In this paper, a novel algorithm based on an equivalent current source is proposed to reconstruct objects buried in a multilayered medium. First, a radiating current source, one part of the equivalent current source, is obtained directly in closed-form from scattering data via the signal-subspace method. Secondly, a nonradiating current source, the other part of the equivalent current source, is represented with the linear superposition of vectors in the noise-subspace. Finally, the objects and equivalent current source are reconstructed efficiently by solving an optimization problem in a lower dimensional linear space with the conjugate gradient (CG) method. To test the new method, the effects of the frequency of incident wave, array aperture size, and SNR are studied in detail. Numerical results show that the proposed method has a high capacity to reconstruct objects buried in a multilayered medium.

A new mutual coupling compensation method for wideband adaptive arrays is proposed. The new method is developed by combining the element pattern reconstruction method and the cubic Hermit interpolation method to achieve wideband mutual coupling compensation. For the employment of this method, mutual coupling matrices at some frequencies obtained by element pattern reconstruction method are needed and stored. By employing the cubic Hermit interpolation method, all entries of mutual coupling matrix for any frequency within the entire frequency band can be obtained accurately and efficiently. A uniform circular array with eight wideband dipole antennas is designed to verify the validity and effectiveness of the proposed wideband compensation method by numerical examples.

The plasmonic behavior of nanostructured materials has ignited intense research for the fundamental physics of plasmonic structures and their cutting edge applications concerning the fields of nanoscience and biosensing. The optical response of plasmonic metals is generally well-described by classical Maxwell's Equations (ME). Thus, the understanding of plasmons and the design of plasmonic nanostructures can therefore directly benefit from lastest advances achieved in classic research areas such as computational electromagnetics. In this context, this paper is devoted to review the most recent advances in nanoplasmonic modeling, related with the latest breakthroughs in surface integral equation (SIE) formulations derived from ME. These works have extended the scope of application of Maxwell's Equations, from microwave/milimeter waves to infrared and optical frequency bands, in the emerging fields of nanoscience and medical biosensing.

We prove the existence of complex eigenfrequencies of open waveguide resonators in the form of parallel-plate waveguides and waveguides of rectangular crosssection containing layered dielectric inclusions. It is shown that complex eigenfrequencies are finite-multiplicity poles of the analytical continuation of the operator of the initial diffraction problem and its Green's function to a multi-sheet Riemann surface, and also of the transmission coefficient extended to the complex plane of some of the problem parameters. The eigenfrequencies are associated with resonant states (RSs) and eigenvalues of distinct families of Sturm-Liouville problems on the line; they form countable sets of points in the complex plane with the only accumulation point at infinity and depend continuously on the problem parameters. The set of complex eigenfrequencies is similar in its structure to the set of eigenvalues of a Laplacian in a rectangle. The presence of a resonance domain in the form of a parallel-plane layered dielectric insert removes the continuous frequency spectrum and gives rise to a discrete set of points shifted to (upper half of) the complex plane.

A low-profile planar monolayer antenna for ultra-wideband (UWB) operation is presented. To achieve a UWB performance along with a compact size, a hybrid square-circular radiator and a rectangular open slotted ground plane with two symmetrical I-shaped tuning stubs are proposed. The antenna is fed by a coplanar waveguide line and has a small size of 44 × 32 × 1.6 mm³. The prototype of the proposed antenna was fabricated and tested in an anechoic chamber. The simulated and measured results show good agreement over the entire ultra-wide bandwidth. The measured results indicate that the proposed antenna can provide a wide impedance bandwidth of more than 154% from 1.7 to 13.3 GHz with -10-dB reflection coefficient. In addition, it is demonstrated that by introducing several antenna designs, the impedance bandwidth can be improved from 43% to 154%. Besides several mechanical advantages, such as compact in size, easy fabrication, and monolayer configuration without any back ground plane, the proposed antenna also shows a good performance in its radiation characteristics and time-domain behaviors. The measured results in both frequency and time domains prove that the proposed antenna can be used in a wide range of UWB applications.

A single layer, single feed microstrip antenna with multifrequency operation in compact size is proposed. A modified inverted π-shaped slot is introduced at the left side radiating edge of the patch to reduce the size of the antenna by reducing the resonant frequency. Multiple resonant frequencies with increased frequency ratio are also obtained by cutting the modified inverted π-shaped slot. The measured result shows that the proposed antenna resonates at 3.3, 4.55, 5.56 and 6.08 GHz in microwave S and C band. The size of the proposed patch is only 0.176λ_L×0.132λ_L at its lower operating frequency. The proposed patch antenna has achieved 68% size reduction as compared with the conventional rectangular microstrip antenna with same patch area. An extensive analysis of the reflection coefficient, voltage standing wave ratio, gain, radiation efficiency and radiation pattern of the proposed antenna is presented in this paper. The proposed antenna is suitable for WiMax and HiPERLAN wireless systems.

A MMW/IR compound Cassegrain antenna system for mono-pulse radar applications is presented in this paper. By comparing different modeling methods of conformal frequency selective surface (CFSS), a sub-reflector, with a good performance of reflection at 93 GHz and transparency at the wavelength of 1.06 μm, is achieved according to sputtering technique. At the wavelength of 1.06 μm, transmittance of the sub-reflector is 67%. Compared to a Cassegrain antenna system consisting of a metallic sub-reflector with identical size, the gain of the compound antenna system has a negligible loss (less than 0.4 dB) at 93 GHz. Compared with the patent in [13], the design can improve the limited size of receiving system and the utilization of aperture of the compound detection system at IR region, and can also enhance the heat dissipation.

In this paper, a high-gain amplifier module has been presented for millimeter wave applications. In order to suppress oscillation of the high-gain amplification block, a rectangular waveguide (WG) is fully integrated into the metal case, on which a cascaded two-stage amplifier is mounted. Due to the integrated WG, additional WG-to-microstrip line (MSL) transitions are required. Therefore, a low-loss and wide-band WG-to-MSL transition is designed and fabricated on a 5 mil thick RT5880 substrate. Two sets of WG-to-MSL transitions in back-to-back structure are assembled in the metal case for the high-gain amplifier module and are characterized. The measured transition loss and operational returnloss (S₁₁) bandwidth less than -10 dB are less than -0.44 dB/a transition and 15.9 GHz from 34.1 to 50 GHz, respectively. The fabricated high-gain amplifier module shows a high gain over 39.7 dB from 38 to 41 GHz. At 38.7 GHz, its maximum gain of 44.25 dB is achieved.

Simulating steady state performance of high quality factor (Q) resonant RF structures is computationally difficult for structures with sizes on the order of more than a few wavelengths because of the long times (on the order of ~ 0.1 ms) required to achieve steady state in comparison with maximum time step that can be used in the simulation (typically, on the order of ~ 1 ps). This paper presents analytical and computational approaches that can be used to accelerate the simulation of the steady state performance of such structures. The basis of the proposed approach is the utilization of a larger amplitude signal at the beginning to achieve steady state earlier relative to the nominal input signal. The methodology for finding the necessary input signal is then discussed in detail, and the validity of the approach is evaluated.

A plasma sheath can significantly alter the electromagnetic properties of an object, which leads to many practical applications. In this article, the electromagnetic scattering properties of a DB metamaterial cylinder coated with unmagnetized plasma are studied. The effects of layer thickness, non-uniform cladding (eccentric coating), electron number density, electron-neutral collision frequency and the frequency of incident wave on radar cross-section (RCS) of the object are discussed. It is found that the RCS of the DB metamaterial objects can be reduced or enhanced by appropriate values of plasma parameters, thickness or eccentricity. The anomalous behavior of backscattering crosssection of plasma coated DB cylinder has been observed at frequencies near plasma frequency. The results may serve as a noteworthy reference for experimentalists working in plasma stealth technology for metamaterials.

Two basic classes of electromagnetic medium, recently defined as P and Q medium, are generalized to define the class of PQ media. Plane wave propagation in the general PQ medium is studied and the quartic dispersion equation is derived in analytic form applying four-dimensional dyadic formalism. The result is verified by considering various special cases of PQ media for which the dispersion equation is either decomposed to two quadratic equations or is identically satisfied (media with no dispersion equation). As a numerical example, the dispersion surface of a PQ medium with non-decomposable dispersion equation is considered.

Dealing with the project of metamaterials scientists often have to design circuit elements at a subwavelength (or ``microscopic'') scale. At that scale, they use the set of Maxwell's equations in free-space, and neither permittivity ε nor permeability μ are formally defined. However, the objective is to use the unit cells in order to build a bulk material with some desired ``macroscopic'' properties. At that scale the set of Maxwell's equations in matter is adopted. To pass from one approach to the other is not obvious. In this paper we analyse the classic definitions of polarization P and magnetization M, highlighting their limits. Then we propose a definition for P and M fully consistent with Maxwell's equations at any scale.

In this letter, a compact four-element microstrip patch antenna array for BeiDou navigation satellite system (BDS) operation at the B3 (1268 MHz) band is proposed. High permittivity dielectric substrate and slit-loaded microstrip patch are used to reduce the antenna element size down to 40 mm × 40 mm which implies an aperture size of only λ₀/6 × λ₀/6 at the B3 band. The right-handed circularly polarized (RHCP) radiation is achieved by connecting two coaxial probes to a 0°-90° stripline hybrid. Four identical antenna elements are distributed with the same polarity and an inter-element separation of 80 mm (λ₀/3 at the B3 band). The overall size of the antenna array, including the stripline feeding network and supporting ground plane, is only 140 mm × 140 mm × 5.5 mm. A prototype was fabricated and measured to verify the design concept. Simulated and measured results will be presented and discussed, showing that the proposed BDS antenna array is suitable for BDS applications.

In this article a method of optimizing wireless communication systems using multiple antennas is presented. This method focuses on the synthesis of antenna radiation patterns that are optimized in terms of mutual information, taking into account the specific limitations of the antenna design, such as the available space (for the antenna structure), polarization, number and arrangement of the antennas. The optimization focuses on volume based channel knowledge and on the theory of the intrinsic capacity. Based on this we developed algorithms that allow to determine optimized fixed radiation patterns also for time-variant channels.

A wide beam, circularly polarized (CP) antenna is presented for satellite communications. The antenna consists of two crossed bent dipoles, two baluns and two pairs of rectangular patches. The two dipoles are fed by the two baluns, respectively. The arms of the dipoles are bent to save the horizontal space and to broaden the beamwidth. The rectangular patches which are connected to the arms of the dipoles form the matching structure of the proposed antenna. The impedance bandwidth of the antenna is broadened by adjusting the length of the rectangular patches. A broadband 90° power divider is used to feed the proposed antenna and to realize circular polarization. The antenna has a -10-dB impedance bandwidths of 77% (1.73-3.89 GHz). The proposed antenna exhibits a measured 2-dB AR bandwidth of 76.3%, from 1.71 GHz to 3.8 GHz. The 3-dB beamwidth is greater than 88°over the whole working band. Results show that the proposed antenna is suitable for the application of satellite communications.

In this article, a compact planar inverted-F antenna with a wide frequency band for WLAN, Bluetooth, HiperLAN, LTE2500, and WiMAX applications in mobile handsets is proposed. The designed PIFA provides two operating bands at 2.5 GHz with a bandwidth of 300 MHz (13%) and at 5.2 GHz with a bandwidth of 5700 MHz (76%). The dual-band performance and the improved bandwidths are realized by two techniques: the integration of a T-shaped slot in the radiating patch of the antenna and the addition of two elements in the side of the PIFA. The two operating bands of the antenna are controlled by adjusting the size of slot and the size of elements 1 and 2. The distribution of the specific absorption rate (SAR) of 1-g and 10-g in the head of human tissues for two positions of the antenna at 2.5 GHz and 5.2 GHz is also studied. The results of simulation and measurement of the proposed antenna are presented and discussed.

In this paper, a one-dimensional numerical framework based on Finite-Difference Time-Domain (FDTD) method is developed to model response behaviour of Ground penetrating radar (GPR). The effects of electrical properties such as dielectric constant, conductivity of the media have been evaluated. A Gaussian shaped pulse is used as source which propagates through the 1D array grid, and the pulse interactions at different media interfaces have been investigated. The objective of this paper is to assess the modelling criteria and success rate of detecting buried object using the framework. A real life application of GPR to detect a buried steel bar in one meter thick concrete block has been carried out, and the results present successful detection of the steel bar along with measured depth of the concrete cover. The developed framework could be implemented to model multi-layer dielectric blocks with detection capability of various buried objects.

This paper presents a new design approach for compact orthogonal broadband printed multiple-input multiple-output (MIMO) antennas based on a coplanar waveguide (CPW)-fed hexagonal-ring monopole antenna (HRMA) element. The design procedure of the basic radiating element is initiated from a stripline (SL)-fed circular monopole antenna (CMA). Then various antennas involved in the design evolution process are introduced to attain a compact CPW-fed HRMA. This basic antenna element has a compact size of 13×10 mm², 50% smaller than SL-fed CMA, and a prototype of this antenna is built and tested. Based on HRMA element, compact two- and four-element MIMO antenna systems are designed, fabricated and experimentally demonstrated for 5-GHz ISM band operation. The MIMO antenna systems use orthogonally configured of identical closely spaced HRMA elements, with CPW-fed printed on one side of the substrate to achieve good isolation. Design simulation is carried out with the aid of Computer Simulation Technology Microwave Studio (CST MWS) and confirmed with High Frequency Structure Simulator (HFSS). The experimental results are in close agreement with the simulated ones, which validates the design principle. Based on experimental results, the two MIMO antenna systems have an impedance bandwidth of more than 2 GHz, good isolation of less than 15 dB, and a low envelope correlation coefficient of better than -26 dB across the frequency band of (4-6 GHz), which are suitable for 5-GHz MIMO applications.

An octagonal shape patch antenna with switchable inverted L-shaped slotted ground is designed for frequency band reconfigurable and experimentally validated. The antenna is capable of frequency band switching at five different states including an ultra wideband (UWB) state, two narrowband states and a dual-band state by using RF switching element p-i-n diodes. In the case of ultrawide band (UWB) state, the proposed antenna operates over impedance bandwidth of 141% (2.87-16.56 GHz) under simulation and 139% (2.85-15.85 GHz) in measurement with return loss S₁₁ < -10 dB. For two narrowband states, 10 dB impedance bandwidth achieved is 16% (5.05-5.91 GHz) and 11% (8.76-9.80 GHz) under simulation and 14% (5.01-5.79 GHz) and 10% (8.68-9.69 GHz) in measurement, respectively. For the dual band state, 10 dB impedance bandwidth of 2.21-2.52 GHz (13%) & 5.07-5.89 GHz (15%) and 2.18-2.52 GHz (14%) & 8.78-9.71 GHz (10%) under simulation and 2.20-2.50 GHz (12%) & 5.05-5.90 GHz (15%) and 2.19-2.50 GHz (13%) & 8.70-9.60 GHz (9%) in measurement with return loss S₁₁ < -10 dB. The proposed antenna is capable to serve in different wireless communication applications such as WLAN [802.11b/g/n (2.4-2.48 GHz), 802.11a/h/j/n (5.2 GHz), ISM band (2.4-2.5 GHz)], Bluetooth (2400-2484 MHz), WiMAX (2.3-2.4 & 5.15-5.85 GHz), WiFi (2.40-2.48, 5.15-5.85 GHz) and UWB (3.1-10.6 GHz). It also works at 9.2 GHz where airborne radar applications are found. Next, the antenna gain is improved with the help of a circular loop frequency selective surface (FSS) and a PEC (perfect electric conductor) sheet. Measured peak gain represents average improvements about 4 dB-5 dB over the UWB band. Experimental results seem in good agreement with the simulated ones of the proposed antenna with and without the frequency selective surface.

Based on the polarimetric scattering model of second-order small-slope approximation (SSA-II) with tapered wave incidence under linear and circular polarization, monostatic and bistatic scattering from two-dimensional dielectric rough sea surface is investigated. The emphasis of the present study is put on the Brewster effect on polarization state of scattering wave under circularly polarized wave incidence. Numerical simulations show that for bistatic configuration under circularly polarized wave incidence, the polarization state of scattering wave strongly depends on incident angle, scattering angle, as well as the Brewster angle associated with medium permittivity.