A time-domain approach for distortion analysis of electromagnetic eld senors is developed in Laguerre functions subspace. Using Laguerre convolution preservation property, it is proved that every electromagnetic eld sensor corresponds to an equivalent discrete-time LTI system. The equivalent discrete-time system is compared to a reference system as a measure of distortion. Further, this analysis may be performed repeatedly to obtain a bandwidth-limited distortion characteristic. The method is employed to compare the distortion characteristic of an asymptotic conical dipole (ACD) to wire monopoles of various lengths. A time-domain simulation is performed in order to nd the distortion characteristics by solving an electric eld integral equation (EFIE) using the method of moments (MoM).

A compact microstrip-line dual-band bandpass filter using a short stub-loaded resonator is presented. The resonator is formed by loading one short stub in shunt to a simple uniform impedance line. A key merit of the filter configuration is that the center frequency and bandwidth of the first passband can be conveniently controlled by properly adjusting the lengths of the short stubs and the coupling between the short stubs, whereas those of the second passband are fixed. To illustrate the concept, a third-order dual-band filter is designed, fabricated and measured. Simulated and measured results are found to be in good agreement with each other.

In this paper, a linear polarization switchable planar array antenna with enhanced gain and better crosspolarization is proposed. The proposed array antenna consists of a fed patch and four parasitic patches. Four switching diodes are loaded on the corners of the fed patch. The boundary condition of the fed patch is controlled by using the ON/OFF condition of the diodes, and the polarization angle of the array antenna can be orthogonally switched to ±45° with better than -22 dB of crosspolarization. The simulated gain of the array antenna is remarkably increased to 12 dBi by using four parasitic patches surrounding the fed patch. For matching the resonance frequency of the parasitic patches with the fed patch, a square slot is formed at the center of each parasitic patch. The characteristics of the proposed array antenna are investigated by the FDTD simulation method. The array antenna is fabricated and the experiment is carried out. Both the simulation and the experimental results of the proposed array antenna demonstrate the polarization switching functionality successfully with the enhanced gain in S-band.

Millimeter-wave (MMW) imaging techniques have been developed for the detection of concealed weapons and plastic explosives carried on personnel at major transportation hubs and secure locations. The combination of frequency-modulated continuous-wave (FMCW) technology and MMW imaging techniques leads to wideband, compact, and cost-effective systems which are especially suitable for security detection. Cylindrical three-dimensional (3-D) imaging technique, with the ability of viewing multiple sides, is an extension of rectilinear 3-D imaging technique only viewing a single side. Due to the relatively long signal sweep time, the conventional stop-and-go approximation of the pulsed systems is not suitable for FMCW systems. Therefore, a 3-D backscattered signal model including the effects of the continuous motion within the signal duration time is developed for cylindrical imaging systems. Then, a modified cylindrical holographic algorithm, with motion compensation, is presented and demonstrated by means of numerical simulations.

An electromagnetic bandgap (EBG) structure is proposed to suppress the simultaneous switching noise (SSN) from 0.45 GHz to 5.3 GHz with an averaged suppression level of −66.4 dB. The design is based on the inductance enhancement by using meander lines to bridge slotted metal patches embedded into the power plane. Numerical simulation and experimental measurement are both used in the study for mutual verification. Compared to the conventional L-bridged EBG structure, the novel design increases the bandwidth by 15% and reduces the lower frequency by 150 MHz. A better omnidirectional SSN suppression is also achieved. For high-speed digital applications, the signal integrity is analyzed and improved.

One of the main techniques for the Finite-Difference Time-Domain (FDTD) analysis of dispersive media is the Recursive Convolution (RC) method. The idea here proposed for calculating the updating FDTD equation is based on the Laplace transform and is applied to the Drude dispersion case. A modified RC-FDTD algorithm is then deduced. We test our algorithm by simulating gold and silver nanospheres exposed to an optical plane wave and comparing the results with the analytical solution. The modified algorithm guarantees a better overall accuracy of the solution, in particular at the plasmonic resonance frequencies.

In the field of space-time adaptive processing (STAP), spare recovery type STAP (SR-STAP) algorithms exploit formulation of the clutter estimation problem in terms of sparse representation of a small number of clutter positions among a much larger number of potential positions in the angle-Doppler plane, and provide an effective approach to suppress the clutter especially in very short snapshots. However, it differs from many situations encountered by other SR application fields in the following ways: (i) it does not require to obtain the exact solution; (ii) it highly requires low-complexity approaches. In this paper, we focus on the performance analysis and parameters setting of STAP algorithms based on five representative fast SR techniques, namely, the compressive sampling matching pursuit, the sparse reconstruction by separable approximation, the fast iterative shrinkage-thresholding algorithm, the focal underdetermined system solution and the smoothed l₀ norm method.

Exact absorbing conditions are used in computational electrodynamics of nonsine waves for truncating the domain of computation when replacing the original open initial boundary value problem by a modified problem formulated in a bounded domain. In this paper we prove the equivalency of these two problems.

A compact dual-band CPW-fed triangle-shaped antenna is proposed for applications in 2.4/5 GHz WLAN and RFID. The designed antenna, including ground plane, is only 28 mm in height and 26 mm in width. By introducing a Π-shaped slot and a T-shaped strip, the proposed antenna can generate two separate impedance bandwidths. Prototypes of the proposed antenna have been constructed and tested. The measured impedance bandwidths, ranging from 2.36 GHz to 2.50 GHz and from 5.01 GHz to 6.33 GHz separately, are obtained with return loss less than -10.00 dB, which meet the required bandwidths specification of WLAN and RFID. Good omni-directional radiation and appropriate gain characteristics in the desired frequency bands have been achieved.

In this paper, a technical concept and design of circular polarization detection patch array antenna using a double-balanced RF multiplier is proposed. The microwave integration technology is effectively employed to realize the proposed array antenna. The double-balanced RF multiplier is integrated with an orthogonal planar array antenna. The array antenna which consists of 12 patch elements and the RF multiplier is realized by embedding four zero bias Schottky barrier diodes on a slot-ring. The Both-sided MIC technology is successfully employed to realize the array antenna. The array antenna is realized in a very simple and compact structure as all the antenna elements, feeding circuit and the RF multiplier are integrated on both sides of a dielectric substrate. The ability of the proposed array antenna to detect the orthogonal circular polarization (LHCP and RHCP) is successfully confirmed by the experimental investigation.

This paper is devoted to the experimental validation of two direct near-field-far-field transformations with cylindrical scanning for elongated antennas requiring a minimum number of near-field measurements. They rely on the nonredundant sampling representations of electromagnetic fields and employ two different source modellings suitable to deal with electrically long antennas. These transformations allow the accurate reconstruction of the antenna far-field pattern in any cut plane directly from the collected near-field data without interpolating them. Their effectiveness is assessed by the good agreement between the so recovered far-field patterns and those obtained by means of the classical near-field-far-field transformation with cylindrical scanning.

In the squint mode airborne spotlight synthetic aperture radar system using the range migration algorithm (RMA), autofocus (AF) technique yields poor results due to the squint spreading of the point spread function (PSF) of a scatterer. Thus, two-dimensional (2D) interpolation is required to direct PSF blurring in cross-range direction, to improve the cross-range resolution ¢y and to remove the spatially-varying sidelobe. Because conventional 2D interpolation requires huge computation time and yields large computation errors, we propose an efficient 2D interpolation technique for squint-mode RMA composed of two 1D interpolations. Simulation results using the measured turbulence data show ¢y was improved considerably and PSF was successfully focused by the proposed method with a reduced computation time.

By mounting the transmitter and receiver of Frequency Modulated Continuous Wave (FMCW) Synthetic Aperture Radar (SAR) system on separate platforms, bistatic FMCW SAR offers more considerable capabilities, reliability and flexibility while maintaining the small size, low cost and agile reaction. The bistatic FMCW SAR raw signal simulator is highly required to quantitatively support the design of bistatic FMCW SAR, to help mission planning, test processing algorithms, and analyze jamming and noises. Bistatic FMCW SAR raw signal can be exactly simulated target-by-target in time domain but with extremely time and memory consuming, especially when extended scenes are considered. In this paper, bistatic FMCW SAR signal model and Bistatic Point Target Reference Spectrum (BPTRS) is proposed, based on which a raw signal simulator is developed in the 2-D frequency domain for the first time, where Chirp-Z Transform (CZT) is used to formulate the range migration terms. By taking advantage of Fast Fourier Transform (FFT), the proposed raw signal simulator highly reduces the computational load with respect to the time domain approach. The simulated raw data is verified by analyzing the corresponding images focused by Range Doppler Algorithm (RDA).

Millimeter-wave (MMW) imaging is a powerful tool for the detection of objects concealed under clothing. Several factors including different kinds of objects, variety of covering materials and their thickness, accurate imaging of near-field scattered data affect the success of detection. To practice with such considerations, this paper presents the two-dimensional (2D) images of different targets hidden under various fabric sheets. The W-band inverse synthetic aperture radar (ISAR) data of various target-covering situations are acquired and imaged by applying both the focusing operator based inversion algorithm and the spherical back-projection algorithm. Results of these algorithms are demonstrated and compared to each other to assess the performance of the MMW imaging in detecting the concealed objects of both metallic and dielectric types.

A fast and efficient multi-dimensional adaptive sampling method (ASM) based on Stoer-Bulirsch (S-B) algorithm for frequency selective surface (FSS) analysis and design is presented in this paper. The multivariate rational function is established according to the functional relation of the scattering parameters with frequency and direction of incident wave, medium parameters and geometry dimensions of FSS structure, et al. In order to evaluate the values of the multivariate rational function fully automatically without determining the coefficients of the targeted rational interpolant, the one-dimensional S-B algorithm is expanded into multidimensional method. The sampling points in each dimension are chosen at the areas of maximum error in an adaptive way. The recursive interpolation results of one dimension are used as the initial values of next dimension in the recursive tabular until n-dimension recursive interpolation is accomplished. The initial values of recursive algorithm are calculated by spectral domain method of moments (MoM) at every sample point. The current distribution of FSS cell is predicted by Rao-Wilton-Glisson (RWG) subdomain basis functions which are applicable for arbitrarily shape elements. Four examples, including FSS with the eight-legged, cross and ring elements and FSS radome enclosed antennas, are considered to demonstrate the feasibility of applying the multi-dimensional ASM to analysis and optimal design of FSS. Numerical results show that the proposed method is superior in computation efficiency compared to the direct MoM. Good agreement between the proposed technique and the direct MoM is observed.

This paper presents a novel quad-band power divider with equal power division ratio. The proposed power divider is realized using two cascaded sections of dual-band transformers based on coupled microstrip lines. Limitations of using dual-band quarter-wavelength transformers based on coupled lines are studied through parametric analysis to obtain useful design guidelines related to available fabrication facilities. General closed-form expressions are used to calculate design parameters. To verify analysis and design methodologies, a prototype of quad-band equal power divider is proposed. Compared to conventional quad-band power dividers using sections of transmission line transformers the proposed power divider records a size reduction of about 20% and reduced parasitic effects at higher frequencies according to the usage of only two resistors instead of four with much smaller ohmic values. In addition, a quad-band power divider is proposed, fabricated and measured for 3G and 4G applications at 2.1, 2.5, 3.5, and 3.8 GHz frequencies. Measured and simulated data are in very good match which validates the novel design.

The effect of temperature on the photonic band gap has been investigated. One dimensional photonic crystal in the form of Si/air multilayer system has been studied in this communication. The refractive index of silicon layers is taken as a function of temperature and wavelength both. Therefore, this study may be considered to be physically more realistic. It may be useful for computing the optical properties for wider range of wavelength as well as temperature. We can use the proposed structure as temperature sensing device, narrow band optical filter and in many optical systems.

In this paper, a bandwidth enhancement technique of asymmetrical slot antennas with two different excitation methods is presented. One method of excitation is the microstrip line feed, and the other is the coplanar waveguide feed. The rectangular slot excited by microstrip line feed gives an impedance bandwidth of 14.76% (|S₁₁| < −10 dB). When the rectangular slot is excited by a coplanar waveguide (CPW), it gives an impedance bandwidth of 26.61%. Both impedance and radiation characteristics of these antennas are studied.

A TM mode analysis in a metamaterial based dielectric waveguide is proposed and introduced. Rigorously derived from Maxwell's equations, the dispersion properties are focussed on the fundamental properties of bound, surface and leaky modes of metamaterial based dielectric waveguide. Comparing with the conventional right handed material based waveguide, typical backward wave characteristic of volume and surface wave modes are found from the distribution of Poynting power to the transverse direction of waveguide.

Handset antennas strongly interact with the human body. When a user holds a handset during a phone call, the proximity of the human head considerably affects the antenna performance and eventually the quality of the wireless connection. Consequently, the assessment of the antenna parameters regarding free-space conditions is not enough to fully characterize the performance of handset antennas and a further analysis taking into account human head interaction is required. In this sense, this paper presents a study that deals with the human head interaction concerning two aspects: functional and biological. The first one analyzes the effect of the human head over the main antenna parameters (reflection coefficient, efficiency, and radiation pattern) whereas the second one evaluates the impact of the antenna over the human head in terms of Specific Absorption Rate (SAR). Four representative prototypes of radiating structures are measured in both conditions in order to compare their performance: a dual-band Planar Inverted F Antenna (PIFA), a hexa-band PIFA with a slotted ground plane, a set of coupled monopoles, and a new architecture referred as compact radiating system based on the excitation of the ground plane through a set of non-resonant ground plane boosters. A figure of merit that relates the antenna efficiency with the SAR values is proposed for comparison purposes. The results demonstrate that losses caused by the human head power absorption can be minimized if the antennas are placed in the edge located at a higher distance from the human cheek. Furthermore, the study reveals the robustness of the compact radiating system taking into account the human presence. This fact reinforces its position as an alternative solution to current handset antennas, capable of providing penta-band operation (GSM850/900, DCS, PCS, and UMTS) through ground plane boosters featured by their reduced volume of only 250 mm³.