A low profile dual-polarized omnidirectional antenna with an overall height of 80 mm is presented in this paper for broadband indoor distributed antenna system (IDAS). The proposed antenna consists of an improved discone antenna for vertical polarization (VP) and a printed dipole array with five pairs of dipoles for horizontal polarization (HP). The VP element is a combination of three radiation patches, a cone-shaped feeding structure, a circular shorted loading patch and a coupling ring. By loading the coupling patch and coupling ring over the top and at the bottom of the radiation patches, the bandwidth for VP is significantly enlarged while the antenna height is reduced. Simulated and measured results indicate that the operating bands of 0.86-5.62 GHz for VP and 1.62-2.71 for HP are realized. Omnidirectional radiation patterns in horizontal plane for HP and VP, good port isolation of greater than 26 dB, low cross polarization level, and stable gain (2.6-5.6 dBi for VP and 2.8-4.2 dBi for HP) are achieved during the operating bands, which demonstrate the proposed antenna can be widely used for broadband IDAS.

In this paper, the computation of forces and torques mutually applied between a helical toroidal magnet and a magnet shaped like an angular plane sector is illustrated. The evaluation considers the magnetostatic field hypothesis. The main aim of this study is to furnish a tool for performing fast and accurate evaluation of forces and torques based on the method of the magnetic charges with reference to helical toroidal magnetic systems. The particular geometry of the case study concerns the development of unconventional configurations of electrical machines. These configurations should reduce the magnetic flux changing during the machine operation. A small change of the magnetic flux reduces all the losses associated to the flux variation. The illustrated model for the computation of forces and moments also represents a starting point for a reliable analytical numerical evaluation of the external/internal actions applied to parts of other kinds of helical toroidal systems as stellarator and similar ones.

In this paper, the design, fabrication, and test of an additive manufactured double-ridged horn antenna optimized to work in ultra-wide-band frequencies is introduced. In particular, to build this antenna, the fused deposition modeling fabrication method is selected. The plastic-made device is then coated by using conductive ink. The double-ridged horn is conceived as a monolithic block. In this way, performance degradations caused by fabrication inaccuracies are minimized. A very good agreement between the simulations and the antenna measurements is demonstrated. The proof-of-concept prototype has an outstanding operational bandwidth performance of 11.5 GHz (fc 8.25 GHz) with a gain of 6 dBi; its total weight is less than 200 gr, and the total prototyping fabrication costs are less than 10 Euro per antenna with a lead time of less than a week.

A compact planar reconfigurable triple band-notched UWB Microstrip antenna is proposed in this paper for UWB applications. A band rejection at ITU 8-GHz is generated by inserting an inverted U-shaped metallic strip at the slotted ground plane. Moreover, by cutting two slots on radiating patch, the second rejection at 3.5 GHz for WiMAX and the third rejection at 5.5 GHz for WLAN application are generated. Then, by embedding two (PIN) diodes along the patch slots, switchable dual or single band-notched behavior is added to the antenna performance. The simulated and measured results show that the antenna can operate in a wider bandwidth from 3.1 GHz to 11 GHz, and it has a good omnidirectional radiation pattern with stable gain. Furthermore, the designed antenna has a simple structure and compact size of 20×20 mm². The proposed antenna can use the full potential of UWB frequency range with reconfigurable band-notched behavior at 3.5, 5.5, 8.1 GHz to avoid interference with WiMAX, WLAN, ITU systems respectively.

Magnetic anomaly detection (MAD) is to find hidden ferromagnetic objects, and a hidden object is often described as a magnetostatic dipole. Many detection methods are based on the orthonormal basis functions when the target moves along a straight line relatively to the magnetometer. A new kind of parabolic trail orthonormal basis functions (PTOBF) method is proposed to detect the magnetic target when the trajectory of the target is parabola. The simulation experiment confirms that the proposed method can detect the magnetic anomaly signals in white Gaussian noise when SNR is -15.56 dB. The proposed method is sensitive to the characteristic time and curvature. High detection probability and simple implementation of proposed method make it attractive for the real-time applications.

The instantaneous measurement of RF & microwave frequencies is widely used in electronic warfare (EW) for the determination of unknown signals over a broad frequency band. This paper presents an enhanced frequency measurement accuracy using three stages of novel RF frequency discriminator (FD) for RF front-end IFM Receivers. The appropriate structure of the designed frequency discriminator is implemented using a conventional PCB fabrication process. The frequency discriminator consists of two different hybrid layouts and one Wilkinson power divider, and all these components are implemented in microstrip technology, which is particularly important due to lower cost and easy integration into the PCB. To demonstrate the feasibility of the proposed structure, an RF-FE instantaneous frequency measurement (IFM) receiver has been realized based on 3-stage RF frequency discriminator. Simulation and measurement results have shown a frequency measurement accuracy less than 1 MHz (RMS) over the entire S-band.

A planar reflectarray/transmitarray antenna which reflects/transmits the incident fields radiating from feed antenna is presented. The antenna works as a reflectarray at 13.85 GHz and a transmitarray at 8 GHz. The unit cell is composed of three layers. The first layer consists of a crossed-dipole element and a square ring frequency selective surface (FSS) on the top and bottom surfaces of a dielectric substrate. The second and third layers are identical and consist of a square ring slot element on both sides of a dielectric substrate. An air gap is inserted between layers. The aperture of the antenna is 225 mm which equals 10.4 wavelengths at 13.85 GHz and 6 wavelengths at 8 GHz. The reflectarray/transmitarray antenna is fabricated, and NSI planar near-field system is used to measure the performances of the prototype. Good agreement between the simulated and measured results has been achieved. The measured gain is 27.1 dB in reflection mode at 13.85 GHz resulting in a 38% aperture efficiency and 23.1 dB in transmission mode at 8 GHz resulting in a 45.7% aperture efficiency.

A novel single-negative magnetic (SNG) metamaterial (MTM) insulator is designed to reduce mutual coupling between high-profile monopole antennas. As a kind of metamaterials, the proposed SNG MTM-resonator utilized concentric rings embedded complementary metal structures. Then, an insulator is achieved with a highly compact structure. The band-gap of the insulator is attributed to the negative permeability of the magnetic resonance. A well-engineered MTM-resonator is then embedded in between a high-profile monopole antenna array for coupling reduction. The antenna array is designed, fabricated, and measured. Both numerical and experimental results indicate a mutual coupling reduction of more than 17 dB. The 20 dB isolation bandwidth about 16% is obtained. The proposed prescription with electrically small dimensions and high decoupling efficiency opens an avenue to new types of high-profile antennas with super performances.

A broadband Perfect Metamaterial Absorber (PMA) on FR-4 Epoxy substrate for X-band and Ku-Band applications is proposed. The unit cell structure is composed of rectangular patches of appropriate shapes and orientation on top of the metal-backed dielectric substrate having a thickness of 2.7 mm (0.16λ_L). The relative absorption bandwidth is 79% (more than 85% absorption) covering the entire X-band and the Ku-Band of the microwave frequencies. The surface current distributions of the top and bottom planes have been analyzed to elaborate the absorption mechanism of the structure. The broadband characteristics of the design support its claim of being useful to a wide range of applications in both commercial and research sectors. Such applications include military and stealth devices, thermal sensors and electronic-cloaking devices.

Characterization measurements of wideband antennas can be a time intensive and an expensive process as many data points are required in both the angular and frequency dimensions. Parallel compressive sensing is proposed to reconstruct the radiation-frequency patterns (RFP) of antennas from a sparse and random set of measurements. The modeled RFP of the dual-ridge horn, bicone, and Vivaldi antennas are used to analyze the minimum number of measurements needed for reconstruction, the difference in uniform versus non-uniform reconstruction, and the sparsity transform function used in the compressive sensing algorithm. The effect of additive white Gaussian noise (AWGN) on the minimum number of data points required for reconstruction is also studied. In a noise-free environment, the RFP of the antennas were adequately reconstructed using as little as 33% of the original data points. It was found that the RFPs were adequately reconstructed with less data points when the discrete cosine transforms (DCT), rather than discrete Fourier transforms (DFT) was used in the compressive sensing algorithm. The presence of noise increases the number of data points required to reconstruct an RFP to a specified error tolerance, but the antenna RFPs can be reconstructed to within 1% root-mean-square-error of the original with a signal to noise ratio as high as -15 dB. The use of compressive sensing can thus lead to a new measurement methodology whereby a small subset of the total angular and frequency measurements is taken at random, and a full reconstruction of radiation and frequency behavior of the antenna is achieved during post-processing.

A slotted meander line printed monopole antenna for low frequency applications at 878 MHz is presented. The operating frequency of the conventional printed monopole antenna is greatly reduced by the presence of the slots and meander line which lead to the reduction of the antenna size. The size reduction up to 70% compared to the conventional reference antenna is achieved in this study. The antenna has a simple structure and small antenna size of 46.8 mm × 74 mm or 0.137λ₀ x 0.217λ₀. The antenna has been fabricated on a low-cost FR4 substrate and measured to validate the simulation performances. Measured results display that the proposed antenna produces omnidirectional radiation pattern of impedance bandwidth of 48.83 MHz and the maximum gain of -1.18 dBi.

We propose a structural optimization method based on a real-coded micro-genetic algorithm to realize a weakly guided 2 × 2 multimode interference (MMI) coupler with low imbalance and excess loss over a wavelength range from 1520 to 1580 nm. The proposed method was applied to silica-based 2×2 MMI couplers with a relative refractive index difference of 5.5%. The optimized result showed an imbalance of less than 8.4×10⁻³ dB, an excess loss of less than 0.14 dB, and a normalized output power of more than 48% over the operation wavelength range. The proposed method achieved an optimized 2×2 MMI coupler after 250 times of propagation analysis per wavelength, which is less than 6.7% of those by the conventional methods for 4×4 and 1×4 MMI couplers, and was proven to be more effective than the conventional methods. To consider realistic optical devices, 2×2 MMI couplers whose values of structural parameters are close to the optimized values within the accuracy of typical fabrication tolerance are also analyzed. The results are comparable to those of the optimized 2×2 MMI coupler.

Linear equations must be solved at each time step as the explicit finite element time-domain (FETD) method is used to solve time dependent Maxwell curl equations, which leads to a huge amount of computational cost in a long period time simulation. A new scheme to accelerate the iteration solution for matrix equation is proposed based on compressed sensing (CS), in which a low rank measurement matrix is established by randomly extracting rows from mass matrix. Meanwhile, to reduce the number of measurements required, a sparse transform is constructed with the help of prior knowledge offered by the solution results of previous time steps. Numerical results of homogeneous cavity and inhomogeneous cavity are discussed to validate the effectiveness and accuracy of the proposed approach.

In this conceptual study, all-optical amplification of the light pulses in two weakly coupled nonlinear photonic crystal waveguides (PCWs) is proposed. We consider two adjacent PCWs, which consist of line defects in a 2D square lattice of periodically distributed circular rods made from dielectric material with Kerr-type nonlinearity. Dispersion diagrams of the PCW's symmetric and antisymmetric modes are analyzed using a recently developed analytical formulation. The operating frequency is properly chosen to be located at the edge of the PCW's dispersion diagram (i.e. adjacent to the photonic crystals low-energy band edge), where in the linear case no propagation modes are excited. However, in case of a nonlinear medium when the amplitude of the injected signal is above some threshold value, solitons are formed propagating inside the coupled nonlinear PCWs. The near field distributions of the propagating light pulse inside the coupled nonlinear PCWs and the output power of the received signal are numerically studied in a detail. A very good agreement between the analytic soliton solution based on the nonlinear Schrödinger equation and numerical result is obtained. Amplification coefficients are calculated for the various amplitudes of the input signals. The results vividly demonstrate the effectiveness of the weakly coupled nonlinear PCWs as an all-optical digital amplifier.

This work deals with the evaluation of the efficiency and optimal control of conductive fluids by using electromagnetic forces. An electromagnetic actuator based on a succession of electrodes and magnets annuli is implemented on the surface of the rotating cylinder of a Taylor-Couette device. Considering a laminar flow, the magnetohydrodynamic (MHD) problem is formulated and solved analytically. The different MHD powers, control efficiency and optimal values of the control parameters are evaluated.

It is a widely held view that analytical integration is more accurate than the numerical one. In some special cases, however, numerical integration can be more advantageous than analytical integration. In our paper we show this benefit for the case of electric potential and field computation of charged triangles and rectangles applied in the boundary element method (BEM). Analytical potential and field formulas are rather complicated (even in the simplest case of constant charge densities), they have usually large computation times, and at field points far from the elements they suffer from large rounding errors. On the other hand, Gaussian cubature, which is an efficient numerical integration method, yields simple and fast potential and field formulas that are very accurate far from the elements. The simplicity of the method is demonstrated by the physical picture: the triangles and rectangles with their continuous charge distributions are replaced by discrete point charges, whose simple potential and field formulas explain the higher accuracy and speed of this method. We implemented the Gaussian cubature method for the purpose of BEM computations both with CPU and GPU, and we compare its performance with two different analytical integration methods. The ten different Gaussian cubature formulas presented in our paper can be used for arbitrary high-precision and fast integrations over triangles and rectangles.

The calibration target is a vital instrument for calibrating space-borne microwave radiometers, and its emissivity performance must be accurately determined before usage. Based on the Kirchhoff's law of thermal equilibrium, the emissivity of a calibration target can be determined from its electromagnetic reflectivity, which is defined as space integration of scattering. However, due to the general shape of periodic coated sharp pyramids, the scattering from calibration targets shows Floquet mode properties with scattering lobes in upper space. That phenomenon must be considered in the reflectivity measurement of calibration target, especially in the mono-static backscattering configuration. To support such backscattering-based reflectivity measurement, the Floquet mode and scattering patterns from periodic unit and finite-sized array are investigated by numerical simulations, more specifically, by the finite-difference time domain (FDTD) algorithm. The investigations include the scattering power distributions among scattering lobes from coated and bare pyramid arrays, and the ratio of total reflection to backscattering in cases of typical parameters. It is found in the millimeter wave region that the scattering power from bare pyramids is still concentrated in the backscattering lobe in the mono-static configuration, while for the coated pyramids the scattering power is distributed around Floquet modes. For the considered geometry and coating parameters, the power ratio of total scattering to backscattering can be more than 10 dB at the cared frequencies. After all, the numerical results provide referencing correction factor for actual measurement studies. It is also validated by numerical results and suggested in practice, to use periodic simulations of low computational burden to evaluate the compensation factor for the mono-static reflectivity measurement.

A novel hybrid antenna capable of both spectrum sensing and then accordingly reconfiguring its operating characteristics is proposed here. The proposed antenna is versatile in nature as it can reconfigure its resonant frequency, polarization state, bandwidth and radiation pattern. The physical structure of antenna is also versatile in nature as different printed parts are used several times in different operating modes using PIN diodes. The proposed versatile antenna senses spectrum over a wide frequency range from 3 GHz-12 GHz by using a separate UWB antenna. After sensing, the antenna can reconfigure its frequency in five different bands using three matching stubs. The proposed antenna can reconfigure its polarization state over two frequency bands by controlling the switchable slot. The antenna can also reconfigure its pattern by shorting the parasitic arc using PIN diodes. The prototype is fabricated, and the functioning is verified through measurement.

A printed loop antenna with a circularly polarized beam parallel with its plane is proposed. The proposed quadrangle loop antenna is fed with microstrip line at one of its corners. The microstrip line part and loop part provide vertical polarization and horizontal polarization, respectively. The proposed antenna is simple in structure and can be easily integrated with other microwave components on the same substrate. Simulated results show that the proposed antenna has a wide impedance bandwidth (|S₁₁| < −10 dB) and wide 3-dB AR bandwidth ranging from 8.0 to 10.5 GHz (27%). A prototype of the proposed antenna is fabricated and tested. The measured and simulated results have good agreement.

In this paper, a new method for radar cross section (RCS) reduction of circularly polarized (CP) microstrip antenna array with small element spacing is proposed. By employing the element rotation technique and loading EBG structures, the in-band and out-of-band RCSs are reduced simultaneously despite the extreme small space between array elements. The simulated results show that the proposed antenna has an average RCS reduction over 10 dB in the X-band for x-polarized and y-polarized incident waves impinging from normal direction compared to the original CP microstrip antenna array, indicating a fractional bandwidth of 40%. The maximum RCS reduction is over 25 dB. Meanwhile, the radiation performance of the proposed antenna array is kept.