In this paper, the finite element method (FEM) is applied to the analysis of three-dimensional (3D) electromagnetic structures. The incomplete Cholesky (IC) preconditioner based on shifted operators is used to solve the finite element linear systems. Several strategies are adopted to raise the efficiency and robustness of the preconditioner. Numerical experiments for several microwave devices demonstrate the superior numerical convergence and robustness of the proposed preocnditioner.

A triple-band bow-tie-shaped CPW-fed slot antenna design for wireless communication applications is proposed. The antenna consists of a signal strip, two conducting strips and bow-tie-shaped slots. With simple tuning geometrical parameters, the proposed antenna is suitable for WLAN 2.4/5.2/5.8 GHz bands. This antenna is designed on a single-layer PCB FR4 substrate with permittivity ε_r = 4.4, loss tangent tanδ = 0.0245 and thickness h = 1.6 mm. The antenna size of the radiating area and ground plane is 60×45 mm². The measured results show a positive agreement with the simulated results.

An efficient optimization technique for frequency selective surface (FSS) radome with nonuniform wall thickness is proposed to improve the power transmission efficiency and the boresight error (BSE) of FSS radome simultaneously. The high-frequency method based on the approximate locally planar technique is used to evaluate the transmission performance of FSS radome. An efficient multi-dimensional adaptive sampling method combined with spectral domain method of moment (MoM) is employed to analyze transmission performance of FSS structure. The immune clone algorithm (ICA) is applied to the design of a FSS radome, in which the linear combination of the maximizing power transmission efficiency and the minimizing BSE is adopted as the affinity function, and the radome wall thickness is optimized. A design example for the three-dimensional tangent ogive radome with nonuniform thickness is given. The results show that the power transmission efficiency is improved significantly and the BSE of the optimal antenna-radome system is also reduced over the antenna scan volume.

An accurate complexity-reduced simplified Volterra (ACR-SV) series is introduced for RF power amplifiers (PAs). Based on the conventional simplified Volterra (SV) series, it takes memoryless nonlinearity and memory effect into consideration separately, while connected with a nonlinear memory effect (NME) in order to increase accuracy of the model. The proposed ACR-SV model is assessed using a GaN Class-F PA driven by two modulated signals (a WCDMA 1001 signal and a single carrier 16QAM signal with 40 MHz band width). The experimental results in forward modeling and DPD application demonstrate that the proposed ACR-SV model outperforms the memory polynomial (MP) model, the augmented complexity-reduced generalized memory polynomial (ACR-GMP), and the SV model. Compared with the MP model, the ACR-SV model shows a normalized mean square error (NMSE) improvement of 2.61 dB in forward modeling, average adjacent channel power ratio (ACPR) improvement of 3.7/4.2 dB in the DPD application with less 13% number of model coefficients. In comparison with the ACR-GMP model, the ACR-SV model shows NMSE improvement of 1.39 dB, ACPR improvement of 0.7/0.6 dB with comparable number of model coefficients. In contrast with the SV model, the ACR-SV model achieves similar model accuracy, but reduces approximately 53% of coefficients.

In this paper, a novel dual notch bands Ultra Wide-Band (UWB) antenna for WLAN and WiMAX applications is presented. The antenna contains a taper rectangular monopole antenna with new feed line which is designed and modified for 2-12 GHz. To achieve notch band at WLAN frequencies, different methods are compared, such as L-shape slots for one notch or dual rings in notch designing. On the other hand, the novel F-shape feed line is designed to achieve dual notch band characteristic. The effects of stubs parameters at notch frequencies are presented. The benefit of this novel feed line is designing multi-band and reconfigurable antenna by changing stub line parameters. The simulated results of prototype antenna are obtained with HFSS and CST. Total size of the antenna is 60 mm×60 mm×1.6 mm. It is fabricated on FR-4 low cost substrate and fed by 50 Ω microstrip line.

In this paper, we present a new design of multi-resonance monopole antenna for use in microwave imaging systems is presented. The antenna configuration consists of an ordinary square radiating patch, a feed-line, and a modified ground plane with pairs of L-shaped slits and parasitic structures which provides a wide usable fractional bandwidth of more than 130% (2.95-14.27 GHz). In the presented design, by cutting a pair of L-shaped slits and also by embedding a pair of inverted L-shaped parasitic structures in the ground plane additional resonances at 9.5 GHz and 13.7 GHz can be achieved. By using these structures, the usable upper frequency of the antenna is extended from 10.3 GHz to 14.27 GHz. The proposed antenna has a symmetrical structure with ordinary square radiating patch, therefore displays a good omni-directional radiation patterns even at higher frequencies. The antenna has sufficient and acceptable gain level and also its radiation efficiency is greater than 86% across the entire radiating band. The designed antenna has a small dimension.

A compact triband asymmetric coplanar strip (ACS)-fed monopole antenna for WLAN/WiMAX applications is proposed and investigated in this paper. The proposed antenna is composed of an ACS-fed folded monopole and two inverted-L branches, which occupies a very compact size of 26.5×12 mm² including the ground plane. By carefully adjusting the lengths and positions of these branches, three desired resonant frequencies can be achieved and adjusted independently. The antenna exhibits three resonances covering the 2.4/5.8 GHz WLAN bands and 3.5 GHz WiMAX band. Details of the antenna design, simulation, and experimental results are presented and discussed. The proposed antenna shows nearly omnidirectional radiation characteristics and moderate gains in the operating bands. The compactness, simple feeding technique and uniplanar design make it easy to be integrated within the portable device for wireless communication.

It is well known that in the pulse compression radar theory, the sidelobe reduction using nonlinear frequency modulation (NLFM) signal processing represents a major and present research direction. Accordingly, the main objective of this paper is to propose an interesting approach related to the design of efficient NLFM waveforms namely, a temporal predistortioning method of LFM signals by suitable nonlinear frequency laws. Some aspects concerning the optimization of the specific parameters involved into analyzed NLFM processing procedure are also included. The achieved experimental results confirm the significant sidelobe suppression related to other NLFM processing techniques.

A folded printed quadrifilar helical antenna (FPQHA) with an integrated and compact feeding network is proposed. The axial length of the proposed antenna is miniaturized of about 54.7% than the conventional PQHA by folding the helix arms into several elements. A T-junction power divider combining with two Wilkinson power dividers is utilized to feed the antenna. A fabricated prototype of the FPQHA using the compact feeding network is presented. The measured positive gain bandwidth covers 380-430 MHz with the reflection coefficient below -20 dB, axial ratio below 1.5 dB and a half-power beamwidth of about 120˚. Details of the proposed antenna design and experimental results are presented and discussed.

In this paper, a compact quad-band planar inverted-F antenna (PIFA) for wireless communication systems is presented. The proposed PIFA consists of a radiating patch with a hook-shaped slot and a modified ground plane with pair of square-ring and rotated I-shaped slots. The antenna is fabricated on an FR4 substrate with dielectric constant of 4.4. By cutting a hook-shaped slit at radiating patch, good dual-band property can be achieved which covers 3.5 GHz worldwide interoperability for microwave access (WiMAX) and 5.2 GHz wireless local area network (WLAN) frequencies. In addition, by using a modified ground plane with a rotated I-shaped an the pair of square-ring slot, additional resonances at the higher frequencies are generated which suitable for 7.25-7.75 GHz downlink of X-band satellite communication systems and 8.02-8.4 GHz international telecommunication union (ITU) applications. Good return loss, antenna gain and radiation pattern characteristics are obtained in the frequency band of interest. The proposed antenna has a small dimension of 24×3×1.6 mm³.

In practical applications, the low-profile spiral antennas suffer from the lack of proper planar feeding ways. The vertical balun always has a significantly long length, inconsistent with the requirements of the low profile spiral antenna geometry. A spiral antenna with integrated parallel-plane feeding structure is proposed in this paper. The antenna used has obviously improved axial ratio compared to the equiangular spiral antenna at low frequencies. And the traditional balun in the third dimension is moved to the planar plane. The antenna and Dyson-style balun have been integrated into a multi-layer structure. The resulting structure maintains the typical radiation behavior and broadband operation of spiral antennas, but the vertical balun is integrated at the same plane with the antenna. The overall size of the spiral antenna is largely reduced.

In this paper, a compact tri-band microstrip bandpass filter (BPF) using tri-section stepped-impedance resonators (TSSIRs) with open stub line and zero-degree feed line is presented. Three tunable passbands are achieved by changing the ratio of impedance. By adding the open stub line, the frequency responses of tri-band at 2.4 GHz/3.5 GHz/5.2 GHz can be obtained precisely. With a proper length of the cone-shaped zero-degree feed structure, we can obtain transmission zeros in stopbands and better return loss in passbands. The proposed tri-band BPF has high selectivity and is simple in fabrication.

Design, simulation, and measurement of a compact filtering microstrip antenna is presented. A coupled line, two hairpin resonators, and a rectangular patch are integrated to form the filtering antenna. The elements together function as a third order bandpass filter with Chebyshev equal ripple response of 0.043 dB at midband frequency of 2.0 GHz. The rectangular patch acts not only as a radiating element, but also as the last resonator of the bandpass filter. The proposed filtering antenna exhibits good out-of-band gain suppression, flat in-band gain response, good selectivity at the band edges, and well-shaped radiation pattern.

An innovative antenna on flexible substrate with two resonators is presented. The antenna is composed of a metallic wire sewn on the substrate. Two dipolar modes in far field are radiated. To understand the interaction of the resonators with the principal antenna, studies with and without the sleeves are done in near field and far field.

To eliminate the average reflectance of antireflection coatings to the greatest extent, a Genetic Programming (GP) algorithm is proposed to design and optimize the graded refractive index distribution profile for broadband omnidirectional antireflection coatings. The proposed GP-index profile in this paper can obtain an extremely low average reflectance of 4.61×10^-7% over a wide range of incident angles and wavelengths which is obviously superior to the average reflectance of 8.09×10^-3%, 3.29×10^-4% and 4.35×10^-5% for linear profile, cubic profile and quintic profile. That means, Fresnel reflection almost can be eliminated by the optimal GP-index profile for omnidirectional incidence over a broad wavelength range. Moreover, it is demonstrated the proposed GP-index profile has better robustness, and it still has the best broadband and omnidirectional antireflection characteristics for the TiO₂/SiO₂ graded-index AR coating. Therefore, the proposed GP-index profile is obviously superior to the conventional linear profile, cubic profile and quintic profile, and the design methodology presented in this paper that uses a genetic programming technique is a quite convenient means to pursue an optimal nonlinear refractive index profile with broadband and omnidirectional antireflection characteristics.

A two-strip narrow-frame monopole antenna for hepta-band WWAN/LTE smartphone applications is proposed. The brightest point of the proposed antenna is that its narrow edge has a width of only 5mm, which is very practical for current smartphone applications with larger touch-screens. In addition, the proposed narrow-frame antenna has a small volume of 60×5×5 mm³ and a simple structure, which comprises of a two-strip monopole loaded with a chip capacitor and an L-shape high-pass filter. Meanwhile, the propose antenna can cover the GSM850/900/1800/1900/UMTS2100/LTE2300/2500 bands. Finally, the operating principle of the proposed antenna is investigated and both simulated and measured results are presented and discussed.

A wideband unidirectional patch antenna with two meandering strips and a Г-shaped feeding structure is designed. The investigation shows that the antenna achieves an impedance bandwidth of 54.2% for VSWR ≤ 2 and a stable gain of around 9 dBi. The far field radiation patterns with low cross polarization which levels are less than -27 dB, low back radiation and symmetrical E-and H-plane patterns are obtained over the whole operating frequency range.

In this paper detailed numerical results are presented for the estimation of the electric field generated by the first return stroke, in order to reproduce the main characteristics of field waveforms measured at distances beyond 50 km. The effect of parameters such as the lightning channel geometry, distance from the source, return-stroke current speed, its attenuation along the channel is discussed by comparing numerical and experimental results.

In this article, the approach involving Dynamic Threshold Optimization (DTO) algorithm is considered to optimize a new compact reconfigurable antenna to be applied to triple band Radio Frequency Identification (RFID) and to ultra wideband (UWB) antenna with multiple bands notched. The antenna is implemented by using the existing techniques, such as loading an L-type band-stop filter, inserting a split ring resonator (SRR) as well as connecting L branches to the radiation disk proposed by us. In case of RFID applications, triple-band RFID 915/2450/5800 MHz are achieved separately. The results prove that this kind of antenna can be applied in RFID reader to avoid interference with other wireless systems. RF MEMS switches are used to reconfigure the antenna to be suitable for the application in the notched UWB communication systems. The DTO algorithm program is implemented using MATLAB-software and linked to the CST Microwave studio software to simulate the antenna. In addition, the optimized antenna is assessed using the Finite Difference Time Domain (FDTD) program written with MATLAB to validate the results. The experimental results for the RFID and UWB antennas show good agreement with simulated ones. The radiation patterns are satisfactorily omnidirectional across the antenna's operation bands.

Investigations have been carried out on the convex lens effect of non-ionizing radiation inside the abdomen of a pregnant woman. Focusing property for a plano-convex lens, which is thicker than twice of its focal length and filled with water, is studied for electric and magnetic fields at different microwave frequencies. It is observed that real image of electromagnetic fields are formed inside the lens itself at the focal plane when a microwave source is placed at a distance much greater than the twice the focal length. A three dimensional homogeneous electrical model of pregnant woman abdomen model behaves like plano-convex lens and creates real image of the microwave source inside the abdomen.