A novel feeding network is investigated both theoretically and experimentally. The proposed system with combination of a Wilkinson power divider and two branch-Line couplers is established. The output signals of the system have the same amplitude and 900 phase difference with each other. The size reduction technique is applied to minimize the physical size of the proposed network. In this technique, the ground of the structure is defected, and distributed capacitors and inductors are added to empty space of the branch-line couplers. Moreover, meandered lines are used in order to match the output impedance of the Wilkinson power divider arms and reduce its size. The initial design realized in 2.5 GHz shows the fractional bandwidth of 24%. Then a miniaturized structure is fabricated with 42% smaller size than the main structure while it shows similar electrical performance. For both cases, measurement and simulation results are in good agreement with each other.

Multiple-input-multiple-output antennas are investigated for terrestrial point-to-point wireless link. The lack of rich scatters in a terrestrial wireless channel results in an ill-conditioned channel matrix for a long range link with compact arrays, which can cause a high bit error rate. This paper demonstrates that the channel matrix can be improved by carefully selecting the antenna spacing. Unfortunately, an optimum antenna spacing that guarantees a good channel matrix is too large to implement for most long range terrestrial wireless links. On the other hand, a channel capacity study of an 8×8 link reveals that multiple antennas do provide more capacity even with small antenna spacing. Constellation multiplexing is then applied to the compact array configuration to solve the unreliable communication problem. In addition, a multilevel maximum ratio combining technique is introduced to improve detection efficiency.

In this paper, the application of Artificial Neural Network (ANN) with back-propagation algorithm and weighted Fourier method are used for the synthesis of antenna arrays. The neural networks facilitate the modelling of antenna arrays by estimating the phases. The most important synthesis problem is to find the weights of the linear antenna array elements that are optimum to provide the radiation pattern with maximum reduction in the side lobe level. This technique is used to prove its effectiveness in improving the performance of the antenna array. To achieve this goal, antenna array for Wi-Fi IEEE 802.11a with frequency at 2.4 GHz to 2.5 GHz is implemented using Hybrid Fourier-Neural Networks method. To verify the validity of the technique, several illustrative examples of uniform excited array patterns with the main beam are placed in the direction of the useful signal. The neural network synthesis method not only allows to establish important analytical equations for the synthesis of antenna array, but also provides a great flexibility between the system parameters in input and output which makes the synthesis possible due to the explicit relation given by them.

This paper presents the design and fabrication of a broadband UHF RFID tag for bio-monitoring applications. The proposed tag is realized with a thin FR4 substrate of 200 μm, which can be considered as flexible. It shows good performances both in free space and placed on human body. For instance, in free space, the tag can be read at 14 m in the UHF RFID band and at an average distance of 4.6 m when it is placed on the human body. The overall tag size is only 80 mm × 50mm × 200 μm.

This paper presents the use of micro-electromechanical systems (MEMS) switches to realize the radiation pattern reconfiguration of microstrip antenna, which works in Ka-band. The antenna was fabricated on a silicon substrate and designed to reconfigure radiation pattern at the operation frequency of 35 GHz. The simulation results show that by controlling the states of MEMS switches between the driven element and two parasitic elements, the antenna can achieve reconfigure into three maximum radiation directions in the H-plane (θ=0°, ψ=90°, θ=14°, ψ=90°, and θ=-14°, ψ=90°, respectively). The measured maximum radiation directions of modes-1, modes-2, modes-3, modes-4 are θ=17°, -25°, 3.5°,0.7° and gains of four modes at the maximum radiation direction are 5.78 dBi, 6.49 dBi, 7.24 dBi, 6.31 dBi, respectively. The measured results are closely consistent with the simulation ones. The proposed antenna can be applied to satellite communication.

In the present paper we focus on the study of polarization properties of biaxial metamaterial, which consist of alternate ferrite and semiconductor layers, located on an ideally conducted metal substrate. The system is placed into an external magnetic field along the boundaries of the layers. The effective medium theory is applied. Effective linear-to-elliptic polarization conversion has been shown, by means of physical and geometrical parameters of the system under consideration.

A categorized radio channel modeling for wireless ultra-wideband on-body body area networks is discussed. Measurements in an anechoic chamber at fourteen antenna locations are conducted in a 2-8 GHz band. The dipole and double loop antenna types are used. Six link classes are formed based on the antenna spots on the torso, head or limb. The limb-limb and the head-limb links have the lowest and highest path losses, respectively. The head-limb links have the shortest channel impulse responses (CIRs) and limb-limb links the longest ones. The CIR amplitudes follow the inverse Gaussian distribution. The tap indexes and the total excess delays are modeled with the negative binomial distribution. In most cases, the CIRs decay faster for the dipole. Otherwise no major differences exist between the antennas.

A compact broadband bandpass filter (BPF) on Composite right/left-handed (CRLH) Quarter-Mode Substrate Integrated Waveguide (QMSIW) is presented and analyzed in this paper. A size reduction is implemented by etching the CRLH interdigital slots (CRLH-IS) in the compact QMSIW cavity to introduce a lower resonant frequency less than that of the QMSIW. The influence of the rotation angle of the CRLH-IS on the frequency response of the CRLH QMSIW BPF is analyzed, and the optimal rotation angle is used to implement a BPF with good out-band rejection. The proposed CRLH QMSIW shows the characteristics of low quality factor and high coupling coefficient that make it a good solution to design a broadband bandpass filter. The measured insertion loss is less than 1.8 dB at 4.43 GHz with a fractional bandwidth (FBW) of around 22%. The measured results agree well with the simulated ones.

In this letter, a new design for patch antenna, which can obtain low radar cross section (RCS) and high gain performance simultaneously, is proposed on the basis of a metamaterial (MTM) superstrate. The superstrate consists of two metallic layers with different patterns on both sides of a dielectric substrate. Low reflection and transmission are obtained from the upper surface which can absorb most of the incident wave to reduce the antenna RCS. The bottom surface, which has partial reflectivity, is used to construct a Fabry-Perot resonance cavity with the ground plane of the patch antenna to improve its directivity. Measured results show that the proposed antenna can achieve RCS reduction in a broad frequency band ranging from 2 to 14 GHz with maximum RCS reduction value of 28.3 dB, and high gain performance is enhanced by 4.3 dB at most compared with the original antenna in the working frequency band extending from 10.9 GHz to 12 GHz. The measured results agree well with the simulated ones.

This paper deals with experimental verification of reciprocity relations for nonlinear quadripole, such as Hall transducer. We suppose that the matrix of quadripole resistances can be decomposed into the sum of matrices: linear and nonlinear. We experimentally confirmed the classical reciprocity relations for linear part of matrix of resistances.

A new defected ground structure (DGS) is designed to reduce the mutual coupling of a dual-frequency printed monopole array. The designed dual-frequency DGS consists of two concentric split ring slots. Each split ring slot produces band rejection characteristics at one resonant frequency of the antennas. An effective equivalent circuit model of the DGS section is proposed with the circuit parameters successfully extracted. Good agreement exists among the circuit simulation, EM simulation and experimental results. With the inclusion of the DGS, the measured mutual coupling of the dual-band array has been effectively reduced by 10 dB and 20 dB at two resonant frequencies, respectively.

As an emerging wireless localization technique, the electromagnetic passive localization without the need of carrying any device, named device-free passive localization (DFPL) technique has drawn considerable research attentions. The DFPL technique detects the shadowed links in the monitored area and realizes localization with the received signal strength (RSS) measurements of these links. However, the current RSS-based DFPL techniques have two major challenges: one is that the RSS signal is particularly sensitive to noise and another one is that it needs the large number of nodes to provide enough RSS measurements of wireless links to guarantee good performance. To overcome these problems, in this paper we take advantage of compressive sensing (CS) theory to handle the spatial sparsity of the DFPL problem for reducing the number of nodes required by DFPL systems and exploit the frequency diversity technique to deal with the problem of the RSS sensitivity. Meanwhile, inspired by the fact that the target's movement is continuous and the target's current location must be around the last location, we add prior information on the support region into the sparse reconstruction process for enhancing sparse reconstruction performance. The effectiveness and robustness of the proposed scheme are demonstrated by experimental results where the proposed algorithm yields substantial improvement for localization performance.

The ever-growing usage of new information and communication technology devices by different age groups is followed with public concerns of exposure induced biological effects. The aim of this paper is to assess and compare personal exposure levels to electromagnetic fields of wireless communications for different age-groups, including children, under the same exposure conditions.Assessment of personal exposure of the following age groups: 08-15, 16-20, 21-35 and 36-60 years old is conducted with sophisticated tri-axial E-field frequency selective personal exposure meters, enabling measurements of electric field strength in 14 pre-defined frequency bands in the range of 80 MHz-6 GHz. Participants are selected to be with similar social conditions and occupation, including children, students and administrative employees. The measurements were conducted in typical residential environments collecting 161 280 measurement samples. The mean value of power density of different wireless technologies is presented for each age-group, including the contribute of specific wireless technology to the total personal exposure. The highest personal exposure values per frequency band for all age groups are in GSM and Wi-Fi 2G. The results show a difference in mean power density levels between different age groups for the same exposure environment. Ultimately, all measured values were far below international safety guidelines and exposure limits.

The image produced by metamaterial slabs is discussed in a number of papers in terms of the electromagnetic field distribution. In this paper a procedure is proposed to efficiently calculate the image of an extended object placed behind a metamaterial slab as it will be seen by an observer - which can greatly differ from the image formed by the intensity maxima. The first step of the procedure retrieves the dispersion relation of a periodic metamaterial slab from the S parameters calculated with full wave electromagnetic simulation of the unit cell. The second step of the procedure utilizes the retrieved dispersion relation in the transfer matrix method to calculate the image of a point source placed behind the metamaterial slab as a function of the observation angle. Knowing the image distance of the point source for all observation angles, the image of an extended object can be efficiently calculated. The procedure is demonstrated with a Fishnet type metamaterial.

Antenna arrays for direction finding (DF) are usually designed and tested in controlled environments such as anechoic chambers. However, antenna pattern may change significantly when antennas are placed in their operational environment. In such perturbing close context, the antennas calibration validity becomes a major issue which can lead to DF performance degradation and costly recalibration process. This paper presents an innovative design and implementation of a non-disturbing solution for quasi-real time antenna monitoring. The proposed system is based on optically modulated scattering (OMS) technique. Its capacity to detect the presence of various types of obstacles, which perturb significantly the antenna radiation pattern, is evaluated. A relation between monitoring mode and DF mode measurement signals is established. Finally, a design and sizing of the overall system is proposed.

Stepped frequency ground penetrating radar (SFGPR) has received increasing attention in the field of ground penetrating radar technology due to its superiority in the detection performance. Compressed sensing (CS) SFGPR imaging reconstruction method can not merely reduce the measured imaging data volume, but also reconstruct target image with less sidelobe. However, the imaging algorithm using CS approach will lose efficacy in strong clutter environment. To solve this problem, a CS SFGPR imaging reconstruction method combined with subspace projection clutter suppression approach is proposed in this paper. First, all frequency domain data at each measurement position are reconstructed from reduced frequency measurements via sparse reconstruction technique. Then subspace projection ground clutter suppression technique is used to suppress the strong ground clutter. Finally, orthogonal matching pursuit (OMP) algorithm is utilized to reconstruct the underground target image. Synthetic and experimental data processing results have verified the effectiveness and accuracy of the proposed imaging method.

A multilayer notch-loaded antenna for dual-band (L & S) operation has been proposed in this paper for wireless communications. The antenna is multilayered with dielectric layers of FR4 and Rogers/Duroid. A superstrate layer has been introduced with square-shaped elements angled at 90 degrees to each other with an empty space just above the patch. The proposed structure of the antenna with superstrate layer is applicable to low frequency consecutive dual band operations. The antenna also shows very good radiation characteristics with a gain of more than 7.0 dB and side lobe levels reduced to a very good extent of around -20 dB.

We systematically study the Cherenkov optical emission by a nonrelativistic charge uniformly moving in parallel to surface of a photonic crystal by the FDTD simulations. It is found that a near-static structure of field oscillations produced by a discontinuity of dielectric permittivity in the surface of photonic lattice is generated. Such oscillations have large amplitude in the Cherenkov group cone and generate a number of well defined spectral resonances corresponding to eigenmodes of the photonic grid. The dynamics and field properties in photonic lattice with random vacancies are investigated too. It is found that even at medium level of a random perturbation the field shape shows the structural stability of the Cherenkov emission field in a photonic crystal.

An analytical formulation has been developed to evaluate the shielding effectiveness (SE) of two coplanar rectangular metallic enclosures with acircular aperture excitedby an internal electric dipole source. The formulation consists of three parts: First, the near-field electromagnetic interference (EMI) of the electromagnetic leakage from the aperture is represented by the electric dipole in one enclosure. Then, the aperture equivalent magnetic and electric dipole moments are calculated according to the Bethe's small aperture coupling theory. Finally, the electric field of the other enclosure is derived by using the equivalent magnetic dipole field, equivalent electric dipole field and the corresponding enclosure's Green's functions in the two fields. In this formulation, the electric field of the enclosure can be expressed as a function of the observation point, the aperture's center point, source point, shape of the aperture and the enclosure's conductivity. The formulation then is employed to analyze the effect of the above factors on the SE. The analytical results have been successfully compared with the full-wave simulation software Computer Simulation Technology (CST) from 0.3~2.4 GHz.

A compact wideband planar double-sided printed quasi-Yagi antenna is presented. This letter focuses on the feasibility of substituting conventional balun for microstrip-to-slotline transition balun to achieve wider bandwidth and relatively smaller size. The proposed antenna, consisting of a feeding balun, a concave arc-shaped reflector, a modified driver with stacked structure and two directors, is designed and fabricated. Good agreement between simulated and measured results is observed. Simulation and measurement results reveal that the proposed antenna can provide an impedance bandwidth of nearly 100% (2.02-6.05 GHz). Additionally, within the impedance bandwidth, the radiation pattern of the proposed antenna has front-to-back (F/B) ratios ranging from 10.1 dB to 19.1 dB, cross-polarization levels in the main radiation direction from 19.8 dB to 36.2 dB and gains from 3.4 dBi to 7.4 dBi.