The Cramer-Rao lower bound (CRLB) for calculating errors and accuracy of direction-of-arrival (DOA) estimation is discussed for a number of planar waves arriving on an antenna array. It is well known that the geometry of antenna arrays imposes restrictions on the performances of the direction-of-arrival estimation. In particular, the influence of the directivity factor of the individual antenna elements on the accuracy of the DOA estimation of the radio emission sources for circular (cylindrical), cubic and spherical antenna arrays consisting of the directional antenna elements is investigated. The directivity factor of antenna elements is changed within wide limits in order to determine the values at which the high accuracy of the direction-finding can be achieved. It is shown that further increasing the directivity factor of each antenna element makes the mean square error in the determination of the coordinates of the signals increase as well. The exact expression for the Cramer-Rao lower bound for the DOA-estimation variance calculation depending on the antenna directivity and the geometry is presented. The obtained exact equation shows the most important factors that the direction-of-arrival estimation accuracy is dependent on. A technique of obtaining antenna arrays with optimal directional elements locations is proposed. Those arrays allow increasing DOA estimation accuracy by several times.

This paper presents a reconfigurable, wide-beam antenna with a modular main radiator for base station applications. The addition of new spectrum and the path to 5G create unique antenna requirements in terms of patterns and impedance matching capabilities. The antenna in this paper exhibits a wide azimuth beamwidth up to approximately 180^o, and implements a modular approach where the antenna can be recongured for impedance matching requirements. Two congurations of the wide-beam antenna are presented; the rst conguration covers the 1.7-2.7 GHz band for 3G/4G/LTE applications where multiple wireless carriers would use the same antenna as a neutral site. This antenna provides wide-beam operation and a 10-dB return loss from approximately 1.64-2.76 GHz. The measured return loss over the 1.7-2.7 GHz band is better than 13 dB. A second conguration of the antenna is tuned for performance from 1.9-2.4 GHz where measured return loss better than 19 dB is achieved in this band. Simulated and measured return losses and patterns are presented that show very good agreement between simulation and measurement, and thorough parametric pattern analysis is presented for the baseline antenna configuration.

A general synthesis approach is proposed for reflectarrays using second order Phoenix cells. It relies on an original spherical representation that transforms the optimization domain in a continuous and unbounded space with reduced dimension. This makes the synthesis problem simpler and automatically guarantees smooth variations in the optimized layout. The proposed mapping is combined with an Artificial Neural Network (ANN) based behavioral model of the cell and integrated in a min/max optimization process. Bi-cubic spline expansions are used to decrease the number of variables. As an application, a contoured beam for space communication in the [3.6-4.2] GHz band is considered. The gain improvement compared to an initial Phase Only synthesis (POS) is up to 1.62 dB at the upper frequency. Full wave simulation of the final array is provided as a validation.

In this communication, a novel design of a hybrid open slot antenna is investigated and experimentally verified. The proposed structure comprises a slotted tuning stub, a proximity fed parasitic element, and slotted ground plane. Tuning and overlapping of best matching frequencies f_r1, f_r2, f_r3, f_r4, f_r5, f_r6, and f_r7 are accomplished by varying the dimension of the parasitic element and elliptical slot which is the part of the elliptical slot. The experimental results reveal that this antenna covers the fractional bandwidth (BW(%) = 200 * (f_h - f_l)/(f_h + f_l)) of 139.5% from 0.98 GHz to 5.5 GHz for |S₁₁|<-10 dB which is suitable for GSM 1800, WiMAX, PCS, and ITM-2000. After the analysis of current distribution, mathematical equations are developed for frequencies 1.04, 1.52, 3.06, 3.67, and 4.58 GHz. The structural analysis is also carried out for optimization and to know the electromagnetic behaviour of the antenna. Asymmetric radiation patterns are found at resonating frequencies due to open slot geometry.

The failure risk of electronic equipment submitted to an electromagnetic aggression may be seen as the conditional probability that the susceptibility level of equipment is reached, knowing that a given constraint is applied. This paper focuses on the estimation of the probability density function of the susceptibility level of equipment. Indeed, the production variability of electric/electronic equipment under analysis implies that its susceptibility level may be considered as a random variable. Estimation of its distribution through susceptibility measurements of a limited set of available equipment is required. Either a Bayesian Inference (BI) or a Maximum Likelihood Inference (MLI) may be used for assessing the most probable density function. Above all, we highlight that they have to be used to delimit a set of probable distribution functions rather than the most probable one. It then provides realistic bounds of the failure probability at a given test level. First both types of inference are carried out on theoretical distributions. Then we compare the two methods on a virtual piece of equipment whose distribution is not known a priori but can be estimated a posteriori. Finally, we apply these inferences on a set of actual susceptibility measurements performed on several copies of equipment. We check that for extremely small sample size (a dozen) the Bayesian approach performs slightly better. However, above around 40, the two methods perform similarly. In all cases, the likelihood estimations provide a clear statement of the probabilistic estimation of the statistics of susceptibility level given a limited sample of pieces of equipment.

Stochastic wave equations are derived to describe electromagnetic wave propagation in an isotropic medium in which the electric permittivity and the magnetic permeability are weakly-random functions of time. Approximate analytical solutions are obtained using separation of variables and the WKB method for some configurations that can be used to model the electromagnetic field in the ionosphere. The form of the initial and boundary conditions determines whether the solution takes a form representing a direct current electric field or continuous pulsation electromagnetic waves. The temporal variation of the calculated induced electromotive force (EMF) is in agreement with observations.

A novel hierarchical characteristic basis function method (HCBFM) is proposed to calculate monostatic radar cross section based on singular value decomposition characteristic basis function method. In order to reduce the number of incident plane waves and accelerate the generation of characteristic basis functions (CBFs), an improved CBFs construction method is studied in this paper. Firstly, the target is partitioned with hierarchical approach, and at each incident plane wave, the high-level CBFs defined in large blocks are expressed as a linear combination of the previously generated low-level CBFs defined in the corresponding small blocks. Finally, the high-level CBFs in large blocks are orthogonalized by using singular value decomposition at multiple excitations, and a set of linearly independent CBFs can be obtained. Numerical results are given to demonstrate the accuracy and high efficiency of the proposed method.

Aiming at the problem of high false alarm rate with respect to adaptive threshold in the ship detection from synthetic aperture radar (SAR) images, a novel strategy increasing robustness when using local adaptive threshold is proposed. In this article, we establish a fusion detection model based on a combination of the information geometry and surface geometry. Information geometry from a metric viewpoint can increase the contrast between targets and clutter in SAR image. Local surface feature gives a brief application of adaptive threshold method in ship detection from SAR images by means of the constant false-alarm-rate. Experiments indicate that the proposed geometry-based approach can effectively detect ship targets from complex background SAR images by using the method of fusion processing.

The generalized function approach for modeling radio wave scattering has been used to develop expressions for the scatter from rough surfaces and for horizontally-stratified media. The scattered field from rough surfaces can be found in closed form if plane wave incidence is assumed, but the method is valid for any realizable source without resorting to using Hertz vectors. This approach was originally developed to model high frequency surface wave radar scattering from the ocean or across layers of ice covering the ocean using vertical polarization. This paper presents three extensions to the existing theory: the x component of the scattered field for rough surface scattering is developed, the assumption of a good conducting surface assumption is removed for a rough surface and the scatter from stratified media is simplified in terms of a scattering coefficient. The shape of the scattered field is not affected by the relative permittivity, but the intensity of the scattered field is weaker due to an increased transmission of energy through the surface. The goal for this research is to better understand how signatures from ice-penetrating radar can be used to distinguish hazardous ice ridges from other ice features. Here, ice ridges are modeled as layered media with a rough surface.

A wideband filter with a notched band is presented. The proposed filter is formed by cascading three coupling units, and each coupling unit is composed of two curved T-shaped microstrip patches at the top and bottom layers and a circular coupling slot at the mid layer. Overlapping three coupling units could result in a wideband filter with a tunable notched band. To analyse the resonance characteristics, the equivalent circuit model is presented. The notched frequency is 5.8 GHz, and within the passband, the insertion and return losses are better than -2 dB and -15 dB, respectively. The group delays are 0.08 ns and 0.12 ns correspondingly, and the upper stopband reaches 15 GHz. The multi-layer structure leads to a compact size and tight coupling characteristics, and the feasibility and excellent performance of the design is verified.

A wideband high gain circularly polarized layered cylindrical dielectric resonator antenna (DRA) that operates in a higher order mode is proposed in the X-band frequency range. The antenna consists of two dielectric layers having different dielectric constants and radii. The results demonstrate a considerably improved performance as a result of adding the outer dielectric layer, where wider impedance and axial ratio bandwidths have been attained in conjunction with a higher broadside gain of ~14 dBic. A prototype has been built and measured with close agreement between experimental and simulated results.

This paper studies the power transfer characteristics of a resonator array for inductive power transfer by means of the accurate analytical solution of its circuit model. Through the mathematical inversion of a tridiagonal matrix, it is possible to obtain closed-form expressions for the current in each resonator and consequently expressions for the power transfer and efficiency of the system. The method can be applied to a resonator array powering a load at the end of the array or a receiver facing the array at any position. With the expressions obtained, it is possible not only to achieve a better understanding of the power transfer characteristics in resonator arrays but also to obtain the conditions for maximum power transfer or maximum efficiency, for several conditions and parameters of the system. A prototype of a stranded-wire resonator array powered by a resonant inverter, capable of delivering power to a load from 65 W to 90 W with efficiency values between 63% and 88%, was built in order not only to validate the expressions obtained but also to show their practical applicability and demonstrate that these arrays can be used for higher power transfer applications.

The current wireless technology demands wide frequency operation, like WLAN 5GHz band, which requires 12.75% frequency bandwidth. In this paper, a unit cell metamaterial structure is proposed, which consists of 4 compact bend triangular resonators (CBTRs) that offer wideband frequency rejection. The single negative metamaterial based resonators give band rejection response, but it is generally bandwidth limited. With the proposed unit cell, rejection bandwidth of 16.78% for rejection level of -12 dB is achieved. It can be further increased by increasing the order of unit cells. The proposed unit cell structure is analyzed for the resonant frequency of 5.5 GHz, and the design is suitable for the application where 15% or more rejection band is required.

In this work, we simulate the electromagnetic field of a rectangular waveguide with side holes. The Helmholtz equations for a given waveguide and dispersion equations are solved. As a result of numerical calculations, the obtained numerical values build the dependence of the modulus of the effective impedance on the wavelength for different types of waves.

Body gesture recognition can be applied not only to social security but also to rescue operations. In reality, body gesture can produce unique micro-Doppler signatures (MDSs), which can be used for identification. In this paper, we first acquired the echo signals of four body gestures via a Ka-band dual polarization radar system under different angles and distances. The four gestures are respectively swinging arm up and down, swinging arm left and right, nodding, and shaking head. Then, time-frequency spectrograms were obtained by short-time Fourier transform, from which we can see that different body gestures have different polarimetric MDSs. Finally, we propose to classify four body gestures using the deep convolutional neural network (DCNN) method. It is shown that by combining HH and HV polarizations, about 92.7% recognition rate is achieved while only about 77.5% and 89.3% rates are obtained by using single HH polarization and single HV polarization, respectively.

Global Positioning System (GPS) is an excellent application example of satellite communication technology. And it is widely used in navigation, measurement, and time service. However, GPS receivers are vulnerable to unintentional interference or jamming because they rely on external radio frequency (RF) signals. RF interference signals can result in degraded navigation accuracy or complete loss of receiver tracking. Thus, GPS receivers have anti-jamming ability to relieve the effect of interference or jamming. In order to improve the anti-jamming performance of GPS receiver, it is of great theoretical significance and practical application value to study the influence of interference on GPS receiver. To this end, this paper investigates the performance of integrator in the presence of single-tone interference in GPS receiver, and a single-tone interference method based on frequency difference is proposed. Specifically, the analytical relationship between single-tone interference and integrator output is given. Then, it shows that the output of integrator depends not only on the power of single-tone interference but also on the frequency difference between single-tone interference and GPS signal. Finally, the vulnerability of integrator or GPS receiver to the presence of interference increases if the frequency difference satisfies the specific condition. Simulation results show that the proposed method is able to improve the chip error rate in GPS receiver.

Due to the limitations of low-resolution radar system and background clutter, the task of target classification with conventional low-resolution radars is relatively difficult. This paper introduces fractional Fourier transform (FrFT) to process aircraft echoes in order to find the optimal fractional Fourier domain, in which signal to noise ratio can reach the maximum, and then applies multifractal theory to the feature extraction of radar targets. Based on the above, we use SVM to do target classification. Experiments show that the multifractal characteristics of aircraft echoes can be enhanced by FrFT, and the features extracted from the optimal fractional Fourier domain can be used effectively to classify different types of aircraft even in the case of low SNR.

This paper presents a polarization-insensitive frequency selective rasorber which has high in-band transmission at high frequency and wideband absorption at low frequency based on square-loop and parallel LC resonance. The rasorber consists of a bandpass FSS and a resistive sheet plus a slot-type metallic four-legged loaded element as the bandpass FSS element. The resistive element is realized by inserting several strip-type parallel LC structures into a resistor-loaded square-loop element, which allows the surface current to be controlled as necessary and the wave at the resonance frequency to be passed with minimum insertion loss. Wideband absorption is realized at low frequency, where the bandpass FSS is nearly totally reflected, and the FSR performs as an absorber. Simulation results show the transmission band at 9.9 GHz with transmissivity higher than 96% and the absorption band with absorptivity higher than 85% from 2.83 GHz to 8.6 GHz for TE-polarized 30˚ incidence and from 3.22 GHz to 8.48 GHz for TM-polarized 30˚ incidence. The absorptive/transmissive performance of the FSR structure is also verifieded by experimental measurements.

Rotationally symmetric sparse circular arrays are synthesized under multiple constraints. By combining the modified differential evolution algorithm based on the harmony search (in short HSDE) with the vector mapping (VM) method, a hybrid algorithm, called VM-HSDE, is proposed for synthesizing sparse circular arrays with low sidelobe levels. Due to the array's specific geometry, the number of optimization variables is reduced, and the constrained optimization problem is simplified. Moreover, infeasible solutions are avoided, and the problem is effectively solved by the VM-HSDE algorithm. Finally, three pattern optimization results verify the effectiveness and reliability of the VM-HSDE algorithm.

This work proposes new filter design techniques to improve the out of band spurious performance of integrated ceramic waveguide filters and ceramic loaded filters. Various resonators of different types like non-uniform width, TEM and half ridge were used. The proposed filter designs offer a considerable miniaturization and significantly improved spurious performance up to 85% without compromising the figure of merits of the filters like Q-factor, return loss, etc. Two sixth order filters with best in-band and out-band performance have been fabricated. Measured results of the fabricated filters are in good agreement with the computer simulations, which confirm the validity and accuracy of designs.