The proposed antenna structure is excited for multiple operational modes by means of meandered strips. The compact planar monopole antenna is demanded enormously for handheld devices especially automatic meter reading and tablet devices. Due to Chu limit, it is extremely vital to miniaturize an antenna by balancing tradeoff between bandwidth and radiation efficiency. The designed antenna is formed by two interconnected broad monopole open slots which covers multi-bands for smart energy meter and tablet computer applications. The cost effective FR4 laminate of size 50 x 200 mm² (0.4λ x 1.6λ) is employed to match standard tablet computer communication module dimensions. The impedance bandwidth, for all excited resonant modes, is above typical requirement of 2%, and the VSWR is well below the necessary requirement of 1.5. The peak gain ranges from 0.94 dBi to 1.92 dBi. Radiation patterns along with other antenna parameters are satisfactorily meeting the demand of Wireless Energy Meter and Tablet Devices. The effects of varying dimensions of a monopole on the radiation characteristics have also been presented. The return loss and radiation patterns computed through simulations are validated through experimental measurements in an anechoic chamber environment.

The problem of impedance synthesis of two-dimensional diffraction arrays of thin linear vibrators, whose geometric centers are located at the nodes of a flat rectangular grid with double periodicity is solved analytically. The problem is formulated as follows: the complex surface impedances of the vibrators should be determined which allows to steer the diffraction radiation maximum of the array to any predefined direction. The problem is solved under following assumptions: array is excited by a polarized plane wave, and the radiation pattern (RP) of each vibrator element in the array coincides with that of an isolated radiator. The correctness of the solution is verified by simulations using the formulas for the vibrator impedances for the 5 by 5 antenna array.

This paper describes the synthesis of a bandpass filter to achieve high selectivity and rejection properties using a new class of filter functions called chained-elliptic function filters. Chained-elliptic filters have higher selectivity than Chebyshev function filters and have the property of sensitivity to manufacturing tolerance reduction in chained-function filters. The proposed design has high selectivity and reduced sensitivity, enabling easier and faster filter fabrication. The characteristic polynomials of chained-elliptic function filters are derived through chaining elliptic filtering function and extracted to form a coupling matrix of the bandpass filter. The novel transfer polynomials are given in detail, and a thorough investigation of the filter characteristics is performed. A theoretical comparison with Chebyshev and elliptic filters of the same order is performed to ascertain the demonstrated advantages of this proposed filter class. A high frequency narrow-band fourth-order chained-elliptic function waveguide filter centred at 28 GHz with a fractional bandwidth of 1.61% is fabricated to validate the proposed design concept. A good match among the measured, simulated and ideal filter responses is shown where the overall responses between measurement and simulation have a difference of approximately 2% which is within the acceptable limit. The chained-elliptic function concept will be useful in designing low-cost high-performance microwave filters with various fabrication technologies for millimetre-wave applications.

In this paper, a graphene-based reflectarray antenna using ENZ (Epsilon-Near-Zero) metamaterial at terahertz (THz) band is proposed, and the performance of its unitcell is investigated. Then, the phase distribution and radiation pattern of the antenna are examined. Benefiting from exceptional complex surface conductivity of graphene which is a novel 2-d material, the size reduction of reflectarray has been facilitated as a result of plasmonic mode propagation within the structure which in turn leads to an increase in propagation constant. Moreover, tunneling phenomenon in ENZ material, a kind of metamaterial which has a relative permittivity under 1, helps reduce the loss. Taking advantage of these outstanding features of both materials, the proposed reflectarray is designed to function at 2.5 THz and is composed of 150×150 elements with square-shape configuration. We have achieved 40 dB of gain using the combination of graphene and ENZ material in reflectarrays, and also it is the first that time they are used together in the reflectarray. This work mainly focuses on the impact of using ENZ material and graphene simultaneously which is not done before, then the results demonstrate that it has a considerable effect on increasing the reflectarray gain.

In this paper, an eight-port antenna array operating in the 2.6 GHz band (2550-2650 MHz) for a multi-input multi-output (MIMO) mobile terminal is presented. The design is composed of four pairs of compact dual-polarized slot antennas that are symmetrically placed at the corners of a mobile-phone mainboard. Each antenna pair consists of miniaturized petal-shaped slot resonators fed by two independent microstrip-feeding lines, thus facilitating radiation pattern and polarization diversity: when acting together, they facilitate multi-channel MIMO operation. The design offers good isolation, dual polarization and full radiation coverage in a smartphone sized package. A low-cost FR-4 dielectric (ε = 4.4, δ = 0.02, and h = 0.8 mm) with a dimension of 75×150 mm² is used as the PCB substrate. The characteristics of the smartphone antenna are examined using both simulations and measurements.

This work reports the application of a microwave sensor in measuring human blood glucose concentration. The main contribution of this work lies on the blood glucose profile which is collected from 69 random patients regardless of their gender, age, and haematology properties, instead of using water as the base or focusing on a single person. Hence the blood glucose profile is more realistic. Blood is extracted from the participants and dropped at the center of the dumbbells section of a microstrip defected ground structure to gather the notch frequency shifting data. On the other hand, the blood samples are measured using Omron Freestyle Glucometer to collect their associated blood glucose readings. Five predicting models have been proposed in this work. Based on the cross-validation, it is found that the blood glucose level can be correlated very well with shifted notch frequency by using a linear model. It introduces least root mean square error (RMSE) of 0.0592 and shows good correlation (R² = 0.9356) between the reading from commercial glucometer and microwave sensor in the range up to 12 mmol/L. The reliability of this microwave sensor is proven once again when the predicted blood glucose data are all falling in Zone A of Clarke Error Grid. The outcome of this work shows the capability of this microwave sensor in measuring the blood glucose level. Since this microwave sensor can be reused under a proper cleaning procedure, it improves the sustainability of conventional blood glucose testing by reducing the disposal of testing strips and cost. It is believed that this sensor will be suitable for extensive blood glucose testing conducted in the laboratory.

This letter presents an approach to design a linear phase substrate integrated waveguide (SIW) bandpass filter with good selectivity. The topology of the proposed filter is implemented based on cross and bypass coupling schemes, which simultaneously introduce a linear phase response and good selectivity, respectively. According to the proposed topology, a multilayer SIW filter is presented to realize the two kinds of couplings and preserve a compact size. Then, the defected ground structure is adopted to further improve the out-of-band rejection. To demonstrate the proposed design method, one double-layered SIW bandpass filter is fabricated and measured. Measured results show that the proposed filter has a linear phase response and good out-of-band rejection, as well as a good agreement between simulated and measured results.

A broadband microstrip-to-waveguide end-wall probe transition using a semicircular loop is proposed in this letter. The simulated 20-dB fractional bandwidth for this transition is 48.3% which could cover the whole Ka-band. Then, a compact broadband waveguide termination is developed by combination of this microstrip-to-waveguide transition and a 50 Ω microstrip termination. To reduce parasitic effects, the microstrip termination is grounded by a microstrip radial stub. The fabricated waveguide termination shows a compact size and has a return loss better than 16.6 dB from 26 to 40.8 GHz.

Recently, modern wireless communication applications are extended to call high frequency bands including millimeter waves for 5G systems. Therefore, the propagation properties of such waves in different media have attracted many researchers. In this work, the results of the S-parameters measurements of mortar with four thicknesses are obtained using a nondestructive free space measurement technique for the frequency bands from 8 GHz up to 32 GHz. The obtained results of the dielectric properties and loss factors for the prepared mortar samples are realized. The variation in both the reflection and transmission coefficients and the dielectric properties with curing time conditions of mortar structure is examined. The dielectric properties of water are realized using the proposed method to subtract the effects of water contents from the prepared mortar samples. The effects of the sample thickness and relaxation frequency are considered. The obtained measurements are compared to the simulated results based on a full wave simulation software package of CSTMWS algorithms. Finally, excellent agreements are achieved between the simulated and measured results.

In order to accelerate the speed of matrix-vector product (MVP) in iteration process for adaptive integral method (AIM), a virtual grids technique (VGT) with the multi-dimensional fast Fourier transform (FFT) is proposed. By adding some uniform virtual grids outside the original region, the indexes of nonzeros in the projection matrix are modified so as to eliminate the padding and unpadding procedures in MVP. The advantages of this method are that first it will not occupy any extra memory, and second it makes the Green's function vector compressed from (2N_x - 1)(2N_y - 1)(2N_z - 1) to 8(N_x - 1)(N_y - 1)(N_z - 1) because of its symmetrical block-Toeplitz property. Numerical results show that per iteration time could be reduced more than 30% by applying this method in comparison with the conventional AIM, without losing accuracy. In addition, the peak memory consumption could also be reduced because the intermediate vectors are eliminated.

In this paper, a novel high-order triple-mode half-mode bandpass filter using a single perturbed substrate integrated waveguide (SIW) cavity and a dual-band diplexer are presented. Circular shape metal via-holes are added in the middle of a square SIW cavity as perturbation. The perturbed TE101, TE102 and TE201 resonant modes of the SIW cubic cavity are used to design the proposed filters, which can be shifted to the desired frequency by adjusting the position and size of via-holes. The proposed method reduces the size of the filter, and the measured results indicate that the bandwidth is higher than previous literatures. The dual-band diplexer with a half-mode SIW (HMSIW) structure can be easily implemented based on the proposed BPF through a T-junction, which decreases the number of resonating elements. A triple-mode half-mode filter using a single perturbed SIW cavity with center frequency of 7.43 GHz is obtained. The designed filter and dual-band diplexer are fabricated and measured to validate the present approach.

In this work, computer-aided impedance analysis and genetic-based synthesis of a multiwall carbon nanotube impedance matching section (MWCNTIMS) are proposed. Transmission line model (TLM) of a multiwall carbon nanotube is used for the computer-aided impedance analysis. Continuous parameter genetic algorithm (CPGA) is used for the genetic-based synthesis. A simple, fast and effective impedance analysis and synthesis approach for an MWCNTIMS is presented. The results of the analysis and synthesis for different examples of MWCNTIMS are given and discussed in detail. The results show that the effect of variation of the distance from the ground plane of the outer shell is very small on the values of input resistance and input reactance. The values of input resistance and input reactance decrease while the value of inner radius or the total number of shells increases. Since the diameter increases with the increasing value of inner radius and the total number of shells, the values of input resistance and input reactance decrease with increasing diameter. While the value of nanotube length increases the values of input resistance and input reactance increase.

This paper highlights the effect of millimeter wave (MMW) radiation on biological tissue for prolonged exposure to record thermal effects. The novel method described in this article isthe exposure of millimeter wave on the tissues and study the heat effects resulting from radiation. To simulate this, a setup to uniformly irradiate a tissue of about 2.2 mm thickness is described, and 3D visualization of MMW propagation is modeled using COMSOL Multiphysics radio frequency module at frequencies around 30 GHz. Heat generation and consequent temperature rise in the three layer tissue structure is followed by analysis of temperature variation due to radiation absorption.

This paper presents a novel quintuple-mode wideband lter based on a circular Substrate Integrated Waveguide (SIW) cavity. To implement this filter, a pair of two metallic perturbation vias loaded around the diameter resonator line is used. An Elliptic Dielectric Resonator (EDR) was introduced in the middle of the cavity to shift certain resonant modes and restrain the higher-order modes. The optimal dimensions and dielectric permittivity of the EDR are investigated. A single SIW resonator filter has been designed, manufactured, and measured as an experimental example to verify the proposed design. Simulation and measurement results agree with 51.7% of fractional bandwidth at 10.1 GHz central frequency, with one transmission zero (TZ) at the lower frequency side and four TZs at the upper side.

In this article, a design of two low-profile multiple-input-multiple-output (MIMO) antenna arrays based on left-handed metamaterial (LHM) structures is proposed for multiband wireless applications. The single-element antenna is a monopole antenna fed by a microstrip transmission-line loaded with a single LHM unit cell. The LHM unit cell structure consists of a right-angled bend interdigital capacitor and dual symmetrical right-angled bend shorted stub inductors. The loaded monopole antenna was previously designed to operate in the left-handed (LH) frequency region at three negative-order resconance modes (i.e. 1.39, 1.88, and 2.35 GHz). Herein, to increase the designed antenna performance in wireless communication systems, two- and four-element MIMO antenna arrays having compact sizes with overall dimensions of 21 × 35 mm² and 35 × 35 mm², respectively, are realized. A close uniform edge-to-edge separation between antenna elements of each configuration equals only 2 mm (0.0093λ₀ at 1.39 GHz), and port isolation less than -18 dB over the entire operating bands is obtained without using extra isolation structures. Envelope correlation coefficient is evaluated, showing good field isolation. The performance of the assembled MIMO antenna arrays is verified numerically and experimentally. The given attributes make the proposed antenna arrays a suitable candidate for multiband MIMO applications.

In order to evaluate the electromagnetic environment of the 750 kV four-circuit transmission lines accurately, and design the optimal tower type and phase sequence of the four-circuit lines, the finite element method is used to analyze the distribution characteristics of power frequency electromagnetic field under the line. The excitation function method and the empirical formula method are used to calculate the radio interference and audible noise distribution under the line respectively. Electromagnetic environment parameters of various phase sequences of two tower types are analyzed to determine the optimal phase sequence of 750 kV four-circuit transmission lines. The results show that the electromagnetic environment of transmission lines is strongly influenced by different tower types and phase sequences. The magnetic flux density and radio interference of the various phase sequences of the two tower types reach the limit of code, and 43.52% and 64.81% phase sequences reach the audible noise limit conditions respectively. Electric field intensity is a main influence factor of electromagnetic environment. The optimal phase sequence layouts of the two tower types are 1661 and 1522, and the electric field intensities are 9.66 kV/m and 9.12 kV/m. The calculation method and results can be used for reference in practical engineering.

This study proposes the idea of a thermotherapy device for the treatment of human knee joint disorders by the thermal effect of microwave radiation. The device is composed of a circular array of dipole antennas operating at 2.45 GHz. A high resolution three dimensional geometric, electric, and thermal model for a human right knee is constructed. Electromagnetic simulations are performed to calculate the specific absorption rate (SAR) distribution within the tissues of the human knee using the finite difference time domain (FDTD) method. The SAR distributions are calculated for four and eight elements circular arrays. The FDTD is applied to calculate the rise in temperature within different tissues of the human knee due to the exposure to different levels of heating microwave power. The effect of the tissue thermoregulatory response on the temperature rise is investigated for each individual tissue type. Moreover, the dependence of the induced steady state rises in tissue temperatures on the absorbed SAR is studied in the case of the SAR at a point in the muscle tissue (local SAR), and the SAR averaged over 1 g (SAR_{1 g}) and over 10 g (SAR_{10 g}). The rise in temperature distribution due to radiation from the circular array of dipoles is calculated at different cross sections.

In this paper, a compact printed monopole antenna with periodic H-shaped slots for WLAN application is proposed, designed and fabricated with standard flexible printed circuit board process. By cutting four H-shaped slots in the radiation patch of the printed monopole antenna, the resonant frequency of the monopole antenna can be reduced; therefore, a compact antenna is realized. The radiator size of the antenna is 0.07λ_g×0.19λ_g, which is much smaller than that of a traditional printed monopole antenna. By utilizing electromagnetic simulation software CST, the antenna is simulated and optimized. Moreover, the performance of the proposed antenna is discussed taking into consideration the possible effects of deformations due to the flexibility of the substrate. A sample antenna is manufactured and measured to prove the predicted performance of our proposed antenna. The measured results agree well with the simulations. Hence, the proposed method in this paper is a promising candidate for the design of compact antennas.

The problem of evaluating the shielding effectiveness of a thin metallic circular disk with finite conductivity against an axially symmetric vertical magnetic dipole is addressed. First, the thin metallic disk is modeled through an appropriate boundary condition, and then, as for the perfectly conducting counterpart, the problem is reduced to a set of dual integral equations which are solved in an exact form through the application of the Galerkin method in the Hankel transform domain. A second-kind Fredholm infinite matrix-operator equation is obtained by selecting a suitable set of basis functions. A low-frequency solution is finally extracted in a closed form. Through a comparison with results obtained from a full-wave commercial software, it is shown that such a simple approximate solution is accurate up to the frequency where the surface-impedance model of the thin disk is valid.

For microwave computational imaging (MCI), the reduction of measurement matrix's coherences permits better reconstruction performance. Therefore, frequency diverse apertures (FDAs) have become a major option of antennas for MCI due to their frequency-varying radiation patterns. The frequency diversity in the patterns reduces coherences; however, the losses in practical materials and the finite sizes of apertures impose upper limits on frequency diversity. For further coherence reduction, the polarization diversity (PD) of aperture elements is as a new approach introduced in this paper. We present an electromagnetic formulation of scattering aperture elements' PD. In the formulation, the PD brings an additional degree of freedom in the generation of the measurement matrix, given the apertures being illuminated with varying polarizations. This new degree of freedom enables a potential of reducing the coherences. Two complementary electric-field-coupled (cELC) scattering apertures, which differentiate in the polarizations of elements, are fabricated for validation. A set of comparisons yielded by the near-field scanning data of these apertures shows that the PD effectively reduces coherences and improves reconstruction performance.