A wideband dual-polarized crossed-dipole antenna with parasitical crossed-strip for base-station applications is presented. By using a pair of orthogonal crossed-dipoles, two linear polarizations (+45°) are obtained. A parasitical crossed-strip is introduced to improve the impendence bandwidth and enhance the isolation (S₁₂) between the two orthogonal polarizations of the upper band. The antenna shows a wideband impedance characteristic about 34.9% for S₁₁≤-10 dB (+45° polarization) and S₂₂≤-10 dB (-45° polarization). High isolation (S₁₂≤-32 dB) between the two polarizations in the required band are obtained. The stable peak gain, unidirectional radiation patterns and low cross-polarization over the whole operating band are also achieved. Due to its good performance, simple fabrication technique and low cost, the antenna is very suitable for potential base station applications in mobile communication such as DCS, PCS and UMTS.

Electromagnetic shielding (EMS) fabrics often need to design rectangular holes for application. However, there is not a mature approach to predict the shielding effectiveness (SE) of the EMS fabric with rectangular hole. This paper proposes that there are a number of loose regions of conductive fibers on the hole edge of the EMS fabric, and establishes a SE prediction model of the EMS fabric with rectangular hole. Firstly, the loose region of conductive fiber is analyzed to build a model of the rectangular hole. Secondly, the SE prediction model of the EMS fabric with rectangular hole is deduced according to the transmission coefficient of the normal region, hole region and loose region, and the determining method of the loose region is given. Finally, the prediction model is verified by experiments. The results show that the model can successfully predict the SE of the EMS fabric with the plain, twill and satin weaves, and the factors such as frequency, fabric density and metal fiber content have little influence on the model. The proposed model can provide a valuable reference for the rational design of the rectangular hole of the EMS fabric.

We propose a general method to design an arbitrarily shaped radome which can extend the scanning angle of a phased array antenna through finite embedded transformation (FET). The main advantage of our method is that the relationship between the incident angle and steered output angle of the radome can be designed in advance (e.g., a linear relation can be achieved). Unlike a traditional FET, which is often applied onto a slab region, we first apply FET onto an arbitrarily shaped region to bestow the desired radome with an arbitrary shape. Two specific examples have been given to demonstrate our method. Numerical simulations show good performance of our radome.

Implanted antennas are widely used in hyperthermia and biomedical applications. The antenna needs to be extremely small while maintaining a permissible Specific Absorption Rate (SAR) and being able to cope with the detuning effects due to the dielectric properties of human body tissues. Most of the proposed antennas for implanted applications are electric field antennas such as Planner Inverted-F Antennas (PIFA) and micro-strip patch antennas. By minimizing the size of an electric field antenna, the near zone electric field will increase, resulting in higher SAR. This work is devoted to design a miniaturized magnetic field antenna to overcome the above limitations. The proposed electrically coupled loop antenna (ECLA) has high magnetic field and low electric field in the near zone and therefore, has a small SAR and is less sensitive to detuning effects. ECLA is designed at the Medical Implanted Communication Service (MICS) band with dimensions of (5×5×3 mm³). ECLA has been simulated inside one-layer human body model, three-layer spherical human head model, human head and human body. From the simulation results, ECLA inside the human body has a 5 MHz -3 dB bandwidth, -14 dB gain, and radiation efficiency of 0.525%. The 1 g average SAR inside the human body for 10 mW input power is about 1 W/kg which is 7 times lower than the SAR for a patch antenna of the same size with the same accepted power.

The paper presents a methodology to achieve efficient low-profile electromagnetic bandgap (EBG) antennas based on thick EBG unit cells. The EBG cells are composed of thick metal patches separated by narrow high aspect ratio (HAR) gaps, and positioned on a PEC-backed substrate. This approach yields new miniaturized EBG cells with considerably reduced electrical size. The miniaturized cells are employed to demonstrate new compact self-excited EBG resonator antennas with considerably reduced operating frequencies. Full-wave simulations and experimental results demonstrate the design approach.

This study presents an equivalent circuit and a design of an H-plane waveguide bandpass filter (BPF) with chamfer. Traditionally, only thin inductive diaphragm with no chamfers considered in the direct-coupled cavity theory, but this will lead to difficulties in the BPF manufacturing. During manufacturing process the chamfer cannot be avoided, and its equivalent circuit and effects on frequency shifting are investigated in this paper. A new design method is proposed in order to compensate the effect of chamfer in the half-wavelength resonator connection between the inductance diaphragm and the waveguide. A modified empirical formula and corresponding procedure are provided for designing such filters. The working center frequency and 3 dB bandwidths (BW) are simulated considering different chamfer radius. The simulated center frequencies are 18 GHz, 26 GHz, 34 GHz and 42 GHz, and BWs are 2.265%, 2.5%, 10%, 15% and 20%. Results show that the modified formula, which conforms better with the simulated results, is superior to the traditional formula. Two H-plane waveguide BPFs are manufactured with center frequency 26 GHz with 2.5% BW and 34 GHz with 2.265% BW. The results of the modified formula are in good agreement with measured ones.

In this paper, we study the scheduler design problems over delay-constrained wireless communication links. Following a crosslayer design approach, the wireless system is modeled as a joint link-PHY layer architecture with a finite-length buffer and continuousstate fading links. A heuristic and efficient fixed rate transmission scheduler scheme (FRT) is proposed. We formulate and analyze the performance of the FRT scheme in terms of power efficiency and packet drop rate. Compared with variable rate schemes, the FRT scheme can considerably simplify the hardware implementation of transmitter. In addition, we show that the optimization of FRT scheme can be conducted with significantly reduced computational cost by utilizing the sparse feature of the transition probability matrix. Moreover, the simulation results show that at the packet drop rate of 10^-3, the optimized average transmit power of FRT scheme is only 0.5 dB higher than the known optimal variable rate scheme, indicating that the FRT scheme is quite power efficient as well. Therefore, we conclude that the FRT scheme is more feasible than variable rate schemes in practical delayconstrained wireless systems with regard to both hardware cost and power efficiency.

In this paper, extended composite right/left-handed (E-CRLH) transmission line (TL) metamaterial structures, with two left-handed (backward) and two right-handed (forward) pass bands, are investigated. Also, design procedures in order to design dual- and quad-band E-CRLH-TLs are presented in detail and the parameters of these structures are extracted by clean formulas, while satisfying arbitrary phase shifts at the operating frequencies. Finally, the dispersion and characteristic impedances of these transmission lines are derived and plotted. The results of this paper can be applied to any type of TL-based dual- and quad-band microwave component.

An approximate self-consistent solution of the problem of plane electromagnetic wave diffraction on a thick grating of metallic bars with slits between the bars filled a Kerr-type nonlinear dielectric is solved. The bistable operating regime of wave transmission through the grating is studied.

In this paper, different causal sub-domain temporal basis functions are investigated to make the explicit marching-on-in time schemes converge and stable for solving two dimensional time domain EFIE. PEC cylinders with arbitrary cross section are illuminated by a TE-polarized Gaussian plane wave. Two different approximations are used for calculation of the singular elements of the impedance matrix analytically. In the Time Domain Method of Moment (TD-MoM) formulation of the Electric Field Integral Equation (EFIE) of the problem, the free-space two-dimensional Green's function and triangular spatial basis function are used. By employing Galerkin's method in spatial domain and point matching in time domain, all time convolution integrals and self-terms are evaluated analytically to increase the accuracy and stability of the proposed technique. The stability and efficiency of the new technique are confirmed by comparison with literature.

In cloaking, a body is hidden from detection by surrounding it by a coating consisting of an unusual anisotropic nonhomogeneous material. The permittivity and permeability of such a cloak are determined by the coordinate transformation of compressing a hidden 2D or cylindrical body into a line. Some components of the electrical parameters of the cloaking material (ε, μ) are required to have infinite or zero value at the boundary of the hidden object. In order to eliminate the zero or infinite values of the electrical parameters, approximate cloaking can be used by transforming the cylindrical body virtually into a small cylinder rather than a line, but this produces some scattering. The solution is obtained by rigorously solving Maxwell equations using angular harmonics expansion. In this work, the scattering pattern, and the backscattering cross section against the frequency for cloaked conducting and dielectric cylinders are studied for both transverse magnetic (TM_z) and transverse electric (TE_z) polarizations of the incident plane wave for different transformed body radii.

In inverse synthetic aperture radar (ISAR) imaging, micro-motion structures on the target will induce additional time-varying frequency modulations to the radar echoes. Due to the disturbance of these mechanical vibration or rotation parts in the ISAR imaging, it will be difficult to obtain a well-focused ISAR image of the target using conventional translational motion compensation methods. To solve this problem, two improved translational motion compensation techniques have been proposed in this paper. Firstly, the power transform is used in the range bin aligment processing to depress the disturbance of the micro-motion parts. Then, a impreoved autofocusing methods based on range bins selection is presented, which only use the range bins of the radar returns of the main body scatterers for the phase adjustment. The results from the measured data are given to verify the validity of the improved translational motion compensation techniques proposed in this paper.

The quest to understand the variation of rainfall microstructures at subtropical and equatorial regions is vital to rain attenuation studies. In this study, point rainfall datasets obtained at Butare (2°36'S, 29°44'E) and Durban (29°52'S, 30°58'E), are compared at the reflectivity threshold of 38 dBz. Joss- Walvogel (JW) distrometer measurements collected from these two locations represent physical rainfall data from equatorial and subtropical climates respectively. The reflectivity threshold enables the classification of rainfall datasets into stratiform and convective (S-C) precipitation regimes. These thresholds, Rth, at Durban and Butare are analysed based on three known rainfall microphysical parameters: rain rate, rainfall Drop Size Distribution (DSD) and radar reflectivity. The results from rain rate distributions at the both regions are similar for both stratiform and convective classes. However, the sampled DSDs indicate the dominance of larger rain droplets at Butare compared to observations at Durban, irrespective of the rain classes. In addition, it is found that the reflectivity distributions at both regions, under stratiform and convective conditions, are distinct in their probability profiles. The overall S-C analysis implied that the structures of the reflectivity and DSD profiles at both regions - result in significant variation of predicted specific attenuation - at microwave and millimeter band. In comparison with other global locations, it is affirmed that the S-C transition occurs globally at rain rates between 6 mm/h and 13 mm/h.

The Doppler phenomena caused by a moving receiver or environmental scatters around a receiver are emulated in an AC(Anechoic Chamber) and a RC(Reverberation Chamber) using platform and mode stirring. In order to verify the emulated Doppler spread spectrum, the measured results in the AC and the RC have been investigated to incorporate Jakes's and 802.11 TGn Doppler models, respectively.

A simple and analytical design methodology for a novel planar four-port structure to implement power divider (PD) or balun with variable power division is proposed in this paper. It consists of two different 3 dB branch-line couplers and one coupled-line phase shifter whose length can be changed to implement variable power division. Different from the previous designs, the power divider and balun with variable power division can be realized in only one circuit by changing the electrical length θ₀ of the coupled line when the impedance ratio g is selected. According to the ABCD parameters and linear algebra calculation, closed-form mathematical equations for the circuit electrical values and scattering parameters can be obtained. A prototype with this proposed circuit, operating at 2 GHz, has been designed and fabricated using microstrip technology. Good agreements between the calculated and measured results verify our design.

Among ship detection methods for SAR image, constant false alarm rate (CFAR) is the most important one. However, several factors, such as detector parameter and distribution of ocean clutter, affect the performance of CFAR detection. This paper proposes a novel hierarchical complete and operational ship detection approach based on detector parameter estimation and clutter pixel replacement, which is considered a sequential coarse-to-fine elimination process of false alarms. First, a simple barycentric algorithm is adopted to estimate target-window size, and a morphology method is used to estimate false alarm rate for CFAR detector. Second, a clutter pixel replacement approach based on the statistical features of sea clutter is presented to obtain statistically independent, stationary, and Weibull distributed random data for CFAR detector to remove all false alarms. Experimental results of the detection methods on a SAR image dataset show that the proposed approach is effective in reducing false alarms and obtains a satisfactory ship detection performance.

An ultra-thin triple-band metamaterial absorber (MA) is proposed in the microwave region, which is composed of a periodic array of three rotated square rings (RSRs) and a continuous metal film separated by only 1 mm dielectric substrate. The fabricated MA exhibits three experimental absorption peaks at 4.88 GHz, 7.88 GHz, and 11.32 GHz with the corresponding absorption rates of 98.8%, 96.5%, and 95.9%, which shows an excellent agreement with the simulated results. The triple-band MA is polarization-insensitive at the normal incidence. Finally, the multi-reflection interference theory is introduced to interpretate the absorption mechanism. The calculated absorption rates of the improved unit cell for the strongly coupled MA coincide well with the simulated results at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.

This paper presents three dielectric resonator (DR) unit elements loaded with one, two, and three narrow slots underneath for designing reflectarrays. The slots are aligned in parallel, and the lengths are varied to function as phase shifter for changing reflection phase. It is found that the dominant TE mode of the square DR element can be easily excited by placing multiple parallel slots beneath a DR element. Study shows that the number and width of the slots can be used as additional design parameters for tuning the reflection loss and phase range of the reflectarray. Rectangular waveguide method has been deployed, showing reasonable agreement between simulation and measurement. It is found that a reasonable reflection phase range of 313° with slow slope is obtainable when the DRA is loaded with two slots beneath, which can be used for designing a small-size reflectarray. The reflection characteristics of the unit elements are studied, along with a complete parametric analysis.

Barrage and deceptive jamming can mask the synthetic aperture radar (SAR) signals and render SAR useless. In this paper, a novel jamming suppression method based on plolarization SAR (PolSAR) is proposed. After range compression, the barrage jamming has a noise-like characteristic while the real echo and deceptive jamming are focused. According to this, the barrage jamming is removed via a minimum entropy algorithm. Based on the different polarization characteristics between deceptive jamming and the real echo, the deceptive jamming can be suppressed by phase compensation in doppler domain. Simulation results are shown to demonstrate the validity of the proposed method.

The adaptive cross approximation is applied to boundary element matrices coming from 2D scattering problems by an infinite periodic surface. This compression technique has the advantage to be applied before the assembly of the matrix. As a result, the computational times for both assembly and solution phases are reduced. Numerical results assess the efficacy of the method on scattering problems with several periodic surfaces.