In passive radar systems, target echoes are submerged in the sidelobes of the static clutter, which includes multiple reflection echoes from the objects located in the operating environment of the considered system. This undesired part of the collected signals degrades the detector performances. Consequently, the reduction of the static clutter contribution is essential to ensuring an efficient operation of passive radars. In the literature, many algorithms and methods have been proposed for clutter suppression, where a good quality of the received signals is required to ensure an efficient clutter suppression. These methods require a considerable amount of data to operate which increases the complexity and the calculation load of the algorithms. In this paper, an important contribution is brought by simultaneously improving the signals quality and reducing the calculation load in the static clutter suppression process. Since the static clutter can be considered as time-invariant, the proposed approach exploits the specific architecture of the DVB-T signals to provide a noise reduction in the receiving channels by averaging the received signals after being split into symbols. Three different methods are proposed to examine the efficiency of the proposed approach. The performances of the proposed approach are validated through a set of simulations and verified using real data.
The aim of the next-generation 5G wireless network is to provide high data rates, low latency, increased network capacity and improved quality of surface (QoS) for wireless communication and internet of things (IoT). The millimetric wave communication is a promising technique with the capability of providing multi-gigabit transmission rate, network flexibility and cost-effectiveness for 5G backhauling. Smart antennas are a critical requirement for the success of millimetric wave communication system, and these antennas have the capability to form a high gain beam in desired direction and a null towards interfering signal. Directional beam-forming mitigates the high path loss associated with millimetric communication & improve signal to interference noise ratio. This article presents comparative analysis, effectiveness, and current limitations of various beam steering techniques for 5G networks based on some figures of merit with the aim of highlighting areas of improvements for each beam steering technique.
In this paper, the Wiener-Hopf technique is used to analyze the plane wave diffraction rigorously by a semi-infinite parallel-plate waveguide with five-layer material loading for E polarization. Introducing the Fourier transform of the unknown scattered field and applying boundary conditions in the transform domain, the problem is formulated in terms of the simultaneous Wiener-Hopf equations satisfied by unknown spectral functions. The Wiener-Hopf equations are solved exactly via the factorization and decomposition procedures leading to exact and approximate solutions. Taking the Fourier inverse of the solution in the transform domain, the scattered field in the real space is explicitly derived. For the region inside the waveguide, the scattered field is expressed in terms of the waveguide TE modes, whereas the field outside the waveguide is evaluated asymptotically with the aid of the saddle point method leading to a far field expression. Numerical examples of the radar cross section (RCS) are presented for various physical parameters and farfield scattering characteristics of the waveguide are discussed in detail.
An original application of stopband (SB) type negative group delay (NGD) electronic function is introduced. The unfamiliar SB-NGD circuit is designed with RLC-network lumped passive topology. The SB-NGD circuit is exploited to operate as a true-time delay (TTD) device for smart dual-beam phased array design. The two-port passive topology for designing an SB-NGD circuit constituted by an RLC-network is described. The theory and design method of the employed SB-NGD passive circuit are detailed. The microwave theory of the SB-NGD topology is elaborated from S-matrix modelling. The SB-NGD canonical form is innovatively introduced in function of the expected specifications. The synthesis design equations allowing to determine the R, L and C component values in function of the NGD specifications are formulated. The SB-NGD behavior is verified by comparison of calculated and simulated S-parameters from two different proofs-of-concept (POC). Illustrative results with a very good agreement showing SB-NGD behavior are observed around the arbitrarily chosen central frequencies f_{1} = 0.7 GHz and f_{2} = 1 GHz over a bandwidth of 50 MHz. The design principle of TTD-based smart dual-beam is described. The dual-band SB-NGD circuit is designed to operate as a dual-band TTD device with fixed delays at t_{1}(f_{1}) = 357 ps and t_{2}(f_{2}) = 875 ps, respectively. A radiation pattern showing the smart dual-beam steering operating system at f_{1} and f_{2} frequencies is discussed.
This paper presents an alternative solution for detecting breast cancer through planar antennas. The designed antenna electric parameters are the best gain for tiny radiation elements, along with the suitable characteristic impedance and bandwidth focusing on a specific application. Antennas are deployed nowadays to provide access to the detection of malignant tumors. That solution coexists with those in the hospitals (X-ray Mammography, Biopsy, Ultrasound, and Tomography), as breast cancer is a worldwide health concern because many women die yearly. Unfortunately, none of these methods are efficient as microwave imaging techniques. In terms of rapidity, efficiency, sensitivity, and accuracy, a small microstrip patch antenna operating at the Industrial, Scientific, Medical (ISM) band (5.72-5.82 GHz) is proposed in this paper for early breast tumor screening. Designed from the High-Frequency Structure Simulator (HFSS), the rectangular microstrip patch-antenna of 12x12x1 mm^{3}, etched on an FR4 HTG-175 dielectric material (relative permittivity of 4.4 and 0.02 of loss tangent) has been simulated, prototyped, and experimentally measured with ZVA50 Vector Network Analyzer (VNA). The defective ground structure technique has been used to achieve the goals of the final prototype. The proposed antenna has 51.22 dB of return loss, 230 MHz of bandwidth, with a radiation efficiency of 82% and a gain of 1.45 dBi at the resonance frequency of 5.73 GHz. Simulation results have been well-concluded through different tumor positions on the breast to take comprehensive precautions. Furthermore, a comparison with other antenna designs has been made. Due to the available laboratory equipment, the suggested work focused on the research part.
A rigorous solution is presented for description of the plane electromagnetic wave diffraction by two parallel slots in a perfectly conducting screen of finite thickness, placed before a dielectric layer, operating as a receiver of radiation in the near zone. The field in this layer is studied for the case of small obstacle dimensions being of the order of the wavelength. It is shown that the best spatial resolution of images from two slots in a dielectric layer is reached together with their optimal focusing, which can be determined by the method proposed earlier for one-slot diffraction.
This paper presents the mathematical formulation for the generalized closed-form expressions to calculate sideband power (P_{SR}) of a nonuniform period time modulated array (NTMA) antenna with volumetric geometry by using pulse shifting strategy. For the arbitrary array geometry, the generalized expression of P_{SR} is obtained by considering the universal omnidirectional element pattern in the form sin^{a}θ|cosθ|^{b}, a > -1, b > -1/2. Then, corresponding to different array structures such as linear, planar, and volumetric ones, the derived expression is simplified for different element patterns with possible combination of `a' and `b'. Through representative numerical results it is demonstrated that the obtained simplified expressions without hypergeometric function are useful to accurately calculate the amount of power losses due to sideband radiations with significantly less time than the conventional numerical integration (NI) method.
Coupling coefficient is a key parameter for the coil design of wireless power transfer (WPT) systems. The accurate calculation of coupling coefficient is an important theoretical basis for optimizing the coil structure and improving the transmission efficiency in WPT systems. In this paper, the magnetic flux density distribution of rectangular spiral coils with double magnetic shielding is studied, and an analytical model of coupling coefficient between arbitrarily positioned rectangular spiral coils is established. First, the incident magnetic flux density is obtained based on the dual Fourier transformation and the relationship between the magnetic flux density and magnetic vector potential. Second, the reflected magnetic flux density in the region of the receiving coil is solved by using Poisson's equation, Laplace's equation and boundary conditions. Finally, the formula for the coupling coefficient between rectangular spiral coils is derived by the spatial frame transformation method and the integral method. The calculation results agree well with the finite element simulation value and experimental measurements, which verifies the correctness of the calculation formula of the coupling coefficient.
A three-dimensional negative index (NI) metamaterial (MTM) is realized at terahertz (THz) frequencies. The structure is comprised of orthogonally oriented cross-bars with arrows on each corner embedded in a dielectric cube. The proposed 3-D MTM is symmetric along all the principal axes and shows a polarization-insensitive, wide-incident-angle negative refractive index regime centered at 0.862 THz with an operational bandwidth of 0.234 THz (27.15{%}). Using staircase approximation, the proposed 3-D NI MTM has been designed into a THz parabolic planoconcave lens (PCL). A PCL made of a NI medium is a counterpart of a positive index planoconvex lens and focuses on the near-field region. The designed PCL shows 3-D focusing functionality for linearly and circularly polarized THz waves at 0.85 THz. The designed PCL has a short focal length and high numerical aperture (NA) with sub-wavelength focusing spot sizes. The computed FWHMs along transversal directions are 0.46λ(x) × 0.49λ(y) for transverse electric (TE) polarized wave, 0.46λ(x) × 0.49λ(y) for left-circularly polarized (LCP) wave and 0.50λ(x) × 0.42λ(y) for right-circularly polarized (RCP) wave, respectively. The corresponding back focal lengths of the realized PCLs are 1.07λ, 1.03λ and 0.98λ and the focal depths are 0.40λ, 0.48λ and 0.41λ for linear, LCP and RCP polarized waves, respectively. A short review of recent progress in manufacturing techniques for the fabrication of the proposed 3-D MTM is further highlighted. Since the proposed 3-D MTM PCL configurations show the far-field focusing of linearly/circularly polarized waves, imaging with high optical power requirements can be met for THz waveband applications.
A compact extreme wide band (EWB) modified ellipsoid monopole antenna utilising electromagnetic band gap (EBG) technology is developed on a Rogers RT/Duroid 5880 substrate for high frequency millimetre (mm) wave applications including cellular, satellite, radar, and medical imaging. The proposed antenna design has an overall dimension of 40 mm x 30 mm x 0.787 mm and achieves EWB characteristics with a frequency range of 23.16 GHz to 776.59 GHz, a fractional impedance bandwidth (FBW) of 188.41%, and a bandwidth ratio (BR) of 33.53 by using a tapered feed and an EBG technique. The proposed antenna design attained a maximum peak gain of 17.91 dB and a peak radiation efficiency of 99.4%. On the basis of its high impedance wide bandwidth (IBW), FBW, BR, peak gain, and peak radiation efficiency, as well as its omnidirectional radiation properties at resonant frequencies, this compact antenna has the potential to be utilised for EWB applications. The HFSS 3-D solver is applied to characterize and analyse antenna performance.