Novel dual-band 90° couplers with arbitrary power division ratios using simplified composite right-/left-handed (SCRLH) transmission lines (TLs) are proposed. With a degree of freedom in the structural parameters, a SCRLH stub can easily be tailored to imitate a conventional 90° section at two arbitrary frequencies with different characteristic impedances, making the resulting couplers with customizable power division ratios, as well as ensuring the size miniaturization and element realizability. To validate our idea, 90° couplers operated at 2.45/5.2 GHz with various power division ratios are designed and fabricated using microstrip technology. Good agreement is achieved between the simulated and measured results, justifying that the SCRLH configuration provides a new way of implementing a compact dual-band 90° coupler with arbitrary power split ratios.

An effective method is introduced to overcome the narrow strip width in unequal Wilkinson power divider with high dividing ratio. In the proposed method, the separated microstrip lines of the Wilkinson power divider are replaced by a uniform asymmetrical microstrip coupled lines. It is shown that in the proposed method, the width of the narrow microstrip line is significantly wider in comparison to the narrow microstrip line in the conventional Wilkinson power divider with the same specification. To design the power divider, a suitable error function is defined and then minimized which led to the final dimensions of the power divider. A sample of the designed power divider with 4:1 dividing ratio is fabricated and tested, which indicate the effectiveness of the proposed method.

We propose a combination chaotic map (CCM) signal model to resolve the limited-word-length problem in digitally realizing chaotic signals used for noise radar. The proposed CCM has approximated infinite dimension, much more complicated phase space structure as well as better chaotic properties. The radar signal based on CCM presents much lower PSLR of auto-correlation as well as much flatter power spectrum, so it is very suitable for generating wide-band radar signal. Simulation experiments are conducted to show the good performance of the signal.

This paper presents the novel theoretical design, CAD modeling, and performance analysis of a compact and reliable microwave beamforming network (MBFN) which has been developed based on the RF Rotman lens switched-beam steered array for operation in Ku frequency band. The objective of this investigation is to develop a passive beam steering microwave network device intended for the potential suitable use in satellite communications beam scanning electronically scanned arrays. A thorough Ku-band satellite microwave network system has been theoretically designed and simulated along with the analysis of its output RF characteristics. The antenna array feeding network is capable of multi-beams generation and wide-band operation in terms of the true-time-delay (TDD) and low dispersive properties in order to allow simultaneous operation of multiple RF beams. The Rotman lens demonstrates the potential appropriateness in order to develop a high-performance and well-established design for advanced satellite microwave systems, services, and devices.

In this work, we show that light intensity modulation can be realized in the system of one-dimensional time-variant photonic crystals. Different from conventional light modulators, the functioning of the proposed structure emphasizes on its spatial/temporal structures instead of inherent material properties. Additionally, our system can perform inherent light modulation without introducing external stimuli, thus avoiding direct contacts with electrodes (or other modulation sources), which would be preferable in certain environments. The influences of parameters such as light frequency, structure dimensions, and refractive index contrasts on the modulation performance of the time-variant photonic crystal were investigated by numerical simulations. The results provide a new strategy for light modulation, which may add functionalities in optical communication, integrated-optics or display technologies.

The aim of this paper is to propose and evaluate a semi-empirical propagation modeling for radiating cable used in indoor environments. This propagation modeling takes into consideration propagation mechanisms such as reflections, penetration loss and cable termination that result from a particular environment, as well as specific cable paths that actual propagation models for radiating cable systems have not considered. The proposed modeling is carried out using three different propagation models and has been experimentally validated by sets of measurements performed in a university building in the frequency range from 900 MHz to 2.5 GHz. A careful selection of the data sets validates the robustness of the proposed model. The results show a mean of the error less than 1 dB while the standard deviation is between 2.2 dB and 4.6 dB in all cases. To the best of our knowledge, this is the first time such a robust modeling for radiating cable operating between 900 MHz to 2.5 GHz has been presented.

The problem of characterizing random sources from near-field measurements and of devising the random field sampling procedure is tackled by a stochastic approach. The presented technique is an extension of that introduced in [A. Capozzoli, et al., Field sampling and field reconstruction: a new perspective, Radio Sci., vol. 45, 2010] and successfully adopted to experimentally characterize deterministic (CW and multi-frequency) radiators and fields. Under the assumption that the source is wide sense stationary, quasi-monochromatic and incoherent, its intensity is reconstructed by time-domain field measurements aimed at extracting information from the mutual coherence of the acquired near-field. The linear relation between the field coherence and the source intensity is inverted by using the Singular Value Decomposition (SVD) approach, properly representing the source intensity distribution by exploiting the a priori information (e.g., its size and shape) on the radiator. The sampling of the radiated random field is devised by a singular value optimization procedure of the relevant finite dimensional linear operator. Experimental results using a slotted reverberation chamber as incoherent source assess the performance of the approach.

We theoretically investigate the possibility of using a metamaterial structure as a spacer, named as metaspacer, which can be integrated with other materials in microfabrication. We show that such metaspacers can provide new optical behaviors that are not possible through conventional spacers. In particular, we investigate negative index metaspacers embedded in fishnet metamaterial structures and compare them with conventional fishnet metamaterial structures. We show that the negative index metaspacer based fishnet structure exhibits intriguing inverted optical response. We also observe that the dependence of the resonance frequency on the geometric parameters is reversed. We conclude with practicality of these metaspacers.

The analysis of scattering of objects buried below a random rough surface is of practical interest. In reality, the random rough surface may be of an extensive periodic structure. To deal with this more realistic situation, this paper presents a Monte-Carlo MPSTD numerical technique developed for investigating the scattering of a cylinder buried below a random periodic rough surface. The computation model is formulated in two steps. In the first step, only the random rough surface is considered and the periodic boundary condition (PBC) is enforced at the two ends of a period of the rough surface. Then, in the second step, a cylinder is placed below the random rough surface and the interaction between the buried cylinder and the rough surface is taken into account. In each of the two steps, the fields are computed employing the MPSTD algorithm developed in the authors' previous work. Sample numerical results are presented and validated.

A novel meander antenna with tri-band operation is presented for WLAN and WiMAX applications. The proposed antenna consists of a rectangular meander with two asymmetrical L-shaped strips. The rectangular meander is used for the lower band operation at 2.5 GHz. The left L-shaped strip is employed to generate the higher resonant mode at about 5.5 GHz, while the right L-shaped strip is employed to create a new resonant mode at 3.5 GHz and enhance the bandwidth of the middle band operation. Prototype of the proposed antenna has been constructed and experimentally studied. The measured 10 dB return loss bandwidths at the resonant frequency of 2.5, 3.5, and 5.5 GHz can be up to 520 MHz (2.18-2.70 GHz), 800 MHz (3.34-4.14 GHz) and 830 MHz (5.07-5.90 GHz), respectively. The antenna is simple in configuration and has a compact dimension of 37×42×1 mm³.

This paper describes a novel permittivity measurement technique using dual open ended coaxial sensors. The magnitude reflection coefficients from two open ended coaxial sensors were used to determine complex reflection coefficients and permittivity of a sample under test.

In this paper two typical arrangements of underground single-core high voltage three-phase power cables (flat and trefoil protected by PVC pipes) inside a closed shield of three different materials (low-carbon steel, non-oriented grain steel and aluminium) are analysed. The shield has two components: a U-shaped base and a flat plate (cover) located on top of the base. Whereas most of previous papers on this subject only dealt with the degree of mitigation obtained with each material, this paper, in addition to also addressing this issue, mainly focusses on the effect that electromagnetic losses induced in the shield have on the ampacity of the cable and the cost involved (material and losses). To obtain the numerical results, a high number of simulations by a well-known commercial finite element method software (COMSOL Multiphysics) have been performed. The results obtained in the numerous cases analysed are widely commented and the solutions that enable an important mitigation with no current derating and at a comparatively low cost are highlighted.

The aperture synthesis technology represents a promising new approach to microwave radiometers for high-resolution observations of the Earth from geostationary orbit. However, the future application of the new technology may be limited by its large number of antennas, receivers, and correlators. In order to reduce significantly the complexity of the on-board hardware requirements, a novel method based on the recently developed theory of compressive sensing (CS) is proposed in this paper. Due to the fact that the brightness temperature distributions of the Earth have a sparse representation in some proper transform domain-for example, in terms of spatial finite-differences or their wavelet coefficients, we use the CS approach to significantly undersample the visibility function. Thus the number of antennas, receivers, and correlators can be further reduced than those based on the traditional methods that obey the Shannon/Nyquist sampling theorem. The reconstruction is performed by minimizing the l₁ norm of a transformed image. The effectiveness of the proposed approach is validated by numerical simulations using the image corresponding to AMSU-A over the Pacific.

In this paper, a wide slot loop antenna with an adjustable back-reflector is introduced. Five working statuses are defined by simply adjusting the distances between the radiator and the reflector. Measured results show the total available operating band with better than 10 dB return loss ranges from 0.84 GHz to 3.04 GHz (113.4%). The radiation properties of the array are tested in an anechoic chamber. Stable unidirectional radiations with more than 8.3 dB gains are observed in the working band. Apart from that, the straightforward two-portion arrangement of the design provides cost-effective solution for mass production. All these features make the antenna an appropriate substitute for multiple narrowband antennas.

In this paper, the performance analysis of the natural frequency-based radar target recognition in the time domain is considered. We investigate the dependence of the probability of correct classification on a specific threshold value, and determine the optimum threshold value for two targets, and the sub-optimal threshold for multiple targets to maximize the probability of correct classification. Based on the probability density function (PDF) of some quantity consisting of the projections of the late time response onto the column spaces of the matrices constructed using the natural frequencies of the specific targets, we propose how to determine an optimum threshold in the sense that the probability of correct classification of two targets is maximized. By extending the scheme for two targets, we show how to determine a threshold value close to the optimal threshold for multiple targets. The scheme is validated by comparing the performance using the analytic method with that using the Monte-Carlo simulation.

This paper deals with the prediction of magnetic field distribution and electromagnetic performances of parallel double excitation and spoke-type permanent magnet (PM) motors using simplified (SM) and exact (EM) analytical models. The simplified analytical model corresponds to a simplified geometry of the studied machines where the rotor and stator tooth-tips and the shape of polar pieces are not taken into account. A 2D analytical solution of magnetic field distribution is established. It involves solution of Laplace's and Poisson's equations in stator and rotor slots, airgap, buried permanent magnets into rotor slots and non magnetic region under magnets. A comparison between the results issued from the simplified model with those from exact model (EM) (which represents a more realistic geometry with stator and rotor tooth-tips and the shape of polar pieces) is done to show the accuracy of the simplified geometry on magnetic field distribution and electromagnetic performances (cogging torque, electromagnetic torque, flux linkage, back-EMF, self and mutual inductances). The analytical results are verified with those issued from finite element method (FEM).

A new planar bow-tie antenna is proposed here for UWB applications. The self-complementary principle has been applied to a planar triangular monopole antenna along with bending the microstrip feed line. The antenna has a wider frequency band compared to the traditional bow-tie antenna, complies with the UWB requirements and it is directly matched to the (SMA) connector via 50 Ω microstrip feed line. This antenna has a simple shape which overcomes the complicated matching techniques using baluns or impedance matching sections that are commonly used in bow-tie antennas for widening their limited bandwidths. Another improvement on this new bow-tie antenna is achieved through fractal self-similarity repetition of the triangular shape on each of the patch and its complimentary slot. The simulation results obtained from the CST and HFSS software packages are verified by experimental measurements.

A minimized wideband antenna array is presented for ultra-high frequency (UHF) radio frequency identification (RFID) reader applications. The antenna array consists of two E-shaped patch antennas and a feeding network, with the overall size 200×100×20 mm³. The feeding network could effectively decrease the antenna mutual coupling and improve the bandwidth. The measured bandwidth is about 68 MHz (896-964 MHz) under the condition of voltage standing wave ratio (VSWR) less than 2, which covers various RFID bands including North American (902-928 MHz), partial Chinese (920-925 MHz) and Japanese (952-955 MHz). The average gain is 4.5 dBi in UHF band. The principles of the antenna and the feeding network are also discussed and analyzed in this paper. At last, the key parameters are studied and show the antenna robustness.

A very compact low temperature co-fired ceramic (LTCC) dual-band filter is designed based on the proposed novel cross-coupling structure in this paper. A six-pole dual-band filter with four transmission zeros is synthesized using an analytical procedure. By incorporating the proposed novel cross-coupling structure and analyzing the coupling characteristic, the dual-band filter is realized with canonical topology in multilayer LTCC. It is demonstrated by the simulation and experiment that the proposed dual-band filter has both compact size and good selectivity.

In this work we investigate the effect of broadband antireflection of a medium by a layer of embedded nano-cavities arranged near the surface. It is shown that this structure is versatile and allows near 100% transmittance in a wide spectral range practically for any dielectric material. The approximate model of nano-structured layer is suggested that allows to determine the parameters of the system necessary for achieving antireflection of any a priori given media without complicated numerical calculations. The transmission spectrum of a medium modified by such a structure is entirely defined by a radius and a depth of bedding of the nano-porous layer.