This paper presents the realization of Nonstandard Finite Difference Time Domain (NS-FDTD) analysis having high accuracy and low computational cost to a negative permittivity metamaterial wire medium for the first time. A sine wave of frequency less than that of plasma frequency of the medium which is in the shape of a slab reflector is allowed to interact after identifying the exact values of the required stability condition of the NS-FDTD. The electric field distribution around the plasma slab obtained for a particular excitation point using NS-FDTD and standard FDTD are demonstrated which show obvious advantages of this high accuracy algorithm. This novel technique may be further extended to various dispersive and metamaterial structures.

The average downlink data-rate in massive Multiple Input Multiple Output (MIMO) networks within realistic urban environments is characterized by means of ray-tracing simulations. The links between the receivers and transmitters are mostly established through rooftop propagation, which requires special treatment due to multiple diffractions near the optical boundaries. The bidirectional ray-tracing method is utilized in order to simulate these effects accurately. The average downlink data-rate is also calculated according to an empirical rooftop propagation model and the differences as well as the similarities with the bidirectional ray-tracing results are demonstrated. Additionally, an iterative Shooting and Bouncing Rays (SBR) algorithm, which improves the computational efficiency of the bidirectional ray-tracing, is introduced. The algorithm aims to maximize the number of rays, which contribute to the result, by setting specific launch directions. The results show that noticeable improvements in the computation time are possible.

In this paper, a wideband polarization diversity multi-input multioutput (MIMO) antenna system is proposed. The structure of the proposed antenna consists of four wideband coplanar waveguide (CPW)-fed monopole antennas with a common ground plane and radiated element. The simulated and measured -10 dB impedance bandwidth is 20% (2.25-2.75 GHz), which covers WiFi (2.4 GHz) and LTE (2.6 GHz) frequency bands. The MIMO antenna system is applied to both an indoor and outdoor wireless access point (WAP) at the covered frequency bands. Due to the common structure of elements in the proposed MIMO antenna, an acceptable mutual coupling between the antennas ports is critical. Hence, a new parasitic element structure is presented to improve mutual coupling between the antenna ports. Acceptable values for the coupling coefficient (<-14 dB) are achieved by adding the parasitic element. The presented antenna system provides a nearly omnidirectional radiation pattern with an orthogonal mode of linear polarization. The results show a polarization diversity gain of 10 dB and an envelope correlation coefficient of less than 0.2. Moreover, each antenna port possesses peak gains of 5.33-6.97 dBi and efficiencies of 51.5-57%. A comparison between the simulation results and experimental measurements reveals good agreement between the two, confirming the validity of the proposed design.

In this paper, a new design approach is presented for achieving a miniaturized quad-band microstrip patch antenna (MPA) suitable to be used for 915-MHz (UHF band), 2.45- and 5.8-GHz (ISM band), and 3.5-GHz (WiMAX band). The proposed antenna is called modified square spiral antenna (MSSA) which is composed of a modified dual-arm square spiral patch strip structure and a tapered-ground plane with coplanar wave-guide (CPW)-fed configuration to feed this antenna, all printed on the top side of an FR4 substrate. The proposed antenna is designed through intermediate systematic design steps of antennas starting from a conventional strip-fed rectangular MPA and ending by achieving MSSA. A CST Microwave Studio (CST MWS) is used to model the designed antenna and simulation results, in terms of return loss (S₁₁), realized peak gain and efficiency, besides to radiation patterns, are obtained. To validate the design concept, the antenna structure is fabricated, and the simulated and measured S₁₁ results nearly coincid with each other. The proposed antenna is characterized by miniaturized size of 28×28 mm², and based on measured -10-dB S₁₁ result, MSSA has four bands, band 1: 915-GHz (872-929 MHz), band 2: 2.45-GHz (2395-2510 MHz), band 3: 3.5-GHz (3470-3550 MHz), and band 4: 5.8-GHz (5698-5900 MHz).

In this work, a simple propagation channel model for microwave-based pinless subsea connectors in the 5 GHz band is presented. Both high electromagnetic attenuation in seawater due to absorption and the near-field working conditions typically present for underwater connectors are taken into consideration. Therefore, a simplified path loss model based on linear regression is identified. The study shows that high-speed pinless subsea connectors are a reality over several cm of seawater gap when appropriate microwave receiver technology is selected with sensitivities of about -100 dBm. Experimental results show that both half-duplex gigabits-per-second and full-duplex 100-Mbps technologies have a strong potential to be developed in the 5 GHz band.

In this paper, a novel high-gain repeater antenna integrating a dual-feed network is proposed to receive and transmit RF signals separately by two ports. The proposed array antenna has four linearly polarized microstrip antenna elements, two feed networks, and one planar magic-T. The distance between the elements of the array antenna is matched to obtain the minimum sidelobe level and maximum half-power beamwidth for transmitting and receiving purpose. The planar magic-T is effectively used to meet two different bi-directional radiation patterns with a simple structure. Performances of the array antenna are experimentally confirmed, and the gain of the antenna for each port is better than 10.3 dBi. The measured 10-dB impedance bandwidth of the antenna is wider than 580 MHz (10%).

The context of the paper is the 50-60 Hz electromagnetic interference between AC power lines/electrified railway lines and pipelines; we present here an algorithm for the evaluation of the AC induced current density, flowing through the holidays (defects) in the pipeline insulating coating, from pipe to soil by modelling this last one as a two-layer structure. Moreover, the value of holidays area is treated as a random variable (as actually is from field experience) so allowing to associate a certain level of probability to the event of exceeding the AC current density limit, established by standards, for AC corrosion risk. The results show that the surface layer soil resistivity is a very significant factor influencing the level of AC induced current density.

In this paper, an electronically switchable ultra-wideband (UWB)/dual-band bandpass filter using defected ground structures (DGSs) is proposed. The proposed filter consists of meandered inter-digital coupled line sections, stepped impedance open stubs, coupled lines, and rectangular DGSs to realize high performance in the operation band with a compact size of 12.5 mm × 10 mm. The proposed filter is designed on an RT/Teflon substrate (ε_r = 2.2, h = 0.7874 mm). The main advantage of the proposed filter is the reconfiguration of ultra-wide bandpass filter to dual-band bandpass filter. UWB has passband from 3.6 GHz to 10.6 GHz with upper wide stopband attenuation better than 20 dB up to 18 GHz. The dual passbands extend from 3.8 GHz to 5 GHz and from 9.5 GHz to 10.8 GHz. This filter is able to provide interference immunity from unwanted radio signals, such as wireless local area networks (WLAN), worldwide interoperability for microwave access (WIMAX) that cohabit within the UWB spectrum, and X (Military) band of satellite from 7 GHz to 8 GHz. The state of filter can be changed by using switching matrix equipment (mini circuit, replacement of PIN diodes). To validate the design theory, an electronically switchable UWB/dual-band bandpass filter using DGSs is designed, fabricated, and measured. Good agreement is found between simulated and measured results.

Convolutional Neural Network (CNN) models applied to synthetic aperture radar automatic target recognition (SAR ATR) universally focus on two important issues: overfitting caused by lack of sufficient training data and independent variations like worse estimates of the aspect angle etc. To this end, we developed a lightweight CNN-based method named SARNet to accomplish the classification task. Firstly, a clock-wise data amplification approach is presented to generate adequate SAR images without requiring many raw SAR images, effectively avoiding overfitting in the course of training. Then a SARNet is devised to process the extracted features from SAR target images and work on classification tasks with parameters fine-tuning under comparative models. To enhance and structurally organize the representation of learned proposed model, various activation functions are explored in this paper. Furthermore, due to the pioneering conducted experiments, training samples in the MSTAR and extended MSTAR database are utilized to demonstrate the robustness and effectiveness of the lightweight model. Experimental results have shown that our proposed model has achieved a 98.30% state-of-the-art accuracy.

In this paper, an antenna composed of an inverted L-shaped feeding strip and a shorting strip with three branches for LTE/WWAN mobile phones is presented. With the help of novel ground plane slots, the proposed antenna can realize miniaturization (34×15 mm²) and multiband to cover LTE/WWAN bands. The measured bandwidth (3:1 VSWR) of the proposed antenna is 156 MHz (810-966 MHz) at the low band and 1937 MHz (1548-3485 MHz) at the high band. Moreover, the lowest measured radiation efficiency of the fabricated antenna is more than 54% in the whole operation band. The proposed antenna has been successfully fabricated and measured, and there is a good agreement between simulated and measured results.

In this paper, a 60-GHz broadband 8-by-1 gap-coupled microstrip antenna array is presented and experimentally investigated. The proposed antenna array has been implemented using a Miniature Hybrid Microwave Integrated Circuits (MHMIC) fabrication process on a thin ceramic substrate with ε_r = 9.9, and h = 127 μm. For a comprehensive characterization and to accurately evaluate losses, as well as manufacturing tolerances, the proposed antenna array structure has been implemented using two different feeding techniques. The first one adopts a grounded broadband via-hole less transition from coplanar to microstrip line (GCPW-to-MS), while the second one has involved a broadband waveguide (WR12) to microstrip transition, based on a ridged waveguide concept. The obtained results have demonstrated that the proposed gap-coupled array configuration provides an improved bandwidth (4.56%) and an enhanced gain (11.8 dBi), while maintaining a lower side-lobe level (13.4 dB). These outstanding performances make the proposed WR12 gap-coupled array structure a potential candidate for the future emerging 60-GHz short-range point-to-point wireless communication systems.

This communication enlightens design, simulation, fabrication and testing of a novel compact CSRR etched ultra-wideband (UWB) patch Antenna with quadruple Band refusal characteristics. To design the antenna, the dimensions are chosen as 28x18x0.8 mm³. The design was done on FR4 substrate of 4.4 dielectric constant, 0.02 loss tangent. The planned antenna contains chamfered bevel slot rectangular radiating material with a complementary split ring resonator (CSRR) etched on one side and an incomplete ground plane on the other side of the substrate. To understand band rejection characteristics, four circular slots with different radii are etched on the radiating material as CSRR to reject bands at Worldwide Interoperability for Microwave Access (WiMAX) at 3.5 GHz, Indian national satellite (INSAT) at 4.6 GHz, wireless local area network (WLAN) services at 5.8 GHz, and Wideband Global SATCOM (WGS) at 8.2 GHz. The rejected bands center frequencies are perfectly coupled at particular slots with different radii. This compact antenna is effective and useful for short areas and can be easily incorporated in small devices. The results show that the antenna has a bandwidth from 2.77 GHz to 13 GHz. This antenna gains a worthy harmony between the simulated and measured results.

A distinct feature of GNSS-R land reflectometry is that random rough surfaces are superimposed on many levels of elevations. The rms elevations are in tens of meters which are many times larger than the microwave wavelengths at GNSS frequencies. Such multiple elevations were not considered in the coherent model nor the incoherent model. In this paper, we studied the electromagnetic scattering of this new rough surface scattering problem using Kirchhoff integral as first-principle. A numerical Kirchhoff simulator is developed to calculate the electromagnetic scattering and the power ratio in the specular direction. The integration is carried out over a footprint of 10 km by 10 km with the specular point as the center. In integration the surface discretization is as small as 2cm by 2 cm so that a total of 2.5×10¹¹ patches are used. Parallel computing is implemented requiring a moderate amount of computer resources. The results of the power ratio of the numerical Kirchhoff simulator differ from the results of both the coherent model and incoherent model. The results show that the phase of the first Fresnel zone is random, and the power contributed by the first Fresnel zone is a small fraction of that over the 10 km by 10 km. The power ratios of the numerical Kirchhoff simulations are much larger than that of the incoherent model and smaller than the coherent model for small RMS heights. The results show that the multiple elevations in land have large effects on GNSS-R specular reflections.

In this article, a new class of dual-/tri-band bandpass filters (BPFs) using a quintuple-mode resonator (QMR) is proposed. The classic odd-/even-mode analysis method is used to analyze the two filters due to their symmetrical structure. Owing to characteristics of the QMR, the dual-/tri-band BPFs based on the same topology are designed. The bandwidths (BWs) of the passbands are controllable. A dual-band BPF with center frequencies of 2.1 GHz/3.43 GHz and a tri-band BPF with center frequencies of 2.35 GHz/3.44 GHz/5.2 GHz are designed, fabricated, and measured. The fabricated filters are compact in size, and measured results are in good agreement with the simulated ones.

Building of compact plasmonic integrated circuits based on domino spoof plasmons (DSPs) is an important requirement and still a challenge. In this work, we report the first demonstration of two kinds of channel domino plasmonic circuitries, which consist of an easy-to-manufacture periodic chain of metallic box-shaped elements inside two finite metallic plates. We reveal that only the channel DSPs itself rather than the hybrid TE₁₀ and DSPs modes is supported in the part of the channel domino plasmonic waveguide with or without the metallic vias on both sides. Two channel domino plasmonic filters based on the efficient transition structures are designed, and the simulated S-parameters and near electric field distributions show excellent transmission performance in broadband. Utilizing the lateral insensitive property of these two channel DSPs, two kinds of broadband plasmonic power dividers/combiners are firstly implemented. Excellent transmission performance validates our optimizations and indicates that the proposed scheme can be easily extended to other bands. This work provides a new route for construction of deep-subwavelength DSP devices in application of high integration of microwave and terahertz circuits.

In this paper suppression of higher order modes of a microstrip antenna array is investigated. The array consists of two radiating elements which are fed by a corporate type microstrip feeding network. They array provides resonance at 5.2 GHz frequency for its fundamental mode (TM10 mode). Beside this fundamental mode, two harmonics at 10.4 GHz (1st harmonic) and 15.05 GHz (2nd harmonic) and few sub-harmonics at 7.8 GHz (TM12), 8.8 GHz (TM22), and 13.3 GHz (TM32) are excited. In order to suppress 1st harmonic, a pair of half wavelength open ended stubs (pair of stub-A) whereas for 2nd harmonic a pair of quarter wavelength open ended stubs (pair of stub-B) are employed. From the simulated results it is noticed that the 1st and 2nd harmonics are successfully suppressed, and the sub-harmonics are also suppressed. Prototypes of the antenna arrays are fabricated and measured. Measured results have good agreement with simulated ones.

We engineer very low aspect ratio Aluminum (Al) based periodic plasmonic nanostructures with period ≈ resonance wavelength for enhanced refractive index and thickness sensing, which offer to access complete ultraviolet-visible-near infrared spectral range for SPR sensors. Al-based periodic nanostructures on top of a thin homogeneous Al metal coated on a BK-7 glass substrate were designed by systematic variation of geometrical parameters using Rigorous Coupled Wave Analysis and finite elements full wave solver, while, taking into account applicable fabrication constraints. The reason of adding a thin layer of homogeneous Al metal between the nanostructure and glass substrate was to convert the signature of Surface Plasmons (SPs) from transmission dips to transmission peaks, using ±1st order diffraction mode. The shift in SP mode excited on the nanostructure-analyte interface was used to measure the variation in refractive index, and the number of waveguide modes with the increase in the thickness of the analyte was used to capture the variation in thickness of the analyte. The proposed nanostructures of period 400 nm and an aspect ratio of 0.1 offered a sensitivity of 400 nm/RIU and full width at half maximum of 18 nm resulting in a figure of merit of 22. These plasmonic nanostructures have potential to be used as refractive index and thickness sensor due to a high figure of merit, high localization of the field, and very low aspect ratio that is needed to maintain laminar flow of analyte.

In order to obtain a wideband sum-and-difference network, a novel ridged substrate integrated waveguide (RSIW) magic-T is designed. The proposed magic-T is composed of a five-layer RSIW structure. The signal input from the coaxial H-plane port is transmitted to RSIW through a stripline and split into two in-phase and equal signals at the output ports on the top and bottom layers because of the vertically symmetric structure. An E-plane SIW power divider is utilized to realize the E-plane input/output port of the magic-T. A remarkable bandwidth improvement is achieved due to the ridged structure and the wide bandwidth of a ladder-shape stripline optimized by genetic algorithm (GA). Measured results indicate that the magic-T has a fractional bandwidth (FBW) of 78.7% (6.4-14.7 GHz) with return loss better than 18.1 dB and great isolation characteristics.

Global Navigation Satellite System Reflectometry (GNSSR) can be used to derive information about the composition or the properties of ground surfaces, by analyzing signals emitted by GNSS satellites and reflected from the ground. If the received power is measured with linearly polarized antennas, under the condition of smooth surface, the reflected signal is proportional to the modulus of the perpendicular and parallel polarization Fresnel coefficients, which depend on the incidence angle θ, and on the dielectric constant ε of the soil. In general, ε is a complex number; for non-dispersive soils, the imaginary part of ε can be neglected, and a real value of ε is sought. We solve the real-valued problem explicitly giving formulas that can be used to determine the dielectric constant ε and we compare the analytical solution with experimental data in the case of sand soil.

A novel null steering method in a multi-mode circular microstrip patch antenna is presented in this letter. A stacked patch configuration, capable of exciting three different radiating modes, namely TM₁₁, TM₂₁, and TM₃₁, is investigated. When two or three modes are excited simultaneously, up to three nulls can be formed in the upper hemisphere, and by tuning the amplitude ratio of these modes, a continuous null steering pattern is realized. It is shown that a full hemispherical null steering of ±90° range can be achieved using the proposed method. The null steering capability with different dielectric permittivities is also presented.