Photonic band gaps of plasma metallic photonic crystals can be tuned dynamically by subjecting it to external magnetic field leading to variety of applications. Dispersion characteristics of 2D photonic crystals are often studied by Finite Difference Time Domain (FDTD) method based on standard Yee's grid discretization schema, in which x- and y-components of fields are defined on different edges of the Yee's cell. However, finite difference equations for electromagnetic wave propagation in magnetized plasma involve interdependence of polarization currents and electric field in a manner that requires both x- and y-components of fields to be evaluated at the same spatial location. A non-conventional discretization technique is presented in which x- and y-components of fields are evaluated at the same spatial location. In this paper analysis of magnetized plasma metallic photonic crystals (PMPC) is presented using the new grid. However, the proposed discretization scheme can be used to introduce magnetized plasmas in any type of structures that can be studied on the basis of standard Yee's grid. For example, topics such as photonic band gap (PBG) cavities based on PMPC, PBG waveguides involving plasma, meta-materials, etc. can be very effectively studied using the approach presented in this paper. Interesting results are found when PMPC is subject to external magnetic field. Several new bands including two dispersion-less flat bands appear and the existing bands with an exception of first band slightly shift upward when PMPC is subjected to an external transverse magnetic field. The location of flat bands and the location and width of forbidden band gaps can be controlled by external magnetic field as well as plasma parameters. New band gaps appearing for lower r/a for magnetized PMPC can be utilized for several applications such as PBG cavity design for gyrotron devices.

The problem of the synthesis of optimal continuous aperture sources to optimally realize the satellite multibeam coverage of Earth is stated and solved. The design approach relies on a far-field representation which exploits at best the degrees of freedom arising from the geometrical structure of the well-known four-colors colour coverage map. The overall synthesis is stated as a convex-programming problem wherein the fast achievement of the (unique) globally optimal solution is guaranteed. The introduced tools allow stating the ultimate theoretical radiation performances achievable by any circular-aperture antenna of fixed size and, at the same time, can be exploited as a reference in the synthesis of isophoric direct-radiating arrays. Numerical examples concerning a mission scenario recently proposed by the European Space Agency are provided.

In this paper, the Sherman-Morrison-Woodbury (SMW) Formula-based algorithm (SMWA) is used to enable the fast direct solution of conducting-dielectric arrays. To speed up the direct solution of the matrix equation, the dense impedance matrix is transformed into a product of several block diagonal matrices via the SMW formula. In the grouping process, the situation that the elements of an array simultaneously belong to two different subgroups at peer level is avoided in order to promote the efficiency. The SMWA conducts the calculation with a respectable reduction in the computational time as well as memory.

A novel implementation of N-way Wilkinson power divider using series and parallel combination of coaxial cables has been proposed in this paper. This arrangement results in a very compact power divider at VHF and lower frequencies, has good isolation between all the ports and is capable of handling high power with a low insertion loss. Frequency tuning and phase equalisation are easily accomplished using this technique. The measured results on fabricated 7-way and 4-way power dividers exhibited good input and output matching as well as amplitude and phase balance with an overall length of less than λ/8 at 221 MHz, with potential for further reduction in length.

The integration of a loop antenna into the top metal frame of a smartwatch wearable device is introduced. The loop antenna was made of a 1-mm thick, rectangular metal frame, which was stacked 1.5 mm above the lower metal frame of the watch having a size of 7 mm × 35 mm × 40 mm. The system circuit board was encircled by the lower, rectangular metal frame with a 1 mm gap between the perimeter of the ground plane and the metal frame. The top metal frame was fed in a corner on the frame's longer edge with two shorting portions short-circuited to the system ground. By carefully positioning the two shorting for the top metal frame, the proposed loop antenna can provide the global positioning system (GPS) operation at 1575 MHz for smartwatch applications.

Nowadays inductive powering has become a widely spread technique in existing and emerging implanted medical devices (IMD). The geometry of coils couple plays a key role in the design, optimization and evaluation of a biomedical inductive powering unit (IPU). We have proposed a relatively fast method for an execution of these procedures, which is based on a mutual induction calculation using GPU parallel computing. Generally, our approach is to calculate mutual inductance as a function of uncontrolled (axial distance, lateral distance, inclination) and controlled (coils radii, turns numbers, distance between turns) geometric parameters of a coil couple. Calculated geometric functions in its turn are used in the design and optimization procedure to evaluate an IPU performance (e.g., load power). Achieved time gain of the GPU calculations in comparison with the host CPU computing is up to 80 for sequential summation and up to 8 for parallel computing. Also, it is shown that precision of our method is comparable to the precision of existing electromagnetic field solvers, and at the same time, computation time is substantially less (time gain is about 7...8 for 2D case and about 100 and higher for 3D case). Additionally, we have verified our method experimentally and shown that results of the calculations are accurate enough to predict real IPU performance. Finally, we have given an example of an IPU design optimization using geometric functions calculated with the help of the proposed method.

This paper deals with the comparison of two actuators with different frameworks, for a direct drive active stick application. Each actuator will be compared with three different sets of specifications which impose many constraints as: high torque, small volume, low temperature, etc. The high required torque per unit of mass and the small volume allowed involve the use of synchronous Halbach permanent magnet (PM) topologies which have the best torque performances. In this article, an analysis and a comparison of two optimized actuators designed with a Halbach configuration are done. It is a linear actuator and a double airgap rotating actuator. The electromagnetic torque is calculated by the Laplace force for which the flux density generated by the Halbach PM configuration is defined by a Laplace equation and a Poisson equation. An analytical optimization under a set of nonlinear constraints will be realized with the analytical expressions of the torque we got previously. In order to validate the analytical model, finite-element analysis (FEA) simulations will be performed on the optimized structure. Finally, two actuators will be compared in order to give the best compromises for the stick application for each set of specifications.

Digital beamforming (DBF) on receive in elevation with a large receiving antenna will be widely adopted in future spaceborne synthetic aperture radar (SAR) missions to improve system performances. Furthermore, DBF can be used to separate echoes corresponding to different sub-pulses in some novel spaceborne SAR imaging modes. This paper proposes an improved DBF processor with a large receiving antenna for separating echoes. The proposed DBF processor includes three important parts: multiples sharp receiving beam generation, range compression and null steering. Compared with the conventional DBF processor in spaceborne SAR, the proposed DBF processor can separate echoes with better performances. Simulation results on point targets demonstrate the validity of the proposed DBF processor.

Although a superdirective array can acquire maximum directive gain with electrically small array, in some practical applications, low sidelobe and deep nulls are also important, which can effectively inhibit directional interferences. In this work, a set of simple superdirective pattern synthesis methods are proposed. By introducing diagonal loading factor and adding virtual jamming constraints, they can keep suitable tradeoff among directive gain, efficiency and anti-jamming performance. Besides, easy realization is another good feature of the proposed methods.

A compact unidirectional slot antenna with front to back ratio (FBR) enhancement is proposed. The antenna consists of a novel compact slot driven antenna, a stepped reflector and a vertical balun from a microstrip to a parallel strip line. Better FBRs are obtained by optimizing the stepped reflector. Impedance bandwidths are enhanced by applying the balun and a pair of microstrip stub etched on the opposite side of the slot. Then, the antenna is manufactured and measured. Measured results show that the proposed antenna has a bandwidth of 76% (1.53-3.41 GHz) for VSWR ≤ 1.5. In addition, from 1.7 to 3.2 GHz, the antenna gains are higher than 8.6 dBi, and the FBRs are greater than 22 dB. Good agreement between the simulated and measured results is obtained. All above indicates that the proposed antenna can be widely used in wireless communications.

A compact half-elliptic monopole antenna with triple notched-bands for UWB application, which is driven with differential feeding systems, is proposed. The basic antenna consists of two symmetrical half-elliptic patches and a modified ground plane. To reject the 5.5-GHz WLAN band effectively, two pairs of Ω-shaped strips are placed as parasitic elements close to the feedline. By introducing rectangular SRRs and an Ω-shaped slot on the radiators, the operating bands of 3.5-GHz WiMAX and 8-GHz ITU can be notched, respectively. Compared with conventional singleended feed antennas, the proposed differential-fed antenna can achieve better polarization purity, especially in the high-frequency band.

This paper presents an independently tunable dual-band bandpass filter based on center shorting-stub-loaded resonators. The center shorting-stub-loaded resonator is a dual-mode resonator that generates odd-even modes approximately equal and coupled when the shorting stub is very short. Two different sizes of center shorting-stub-loaded resonators produce two separated resonant frequencies, which are mutually independent. The coupling between the source and load is introduced in the circuit by designing an appropriate coupling structure, and the skirt selectivity of the filter is greatly improved. Four varactor diodes are placed at the two open-circuit ends of the center shorting-stub-loaded resonator to control the two separated resonant frequencies. A prototype of a tunable dual-band filter with Chebyshev response is designed and fabricated. The measured results are in good agreement with the full-wave simulated results. Results show that the first passband varies in a frequency range from 0.81 GHz to 0.95 GHz with a 3 dB fractional bandwidth of 4.2% to 5%, whereas the second passband can be tuned from 1.51 GHz to 1.79 GHz with a 3 dB fractional bandwidth of 6.8% to 8%.

In this work, an analytical expression is derived for the radial distribution of the quasi-static vertical magnetic field of a current-carrying large circular loop placed on a homogeneous earth. The obtained expression results from applying a rigorous procedure, which leads to cast the Hankel transform describing the vertical magnetic field component into a form consisting of two elliptic integrals and a fast-convergent sum of spherical Hankel functions. The derived solution ensures the same degree of accuracy as the finite difference time domain method, but, as a purely analytical formula, has the advantage of requiring less computational time. Numerical results are presented to illustrate the validity of the developed formulation.

A wideband bandpass filter with multiple transmission zeros using a shorted stub-loaded stepped-impedance ring resonator is proposed. The resonant characteristics are investigated by even- and odd-mode analysis. In order to obtain a wideband response, the even resonant frequencies can be lowered by the shorted stub and the stepped-impedance ring. The transmission line theory is used to analyze the transmission zeros. Besides the parameters of the shorted stub and stepped-impedance ring, the transmission zeros can also be adjusted by the port separation angle. To verify the proposed design concept, a filter with 132% 3 dB fractional bandwidth and five transmission zeros in the upper stopband is designed, simulated, and fabricated. Good agreement is observed between the simulated and measured results.

A new design of a circularly polarized planar magneto-electric dipole antenna is proposed and presented. This antenna consists of dual horizontal T-shaped electric dipole and an inverted U-shaped feed line. The antenna possesses 21.1% impedance bandwidth, from 8.9 GHz-11.0 GHz, provides 3-dB axial ratio bandwidth of 9.52% ranging 10.0 GHz-11.0 GHz, exhibits stable omnidirectional radiation pattern with almost equal E-plane and H-plane radiation patterns and provides a peak gain of 6.2 dBi. Due to its good electrical characteristics and radiation parameters, the antenna is suitable for satellite and RADAR communication in X-band.

A compact miniaturized frequency selective surface (FSS) withstable resonant frequency is proposed in this letter. The proposed FSS is composed of four spiral triangles connected in the middle of the unit cell, symmetrically. Simulated results show that the dimension of the element is only 0.0558λ₀×0.0558λ₀, and reduction in FSS size is up to 97.7% with respect to conventional cross-dipole FSS operating at the same frequency of 2.7 GHz. Also, the proposed FSS has great angular stability, and the resonant frequency deviation keeps below 0.4% for both TM and TE polarizations of 60° incident angle.

This paper represents a new simple technique to calculate force between two ring magnets using adaptive Monte Carlo integration technique. Elementary magnetic force is calculated by discretizing the pole faces of the passive magnets into tiny surfaces. To obtain the resultant force this elementary force equation is integrated over the dimensions of the ring magnets, which incur a multidimensional integration with complicated integral function. This multidimensional integration is solved using adaptive Monte Carlo technique considering singularity treatment and importance sampling. This method is advantageous over existing analytical or quasi analytical methods regarding singularity treatment and computational burden. It is more flexible, especially for using in digital computer. The result of the proposed technique is verified with finite element method and also validated by laboratory experiment. It is observed that the proposed result matches very well with the practical test result, particularly if self demagnetization is considered. So taking into account of simplicity, less computational burden and usefulness, the proposed method may be an alternative choice for magnetic force calculation.

A novel polarization conversion metasurface (PCM) is proposed and applied to radar cross section (RCS) reduction. The proposed design has the advantage of simple geometry while simultaneously reducing RCS over broadband. The metasurface is created by the combination of an oblique split ring resonator (SRR) and a cut-wire resonator, which is capable of converting a linear polarization state into its orthogonal one. The simulation results show that the 10 dB bandwidth of polarization conversion is obtained in wideband from 9.4 to 19.2 GHz, with an average polarization conversion ratio (PCR) of nearly 100%. Due to the high PCR, RCS reduction of 10 dB can be realized over 60% frequency bandwidth with respect to the equal-sized PEC ground plane. The maximum reduction is 32.8 dB. To validate the simulation results, prototypes of the PCM are fabricated and measured. Excellent agreement between simulations and measurements is achieved.

A novel hybrid antenna capable of both spectrum sensing and frequency reconfigurability is proposed in this paper. The proposed hybrid antenna senses spectrum over a wide frequency range from 1 GHz-12 GHz and accordingly reconfigures its operating frequency in any of the four different frequencies i.e., 2.1 GHz, 2.96 GHz, 3.5 GHz and 5 GHz. Since wideband response for spectrum sensing and each frequency state works independently, there is no interference among various signals. The wideband response for spectrum sensing is obtained by exciting semicircular arc having staircase-shaped slot in the ground plane. Frequency reconfiguration is achieved by electronic switching among various matching stubs. Both simulated and experimental results for the return loss, gain and radiation patterns are presented. The proposed hybrid antenna shows a measured return loss better than -20 dB in all the operating bands, a bidirectional radiation pattern and 4.8 dB gain in θ = 20˚ and 120˚ in E plane.

In this paper we provide new recommendations for a type of antenna design in applications where a human is present in the vicinity of a wireless power transfer (WPT) system by means of power transfer efficiency (PTE) and specific absorption rate (SAR). The interaction between a homogenous human model and different WPT systems is investigated at 13.56 MHz using spherical mode theory antenna model (SMT-AM) and full-wave numerical analysis. The human model exposure and the performance of the proposed WPT system are analyzed further for some typical scenarios. It is shown that the position in which the human model is closer to the receiver is favorable over the position closer to the transmitter, concerning both PTE and SAR. Also, the consideration of variable receiver load indicates that different levels of SAR coupled by degraded PTE can be expected. The proposed antennas are designed and proof of concept WPT measurements are carried out.