An accurate characterization of the wave propagation inside tunnels is of practical importance for the design of advanced communication systems. This paper presents a five-zone propagation model for large-size vehicles inside tunnels. Compared with existing models, the proposed model considers the influence of the large size of the vehicle, and covers all propagation mechanism zones and their dividing points. When a large-size vehicle is passing the transmitter, the received power suffers a deep fading as the direct wave is blocked by the vehicle itself. This zone is called the near shadowing zone. Then, when the vehicle has moved past the transmitter, the line of sight is recovered. If the vehicle is still close to the transmitter, the free space propagation zone starts. Then, as the distance increases, the vehicle enters the multi-mode propagation zone, where higher order modes are significant. Further away, when high order modes are greatly attenuated, guided propagation is stabilized. Finally, when the vehicle is extremely far from the transmitter, the waveguide effect vanishes because of the attenuation of reflected rays. Two sets of measurements are employed to validate the model. Results show good agreement, and therefore, the model presents an effective way to predict the propagation inside tunnels for large-size vehicles.

This paper analyzes and discusses the effect of the electromagnetic absorption by human head against variation of head dielectric properties at 900, 1800 and 1900 MHz. The characteristics of helical antenna and its substrates with variation in human head dielectric properties are simulated by implementing finite-difference time-domain (FDTD) method using CST Microwave studio. The variations in human head dielectric properties were manipulated by increasing and decreasing 10% and 20% of each of the human head dielectric properties. In this paper, SAR values increase with increment of head conductivity, and increment of head permittivity and head density lead to decrement of SAR values. Helical antenna with substrate of FR4 results in higher SAR values in all frequency exposures. The head SAR values are higher with higher frequency exposures. The helical antenna with substrate of Rogers RO3006 (loss free) is found to be better over FR4 and Rogers RO4003 (loss free), which contributes towards much lower SAR values in all GSM frequency bands exposure.

In order to analyze the Doppler spectrum of three-dimensional (3-D) moving targets above a time-evolving sea surface, a hybrid method with acceleration techniques is proposed to simulate the electromagnetic (EM) scattering from the composite moving model. This hybrid iterative method combines Kirchhoff approximation (KA) and the multilevel fast multipole algorithm (MLFMA) to solve the EM backscattering from the rough sea surface and the targets, respectively, then mutual EM coupling effects between them are taken into account through an iterative process. To overcome the vast computational cost in the iterative process, acceleration approaches which can greatly reduce the calculation time are applied. Coupling area on the sea surface is truncated according to geometrical optic principle. Then a fast far-field approximation (FAFFA) is applied to speed up the mutual interactions between the targets and the sea surface. A successive iteration method is proposed to reduce the convergence steps for the MLFMA process. The accuracy and efficiency of this hybrid method with accelerations are demonstrated. Doppler spectra of backscattering signals obtained from such numerical EM simulations are compared for different incident angles, target velocities and surface models. The broadening effects of the Doppler spectra due to the mutual EM coupling interactions are studied.

A technique is described for the electromagnetic reconstruction of the location, shape, dielectric constant, and conductivity of buried homogeneous cylinders of elliptic cross-section. The inversion procedure is based on the Differential Evolution algorithm and the forward problem is solved using the single boundary integral method. Simulation results are presented which demonstrate that this hybrid approach can offer a conceptually simple yet efficient and reasonably robust method for the imaging of buried objects and voids.

Conventional reflector based Impulse Radiating Antennas (IRA's) are designed with conical taper transmission line feed. A novel feed design approach is used to enhance gain of the IRA without increasing diameter of the reflector. This paper discuses conventional and new IRA designs of different input impedances. IRA with conventional feed and with new dipole feed is designed for both 200 Ω and 100 Ω input impedance category. The IRA with new feed design offers better gain compared to conventional IRA for both 200 Ω and 100 Ω input impedance category. These antenna designs are analyzed using the Finite Difference Time Domain (FDTD) method and the result obtained shows that IRAs with new dipole feed offers better gain than IRAs with conventional feed for respective input impedance category without any compromise in time domain characteristics. A half IRA with new feed with input impedance of nearly 50 Ω was realized and measured to establish the advantage of new dipole feed IRA.

The lumped network alternating direction implicit finite difference time domain (LN-ADI-FDTD) technique is proposed as an extension of the conventional ADI-FDTD method in this paper, which allows the lumped networks to be inserted into some ADI-FDTD cells. Based on the piecewise linear recursive convolution (PLRC) technique, the current expression of the loaded place can be obtained. Then, substituting the expression into the ADI-FDTD formulas, the difference equations including an arbitrary linear network are derived. For the sake of showing the validity of the proposed scheme, lumped networks are placed on the microstrip and the voltage across the road is computed by the lumped network finite difference time domain (LN-FDTD) method and LN-ADI-FDTD method, respectively. Moreover, the results are compared with those of obtained by using the circuital simulator ADS. The agreement among all the simulated results is achieved, and the extended ADI-FDTD method has been shown to overcome the Courant-Friedrichs-Lewy (CFL) condition.

A slim wideband patch antenna designed for the ultra-high frequency (UHF) band radio frequency identification (RFID) tag is presented in this paper, which can be mounted on flat or curved metallic surfaces directly. The presented antenna is fabricated on a very thin (only 0.5 mm) PET substrate (ε_r=3.8, tanδ=0.02). The proposed design consists of tow coplanar patches which are electrically connected to the metallic ground through two symmetrical shorting walls. Double symmetrical U-shaped slots are etched out to improve the antenna bandwidth. A perfect matching between antenna and tag chip can be obtained by varying the geometry parameters of the slots. The simulated bandwidth is about 97 MHz, which covers the Europe and North America UHF RFID frequency range. The measured maximum reading range of the proposed antenna can be up to 5 m when the tag is mounted on a metal plate whose size is 150×150×8 mm³.

A high linearity down-conversion mixer for the application of the fourth generation (4G) mobile communication systems is presented. The presented 2.3 to 5.8 GHz broadband mixer adopts current-reused and bulk-controlled techniques. The linearized transconductor stage is composed of the CMOS amplifiers and the bulk-controlled compensation (BCC) transistors. The bulk-controlled voltage is applied to adjust the threshold voltage of the BCC transistor. Thus, the equivalent third-order intermodulation (IM3) term of the CMOS amplifiers and the BCC transistors can be mitigated so as to improve the linearity. Furthermore, the current-reused architecture enhances the conversion gain of the proposed mixer and compensates the loss caused by the shunt feedback matching network. The presented mixer consumes 4.8 mA from a 1.5 V power supply. The measurement results of the mixer exhibit the maximum power conversion gain of 11.3 dB. The input third-order intercept point (IIP3) of 4.7 dBm over the entire 2.3-5.8 GHz band is observed.

We propose a general rule that can be used to design multibranch high-order mode converters. We used the modal theory to analyze the proposed structure rigorously and presented the general principles. The well-established finite-difference beam propagation method was used to simulate the proposed device. The numerical results show that the proposed devices could really function as an all-optical mode converter device. It would be developed to quantify the applications and benefit applications of optical signal processing and computing systems.

A map of a building using through-the-wall radar imaging (TWRI) can be best obtained by detecting and identifying its internal principal scatterers, where estimation of the pose angle of a trihedral formed by the wall-wall-floor structure is important in this application. In this paper, an image-domain based method is proposed to estimate the pose angle of trihedral using a feature called amplitude ratio (AR). The estimated pose angle of a trihedral is determined according to AR. Firstly, the imaging geometry of the radar with a multiple-input multiple-output (MIMO) array and the definition of AR in the echo-domain are described. Secondly, a parametric back-scattering model based on geometrical theory of diffraction (GTD) is applied to analyze AR in the echo-domain when a trihedral is in different pose angles. Thirdly, a virtual aperture imaging model is developed to describe the imaging procedure using MIMO array. Based on the imaging model, the AR of each trihedral can be calculated in the image-domain instead of the echo-domain. Finally, the proposed estimation method is validated by the real data collected in an anechoic chamber.

Transmission tunneling properties and frequency response of multilayer structure are theoretically presented by using transfer matrix method. The structure is composed of double-negative and double-positive slabs which is sandwiched between two semi-infinite free space regions. Double-negative layers are realized by using Lorenz- and Drude-medium parameters. The transmission characteristics of the proposed multilayer structure based on the constitutive parameters, dispersion, and loss are analyzed in detail. Finally, the computations of the transmittance for multilayer structure are presented in numerical results. It can be seen from the numerical results that the multilayer structure can be used to design efficient filters and sensors for several frequency regions.

A compact tri-band power divider based on triple-mode resonator is proposed in this paper. This tri-mode resonator comprises a conventional half-wavelength resonator, a short stub and an open stub. The interdigital coupled-lines are introduced at the input and the output to improve the performance of this power divider. The proposed tri-band power divider working at 1.57 GHz, 2.45 GHz, 3.50 GHz is simulated and fabricated, and good agreement between the simulated results and the measured results are observed.

Contour reconstruction and accurate identification of dielectric objects placed on a conducting surface are the aims of the millimeter-wave Synthetic Aperture Radar (SAR) imaging processing system presented in this paper. The method uses multiple frequencies, multiple receivers and one transmitter in a portal-based configuration in order to generate the SAR image. Then, the information in the image is used to estimate the contour of the body under test together with the permittivity of the dielectric region. The results presented in this paper are based on synthetic scattered electromagnetic field data generated using an accurate Finite-Difference Frequency-Domain (FDFD)-based model and inversion based on a fast SAR inversion algorithm. Representative examples showing the good behavior of the method in terms of detection accuracy are provided.

This paper introduces a flexible antenna, printed on a low-cost Polyethylene Terephtalate (PET) substrate for UHF applications. The RF characteristics of the PET substrate are examined using a microstrip resonator to characterize the substrate's relative permittivity and the loss tangent at UHF band. The PET substrate is used to print an antenna designed to work in the 868 ISM-Band. The printing process described is carried out using a semi-industrial roll-to-roll (R2R) machine with mass production capability. The fabricated dipole antenna was mounted on cylindrical objects made from several materials such as paper and glass, and its RF characteristics were measured and discussed.

In this paper, reflectarrays mounted on or embedded in cylindrical and spherical surfaces are designed, analyzed, and simulated at 11.5 GHz for satellite applications. A unit cell consists of a square dielectric resonator antenna (DRA) mounted on or embedded in metallic conformal ground plane is investigated. The radiation characteristics of the designed reflectarrays are investigated and compared with that of planar reflectarray. A 13 x 13 planar reflectarray antenna on the x-y plane was designed. By varying the length of the DRA element between 2 mm and 6.2 mm a full range from 0° to 360° phase shift can be obtained. The size of each element is equivalent to a compensation phase shift. A maximum directivity of 24.3 dB was achieved while the side lobes were below -12.94 dB in E-plane and -15.79 dB in the H-plane for planar reflectarray. A Full-wave analysis using the finite integration technique (FIT) is applied. The results are validated by comparing with that calculated by transmission line method (TLM).

Temperature and thermal stress responses of an improved TTSV structure under the impact of hotspots are numerically analyzed in this paper. A Fin structure is added to the circular TTSV to strengthen the effect of thermo-mechanical mitigation. The nonlinear finite element method (N-FEM) is presented to obtain the coupled thermal and mechanical fields. Running time of the N-FEM algorithm is compared with that of commercial software to indicate its efficiency. The model of state-of-the-art 3D Dynamic Random Access Memory (DRAM) is adopted in our simulation. Besides the single-layer TTSV and TTSV array, the extended case of multi-layer TTSVs is also investigated. To take into consideration the nonlinear effects, the temperature dependent results for the issues of hotspot alignment and liner materials selection are provided, both of which are compared with the corresponding temperature independent results. This paper is aimed to provide some practical guidance to the design of TTSV for effective thermo-mechanical management.

In this paper, an efficient method is proposed to reduce the peak transient grounding resistance (P-TGR) of a grounding system. By surrounding the lifting line with a material volume, the P-TGR of the grounding system is greatly reduced. The effect of the surrounding volume conductivity and relative permittivity on the P-TGR is also tested. Second, the rectangular surrounding material volume is shielded with a metallic pipe to reduce the P-TGR further. Third, the shielding metallic pipe is connected to the grounding electrode with thin wire, and the effect of the number of the wires on the P-TGR is also analyzed. It is demonstrated that the P-TGR of the grounding system has been reduced significantly.

A novel band-pass filter (BPF) with lower and upper stopband zeros is proposed. The filter mainly consists of two antisymmetric modified anti-parallel coupled-lines and double pairs of transmission lines. Compared with the traditional anti-parallel coupled-line, the new filter has a better performance at both pass band and stop band. On the basis of even-odd mode method and network theory, the filter has been analyzed in detail. In addition, a simple method to create transmission zeros is investigated, which is beneficial for controlling the stopband zeros. The proposed filter is implemented on RT/Duroid 4350 substrate. Measured results show low insertion loss of less than 1.6 dB in the pass band and good suppressing of more than 22 dB in the lower stop band. Measured results show a good agreement with simulated results.

An overall Low-Temperature Co-fired Ceramics (LTCC) package solution for X-band T/R module has been presented in this paper. This tile type package contributes to a dramatic reduction in size and weight of the T/R module. Moreover, an obvious merit of ceramic housing is better consistency of Coefficient of Thermal Expansion (CTE), compared with the traditional combination of ceramic board and metal housing. The schematic diagram and 3-D structure of the T/R module have been presented and a novel vertical interconnection based on Ball Grid Array (BGA) has been proposed to connect vias in the lid and those in the stage of the main LTCC pan. The LTCC T/R module has been fabricated and measured. It is compact in size (20×20× 2.6 mm³) and has a weight of 3.5 g. The measured transmit output power is 33±1 dBm in the frequency range from 8.8 GHz to 10.4 GHz, and the measured receive gain and Noise Figure are 29-30.5 dB and 2.6-2.8 dB, respectively.

A wideband dual-polarized antenna with high isolation is presented. Four printed quadrant planar folded dipole placed above a U-shaped reflector are adopted as the main radiation elements. Curved slots cut on the planar folded dipole are used to reduce the size of the antenna. Parameter is studied, and the values are adjusted in order to obtain wideband and compact properties. Measured results show that the antenna achieves a VSWR < 2.0 from 1.64-2.33 GHz. The isolation between the two polarizations is better than 29.5 dB. The radius of the quadrant planar folded dipole is only 34 mm (about 0.18 wavelength at 1.64 GHz).