In this paper, a simple method and structure to design a dual-band bandpass filter (BPF) by using a dual feeding structure and embedded uniform impedance resonator (UIR) is presented. In this structure, two passbands can be designed individually and several transmission zeros can be created to improve the band selectivity and stopband performance. The first passband is determined by the dual feeding structure and the second passband is determined by the UIR. Moreover, by using the inter coupling in the UIR, the performance of the second passband can be easily tuned without degrading the first passband. In order to verify the design concept, two filter examples, including 0.9/1.575 GHz for multi-services communication and 2.4/5.7 GHz for wireless local area network (WLAN), are designed in this study. Experimental results of the fabricated samples show a good agreement with the simulated results.

This paper discusses for the first time the combined optoelectronic-electromagnetic modelling of a new technology that represents a paradigm shift in the way millimetre-wave and terahertz electronics can be implemented using the REconfigurable Terahertz INtegrated Architecture (RETINA) concept. Instead of having traditional metal-pipe rectangular waveguide structures with metal sidewalls, RETINA structures have photo-induced virtual sidewalls within a high resistivity silicon substrate. This new class of substrate integrated waveguide (SIW) technology allows individual components to be made tuneable and subsystems to be reconfigurable, by changing light source patterns. Detailed optoelectronic modelling strategies for the generation of virtual sidewalls and their electromagnetic interactions are presented in detail for the first time. It is found with double-sided illuminated RETINA structures that an insertion loss of 1.3 dB/ λ_g at 300 GHz is predicted for the dominant TE₁₀ mode and for a cavity resonator a Q-factor of 4 at 173 GHz is predicted for the TE₁₀₁ mode. While predicted losses are currently greater than other non-tuneable/reconfigurable SIW technologies, there is a wide range of techniques that can improve their performance, while still allowing completely arbitrary topologies to be defined in the x-z plane. For this reason, it is believed that this technology could have a profound impact on the future of millimetre-wave and terahertz electronics. As a result, this paper could be of interest to research groups that have the specialised experimental resources to implement practical demonstrator exemplars.

The purpose of this paper is to provide some further observations on the use of reverberation chambers to imitate real wireless channels. It is shown, that when RMS delay spread is calculated appropriate threshold has to be chosen. Based on the threshold value the required dynamics of measurements performed for realistic wireless channels can be estimated. It is also shown, that the reverberation chamber loading method allows only for representing outdoor channels.

We numerically compare the mode birefringence and confinement loss with four patterns of index-guiding photonic crystal fibers (PCF) using the finite element method. These PCFs are composed of a solid silica core surrounded by different sizes of elliptical air holes and a cladding which consist of the same elliptical air holes in fiber cladding with tetragonal lattice. The maximal modal birefringence and lowest confinement loss of our proposed case A structure at the excitation wavelength of λ=1550 nm can be achieved at a magnitude of 5.3×10^-2 (which is the highest value to our knowledge) and less than 0.051 dB/km (an acceptable value less than 0.1 dB/km) with only four rings of air holes in fiber cladding, respectively. The merit of our designed PCFs is that the birefringence and confinement loss can be easily controlled by turning the pitch (hole to hole spacing) of elliptical air holes in PCF cladding.

A new type of miniaturized stepped impedance resonator (SIR) for bandpass filter applications is proposed in this paper. The new resonator incorporates a ground plane window with a floating conductor in the backside of the substrate. The ground plane window increase the characteristic impedance of the lines used to implement the inductive region of the quasi-lumped resonator, thus allowing some size reduction. Moreover, the presence of a floating conducting patch printed below the capacitive region of the resonator pushes up the first spurious band of the filter. A meaningful improvement of its out-of-band rejection level is then achieved. The coupling between adjacent resonators is also enhanced thus leading to wider achievable bandwidths. Some filter designs using the new resonator and other standard resonators are included for comparison purposes.

This paper proposes a metamaterial reflective surface (MRS) as a superstrate for a single-feed circularly polarized microstrip patch antenna (SFCP-MPA). It illustrates a simultaneous enhancement on antenna gain, impedance bandwidth (ZBW) and axial-ratio bandwidth (ARBW) by adding the MRS atop the SFCP-MPA. The MRS can enhance the ZBW and ARBW by 3.5 and 9.9 times, respectively, compared to the circularly polarized patch source. Moreover, the gain of the CP-MPA with the MRS is 7 dB higher than that of the conventional CP-MPA. The small spacing between the MRS and patch source is another merit in the present design, which is as low as λ_o/16 as it results in a low-profile antenna design that well suits modern wireless communications.

In this paper, a new simple design procedure of multi-frequency unequal split Wilkinson power dividers (WPDs) is presented. The procedure is based on using N-sections of transmission line transformers, instead of the conventional quarter-wave WPD branches, to realize a WPD that operates at N frequencies. Good isolation is achieved by using lumped resistors without any extra modification to the conventional structure of WPDs. The analysis, design procedure, and mathematical expressions are presented for arbitrary design frequencies, and arbitrary power split ratio. For verification purposes, a 1:2 dual-frequency, a 1:2 tri-frequency, and a 1:2 quad-frequency WPDs are designed and fabricated. The measured results show good agreement with those obtained using the presented design methodology and with full-wave simulated results.

To measure the phase of signal with very high working frequency such as THz, and optics band is still a challenging problem. In this paper, based on the relationship between radiating current and measured intensity of electrical field a novel phase retrieval algorithm has been developed. As opposed to the existing approaches of phase retrieval where usually the Fourier coefficients of measured data will be firstly reconstructed, the proposed approach is to reconstruct the so-called radiating currents, with more physical meaning than the former. It has a much smaller number of freedoms of radiating current than that of measurements, which means that the obtained equations are over-determined. Thus one can efficiently model the intensity of measured electric field via the radiating part, and reconstruct it quickly and stably. The novelty is that this physical consideration 1) leads to efficiently avoiding false solutions due to the ill-posedness of phase retrieval problem, and 2) offers a good initial guess for inverse scattering based imaging algorisms. Importantly, a closed-form formulation of phase retrieve also has been derived when the intensity of incident wave is much stronger than one of the scattered wave, for example, for the weak scattering objects. Finally, several numerical experiments are provided to show the high performance of proposed algorithm.

An efficient hybrid MPI/OpenMP parallel implementation of an innovative approach that combines the Fast Fourier Transform (FFT) and the Multilevel Fast Multipole Algorithm (MLFMA) has been successfully used to solve an electromagnetic problem involving 620 millions of unknowns. The MLFMA-FFT method can deal with extremely large problems due to its high scalability and its reduced computational complexity. The former is provided by the use of the FFT in distributed calculations and the latter by the application of the MLFMA in shared computation.

The problem of imaging three-dimensional strong scatterers by means of a two-dimensional sliced tomographic reconstruction algorithm is dealt with. In particular, the focus of the paper is on the experimental validation of the involved inversion algorithm thanks to measurements collected in a controlled environment. A simple strategy exploiting reconstructions obtained at di®erent time instants in order to detect slowly moving scatterers is also experimentally validated.

An analysis is presented of a three-layer tapered core liquid crystal optical fiber (TLCF) having the outermost clad section made of radially anisotropic liquid crystal. TE mode propagation through TLCF is demonstrated with maximum distribution of power in the liquid crystal section under the situation that the TLCF core and the inner clad regions are constructed of homogeneous and isotropic dielectric materials. Such a propagation feature is attributed to the radial anisotropy of the liquid crystal outer region, and attracts useful applications of TLCFs in evanescent field optical sensing and other coupling devices primarily used in integrated optics.

Density is an important parameter to determine the strength of road, and it will ensure the safety of the use as well as maintaining the quality of road pavement. In this paper, the validation of GPR mixture model based on the microwave nondestructive free space method to determine the density of road pavement typed Hot Mix Asphalt (HMA) will be presented. The frequency range of operation used is 1.7-2.6 GHz. The attenuation is a major factor for gathering the density of road pavement predictably. The existing mixture model has been used to produce simulation data for determining the predicted complex permittivity and attenuation due to various densities of road pavement. The GPR laboratory measurement is performed where the measured attenuation due to various densities was obtained. The comparison results between measurement and simulation were investigated, and the relative errors in between were calculated to see the performance of the model. The best performance of mixture model was selected in the optimization technique due to the smallest mean error. An improved attenuation formula or optimized mixture model was obtained from the optimization technique to produce the better model. The finding from the optimization process suggested that three additional constant parameters which are volume factor, permittivity factor and attenuation factor need to be included to improve the existing mixture model. The optimized mixture model is introduced as GPR mixture model in this work. The validation process at field test had been conducted to evaluate the performance of optimized GPR model and produce the error range from 3.3% and 4.7%. At the end of this project, the GPR mixture model can be used as a calibration curve where the values of predicted density of a given real road pavement can be read directly once the attenuation values are known.

A wideband elliptical bowtie impulse antenna is proposed and investigated in this paper. Simulated results reveal that it can achieve an impedance bandwidth of 141% for S₁₁≤-10 dB, a broadside gain of 2.4-5.3 dB, and stable radiation pattern over the whole operating band. The measured reflection coefficient is less than -10 dB over the frequency from 1.30 to 6.65 GHz, and it agrees well with the simulated results. The characteristics of frequency-domain such as radiation pattern, phase center and time-domain behaviors are discussed. The antenna electrical dimension is 0.31λ₀, where λ₀ is the free-space wavelength at lower edge of the operating frequency band. Parameters are studied to optimize the antenna performance.

We present a new RADAR system able to perform Phase Conjugation experiments over the ultrawideband [2-4] GHz. The system is equipped with a transmit/receive linear array made of eight antennas connected to a 2-port Vector Network Analyzer through eight independent couples of digitally-controlled RF attenuators and phase shifters. Thus, each channel can selectively transmit or receive and can as well attenuate and phase shift the RF signal. For each frequency, either the Phase Conjugation or the Decomposition of the Time Reversal Operator (DORT) is applied to the received signal and the appropriate amplitude and phase law is coded into the prototype; the focusing wave is then experimentally re-emitted by the array. The quality of the achieved backpropagation is evaluated both in frequency and time domain: in this sense we can speak of Time Reversal. The excellent agreement between measured and theoretical results validates the potential of our system.

Strong interests are recently emerging for development of solid-state devices operating in the so-called "terahertz gap" region for possible application in radio astronomy, industry and defense. To fill the THz gap by using conventional electron approach or transit time devices seems to be very difficult due to the limitation that comes from the carrier transit time where extremely small feature sizes are required. One way to overcome this limitation is to employ the traveling wave type approach in semiconductors like classical traveling wave tubes (TWTs) where no transit time limitation is imposed. In this paper, the analysis method to analyze the properties of drifting plasma waves in semiconductor-insulator structure based on the transverse magnetic (TM) mode analysis is presented. Two waves components (quasi-lamellar wave and quasisolenoidal wave), electromagnetic fields (E_y, E_z and H_x) and ω-and k-dependent effective permittivity are derived where these parameters are the main parameters to explain the interaction between propagating electromagnetic waves and drifting carrier plasma waves in semiconductor. A method to determine the surface impedances in semiconductor-insulator multi-layered structure using equivalent transmission line representation method is also presented since multi-layered structure is also a promising structure for fabricating such a so-called plasma wave device.

Electromagnetic scattering by conducting bodies of revolution (BOR) coated with homogeneous chiral media above a lossy half-space is formulated in terms of the Poggio-Miller-Chang-Harrington-Wu surface integral equation combined with combined field integral equation. A field decomposition scheme is utilized to split a chiral media into two equivalent homogeneous media. The spatial domain half-space Green's functions are obtained via the discrete complex image method. Due to the rotational symmetry property of BOR, the method of moment for BOR (BORMoM) is applied to the linear system solved by the multifrontal direct solver. Numerical results are presented to demonstrate the accuracy and efficiency of the proposed method.

Characteristics of electromagnetic wave propagation through a magnetized plasma slab with linear electron density profile is analysed. In the numerical analysis, cold, weakly ionized, collisional and steady state plasma layer is divided into sufficiently thin, adjacent subslabs, in each of which plasma parameters are constant. Reflection and transmission coe±cients are calculated for discretised plasma by considering electron density profile with positive and negative slopes. Wideband absorbtion characteristic is obtained with high collision frequency and high electron density combination in linearly decreasing profile as well as wideband transmission characteristic is obtained for low collision frequency and low electron density combination in linearly increasing profile of finite length. The general results show that in steady state, plasma layer behaves as a frequency selective medium satisfying the major requirements of current shielding applications as the function of plasma parameters and the strength of external magnetic field excitation. Proposed plasma layer can be used in current shielding and stealth applications as a matching layer between the surface and the incident electromagnetic wave.

In this paper, a directional slot antenna with parasitic patch and windowed superstrate is presented. Through this composition, high-gain property can easily be obtained by this proposed antenna. The proposed antenna has a measured impedance bandwidth of 2.41-2.49 GHz for S11<-10 dB, which can cover the 2.4-2.484 GHz frequency band of WLAN application. Simulated and measured results show that high-gain features up to 11.50 dBi across the corresponding impedance band are achieved. Details of the proposed slot antenna configurations and design procedures are given; the experimental results are also given and discussed.

A novel rectangular slot antenna with embedded self-similar strips is proposed for wireless local area network (WLAN) applications. The proposed antenna comprises a T-shaped monopole and inverted self-similar strips embedded in the rectangular slot etched on the ground plane. The measured results of the fabricated antenna show that the impedance bandwidths (VSWR<2) are 180 MHz from 2.36 to 2.54 GHz and 920 MHz from 5.05 to 5.97 GHz, which cover all the 2.4/5.2/5.8 GHz WLAN operating bands. And the radiation patterns are almost omni-directional in the azimuthal plane within the lower operating bands.

In this paper, we apply the parallel method of moments (MOM) to solve the Electric and Magnetic Current Combined Field Integral Equation (JMCFIE) for scattering by large, three-dimensional (3-D), arbitrarily shaped, homogeneous dielectric objects. We first derive the JMCFIE formulation which produces well-conditioned matrix equation when the MOM with Galerkin's type testing and Rao- Wilton-Glisson (RWG) functions is applied. We then develop a parallel conjugate gradient (CG) method on personal computer (PC) clusters using message passing interface (MPI) for solving the matrix equation obtained with JMCFIE. The matrix is decomposed by the row and stored in distributed memory of the node. Several numerical results are presented to demonstrate the accuracy and capability of the proposed method.