The engine of a fighter plane is one of the largest scattering centers of the entire aircraft. One possible way of reducing the radar cross section (RCS) of the engine is to use an S-shaped bending air inlet to avoid direct radar wave illumination and reflection. We evaluate the efficacy of an S-shaped air inlet on RCS reduction by simulating the boresight and ±15˚ bistatic RCS for a digital model of an engine located behind an S-shaped inlet, using a multi-level fast multipole method (MLFMM) code in the S and X bands. The results show that a curved S-type air inlet can reduce the engine boresight bistatic RCS by ~10-12 dBsm at 3 GHz, and ~16 dBsm at 10 GHz when radar wave is incident from boresight, but not to the level required by RF stealth standards. When the radar waves are incident from θ=105˚ φ=90˚ or θ=90˚ φ=345˚, the RCS reduction is less effective, which is the results of the bend direction of the S-type air inlet.
This paper introduces a robust constant false alarm rate (CFAR) method to detect continuous noise jamming in coherent radar systems with a single antenna having no pattern control. The proposed detector is robust to interfering signals such as strong spikes from neighboring radars and returns from targets of interest and is resistant to land, sea, and weather clutter. The detector operates on data vectors extracted from a real-valued Range-Doppler data matrix generated at the output of Doppler processing for each azimuth cell within the entire scanning sector. Each data vector consists of statistically independent range samples associated with one of the specified Doppler bins. These samples are selected from non-overlapping range intervals allocated within the noise-dominant region in the full range coverage to mitigate the effect of clutter on the detector's performance. To perform jamming detection for each cell under test (CUT) in the current antenna scan, the proposed detector uses the CUT-associated data vectors generated in the current antenna scan and CFAR reference data vectors generated in the previous antenna scan. These reference data vectors are extracted from Range-Doppler data matrices associated with reference azimuth cells uniformly distributed within the entire scanning sector. The proposed detector achieves robustness to interfering signals by using a two-step detection algorithm. The first step performs censored video integration (CVI) for the CUT and reference data vectors and individual adaptive CFAR detection in each specified Doppler bin. The detector applies the "m-of-m" detection strategy to a complete set of decisions declared by the individual CFAR detectors in the second step. This strategy provides immunity to the simultaneous presence of interfering signals in the specified Doppler bins. The robustness of the proposed noise jamming detector is verified using Monte-Carlo simulations.
The paper is focused on reliable modeling and analysis of the effects connected with the resonant transformation of the field of a plane and density-modulated electron beam flying over the periodic rough boundary of a natural or artificial medium. In the paper such a medium occupies a part of the half-space, limited in thickness. Therefore, the numerous effects appeared due to transverse (in the thickness of the periodic structure) resonances, and the coupling of eigen regimes of two different periodic interfaces also contributes to the anomalies appearing due to excitation of the surface eigen waves of the periodic boundary interface that had been discussed in previous papers of this series.
A novel high gain two port planar antenna for 5G millimetre-wave and satellite band is presented. The proposed antenna besides working in the millimetre-wave range has an added feature to work for the satellite X-band as well. The antenna has a miniaturised low-cost planar geometry having the dimensions of 1.83λ x 1.83λ x 0.07λ at 27.5 GHz, designed and fabricated on a Rogers RT/duroid substrate of thickness 0.8 mm. The proposed antenna has return loss values of 12.34 dB and 17.94 dB for the two resonant millimetre wave frequencies of 27.24 GHz and 28.88 GHz respectively and 12.66 dB for the satellite band frequency of 8.42 GHz. The antenna attains a peak gain of 10.2 dBi for 28 GHz millimetre wave band and 6.2 dBi for satellite X-band by exploiting an inverse micro-strip Yagi director geometry. The isolation between two ports has been found satisfactory thus making it operate efficiently forthe available Ka and X band capacity of the Wideband Global Satcom system (WGS). The experimental results regarding the fabricated prototype are presented and compared with the simulated results, which are in good agreement. The performance of proposed antenna regarding radiation efficiency, directivity, gain, radiation pattern, and good isolation between the two ports makes the antenna employed as a suitable candidate for satellite communication and especially for 5G millimetre-wave communication.
In this paper, a built-in hybrid magnetic bearing (BHMB) with a permanent magnet (PM) motor is proposed to reduce the axial length of the system. The BHMB shares the same distributed hollow rotor with an external PM motor. The structure and principle of BHMB are illustrated. The mathematic model of BHMB is deduced to design parameters, and the influences of parameters are analyzed. To improve the performance indexes of BHMB, a multi-objective optimization method based on Taguchi method is proposed. The values of parameters of BHMB can be chosen according to the proportion of each parameter. Finally, the finite element analysis (FEA) and experiment are used to verify the correctness of BHMB.
A new method for obtaining an orthogonal system of eigenwaves of an open cylindrical waveguide filled with a gyrotropic medium and located in free space is presented. The advantage of the method is that it enables one to explicitly represent the fields of eigenwaves, which correspond to the discrete and continuous parts of the eigenvalue spectrum of such a guiding structure. Orthogonality relations for the eigenwaves and the procedure of expanding an electromagnetic field in terms of these modal solutions are discussed. The limiting transition from the case of a closed cylindrical waveguide with a perfectly conducting wall and a coaxial cylindrical gyrotropic core to the case of an open waveguide is considered. To illustrate the completeness of the obtained system of eigenwaves, a given field is expanded in terms of the found discrete- and continuous-spectrum waves and then resynthesized by evaluating the corresponding expansion numerically. Perfect coincidence between the initially specified field and the result yielded by this evaluation is demonstrated.
The aim of this paper is to prove that the power generated by a wearable textile patch antenna experiences reduced absorption in the phantom when the antenna ground-plane is increased. First, the dedicated human torso-equivalent phantom and two antennas were fabricated, which are multi-layered, with orientation normal to the body and made of the same materials. One of the antennas has a double in size ground-plane with regards to the other antenna, while the rest of their dimensions are identical. According to the proposed measurement procedure, once the radiation efficiencies of both antennas are measured in free space and with the phantom, the total absorption coefficient and the phantom losses are evaluated. The comparison of the measurement results proves that the increased ground-plane reduces the absorption on the phantom body of the antenna EM power (by 30.5%). Simulations and measurements were found in good agreement, with maximum deviation between the two up to 6% in terms of radiated efficiency. Hence, the proposed experimental evaluation of the impact of the ground-plane size of a wearable textile patch antenna on the reduction of the power absorbed by the user's body can be considered as a simple, reliable and cost-effective measurement method.
In this research project, the hardware implementation of a Field-Programmable Gate Array (FPGA) based Fast Fourier Transform (FFT) will be carried out by using Verilog Hardware Description Language (HDL). Since FFT serves as the core for the Range Doppler Algorithm (RDA) in Synthetic Aperture Radar (SAR) processing, it is of paramount importance to evaluate the algorithm and its computational complexity for the design of an efficient FFT hardware architecture. The design process and Verilog hardware description language which is used to describe and model a digital FPGA-based SAR processor will be introduced. Detailed explanation of the hardware implementation for FFT and Inverse Fast Fourier Transform (IFFT) in SAR processing are thus presented. The performance evaluations of the proposed processors including the comparison of the proposed processor with MATLAB-based processor, timing considerations of the processor, and lastly the hardware resources usage considerations are delivered at the end of this paper.
In this article, we present a compact and efficient diametrically-fed dual port fractal UWB MIMO antenna for portable handheld wireless devices. The electromagnetic behaviour on conducting body is analyzed through classical approach based characteristics mode analysis (CMA). Their intrinsic characteristics are explored on the basis of (a) modal surface current distributions, (b) narrow/broad bandwidth capability and (c) radiation potentials. Concurrent analysis is persuaded on diametrically-fed dual port fed fractal conducting surface, that provides interesting facets on the combinatory effect of electromagnetic performance and physical behaviour on metallic radiator, metallic ground planes (unconnected/connected) and combination of two aforementioned metallic compact geometries. Theoretical insights are investigated for essential/non-essential modes existing in proposed geometry. The investigation through CMA also gives plethoric information on the feed location of antenna on modal surface currents and similar trends to capture its radiation potentials on the current nulls existing in the physical body. A broad classification of modes is explained, covering the CMA modal dynamics such as (a) characteristics angle (CA), (b) eigen values (EV) and (c) modal significance (MS). These additive parameters in general reflect the resemblance of Q-factor≈B.W. for narrowband/wideband traits, electrically/magnetically coupled energy behaviour and radiative potential for far-field propagation. Thus, in a nut-shell, it can be inferred that `CMA provides physically intuitive guidance for the analysis and designing of antenna structures'. To support the findings highlighted in this particular study, a concise review about the theory of characteristic modes and the practical examples that use such concepts are taken into consideration.
The capacitance matrix relates potentials and charges on a system of conductors. We review and rigorously generalize its properties, block-diagonal structure and inequalities, deduced from the geometry of system of conductors and analytic properties of the permittivity tensor. Furthermore, we discuss alternative choices of regularization of the capacitance matrix, which allow us to find the charge exchanged between the conductors having been brought to an equal potential. Finally, we discuss the tacit approximations used in standard treatments of the electric circuits, demonstrating how the formulae for the capacitance of capacitors connected in parallel and series may be recovered from the capacitance matrix.