For reducing the computational complexity of direction-finding algorithm in sparse multiple-input multiple-output (MIMO) radar, a low-complexity partial spatial smoothing (PSS) algorithm is presented to estimate the directions of multiple targets. Firstly, by dealing with a partly continuous sampling covariance vector in PSS technology, an incomplete signal subspace can be obtained. Then, a special matrix can be obtained by using this incomplete signal subspace. Meanwhile the incomplete signal subspace can also be repaired by the special matrix. At last, the multiple signal classification (MUSIC) algorithm is used to obtain direction estimations. In the process of obtaining signal subspace, no eigenvalue decomposition (EVD) needs to be performed. Compared with the traditional spatial smoothing (SS) technology, the proposed algorithm has lower computational complexity and higher estimation precision. Many simulation results are provided to support the proposed scheme.

In this paper, a novel microstrip-fed compact antenna with dual band-notched characteristic is presented for ultra-wideband (UWB) applications. Assisted with symmetrical open-circuited stubs, a UWB impedance matching can be achieved. A novel modified capacitively loaded loop (CLL) resonator is proposed to realize the dual notched bands. By symmetrically placing a couple of proposed resonators in the vicinity of the feed line, dual band-notched properties in 3.4-3.7 GHz for WiMAX and 5.15-5.825 GHz for WLAN are generated. The good performance of the dual notched bands, stable gain, and radiation patterns in the operating bands make the proposed antenna a good candidate for various UWB applications.

The aim of this letter is to provide a novel method connecting statistical optimization and information geometry for ship detection in synthetic aperture radar (SAR) imagery. The method consists of two steps: initial detection and iterative optimization. For the first stage, the Weibull clutter model is used for initial detection. For the second step, the metric tensor of the Weibull distribution manifold is constructed for iterative optimization. Experiments show that the proposed method is effective in reducing false alarms and obtains a satisfactory detection performance.

The available polarizers either cannot afford gigawatt-class high-power microwave applications or are large in length. In this letter, a novel grooved polarizer is proposed. The grooves are proposed to be created in an over-mode circular waveguide to improve the power capacity and bandwidth. Moreover, the symmetric elliptical grooves are adopted to suppress high-order modes and realize the desired phase difference. An X-band polarizer prototype is designed and manufactured with length of 91 mm. Simulated results show that the power capacity of the polarizer is more than 1.5 GW. Measured results in accordance with simulations show that the axial ratio is less than 3 dB from 8.6 to 12.2 GHz, with relative bandwidth of 34.6%. The measured return losses are better than -12.7 dB in the same frequency range.

A compact tri-band antenna is designed and analyzed to achieve both transmission and reception of direct broadcast service (DBS) and fixed satellite service (FSS) in Ku band. The proposed antenna design consists of a truncated E-shaped slot, eight rectangular slots, two C-shaped slots in the patch and eight defected ground structure (DGS) slots. The three frequency bands of 11.40-12.91 GHz, 13.86-14.53 GHz, and 17.20-17.86 GHz are achieved with impedance bandwidths of 12.32%, 4.73%, and 3.77% respectively. Conversely, the measured frequency bands of 11.40-12.98 GHz, 14.21-14.86 GHz, and 17.41-18.98 GHz with the impedance bandwidth of 12.70%, 4.48%, and 8.63% respectively are obtained. The simulated results of the proposed antenna are compared with the results of fabricated antenna and are found to be satisfactory for reflection coefficient, impedance bandwidth, polarization, efficiency, gain, and radiation pattern. Moreover, the proposed antenna design can be used as an element in an array configuration to achieve high gain in both transmission and reception modes of FSS and DBS.

In this work a reconfigurable Ultra Wide Band (UWB) antenna for Wireless Body Area Network (WBAN) is presented. The antenna is completely composed of fabric materials and is able to switch its topology from a monopole-like structure (for on-body communications) to a microstrip-like structure (for off-body communications) maintaining UWB characteristic stable both on body and in free-space. This antenna presents good radiation properties in both configurations. In order to describe its time domain and frequency domain behavior a System Fidelity Factor (SFF) analysis has been done for both topologies.

Time domain finite element methods (TD-FEM) for computing electromagnetic fields are well studied. TD-FEM solution is typically effected using Newmark-Beta methods. One of the challenges of TD-FEM is the presence of a DC null-space that grows with time. This can be overcome by solving Maxwell equations directly. One approach, called time domain mixed finite element method (TD-MFEM), discretizes Maxwell's equations using appropriate spatial basis sets and leapfrog time stepping. Typically, the basis functions used to discretize field quantities have been low order. It is conditionally stable, and there is a strong link between time step size and mesh dependent eigenvalues, much like the Courant-Friedrichs-Lewy (CFL) condition. This implies that the time step sizes can be very small. To overcome this challenge, we use the Newmark-Beta approach. The principal contribution of this work is the development of, and rigorous proof of, unconditional stability for higher order TD-MFEM for different boundary conditions. Further, we analyze nullspaces of the resulting system, and demonstrate stability and convergence. All results are compared against the conditionally stable leapfrog approach.

This paper presents a practical scheme for threefold stubs etched on the ground plane (GP) to reduce mutual coupling between adjacent patching elements. The multiple input multiple output (MIMO) antenna array consists of two concentric polyhedron annulus patches, a conventional dielectric substrate, threefold fork-shaped stubs (TFSS) and a microstrip line feeder. The equivalent band-stop filtering function of the TFSS suppressing surface wave propagation has been demonstrated in commercial Advanced Design System (ADS) software. The results of previous case studies indicate that the mutual coupling about 5 dB to 47 dB was reduced from 8 GHz to 9.3 GHz (S₁₁ < -10 dB) for antenna arrays. The capabilities of the antenna (in envelope correlation coefficient = 0.018, voltage standing wave ratio = 1.2892, and diversity gain = 20 dB) have been confirmed in a center frequency of 8.97 GHz. An examination of TFSS antennas shows that the side lobes in both the E-plane and the H-plane descends alongside an increasingly broad radiation pattern. The above results demonstrate that the proposed design is highly efficient in MIMO antenna applications.

In this paper, we experimentally demonstrate the performance of a multi-beam antenna based on inductor-capacitor (L-C) transmission line networks. The lumped element parameters of the antenna are derived according to the mapping relations between the Maxwell's equations and L-C network equations. The simulation results are in good agreement with the measurement ones, and the antenna performs well at a wide bandwidth with high directivity. The antenna has potential applications in future communication systems.

Wide axial ratio bandwidth is imparted by placing rigorously designed radial slits on an asymmetrically fed circular radiating patch antenna with parallel bilateral truncations. A partial ground plane with beveling on both the upper corners and a double stepped notch embedded on it makes the antenna suitable for ultra-wideband and X-band applications. The antenna exhibits a −10 dB impedance bandwidth of 8.6 GHz from 3.4 GHz to 12 GHz (111.6%) and a 3 dB axial ratio bandwidth of 8.7 GHz from 3.3 GHz to 12 GHz (113.7%) thereby contributing an effective operating bandwidth of 8.6 GHz (111.6%). The prototype manifests an exceptional far-field radiation pattern and fair gain throughout the passband.

In this study, the physical relationship between the shape parameter v of the K-distribution and the spatial correlation of a sea clutter signal received with a radar is demonstrated through simulation results. The spikiness of the sea clutter is well modeled by the shape parameter v of the K-distribution. According to a well-known empirical formula, the shape parameter v changes with the radar resolution based on a constant power-law relation. However, as with most empirical findings, this finding is valid only for the environmental conditions under which the formula was developed. In other words, the existing power-law models for the shape parameter of the K-distribution for sea clutter do not consider the relative ratio of the cross-range resolution R_c to the spatial decorrelation length R_dec of the sea surface. Our study investigates this relation using statistical simulations based on the principle of superposition for backscattered signals that represent sea clutter within a resolved area on the sea surface. This study shows that the constant factor α in the power-law relation must be modified to a function of the ratio R_c/R_dec. The findings of this study will be useful for the evaluation of detection performance in designing radar systems operating in the maritime environment.

According to theory, once certain conditions are fulfilled, current and voltage pulses propagate along ideal transmission lines with the speed of light. One can reach such a conclusion only when the conductors are assumed to be perfectly conducting, which cannot be realized in practice. A wave can only propagate along a transmission line with the speed of light if no energy has to be spent in establishing the current in the conductor. However, in establishing a current in a transmission line, energy has to be supplied to the electrons to set them in motion since they have a mass. The energy transfer to the electrons manifests itself in the form of an inductance which is called the kinetic inductance. The effect of the kinetic inductance has to be taken into account in signal propagation along high carrier mobility conductors including super conductors. In the case of transmission lines, the kinetic inductance leads to a change in the characteristic impedance and a reduction in the speed of propagation of waves along the transmission line. The goal of this paper is to show that the kinetic inductance will set an upper bound to the speed of propagation of waves along transmission lines, which is smaller than the speed of light.

In this paper we present an analytical method, employable with commercial full-wave electromagnetic CADs, which allows full-wave simulations of electromagnetically (EM) large structures, in terms of wavelength, such as linear accelerator cavities (LINACs) and a very accurate estimation of their operating frequency. The proposed technique is based on the exploitation of rotational symmetry through the definition of equivalent axially-symmetric volumes which replaces the non axially-symmetric ones inside the structure being analyzed. After a theoretical study, we show the successful application of the method in the real case study of a Drift Tube Linac (DTL) cell.

In this paper, a switchable beam and super-directive Electrically Small Antenna (ESA) dipole deployed at an IoT network gateway at 868 MHz is presented. It consists of one fed dipole and one loaded parasitic dipole. The nature and value of the load are obtained using the Uzkov equations, allowing determining current weighting coefficients in the case of two separately fed antennas, in order to maximize the gain and the directivity in a given direction. Reconfigurability in two directions is achieved using a pair of anti-parallel PIN diodes to steer the beam to the desired direction. The array final dimensions are 109 × 43 mm² (0.3λ × 0.1λ) generating a high directivity of 6.8 dBi in simulation and 6.7 dBi in measurement at 868 MHz for each beam in the azimuth plane.

In this paper, a broadband reader antenna is designed and manufactured for wearable ankle strap applications. The frequency range covered for S₁₁ < -10 dB is from 850 MHz to 1650 MHz with dipole like radiation pattern in free space. The proposed broadband antenna is manufactured with a semi-flex (Taconic RF-35) and flexible (Kapton) substrates. A good agreement between simulations and measurements has been achieved. Prototypes performances have been tested by measuring the reading distance. The maximum reading distance obtained is about 1.46 m at 865 MHz with an output power of the transmitter (P_TX) of 25 dBm. Results of functional RFID test show that the proposed antenna can be used as an RFID reader antenna when it is placed on the ankle of the human body.

The objective of this work is to estimate the Direction of Arrival (DOA) of signals from multiple closely spaced non-Gaussian sources corrupted by additive Gaussian noise. Generally, this is achieved by using higher order statistics (HoS) based MUSIC spectrum. In HoS, the Fourth order Cumulant is utilized because of its property of insensitivity to Gaussian process. But in the case of resolving closely spaced sources, a large number of sensor elements are required; otherwise, the resolution gets deteriorated. The large number of sensor elements leads to high computational burden. We propose a computationally efficient modified Spectrum that combines Fourth order Cumulants based MUSIC spectrum and its second-order differential counterparts. The proposed spectrum for DOA estimation offers good statistical performance and better accuracy the existing methods even in the case of extremely closely spaced signal sources. The improvement in the aspects of resolution and accuracy is substantiated by means of various simulation results such as Monte-Carlo simulations, spectral width, resolution with respect to angular separation, and comparison of RMSE with respect to number of array elements, number of snapshots, and SNR. The computational complexity analysis of the proposed method is also presented.

In order to study the distribution feature of the underwater electric field intensity produced by a ship in restricted seawaters, the horizontal DC electric dipole is used as the equivalent field source. Firstly, four kinds of field models are established. Secondly, the expressions of underwater electric field strength produced by a a horizontal DC electric dipole in the sea areas with upright bank is derived based on the mirror theory of static electric field. Then, based on this, the distribution features of the electric field intensity and the influence of the bank on the electric field are studied by numerical simulation. The simulated results show that the main characteristics of field strength distribution in restricted seawaters are consistent with those without bank, but it makes the absolute value of electric strength increased. The field point is closer to the vertical bank, and it generally presents greater influence on the absolute value of electric strength. But the influences of single vertical and parallel banks on the three-component field strength are different. The effect of bank on field intensity distribution in other restricted seawaters can be regarded as a superimposed effects of a series of vertical or parallel banks. Finally, the rectangle marine environment is simulated in laboratory, and the horizontal components of electric field intensity distribution on a certain depth plane under the simulated field source are measured. These theoretical derivation and analytical conclusions of simulation are further confirmed by comparing with the simulated results.

A dual-mode band-pass filter (BPF) for the fifth generation (5G) N78 band applications is proposed based on a 2-layer low temperature cofired ceramic (LTCC) substrate. The proposed BPF is built with a square resonator and two pairs of open-stubs, which suppressed the 2nd-order and 3rd-order 27 and 21 dB, respectively. The proposed BPF not only achieved a size reduction of 50% compared with a single-mode implementation, but also possessed a non-orthogonal input/output (I/O) feeding style, which presents convenient interconnection and integration with neighboring devices. Moreover, the dual-mode BPF does not need a conventional disturbing element to excite two degenerate modes. Comparison and discussion are carried out as well.

In this paper, a three-dimensional (3-D) tunable band-stop frequency selective surface (FSS) with wide tuning range is presented. The proposed tunable 3-D FSS consists of a periodic array of an annular resonator loaded with two varactor diodes. By controlling the reverse voltage of the varactor diodes, the resonance frequency could be tuned in a wide frequency range. Full-wave simulation shows 100% tuning range from 3.0 GHz to 6.0 GHz with respect to lower resonance frequency. The simulated results exhibit stable band-stop performance under different incident angles (up to 45˚). By cascaded two 3-D tunable FSSs, the bandwidth and selectivity performance could be further enhanced. The proposed 3-D FSS with its stable stop-band performance can be a potential candidate to shield the RF signals which is the major source of problem leading to RF device malfunctions.

In this research work, a planar crossed exponentially tapered slot antenna with a multi-resonance function is introduced. The presented antenna design is ascertained on a low-cost Rogers 5870 dielectric with a circular schematic. The antenna is designed to support several frequency spectrums of the current and future wireless communications. The configuration of the design contains a pair of crossed exponentially tapered slots intersected by a star-shaped slot in the back layer and a bowtie-shaped radiation stub with a discrete feeding point extended among the stub parts. The crossed exponential slots exhibit a wide impedance, and the star slot generates an extra resonance at the upper frequencies. For S₁₁ ≤ -6, the antenna provides a wide operation band of 1.7 to 5.9 GHz supporting several frequency bands of 3G, 4G, and 5G communication. The fundamental characteristics of the proposed slot radiator are studied, and good performances have been achieved.