An accurate and efficient computational approach is presented for analyzing radiation characteristics of large antenna arrays with radome. This approach is based on the hybrid finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA). Unlike the conventional single-domain FE-BI-MLFMA, the whole domain of the antenna array with radome is separated into many disconnected domains. A large free space area unavoidable in the single-domain FE-BI-MLFMA is eliminated in this multi-domain FE-BI-MLFMA formulation, thus the number of unknowns is greatly reduced in the presented multi-domain FE-BI-MLFMA approach. Different from the single-domain FE-BI-MLFMA, many integral equations are required in this multi-domain FE-BI-MLFMA. The numerical experiment shows that the presented multi-domain FE-BI-MLFMA is more efficient than the single-domain one while maintaining the same accuracy. A whole complicated system of a slotted-waveguide array with radome mounted on an aircraft is analyzed to further demonstrate the generality and capability of the presented multi-domain FE-BI-MLFMA.

This study discusses the operating characteristics of a large-orbit electron gun and a corresponding permanent magnet system of a 3rd harmonic peniotron. After optimization, a novel axis-encircling electron beam with axial velocity spread 4.48%, guiding centre deviation ratio 6.97% and high velocity ratio 2.03 is obtained. Driven by the electron gun, an output power of 35.4 kW is obtained, and the device efficiency is up to 56.0%, which is an attractive result in laboratories. The main advantages of such a peniotron are its compact size and low cost, which can meet the needs of vehicle, airborne and other mobile devices. The numerical analysis reveals that the relative axial position between the electrode system and magnet system has a great influence on the device performance, which needs careful control and precise adjustment.

In this paper, a theoretical analysis of numerical dispersion of the three-dimensional (3-D) high-order finite-difference time-domain (FDTD) method with weighted Laguerre polynomials (WLPs) is presented. The phase velocity of numerical wave modes is relevant to the direction of wave propagation, grid discretization and time-scale factor. The formula to determine a suitable time-scale factor is derived. By a theoretical evaluation, the dispersion errors for the 3-D high-order WLP-FDTD scheme with different time-scale factors are obtained. Finally, one numerical example is included to validate the effectiveness of the theoretical solution of the time-scale factor.

A novel method for a dual-band filter and quad-channel diplexer design is presented in this paper. This method, by altering the gap between resonators, realizes a transformation from bandpass to dual-band for the filter and diplexer. At first, a high selectivity bandpass filter (BPF) with four controllable transmission zeros (TZs) is designed. Then altering the gap between resonators, a band gap is generated and utilized to split the passband of the proposed BPF into two bands, which transforms the BPF to a dual-band filter with narrow passband separation. The center frequency and bandwidth of the new dual-band filter are controllable by adjusting the frequency and width of band gap. Based on the dual-band filter, a quad-channel diplexer with stepped impedance T-junction is designed, and it can be transformed to a wideband diplexer. For demonstration, the dual-band filter and quad-channel diplexer are fabricated and measured.

An equivalent-circuit model for a reconfigurable unit cell is proposed. This circuit model facilitates fast prediction of scattering parameters and dispersion analyses of a reconfigurable periodic structure. The cutoff frequencies obtained using equivalent-circuit models are in excellent agreement with those from measurements and full-wave numerical simulations. The proposed circuit model is then modified to include non-ideal, commercial RF FET switches. The effect of such a switch in each state, On or Off, is modeled by a frequency-dependant impedance, derived from the scattering parameters of the switch. The proposed technique can be used to analyze a reconfigurable periodic structure with any type of switches. For the structure with 24 unit cells considered here, the equivalent circuit model is about five orders of magnitude faster than full-wave simulations.

A switchable square loop frequency selective surface (FSS) design is presented. The FSS is switched between reflective and transparent state by using one gap for each unit cell. Measured and simulated results are compared. PIN diodes are integrated to the FSS for electrical switching. The PIN diodes equivalent circuit capacitance element is varied to investigate its effect on the switchable FSS performance. The switchable FSS power percentages of the reflected and transmitted states are presented in tables and discussed.

One of the main concerns for transcutaneous energy transfer via inductive coupling is misalignments of coils, especially in the case of mechanical circulatory support systems, when coils placed on a chest wall or an abdomen. We proposed a space-frequency approach to this problem. It is possible to find values of so called splitting frequency by expression which incorporate the value of coupling coefficient. Given that coupling coefficient depends on the system geometry, it allows one to determine the optimal operating frequency for the specified relative position of the coils. Numerical calculations of transcutaneous energy transfer parameters show the capability of the proposed method. It was found that the operation at splitting frequency provided more stable output with respect to changes in a system geometry. The output power of the proposed system changes for not more than 5% for a distance in a range of 5...25 mm. At the same time, the output power of the system which operates at fixed resonant frequency changes for about 40%. Similar results were obtained for a lateral displacements in a range of 0...20 mm.

In this work, numerical analysis of nonlinear ferromagnetic problems is presented using the three-dimensional time-domain finite element method (TDFEM). Formulated with the secondorder nonlinear partial differential equation (PDE) combined with the inverse Jiles-Atherton (J-A) vector hysteresis model, the nonlinear problems are solved in the time domain with the Newton-Raphson method. To solve the ordinary differential equation (ODE) representing the magnetic hysteresis accurately and efficiently, several ODE solvers are specifically designed and investigated. To improve the computational efficiency of the Newton-Raphson method, the multi-dimensional secant methods, aka Broyden's methods, are incorporated in the nonlinear TDFEM solver. A nonuniform time-stepping scheme is also developed using the weighted residual approach to remove the requirement of a uniform time-step size during the simulation. The capability and the performance of the proposed methods are demonstrated by various numerical examples.

A problem of electromagnetic waves radiation by an impedance vibrator located over finite-dimensional perfectly conducting screen is solved. The vibrator may have surface impedance distributed over its length. The solution is derived using asymptotic expressions for the current in a horizontal impedance vibrator placed over an infinite plane, obtained by averaging method. The problem was solved provided that the diffracted fields from the edges of the screen have little effect on the vibrator current amplitude, i.e. if the screen dimensions are comparable to or larger than the wavelength. Full radiation fields in all observation space in the far zone were found by the uniform geometrical theory of diffraction. The vibrator dimensions, value and type of surface impedance, removing from the screen and screen sizes were used as parameters. The multivariable electrodynamic characteristics of the resonant impedance vibrators placed above an infinite plane and square screen were studied. Characteristics dependences upon the vibrator dimensions, value and type of the surface impedance, removing from the screen, and screen dimensions were obtained.

We describe a surface integral-equation (SIE) method suitable for computation of electromagnetic fields scattered by 2D-periodic high-permittivity and plasmonic scatterers. The method makes use of fast evaluation of the 2D-quasi-periodic Green function (2D-QPGF) and its gradient using a tabulation technique in combination with tri-linear interpolation. In particular we present a very efficient technique to create the look-up tables for the 2D-QPGF and its gradient where we use to our advantage that it is very effective to simultaneously compute the QPGF and its gradient, and to simultaneously compute these values for the case in which the role of source and observation point are interchanged. We use the Ewald representation of the 2D-QPGF and its gradient to construct the tables with pre-computed values. Usually the expressions for the Ewald representation of the 2D-QPGF and its gradient are presented in terms of the complex complementary error function but here we give the expressions in terms of the Faddeeva function enabling efficient use of the dedicated algorithms to compute the Faddeeva function. Expressions are given for both lossy and lossless medium parameters and it is shown that the expression for the lossless case can be evaluated twice as fast as the expression for the lossy case. Two case studies are presented to validate the proposed method and to show that the time required for computing the method of moments (MoM) integrals that require evaluation of the 2D-QPGF becomes comparable to the time required for computing the MoM integrals that require evaluation of the aperiodic Green function.

A new microstrip narrow bandpass filter with good selectivity and wide stopband rejection for Ku-band application is proposed in this letter. The characteristic of the triple-mode stub-loaded resonator has been investigated. The resonance frequencies of the degenerate modes can be adjusted easily to satisfy the bandwidth of the narrow bandpass filter. Two parallel-coupling feed structures with cross-coupling have been used to generate two transmission zeros at the lower and upper stopband, which can improve the filter selectivity. To validate the design theory, a new microstrip Ku-band narrow bandpass filter has been designed, fabricated, and measured. Simulation and experimental results are provided with good agreement.

This paper presents design and development of a Circularly Polarized microstrip antenna array for C-band application. The proposed antenna exhibits convenient trade-off between bandwidth and dimension. The array design is based on the Sequential Phase Arrangement (SPA) of 2×2 non-identical disc based patch elements, operating in modal degeneration. Exploiting the properties of the SPA, capable to force CP even operating on linear polarized elements, each disc is independently detuned to operate on non perfectly overlapped bandwidth. When properly fed by a Sequential Phase Network (SPN), the set of four discs seamlessly covers the wide cumulative bandwidth which is the combination of the four sub-channels. To verify the design, a single-layer via-less array is fabricated in a compact printed square board of side 40 mm, meaning a surface of 0.64λ²₀ at the center frequency of 6.0 GHz, assembling the elements with a compact space-filling SPN. The measurements show a wide 10 dB return loss bandwidth of 28.5%, a 3 dB Axial Ratio (AR) bandwidth exceeding 1 GHz, and a realized gain ranging from 4.1 dB to 7.25 dB inside the AR bandwidth. The global bandwidth of the proposed array, almost coincident with the AR bandwidth, is 17.0%.

A novel design for a transparent circularly polarized circular slot antenna fed by a coplanar waveguide (CPW) is presented in this paper. The circular polarization is achieved by introducing a tapered split gap in the ring patch of the circular slot antenna in combination with unequal CPW ground arms. The antenna is designed using AgHT-4 laminated on a 2 mm thick glass with a relative permittivity of 7. The proposed antenna is designed to operate at 5.8 GHz for WLAN applications. The tapered split gap and inequality in the lengths of the CPW ground arms contribute to a 3 dB axial ratio bandwidth from 5.4 to 6.2 GHz. The proposed antenna has been studied theoretically and fabricated. The measured results show that the proposed antenna has a gain of 0.92 dB at 5.8 GHz. Reflection coefficient (S₁₁), axial ratio (AR), and radiation patterns are presented and briefly discussed.

This paper presents the frequency response of a stratified structure consisting of double-positive and dispersive double-negative chiral metamaterial layers. The structure is inserted between two half-spaces of fractional dimensions. Transfer matrix approach is used for the analysis. Dispersion within the double-negative chiral layers is realized by using Lorentz/Drude model. The effect of fractionality of the dimension is particularly investigated. Numerical results, for a five layer structure, are presented for various parametric values of the stratified structure and fractionality of the host media. It is shown that the fractionality of host media can be used as yet another parameter to control the frequency response of such a filtering structure. For integral values of dimensions, the results are shown to converge to the classical results thus validating the analysis.

We apply the method of the Broadband Green's Functions with Low wavenumber extraction (BBGFL) to calculate band diagrams in periodic structures. We consider 2D impenetrable objects placed in a 2D periodic lattice. The low wavenumber extraction is applied to the 2D periodic Green's function for the lattice which is used to formulate the surface integral equation. The low wavenumber extraction accelerates the convergence of the Floquet modes expansion. Using the BBGFL to the surface integral equation and the Method of Moments gives a linear eigenvalue equation that gives the broadband (multi-band) solutions for a given point in the first Brillouin zone. The method only requires the calculation of the periodic Green's function at a single low wavenumber. Numerical results are illustrated to show the computational efficiency and accuracy of the method. Because of the acceleration of convergence, an eigenvalue problem with dimensions 49 plane wave Floquet modes are sufficient to give the multi-band solutions that are in excellent agreement with results of the Korringa Kohn Rostoker (KKR) method. The multiband solutions for the band problem and the complementary band problem are also discussed.

In the past few years, several satisfying various objectives and designs of reconfigurable integrated microwave filter and antenna have been proposed for wireless communication systems. Several designs are new concepts and techniques, whereas others are inspired from previous works. The improvement concepts of these designs can be reviewed from this compilation of studies. This paper begins with an explanation of the reconfigurable filter, reconfigurable antenna and reconfigurable integrated microwave filter and antenna, followed by discussion on several designs in terms of size, measurement, performance and technology used. Among various designs, reconfigurable on planar structures are extensively used because of their simple design procedures and easy to tune on the desired frequency, bandwidth and attenuation. Most of the existing studies are focusing tunable on single element, i.e. either on filter or antenna side; however, it limits the tunable range and flexibility of the filtering antenna response. An alternative design of filtering antenna can be suggested to produce reconfigurable tuning capabilities on both microwave filter and antenna to produce overall good performance for multifunction operation in RF/microwave applications.

In this manuscript, a reduced size, ground slotted monopole antenna, operating in the range of 3.1-10.6 GHz is designed and implemented for breast cancer detection using time reversal MUSIC. A homemade breast mimicking phantom has been experimentally designed to facilitate the detection implementation. The simulated and measured results are in good agreement. The slots and blending edges of the ground, along with the feed step are some techniques applied to the designed antenna in order to achieve a broad bandwidth and reduce considerably the reflection coefficient. The resulting dielectric constant from the breast phantom is relatively close to the real normal breast tissues. After the design has been completed, some techniques of time reversal MUSIC were employed to mimic the breast cancer detection. The experimental results show that both temporal and spatial images of the cancer (tumor) are well represented here.

In this work, a numerical solution of nonlinear ferromagnetic problems is formulated using the three-dimensional time-domain finite element method (TDFEM) combined with the inverse Jiles-Atherton (J-A) vector hysteresis model. After a brief introduction of the J-A constitutive model, the second-order nonlinear partial differential equation (PDE) is constructed through the magnetic vector potential in the time domain, which is then discretized by employing the Newmark-β scheme, and solved by applying the Newton-Raphson method. Different Newton-Raphson schemes are constructed and compared. The capability of the proposed methods is demonstrated by several numerical examples including the simulation of the physical demagnetization process, the prediction of the magnetic remanence in the ferromagnetic material, and the generation of higher-order harmonics.

In this article, the design and analysis of a compact asymmetrical coplanar strip (ACS) feed multiband monopole antenna operating over the frequency range of Bluetooth/IMT-E (2.4-2.484/2.5-2.6 GHz), worldwide interoperability for microwave access (WiMAX: 3.3-3.6 GHz) and wireless local area network (WLAN: 5.15-5.825 GHz) for Personal Wireless Communication Systems (PWCS) applications has been investigated. The proposed antenna consists of a semi-circular arc and L-shaped stub which forms a vertically flipped G structure that facilitates the multi-band operation at 2.4 GHz and 3.5/5.5 GHz respectively. The antenna is fabricated on a low cost FR-4 substrate having thickness of 1 mm and has compact dimensions of 24 × 10 mm². The proposed antenna yields a highly isolated measured impedance bandwidth of 2.3-2.7 GHz, 3.25-3.65 GHz and 5.1-6 GHz for Bluetooth/IMT-E, WiMAX and WLAN bands respectively and exhibits symmetrical radiation pattern, stable gain across all operating frequency bands which makes the antenna a suitable candidate for PWCS applications.

An approach is proposed for determination of the complex permittivity and permeability of low-loss materials, eliminating half-wavelength resonances occurring in transmission/reflection (T/R) measurements. To this end, we apply the time-domain smoothing for removing resonant artifacts from the wave impedance obtained with the conventional T/R method, with an assumption that we do not have such artifacts in the refractive index. Accordingly, the permittivity and permeability are found from the smoothed wave impedance and conventional refractive index. In this paper, our method is validated by measurements for two different low-loss materials, nylon and lithium ferrite, and those results are discussed. Further, results from the present approach are compared to those from the approximate approach derived in our previous work.