An efficient nature inspired algorithm based on particle swarm optimization (PSO) is presented in this paper for the optimal design of planar multi-layered radomes for multiband applications. Material layer sequence and thickness profile are the two critical factors determining the position of pass bands in the frequency range of operation as well as the transmission performance in those bands. These design aspects have to be appropriately optimized to achieve the desired performance, and it becomes a daunting task for radome designers when a comparatively large database of suitable materials is available in the solution space. Even though commercially available software packages provide options (like particle swarm optimization (PSO), genetic algorithm (GA) etc.) for the optimization of thickness profile, they do not have the functionality for optimizing the position of a specific material inside the multi-layered radome wall configuration. In this regard, the proposed PSO-based algorithm automatically chooses suitable materials from the predefined database and optimizes the thickness for each layer, in order to achieve superior transmission in user defined pass bands. Furthermore, the superiority of the indigenously developed algorithm over the optimization techniques available in full wave simulation software (FEKO) w.r.t. accuracy and computational efficiency is also established using suitable case studies and validations. Although PSO has been used in the context of radomes, its application for the simultaneous optimization of material layer sequence and thickness profile of multi-layered radomes is not reported in literature to the best of our knowledge.

There is complex electromagnetic interference in the substation. In order to improve detection accuracy, a digital lock-in amplifier is used in the detection of the grounding grid. This paper introduces the principle of non-destructive testing of grounding grid based on electromagnetic method. Firstly, the distribution characteristics of surface magnetic induction intensity at different frequencies are obtained by CDEGS simulation. At the same time, it describes the principle and structure of an orthogonal vector type digital lock-in amplifier in detail. In order to realize the high-precision grounding grid detection system, the hardware circuit of the digital lock-in amplifier is designed by FPGA and analog-to-digital converter. The digital lock-in amplifier algorithm is implemented in the FPGA. Finally, the digital lock-in amplifier is tested. The test results show that when the signal-to-noise ratio of the signal to be tested is -20 db, the signal amplitude measurement error is less than 3%. The designed digital lock-in amplifier is applied to the actual grounding grid detection, and the topology and corrosion of the grounding network can be detected. Therefore, the digital lock-in amplifier can be effectively applied to non-destructive testing of grounding grid.

The design of a wideband antenna using truncated corners partial ground plane loaded with L-shaped stubs and inverted T-shaped slots has been presented in this manuscript. The different concepts and structures related to antenna designing have been employed to attain the optimized model of antenna. L-shaped stubs and inverted T-shaped slots incised in the structure of antenna improve the impedance matching and bandwidth of proposed antenna. The fed 50Ω microstrip line has been applied to the proposed structure for attaining distinct performance parameters like reflection coefficient, gain and radiation pattern. The distinct structures of proposed antenna have been juxtaposed, and it is found that the structure with L-shaped stubs and inverted T-shaped slots shows improved antenna performance parameters. The designed antenna exhibits the bandwidth of 133.04% (3.14-15.62 GHz) and 16.96% (18.56-2.0 GHz) with improved reflection coefficient and gain. The proposed antenna has also been fabricated and tested for validation of simulated and measured results, and found in good agreement with each other. The design of proposed antenna is carved on a low cost thick substrate with compact electrical size of 0.566λ x 0.452λ x 0.0301λ mm³ at 5.45 GHz frequency and can be used for different wireless applications in the frequency range 3.14-15.62 GHz and 18.56-22.0 GHz.

A novel hybrid resonant structure is proposed to decouple a dual-band microstrip antenna array. The decoupling structure is composed of two H-shaped strips, and the lower and upper ones respectively collaborate with an X-shaped slot to reduce mutual coupling at 4.5 GHz and 5.5 GHz. Two sub-patches of different sizes share a connection feeding line to construct the dual-band array element, which is arranged along H-plane with the edge-to-edge spacing 0.15 λ_l and 0.24λ_h (λ_l and λ_h are the free-space wavelengths of 4.5 GHz and 5.5 GHz, respectively). Simulated and measured results indicate that through loading the hybrid resonant structure, 31.6dB and 24.0dB reductions of mutual coupling at two frequencies are obtained, while the levels of coupling coefficients are both below -30 dB in two operating bands. Moreover, the modified radiation patterns, improved diversity metrics and weakened coupled current distributions further verify its superior decoupling capability. The proposed decoupling structure reveals its promise in being employed in communication system and multielement linearly antenna arrays.

The coaxiality of the transmitter and receiver has a significant impact on the efficiency in a wireless power transfer system. In order to keep high system efficiency, a novel coil structure is studied in this paper. Several plane coils are crossed to make up a three-dimensional coil structure in the transmitter, which will make sure the system in the state of strong magnetic field coupling. In the theory part, the magnetic field equation of different relationships between transmitter and receiver is deducted in detail. In the simulation part, the performance of the three-dimensional coil structure has been studied. The simulation results show that the new coil structure can generate a rotating magnetic field, and the rotating magnetic field will keep the system in the state of the strong magnetic field coupling in the simulation model. In the experimental part, the three-dimensional coil structure has been compared to a plane coil structure. The experimental results show that the efficiency of the three-dimensional coil structure is increased above 10% in the misalignment situation. The simulated and experimental results show that the new three-dimensional coil structure has a better performance in the misalignment situation than the plane coil structure in a wireless power transfer system.

An elliptical array, composed of 10 uniform elliptical apertures as the radiating elements, is presented. Assume that each aperture in an electric conducting plane spreads on the elliptic orbit and is fed by the uniform plane wave in order to obtain a low SLL array pattern with high directivity, the elliptic orbit eccentricity and the angular position of each array element are stimulated. The applied parameters are determined by an elaborate optimization procedure. The utilized procedure, comprising the geometric computational technique (GCT), and angular positions excitation (APE) is stated in detail, respectively to determine a satisfactory eccentricity and the angular position of each element.

In this manuscript, the thermal effect on a lumped element balanced dual-band band-stop filter (BSF) has been discussed in detail for the first time. The response of a novel filter should maintain consistency over a wide range of temperature. Although any microwave filter in general is designed for room temperature condition, the filter is employed for applications where the operating temperature constantly changes. Therefore, it is necessary to check the reliability of the filter response within a specific temperature range based on its application. Modern simulation software helps to make an initial assumption about the filter performance at different thermal conditions before its lab testing or actual application. Here, a quantitative analysis has been provided to show how change in temperature contributes to the change in each component value of a lumped element filter. This analysis is followed by a simulation to show that a balanced lumped element filter exhibits lower loss than its single-ended counterpart. Also, as the temperature varies, the balanced design demonstrates less deviation in the loss value than a two-port design. Next, a balanced dual-band BSF prototype with center frequencies 1.151GHz and 1.366GHz (25℃)is characterized with a 4-port network analyzer under different temperature conditions. The experimental results exhibit a good match with the simulation results. For a variation of 80℃ in temperature, the maximum deviation obtained for the filter center frequency, absolute bandwidth (ABW) and insertion loss (Sdd21) are 5MHz, 2.8MHz and 2dB, respectively.

Quadrature feeding is an essential in magnetic resonance imaging radio frequency (MRI-RF) coils, to improve the homogeneity of the magnetic field of surface coil, the signal to noise ratio (SNR) of the image by a factor of √2 , and to create a circularly polarized magnetic field inside the volume coil. The quadrature feeding is incorporated, using hybrid coupler. However, at 63.87MHz the Larmor frequency of hydrogen proton, corresponding to 1.5 Tesla, the size of the hybrid coupler and other microwave circuits become large. So, to minimize its physical size, a coaxial cable transmission line with lumped capacitive loading has been proposed. The size of the proposed hybrid coupler is reduced by 68%, as compared to the conventional hybrid coupler. The proposed device is then fabricated as a both rigid and flexible structure, which provides isolation (S₄₁) of around 19 dB and a 900phase difference between coupled and the through ports. Both structures provide return loss S₁₁ > -15 dB and coupling at output ports S₂₁, S₃₁ around 3 dB.

Microwave testing is an area of research where material characterization is done using interrogating microwaves over a frequency band, and this technique can provide excellent diagnostic engineering, geophysical prospecting. Every material has a unique set of electrical characteristics that are dependent on its dielectric properties. Accurate measurements of these properties can provide valuable information about the material. This work presents a non-destructive technique for the detection of adulterants in food using the proposed RF sensor. The proposed RF sensor is operational at C-band with its resonant frequency at 5.7 GHz. The structure is designed using Ansys HFSS, and a predicted model of the proposed sensor is developed and fabricated. Some common food samples are tested using the fabricated sensor, and a shift in resonant frequency is obtained, which indicates the rate of adulteration. From the obtained results, a general conclusion is obtained on the dependency of the rate of adulteration and permittivity of the food sample. A precise correlation of permittivity of common food samples and its resonant frequency is obtained. The predicted model and the experimental results harmonize, which indicates that the model is proficient in real time testing.

We deploy the general momentum space theory developed in Part I in order to explore nonlocal radiating systems utilizing isotropic spatially-dispersive metamaterials. The frequency-dependent angular radiation power density is derived for both transverse and longitudinal external sources, providing detailed expressions for some special but important cases like time-harmonic- and rectangular-pulse-excited small dipoles embedded into such isotropic metamaterial domains. The fundamental properties of dispersion and radiation functions for some of these domains are developed in examples illustrating the features in nonlocal radiation phenomena, including differences in bandwidth and directivity performance, novel virtual array effects, and others. In particular, we show that by a proper combination of transverse and longitudinal modes, it is possible to attain perfect isotropic radiators in domains excited by small sinusoidal dipoles. The directivity of a nonlocal small antenna is also shown to increase by possibly four times its value in conventional local domains if certain design conditions are met.

In this paper, a compact modified hexagonal spiral resonator-based tri-band patch antenna with an octagonal slot is presented for Wi-Fi/WLAN applications. The proposed antenna is designed on a low-cost FR4 substrate with a dielectric constant of ε_r=4.4 and loss tangent δ=0.02. The tri-band operations have been achieved by the a Modified Hexagonal Complementary Spiral Resonator (MHCSR) and an Octagonal slot. The loading of the MHCSR at the bottom of the substrate is to cover the 900MHz (IEEE 802.11ah) band, and an Octagonal slot on top of the 5 GHz (IEEE 802.11a/h/j/n/ac/ax) rectangle patch is to cover the 2.4 GHz (IEEE 802.11b/g/n/ax)band. The prototype of the proposed antenna is fabricated and tested to validate the simulation results. The measured impedance bandwidth is 105 MHz at 900 MHz, 160 MHz at 2.4 GHz, 18 0MHz at 5 GHz. The designed antenna has a compact size with overall dimensions of 0.054λ₀ x 0.066 λ₀ x 0.0048 λ₀ (18 x 22 x 1.6 mm³). The 82.2% reduction in size has been accomplished as compared to a conventional patch antenna at 900MHz (lower resonance frequency). The waveguide setup method has been used to validate a negative permittivity property of the MHCSR. The parametric analysis of the proposed antenna had been carried out using the Ansoft HFSS19 software.

This paper focuses on an efficient antenna selection strategy for a distributed massive MIMO system. The objective of the proposed algorithm is to attain ergodic achievable rate as much as possible with antenna selection in a constrained capacity limited system. In this proposed work, the initial selection of antenna set is based on channel amplitude and correlation which then follows an iterative approach in order to select the best subset of transmit antenna elements from the overall antenna set. The proposed scheme significantly outperforms, in terms of ergodic rate with low complexity, the prevailing transmit antenna selection methods. Simulation results show that the performance of the proposed antenna selection method is close to select all transmission with a minimum throughput loss. Thus the proposed method is best suited for a large scale distributed Massive MIMO system without degradation in system performance and is of low computational complexity.

A new wideband 3-dB tandem coupler is presented that has wide bandwidth using four 90° short stubs. The proposed tandem coupler does not require a higher transmission line impedance or a narrower coupling gap than conventional couplers. Measurements of the fabricated tandem coupler operated at a center frequency of f₀ = 1 GHz are presented as verification of the design concept. The fractional bandwidth (FBW) at which the return loss is suppressed to a level better than 15 dB was 71%. Theoretical calculations and measurements of the tandem coupler were in good agreement

This article reports a very efficient Frequency Selective Surface (FSS) with Convoluted Square Loop (CSL) shape is designed for applications in the X-band. They are designed on the surfaces of an FR-4 substrate. Frequency selective surface (FSS) is a combination of a periodic structure designed to selectively absorb, reflect, and transmit the electromagnetic (EM) waves. FR-4 material provides durability and flexibility. A convoluted square loop structure reduces the size of the unit cell, and it also has a better stability with good gain. So, a CSL patch with a CSL FSS array with a slot on dual FR4 substrates is introduced for the improvement in overall gain and bandwidth. As per the design parameters, a structure is designed at 10GHz. This structure is designed with ANSYS HFSS. The proposed antenna structure has a return loss of -36.424 db, and VSWR value is 1.0307. The measurement results show a gain improvement of 6.266db and bandwidth of 5.882 db.

Nonlocal radiating systems are new functional structures composed of externally applied currents radiating in nonlocal material domains, for example hot plasma, optically active media, or nanoengineered spatially dispersive metamaterials. We here develope the requisite mathematical foundations of the subject needed for investigating how such new generation of radiating systems may be analyzed at a very general level (Part I), while radiation pattern constructions for applications are provided in Part II. A key feature in our approach is the adoption of a fully-fledged momentum space perspective, where the spacetime Fourier transform method is exploited to derive, analyze, and understand how externally-controlled currents embedded into nonlocal media radiate. In particular, we avoid working in the spatio-temporal domain popular in conventional local radiation theory. Instead, we focus on the basic but nontrivial problem of infinite generic (anisotropic or isotropic) homogeneous nonlocal domain excited by an external source and investigate this structure in depth by deriving the dyadic Green's functions of nonlocal media in momentum space. Afterwords, the radiated energy in the far-zone is estimated directly in the spectral domain using a generalized momentum space energy density concept after the use of a suitable power theorem. The derived expressions of the radiation power pattern of the source can be computed analytically provided that the medium dielectric functions and the dispersion relation data of the nonlocal metamaterial are available. Detailed examples and applications of the theory and its algorithm are given in Part II of the present paper.

A complete energy harvesting system via Radio Frequency (RF) is designed in a broadcast station where multiple frequency sources are readily available. These frequency sources are the Intermediate Frequency (IF), 70 MHz, Wi-Fi frequency band, 2.4 GHz, and the Ku-band frequency, 13 GHz. The RF source via the Wi-Fi band (2.4GHz) is harvested via a microstrip patch antenna designed with its matching network. The harvested RF energy is transformed into usable DC power via a 8-stage Villard voltage doubler circuit. The DC power is managed by a power management system handled by the BQ25570 circuit which gives a regulated output of 3V, powers up a low power motion sensor and charges a battery at the same time. This system comes with a backup source which is the battery and able to take over the system in case the incoming RF signal fails. The RF energy harvested from the IF 70 MHz and Ku-band at 13 GHz is derived from coupler outputs which are available in broadcast stations, transmission lines, etc. Both these RF signals are converted to DC signals via a 5-stage Villard voltage doubler circuit with different matching networks. The DC power is managed by a power mux via the TPS2122 which selects the highest available power. Over the years, no works on RF harvesting have focused on smart phone charging as its application, due to the limitation in power availability. This work strives to provide enough power to charge phones and effectively gives a 5V output to charge smart phones with a charging current of 0.5A which is similar to a USB charging port.

Aiming at the problem of look direction error in the desired signal, a novel robust adaptive beamforming method based on covariance matrix reconstruction is proposed. Firstly, the Sparse Bayesian Learning (SBL) is performed to acquire the true signal direction and the spatial spectrum simultaneously. Secondly, the SBL spatial spectrum is used to reconstruct the interference-plus-noise covariance matrix. Compared with other reconstruction algorithms, this approach can realize the position estimation without any optimization procedures. Theoretical analysis, simulation results and water pool experiments demonstrate the effectiveness and robustness of the propose algorithm.

In this manuscript, a porous one-dimensional Photonic Crystal (1D-PhC) based sensor is designed for bio-chemical sensing application (i.e. hemoglobin concentration). The alternate layers of silicon are considered for design optimization, where, the porosity is introduced to obtain the desired index contrast value. The sensing capability of the proposed design is enhanced by modifying the dispersion property of the structure. For this, a defect middle layer is deliberately introduced. The number of layers, defect layer optical thickness and porosity values are optimized to confine a defect mode of desired wavelength. Finally, the detailed analysis of proposed structure is carried out. This provides the average sensitivity of around 323nm/RIU (0.05nm/(g/L) along with considerably higher FOM of 517RIU^-1.

On the basis of serious electromagnetic interference (EMI) produced by power electronic equipment,coupling capacitance existing between transistor and transistor is considered as the main factor disturbing differential-mode(DM) loop. Calculation model of coupling capacitance is established by using FEM (Finite Element Method)and Moment method, and computing method is also derived.EMI improvement method for converter system is proposed by controlling the coupling capacitance impedance. Experimental results show that changing the placement distance and position of the transistor can reduce the conducted interference.

The sensitivity of dual-polarized Sentinel-1 backscatter towards biophysical parameters (height and biomass) of wheat and mustard crop was investigated. The plant height and biomass observations categorized into three groups, were useful in understanding the sensitivity across a particular biomass and height range whose significance was determined using a statistical measure (student's t-test). The crop parameters were retrieved only for the C-band sensitive biomass (< 5 Kg m^-2) and height (< 160 cm for mustard and < 80 cm for wheat) range considering the saturation of signals at advanced crop stages and based on the detailed investigation. The sensitivity towards the mustard plant height becomes very weak as the crop proceeds to a height > 190 cm. A low RMSE (11.50 cm) was observed when the retrieval was done for height < 160 cm. The cross-polarized responses were more sensitive to crop biomass than co-polarized responses mainly due to the dominant depolarization of the transmitted power. An early saturation was found at co-polarized VV (4 Kg m^-2) as compared to cross-polarized VH (6 Kg m^-2) particularly for planophiles like mustard and little later in the case of erectophile such as wheat. The backscatter response was found to be sensitive at early crop stages for both the crop geometry, and hence retrieval of biophysical parameters at these stages can yield better accuracy than the overall retrieval. The retrieval of wheat height resulted in a low RMSE of 9.25 cm when the retrieval was carried out for crop height < 80 cm. Retrieval was attempted using the simplistic logarithmic model which can find ways in the operational application using wide swath dual-polarized datasets.