Due to the limitation of low-resolution radar system and the influence of background clutter in the detection process, it is hard for low-resolution radars to classify and identify aircraft targets. To solve the above problems, a classification method for aircraft based on Ensemble Empirical Mode Decomposition (EEMD) and multifractal is proposed, in which the intrinsic modes are obtained by EEMD, and the waveform entropy in the Doppler domain is used to screen and reconstruct the intrinsic modes. The multifractal feature of the target echo data is extracted from the reconstructed signal, and then the aircraft target classification and recognition experiment is carried out with support vector machine. The experimental results show that the feature data extracted by ensemble empirical mode decomposition and multifractal analysis can be used for the classification and identification of civil aircraft and fighter aircraft, and the accuracy rate is about 98.5%, which is higher than that of time-domain multifractal method.

In the present scenario, multiple-input-multiple-output (MIMO) elements provide the capacity to generate more than one radiation pattern with different polarizations, which show a prodigious role in the modern telecommunication sector. A new two-element MIMO antenna with minimization in mutual coupling is presented in this paper. The proposed design reduces mutual coupling between antenna elements. The strip-line mechanism is used as a feed and is simulated using HFSS v 15. MIMO element design is done with four T-shaped slots in all directions of the patch, further enhancing the cross-correlation. MIMO antenna consists of two radiators on a 50 x 25 mm² FR-4 substrate. A T-shape ground stub, along with a slot, reduces mutual coupling (MC) and Impedance Bandwidth (IBW) of the proposed design. The design provides multi-band characteristics in the entire UWB range with practical applications like WiMAX (3.5 GHz), WLAN (5.9 GHz), X-band SATCOM applications (7.9 GHz) and Radar, Mobile phones, and commercial WLAN (9.3 GHz). The spacing between elements is in the order of 0.215λ₀. MC reduction of 20 dB is achieved at every resonant frequency.

A conformal quasi-isotropic dielectric resonator antenna (DRA) is first investigated for wireless capsule endoscope (WCE) application under the 5.8-GHz industrial, scientific, and medical (ISM) standard. The probe-fed hemispherical DRA (HDRA) is studied to match the shape of the spherical dome end, and the characteristic mode analysis (CMA) tool is applied to analyze the resonant modes of the proposed antenna to reveal the intrinsic behavior of the dielectric resonator. It is found that the quasi-isotropic radiation pattern can be achieved by combining HDRA's TE_111sinφ mode which radiates like a magnetic dipole and a small ground plane's TM₁₀ mode that radiates like an electric dipole. In order to reach the requirement of 5.8 GHz in ISM, a ceramic hemispherical dielectric resonator with dielectric constant of 21.984 is investigated. The radius of the hemisphere is set to 5.35 mm. In free space, the measurement results show that the proposed antenna achieves 3.25% bandwidth, 86% maximum efficiency and 7.2 dB gain deviation. The antenna is also measured in pork to approximate human body environment. The measurement results demonstrate that the antenna achieves 3.20% bandwidth, 8.15% maximum efficiency and 9.0 dB gain deviation. Accordingly, the proposed antenna is suitable for WCE application at 5.8 GHz ISM standard.

Optical amplification by nonlinear wave mixing offers wideband high-gain amplification that is desirable for a variety of applications. When the wave mixing process occurs in an interaction medium with sufficient length, the attained gain per excitation pulse is usually higher than that can be attained by lasers. Furthermore, the bandwidth of amplification via nonlinear wave mixing is much higher than the bandwidth allowed by laser transitions of laser gain media. However, optical amplification by nonlinear wave mixing offers negligible gain in the micrometer scale, due to a very limited length of the interaction medium. In micro-resonators, such a short interaction length does not offer sufficient small signal gain to compensate the round-trip loss. In this study, we present a Fletcher-Reeves algorithm-based nonlinear programming of the wave mixing process that tunes the frequencies of the excitation pulses of the source device in order to provide an ultra-high optical gain in the micro-scale via maximizing the electric energy density in a micro-resonator. Using this smart wave mixing approach, we obtained a micro-resonator gain of 4.7x10⁷ for an input wave at 640 THz, and a gain of 1.5x10⁸ at 100 THz. The results of our mathematical formulation are compared with well-known experimental results, and a mean accuracy of 99% is observed. The study aims to show that optical amplifiers that are based on the principle of nonlinear wave mixing can be used in the micro-scale for wideband ultra-high gain operation.

Minimum variance distortionless response (MVDR) beamformer is an one of the well-known space-time antijamming techniques for global navigation satellite system (GNSS). It can jointly utilize spatial filter and temporal filter to suppress interference signals. However, the computational complexity is usually so high that it is difficult to apply in engineering problems. In order to solve this problem, a novel MVDR algorithm based on rank-reducing transformation (RRT) and multistage wiener filter (MWF) is proposed for reducing the computational complexity, named as RRT-MWF-MVDR algorithm. Via the characteristics of the oppressive jamming environment and the steering vector of satellite signal, a rank-reducing transformation is given. By the rank-reducing transformation, a rank reduction is realized for the high dimensional received data. Taking these received data with reduced rank as the input of the MWF, the forward decomposition and backward iteration are accomplished. Then the equivalent reduced rank matrix and equivalent weight vector of MWF can be given, respectively. Finally, the space-time two-dimensional antijamming weight vector is given by the mathematical relationship between the reduced-rank matrix and the weight vector.The proposed method can effectively avoid the inverse of high-dimensional matrix. The proposed method offers a number of advantages over the existing algorithms. For example, (1) it has less computational load and is easier to be executed in practical application. (2) It can maintain higher output signal-to-interference-noise ratio (SINR). Simulation results verify the effectiveness of proposed method.

Space-time adaptive processing (STAP) algorithms can provide effective interference suppression potential in global navigation satellite system (GNSS). However, the performance of these algorithms is limited by the training samples support in practical applications. This paper presents an effective STAP based on atoms extension (named as AE-STAP) algorithm to provide better anti-jamming performance even if within a very small number of snapshots. In the proposed algorithm, a spatial-temporal plane is constructed firstly by the sparsity of received signals in the spatial domain. In the plane, each grid point corresponds to a space-time steering vector, named as an atom. Then, the optimal atoms are selected by searching atoms that best match with the received signals in the spatial-temporal plane. These space-time steering vectors corresponding to the optimal atoms are used to construct the interference subspace iteratively. Finally, in order to improve the estimation accuracy of interference subspace, an atoms extension (AE) method is given by extending the optimal atoms in a diagonal manner. The STAP weight vector is obtained by projecting the snapshots on the subspace orthogonal to the interference subspace. Simulation results demonstrate that the proposed method can provide better interference suppression performance and higher output signal-to-interference-plus-noise ratios (SINRs) than the previous works.

For the application of electro-magnetic (EM) wave with orbital angular momentum (OAM), which is also called the vortex beam, it is essential to determine the real OAM mode of the transmit antenna, i.e., accurately measure the OAM mode of the manufactured antenna with systematic error. The traditional methods measure the OAM mode based on the OAM far-field approximation or the phase gradient in the transverse plane. The corresponding performance degrades when alignment error is not negligible or OAM modes increases. In this paper, an accurate OAM measurement of EM wave based on rotational antenna is proposed. Specifically, the EM beam with helical phase fronts can be well measured via frequency shift detection by rotating the OAM wave at the transmitter. The accuracy can be greatly improved compared with the traditional ways.

To ensure better performance of modern electronic systems with electromagnetic compatibility (EMC) compliances, the reduction of electromagnetic interference (EMI) between modules or components of an integrated circuit (IC) is necessary. This can be achieved by developing a near field (NF) coupling model of radiating source and victim using analytical, experimental, or numerical simulation techniques. The accurate modeling of a radiation source can be performed using an array of elementary dipole moments obtained using near-field scanning measurement. This paper discusses the various techniques used in the equivalent dipole moment model to reduce the complexity and simulation time and at the same time increase the accuracy and reliability.

In this article, the drawbacks of Li's formula is rectified and extended to compute accurately the resonant frequency of a rectangular patch antenna in multi-dielectric layers. Computed results employing the present model are compared with experimental and simulation results. The present model shows excellent improvement in accuracy compared to the previously reported investigations.

A multiband four-element multiple-input-multiple-output (MIMO) antenna configuration is proposed. The antenna consists of split ring resonators (SRRs) along with inverted L-shaped monopole antenna (ILA) structure on the top of the substrate and a slotted ground plane. The antenna without the SRRs exhibits resonances at 2.4 GHz, 3.66 GHz, and 5.5 GHz with with the impedance bandwidth (IBW) of 14.5%, 35.1%, and 9.6%, respectively. With the addition of SRRs the antenna exhibits additional resonance at 5.1 GHz with improved bandwidth and minimizes the reflections. Consequently, the impedance bandwidth at 5 GHz frequency band gets improved to 17.2%. Overall, the proposed antenna will cover the 2.4 GHz wireless local area network (WLAN) & industrial, scientific, medical (ISM) band, 3.5 GHz worldwide interoperability for microwave access (WiMAX), and 5 GHz WLAN 4G/5G applications. In spite of very compact area (0.094 λ₀², for the highest operating wavelength) and presence of common ground, the antenna exhibits high inter-element isolation of ≥ −14 dB and S₁₁ ≥ −10 dB. The proposed antenna design is fabricated, tested, and analyzed.

This paper presents a compact generalized T-shaped printed pseudo-monopole antenna (GeT-PPMA) driven dual-band Yagi-type pattern diversity antenna. In contrary to the common practice, here impedance matching at the lower band is attained by increasing the quality factor (Q) through folding a monopole strip. Afterwards, a GeT-PPMA having relatively lower Q than that of the T-PPMA is proposed. Compared to the simple T-PPMA, the GeT-PPMA has 1.5 times more bandwidth (BW) at the lower band. The dual-band GeT-PPMA is 15.11% more compact than the corresponding straight PPMA(S-PPMA). A highly compact dual-band Yagi-type pattern diversity antenna of size 45.5×63 mm² i.e. 0.35λ0 x 0.48λ0, where λ0 is the free space wavelength at the lowest frequency of operation, is designed by using a novel arrangement of two directors and two common folded reflectors. The compactness owes to the folding of the reflectors. The length of the reflector is optimized for providing good front-to-back-ratio (FBR) in the lower band. The length of the two directors is optimized to improve the FBR at the upper band. Usage of the folded reflector is found to degrade the isolation level in the lower band. Near-field analysis is carried out to investigate the mechanism of mutual coupling. Being guided by the near-field study, a λg/2 isolator, where λg is the guided wavelength at the lower band, is placed in the gap of the folded reflectors, and the mutual coupling is reduced by about 5 dB.

For rapid Rotman lens design, the symmetry plane is utilized to reduce the structure size by employing the odd and even mode characteristics. Solutions of half the structure for odd and even modes (short and open walls or electrical and magnetic walls, respectively) are much more efficient than the one-time solution for the whole structure. Then, s-parameters from both solutions are processed to obtain the s-parameters of the full lens. To support the wideband and wide scanning range, DRA array is used because of its ability to support these characteristics. Two examples are considered. The first example that employs four cylindrical DRA elements is built and measured to test the concept of terminating the dummy ports by absorbing materials instead of matching loads. This termination tremendously simplifies the structure and reduces the cost by saving the terminating connectors and the matching loads. Here, thin planar absorbing material is used on top of the microstrip lines of the dummy ports. The simulated and measured results are in good agreement. The second example utilizes 8 rectangular DRA array elements and is studied numerically.

In this paper, a novel three-dimensional (3D) bandpass frequency selective surface (FSS) is presented based on a square waveguide structure using 3D printing technology. The proposed 3D FSS is composed of a periodic array of the square waveguides with dumbbell slots embedded in waveguide walls. The square waveguide of the unit cell provides a propagation path, which can excite two resonant modes, leading to a bandpass response with one transmission pole and one transmission zero below the cutoff frequency of the square waveguide. To explain the operating principle of the proposed 3D FSS, the electric field distributions at the frequencies of transmission pole/zero are analyzed, and an equivalent circuit model is also established. For validation, a practical example is manufactured simply and rapidly, by using 3D printing technology. To verify the performance of the proposed 3D FSS, the frequency selective characteristics of the implemented 3D FSS for both TE and TM polarizations under different incident angles are measured. The measurement results show that the proposed structure exhibits dual polarizations and provides good frequency stability under incident angles from 0° to 40°.

The purpose of this paper is to provide simple analytical homogenization methods for composite materials containing a metallic wire grid. Estimating their effective electrical properties facilitates the numerical simulation of composite structures for shielding applications in the automotive industry. The presented methods are based on surface impedance approaches and effective media theory. The obtained results show that the shielding properties of the described wire grid composites can be accurately estimated and bounded, using the proposed theories in the low frequency range. The frequency limits vary according to the studied sample. For the presented materials, the validity of the results is shown to be up to a few megahertz. The experimental validation is done by measuring the shielding effectiveness of composite samples using a near-field test bench.

We hereby present a new equivalent circuit model including both lumped and distributed elements for GCPW-MS transitions (GCPW for Grounded Coplanar Waveguide and MS for Microstrip). In order validating the modelling results, such transitions have been fabricated on a 20 µm-thick BCB (Benzocyclobutene resin) substrate using grounding pads including via-holes of different diameters. The study focuses on the impact of the via-hole design on the performance of the transition and more specifically on its bandwidth. The transitions were made using a simple technological process based on photosensitive polymer. ADS simulation data of the new equivalent circuit model were in very good agreement with measured S-parameters. Both theoretical and experimental results show that the bandwidth of such a transition can reach up to 100 GHz bandwidth using via-holes of 900 µm diameter.

The quaternion multiple signal classification (Q-MUSIC) algorithm reduces the dimension of covariance matrix, which would result in performance degrading of DOA estimation. An augmented quaternion MUSIC algorithm (AQ-MUSIC) based on concentered orthogonal loop and dipole (COLD) array is presented in this paper. The proposed algorithm uses an augmented quaternion formalism to model the completely polarized signals, which allows a concise and novel way to an augmented covariance matrix. The fact reveals that more accurate DOA parameters could be extracted from an augmented covariance matrix. Even compared with the long vector MUSIC (LV-MUSIC) algorithm whose dimension of covariance matrix is the same as AQ-MUSIC, the accuracy of DOA parameter estimation is also improved. Simulation results verify the performance promotion of the proposed approach.

A wideband coplanar waveguide (CPW) fed monopole antenna designed for Wi-Fi5 and Wi-Fi6 applications is proposed. The proposed antenna (main radiator) has a designed footprint of only 20 × 8.7 × 0.4 mm³, which is composed of an oval-shaped ring radiator with three concentric rings and a double-T structure loaded with a J-shaped slot. The main novelty of this work is that the measured wideband operation of 34.5% (5.15-7.29 GHz) is contributed by only a single resonance at 6.2 GHz, conforming to the bandwidth requirement of Wi-Fi5 (5.15-5.85 GHz) and Wi-Fi6 (5.925-7.125 GHz). Furthermore, the proposed antenna also exhibits good radiation characteristics, including a gain around 2.25 dBi, a radiation efficiency above 80%, a total efficiency above 70%, and omnidirectional radiation patterns with a low magnitude of cross polarization throughout the bands of interest.

Different global and national electromagnetic regulatory standards have been developed based upon significantly diversified premises, developmental backgrounds and objectives to safeguard life. Some standards aim at minimizing short duration thermal effects, some try to mitigate non-thermal effects over prolonged duration and rest have adopted precautionary limits. As a consequence, these global and national electromagnetic standards substantially differ from each other. Moreover, in spite of lossy dielectric nature of plant tissues, electromagnetic energy absorption rate level estimations for a complete plant model have neither been reported in literature nor been considered while preparing safety standards. To this end, Specific Absorption Rate levels have been estimated for a typical Catharanthus roseus plant model --- typical geometric shape of the plant prototype has been modelled considering the most practical scenario. Detailed analyses on variation of Specific Absorption Rate levels due to wide discrepancy among the existing electromagnetic regulatory standards have been reported in a quantitative manner. This particular work encompasses dielectric properties measurement of different Catharanthus roseus plant samples, modelling a typical Catharanthus roseus plant containing leaves, flower and twig with appropriate dielectric properties defined, and finally the simulation-based investigations to estimate the variation in Specific Absorption Rate levels based on the contrasting electromagnetic exposure standards. Specific Absorption Rate levels have been reported at five different telecommunication bands as per two occupational and four public exposure scenarios. Variations among the estimated Specific Absorption Rate levels have been noted to be significant and presented in detail in this article. A total of thirty rigorous simulations have been carried out along with one hundred and twenty Specific Absorption Rate data evaluations to ensure accurate comparison among different electromagnetic standards. Noted vast variations among estimated Specific Absorption Rate levels based on contrasting electromagnetic standards over the frequencies indicate the necessity of re-evaluating all existing guidelines and also call for the need of maintaining a global uniformity among the existing electromagnetic standards worldwide.

The propagated fields within and radiated fields outside a rectangular dielectric cylinder are represented as guided and radiation modes respectively. These fields of the cylinder are related with incident, backward scattered fields at x=0 and transmitted fields at x=a by Mode Matching technique. The expressions for guided and radiation mode amplitudes are derived by applying the orthogonal property of the modes. The unknown functions (mode amplitudes) in each of these equations that are defining discrete functions of the guided modes field and angular spectrum for the radiation field are determined numerically. The powers due to discrete guided modes (even and odd) are calculated. The integrals related with the backward and forward scattered fields and the powers associated with them are approximately evaluated by the method of steepest descents.

A method of loaded patch antennas with shorting pins and erected walls in between patch antenna arrays is introduced to reduce surface wave and free space wave coupling in both E and H-plane. This simple technique works equally well in both orientations by reducing coupling up to -19 dB and -15 dB (measured value) in E-plane and H-plane, respectively, as compared to a conventional patch antenna array. The scattering parameters are studied, and conclusions are made on amounts of mutually coupled power and the bandwidth of the rejection band (S₁₂). A parametric study of the variation in the level of mutual coupling with respect to height of the wall has been carried out in both E and H-planes. The simulation results are well verified through measurements.