Dipole antennas on a substrate without a ground plane are common in wireless sensor networks and RFID applications. This paper reviews a number of theoretical approaches to solving for the effective permittivity when the substrate material is thin. The surface impedance and slab waveguide propagation techniques are compared to a capacitive solution and an insulated wire antenna. The insulated wire method gives most accurate results (< 3.5%) and was verified using numerical modeling and experimental work. Measurements on a planar straight dipole on FR4 (f_c = 1.50 GHz) compare favorably with the antenna modelled without the substrate and scaled using the insulated wire technique at (f_c = 1.49 GHz). The method can be readily incorporate the effect of an RFID antenna on a thin plastic film placed on a wide variety of lossy and lossless objects.

In order to improve the reconstruction accuracy of near-field SAIR, a novel regularization imaging algorithm based on an accurate G matrix is proposed in this paper. Due to the fact that the regularization reconstruction is usually an underdetermined problem, inaccurate operation matrix G will lead to great reconstruction error in the imaging results, or even the normal imaging cannot be obtained. In this paper, we establish an accurate G matrix based on the accurate imaging model of near-field SAIR. Compared with the traditional G matrix with some unnecessary approximations, the proposed G matrix without approximation can improve the reconstruction accuracy effectively. For improving the accuracy of matrix G further, the corresponding parameters are corrected according to the RMSE between the imaging results of the regularization method and modified FFT method which is not sensitive to the parameters' change. The effectiveness of this calibration method has been tested by 1D simulation experiments. Moreover, the 2D simulation experiments demonstrate that the proposed accurate G matrix can improve the imaging accuracy of regularization method effectively. Finally, the 1D imaging experiment is performed to test the effectiveness of the proposed method for the actual synthetic aperture imaging further.

Broadside coupling mechanism between different patch resonators is deployed for designing power dividers to provide bandpassing effect. To demonstrate, two sector-shaped patches are combined and concentrically stacked on top of a circular microstrip resonator where pairs of concentric arc-shaped slots and radial notches are etched to perturb the current distribution so that an additional pole can be obtained to broaden the operational bandwidth. The use of circular patch enables the expansion of output ports without increasing the design complexity. Also, it was found that broadside coupling generates transmission zeros which can be used to sharpen the rolloff skirt for a better selectivity. In this paper, the corresponding design theory and methodology are elucidated, together with the detailed parametric analysis.

A broadband circularly polarized (CP) slot antenna array fed by an asymmetric coplanar waveguide (CPW) with stepped and inverted T-shaped strips is proposed. Using four square slot antenna elements with sequential rotation oblique feed and a modified sequential-phase (SP) feeding network, broadband CP can be achieved. The measured -10 dB reflection coefficient bandwidth and 3 dB axial ratio (AR) bandwidth are 55.4% (1.63-2.88 GHz) and 58% (1.65-3 GHz), respectively. Good radiation characteristics with gain more than 6 dBic over the operating band are obtained by the proposed antenna array with a compact size of 155×155×0.8 mm³. Details of the proposed antenna array design and experimental results are presented and discussed.

The pattern synthesis for large antenna arrays has drawn significant attention because of its wide applications.This paper introduces a hybrid approach for the fast pencil beam pattern synthesis of the large non-uniform linear or planar array, which can significantly reduce the computational cost, the number of antenna in the array, the minimum sidelobe level and the null control.The proposed method has an iterative scheme which is composed of the nonuniform Fourier transform (NUFFT) and the global optimization method to minimize the peak sidelobe level and control the null. The NUFFT is utilized to determine excitation magnitudes for a fixed positions non-uniform array. The global optimization is used tofind the optimal postions lead thepeak sidelobe level minimum alternatively.The lower excitations can be deleted due to yielding less performance on sidelobe level, which is calledthe array removal strategy.Compare with conventional methods,the simulations on synthetic models show thata minimum sidelobe level and null control can be obtained in processing sparse linear and concentric circular antenna arrays more efficiently.

A Planar elliptic broadband antenna with reconfigurable dual stop-bands performance was successfully designed and performedfor multi-standard wireless communication systems. The proposed antenna consists of a broadband micro-strip fed printed monopole operating in the frequency range 0.75-6 GHz. The notch-band characteristic was obtained by printing two Open Loop Resonators (OLRs) on the front side of the substrate close to the micro-strip feed-line. By adjusting the OLRs parameters, mono or dual band-rejection can be obtained. The passive broadband antenna was optimized to achieve narrow band rejection over the UMTS-band (around 2.1 GHz) and the WiMAX-band (around 3.5 GHz). The agility was produced by loading a varactor diode on each OLR. The major advantages of this structure are the high selectivity of the dismissed-bands, continuous reconfiguration and wide tuning range of the notched bands. Four prototypes were realized and experimentally characterized. The measured tuning rangescorresponding to the notched bands are about 850 MHz (2.25-3.1 GHz) for the rejected UMTS-bandand 570 MHz (3.84-4.41 GHz) for the WiMAX-band. Simulated and measured resultsare presented and discussed.

A compact UWB bowtie-slot antenna (36×23 cm²) fed by a CPW transition is proposed for an improved ground-coupling radar. The antenna has an operating frequency band in the range [0.46 ; 4] GHz. Full-wave modeling using the FDTD approach has allowed to study in details the antenna radiation characteristics in air and in the presence of a soil. Afterwards, a radar system made of a pair of independent shielded bowtie antennas has been considered to probe the sub-surface very close to the air-soil interface. The polarization diversity in the E and H-planes is an important aspect which has been studied in order to further detect the orientation of damages (cracks, delaminations…) in civil engineering structures. Measurements in a dry and wet sand in different system configurations have allowed to first characterize the GPR system and to draw comparisons with numerical results. The ability of the radar to detect small buried objects is investigated.

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.