spilling breakers are approximately modeled with the wedge-like waves, and the ship bow waves are simulated based on the Kelvin model. With the modified four-path model, each scattering component is evaluated with the high frequency approximation methods for the total composite scattering. Due to the volume scattering, the composite scattering at large incidence angles is strongly enhanced by the non-Bragg scattering. The relationship of the composite scattering and the ship motion is analyzed. The numerical results of sea surface scattering agree with the measured data well, and the complex physical mechanism of the low-grazing-angle composite scattering is explicitly evaluated in this paper.

The design of a 2ⁿ×2ⁿ Butler matrix is usually based on an iterative process. In this paper, recurrence relations behind this process are found, and the close-form solutions, i.e., non-recursive functions of n, are reported. These solutions allow the direct derivation of the scattering matrix coecients of symmetric and large Butler matrices.

The satellite-borne SAR (Synthetic Aperture Radar) is a quite promising tool for high-resolution geo-surface measurement. Recently, there has been a great interest in Coherent Change Detection (CCD), where the coherence between two SAR images is evaluated and analyzed to detect surface changes. The sample coherence threshold may be used to distinguish between the changed and unchanged regions in the scene. Using COSMO-SkyMed (CSK) images, we show that for changed areas, the coherence is low but not completely lost. This situation, which is caused by the presence of bias in the coherence estimate, considerably degrades the performance of the sample threshold method. To overcome this problem, robust detection in inhomogeneous data must be considered. In this work, we propose the application and improvement of three techniques: Mean Level Detector (MLD), Ordered Statistic (OS) and Censored Mean Level Detector (CMLD), all applied to coherence in order to detect surface changes. The probabilities of detection and false alarm are estimated experimentally using high-resolution CSK images. We show that the proposed method, CMLD with incorporation of guard cells (GC) in the range direction, is robust and allows for nearly 4% higher detection probability in case of low false alarm probability.

According to the uniqueness theorem, the far field radiation pattern of radiators such as antennas can be determined from the measured tangential electric or magnetic field components over an arbitrary Huygens' surface enclosing the radiator. In this paper, a method using the spherical electric field measurement is developed to calculate the far field radiation. Following the Schelkunoff's field equivalence principle, a spherical region surrounding the radiator is assumed and its internal space is filled up with the perfect electric conductor (PEC). The radiated field from the Huygens' equivalent electric current is zero. Referring to the Ohm-Rayleigh method and the scattering wave superposition, the dyadic Green's function (DGF) with the presence of a PEC sphere is expanded by a series of spherical vector wave functions. Based on the DGF and the measured tangential electric field, the radiation behavior of the radiator can be directly predicted without involving the uncertainty from the inverse process. The robustness and accuracy of the proposed method are verified through several canonical antenna benchmarks.

The problem of excitation of electromagnetic fields by a material body of finite dimensions in presence of coupling hole between two arbitrary electrodynamic volumes is formulated. The problem is reduced to two-dimensional integral equations for the surface electric current on a material body and the equivalent magnetic current on a coupling hole. A physically correct transition from the initial integral equations to one-dimensional equations for the currents in a thin impedance vibrator which, in general case, may have irregular geometric parameters, and a narrow slot is justified. A solution of resulting equations system for the transverse slot in the broad wall of rectangular waveguide and a vibrator with variable surface impedance in it was found by a generalized method of induced electro-magneto-motive forces. The calculated and experimental plots of electrodynamic characteristics of a vibrator-slot structure in a rectangular waveguide are presented.

The paper gives an analytical transition from the Maxwell Garnett model of a biphasic mixture (dielectric host and dielectric or conducting inclusions) to the parameters of a single- or double-term Debye representation of the material frequency response. The paper is focused on modeling biphasic mixtures containing cylindrical inclusions. This is practically important for engineering electromagnetic absorbing composite materials, for example, containing carbon fibers. The causal Debye representation is important for incorporation of a composite material in numerical electromagnetic codes, especially time-domain techniques, such as the finite-difference time-domain (FDTD) technique. The equations derived in this paper are different for different types of host and inclusion materials. The corresponding cases for the typical combinations of host and inclusion materials are considered, and examples are provided. The difference between the original Maxwell Garnett model and the derived Debye model is quantified for validating the proposed analytical derivation. It is demonstrated that in some cases the derived equivalent Debye model well approximates the frequency characteristics of the homogeneous model based on the MGA, and in some cases there is an exact match between Debye and Maxwell Garnett models.

In order to study beam-propagation factor (M²-factor) of partially coherent Laguerre-Gaussian (PCLG) beams in non-Kolmogorov turbulence, a generalized exponent and a generalized amplitude factor are introduced. Based on the extended Huygens-Fresnel principle and second-order moments of the Wigner distribution function (WDF), the analytical formula of M²-factor for PCLG beams in non-Kolmogorov turbulence is derived. The corresponding numerical results are also calculated. Results show that for PCLG beams propagating in non-Kolmogorov turbulence, the bigger the beam order or outer scale is, or the smaller the correlation length, C²_n, or inner scale is, the smaller the value of the normalized M²-factor is. Furthermore, the normalized M²-factor of PLG beams increases with the increasing of α until it reaches the maximum point, then it gradually decreases with the increasing of α. ²

An infinitely flanged coaxial line is analytically solved with the mode-matching technique and Green's function to propose a precise yet fast-convergent scattering solution for complex permittivity measurement. Based on virtual current cancelation, we formulate the open half-space fields in terms of coaxial modes and related Green's functions and thus obtain the simultaneous equations with rapidly convergent integrals. Numerical computations were performed in terms of reflection coefficients and radiation patterns.

We present an approach for very quick and accurate approximation of infinite series summation arising in electromagnetic problems. This approach is based on using asymptotic expansions of the arguments and the use of fast convergent series to accelerate the convergence of each term. It has been validated by obtaining very accurate solution for propagation constant for shielded microstrip lines using spectral domain approach (SDA). In the spectral domain analysis of shielded microstrip lines, the elements of the Galerkin matrix are summations of infinite series of product of Bessel functions and Green's function. The infinite summation is accelerated by leading term extraction using asymptotic expansions for the Bessel function and the Green's function, and the summation of the leading terms is carried out using the fast convergent series.

We propose an all optical switch in a dual-core photonic crystal fiber (PCF) that has the core region consisting of soft glass and has nematic liquid crystal filled holes in the cladding region. Light waves are guided in this PCF by total internal reflection (TIR) due to the refractive index contrast between soft glass and liquid crystal (LC). Its wavelength dependent coupling, birefringence and dispersion are calculated and later use these parameters to evaluate the switching characteristics of short pulses propagating through this optical waveguide. The switch demonstrates tunability with external perturbation such as applying external heat source or electric field. Refractive index sensitivity of LC with these perturbation as well as polarization of the light signal determines the coupling, birefringence and dispersion properties of the overall waveguide and its switching characteristics.

A novel perturbation technique is formulated that enables the efficient calculation of current on surfaces undergoing time-varying mechanical deformations. The technique computes the current on the perturbed surface using as its starting point the solution for a related static case. This is initially derived using a standard analytical or numerical technique. The key advantage of this approach is that only an initial (computationally expensive) electromagnetic characterisation of the static problem is required. The surface current perturbation terms (and hence the radiated fields) are then directly computed from the static problem with a very low computational overhead.