In this paper we focus on multi-objective optimization in electromagnetic problems with given priorities among the targets. The approach proposed in this paper is able to build a proper cost function capable to correctly implementing the design criteria and their priorities avoiding the evaluation of the Pareto front of the solutions, which is a very time consuming task required in the classic a-posteriori methods. The resulting function, named Quantized Lexicographic Weighted Sum (QLWS), can be used as cost function in a very large class of electromagnetic problems. In this paper we demonstrate its usefulness in two common situations in antenna array design: the synthesis of a sparse linear array and a sparse isophoric ring array.

This paper proposes a novel planar beam tracking antenna and brings a new prototype antenna in wireless communication systems. The proposed antenna consists of a magic-T, two antenna elements and two phase shifters. The main idea for the antenna is to adjust the phase shifter using the difference of the signals received by the two antenna elements to tilt the beam in the direction of the arrival wave. Theoretical discussion is presented to explain the concept. Both-sided MIC technology is effectively used to integrate the magic-T and the phase shifters with the antenna elements in a simple structure. A prototype antenna of the new design for E-plane beam tracking is fabricated, and the radiation pattern and return loss are measured. Simulated and experimental results of the beam direction vs. applied voltage are successfully compared, and the proposed concept is experimentally demonstrated. An antenna structure for beam tracking in H-plane is also demonstrated in this paper.

``Curve-fitting'' method is an important method to extract dielectric parameters of substrate materials from planar transmission lines. At gigahertz frequencies, effective conductivity concept is adopted to model the conductor's surface roughness effects in planar transmission lines, and differential extrapolation method is used to remove surface roughness effects. However, such a concept and method lose their accuracy at extremely high frequency such as terahertz waves. This paper details some new limitations in the terahertz regime and proposes corrections in calculating effective conductivity with rough conductor and curve-fitting method for transmission performance characterization in eliminating the effects of surface roughness. The proposed method is validated by simulation data for conductivity with parallel plate waveguide model, and the corrected method presented here can effectively extract dielectric parameters with an error less than 7% .

Metamaterial absorber (MMA), as a kind of new-style artificial absorption material, has been extensively researched and discussed. Currently, however, the research focuses mainly on the development and application of the novel structure MMA, and only little work is aimed at the physical mechanism of the MMA. In order to deeply understand the absorption mechanism, in this paper, the numerical simulation results of an MMA are given. Then, based on the reflection theory modal, the numerical simulation results are well discussed and explained in detail. It is found that the theoretical results agree well with that of the simulation, which suggests that the reflection theory modal is effective for analyzing the absorption mechanism of the MMA. The main contributions of this paper are to quantitatively discuss and explain the absorption mechanism of the MMA by using the reflection theory and thus offer a consultation in design and fabrication of the advanced MMA for engineers.

A novel structure of a near-field communication (NFC) loop antenna for mobile phones with a metal back case is proposed. The proposed structure of the metal back case itself can operate as an NFC loop antenna through the design of a simple single turn loop antenna on the top portion of the metal back case, so that the simple structure of the proposed NFC loop antenna can reduce the overall thickness of the NFC antenna for slim mobile phones. Since a sintered ferrite sheet with generally higher relative permeability (μr ≈ 200) must be used to reduce the performance deterioration of the conventional NFC loop antennas due to the eddy current in the battery pack of a mobile handset, the cost of these conventional NFC antennas is high, and they are considerably fragile. In this paper, the proposed NFC antenna is designed without the ferrite sheet and in the optimal location to ensure minimum interference from the adjacent metallic components.

A novel method for further wideband RCS reduction on metasurface (MS) is proposed in this paper. By introducing a phasor interference element to the original MS composed of two elements, RCS of the proposed MS constructed by three elements can be further remarkably decreased in broadband. The measurement procedure on scattering performances of samples is conducted in an anechoic chamber, in which the experimental results indicate that the proposed MS can achieve further 3-dB RCS reduction from 6.94GHz to 15.35GHz compared to the original MS, and the maximum further reduction reaches 24.9dB. As a result, compared with a same-size metallic plate illuminated by a normal plane wave, RCS of the proposed MS can be reduced by more than 8.5-dB from 6.68GHz to 15.38GHz with the relative bandwidth of 78.9%.

In the paper, the electromagnetic scattering (EM) from a one-dimensional (1-D) perfectly electric conducting (PEC) randomly rough sea surface with large windspeed is investigated by the iterative physical optics (IPO) algorithm. In this method the multiple coupling interactions among points on sea surface are considered. To improve computational efficiency, the local coupling technique is adopted to accelerate the iterative process. In numerical results, the EM scattering by 1-D sea surface for different polarizations is calculated and compared with that by the conventional method of moments (MOM), as well as the computing time and memory requirements. In addition, the influence of some parameters on the scattering of sea surface are investigated and discussed in detail, such as the threshold of coupling distance, iteration numbers, and windspeed.

As ultra high frequency (UHF) radio frequency identification (RFID) technology, a smart recognition technology, has been gradually spreading to various applications, and several sub-1 GHz wireless technologies are being standardized and developed. As such technologies operate at a specific frequency band (902-928 MHz industrial, scientific, and medical (ISM) bands), the impact of RF interference due to performance degradation of UHF RFID technology on the interference signal is emerging as a new obstacle. In this paper, we investigate the interference analysis and experimental results of passive UHF RFID systems in sub-1GHz wireless communications systems. By considering interference signal frequency and power, interference deployment, antenna polarization, RF system-level analysis, and experimental verification are conducted to evaluate the impact of performance degradation in the UHF RFID system on the interference signal.

A wide slot antenna with a Y shape tuning element for wireless applications (GSM 1800, WiMAX, PCS and ITM-2000) is presented. The proposed antenna is fabricated on an FR-4 substrate (tan(δ)=0.02, εr=4.3) with the thickness of 1.6 mm. On the top layer of the substrate, a 50 ohm microstrip line is fabricated which is terminated in Y shape tuning element. On ground plane, an irregular wide slot and triangular notch are etched. In addition, for performance improvement two triangular shaped parasitic slots are embedded on the ground plane. The proposed antenna is energized by the microstrip line. It exhibited the bandwidth of 127.55% from 1.15 GHz to 5.2 GHz for |S11| < -10 dB. Surface current distribution and radiation pattern at resonating frequencies 1.15, 1.25, 1.9 and 4.2 GHz are analyzed. Impact of parameters on S11 characteristic is also studied to know the behavior of the antenna.

In this paper an ultra-wide bandwidth double-layered Vivaldi antenna (DLVA) integrated in Radome housing is proposed. First the conventional Vivaldi antenna is designed with bandwidth extended from 1.8 to 6 GHz at VSWR (3:1). Then for wider bandwidth, two slots are etched in the antenna ground plane to extend the antenna bandwidth from 1.7 to 9 GHz. For more improvement in antenna bandwidth, circular slots as electromagnetic band-gap structure (EBG) are etched to further extend the antenna bandwidth from 1.45 to 10 GHz. For gain enhancement double layers of Vivaldi antenna ground plane are designed with the same feeding line to reach 29 dBi peak. High frequency structure simulator (HFSS) ANSYS is used to design to simulated all the design steps. The proposed antenna is fabricated and measured. Finally, DLVA is integrated inside the Radome to improve the antenna gain and protect the proposed antenna from environmental factors. The antenna is fabricated and tested, and a good agreement between simulated and measured results is found.

The ionospheric GPS signal delay which is a function of TEC plays a major role in the estimation positional accuracy of satellite based navigation systems and detrimental to position estimation especially in strategic applications. Ionospheric TEC is a function of geographical location (Latitude, Longitude), time, season, etc. In this paper, we propose a system theory based Grey Model (GM(1,1)) which uses past and present data for forecasting TEC (GPS signal delay). In this model, data of nine sequential days data from five stations of a GPS Aided Geo Augmented Navigation (GAGAN) system network located at different places representing different latitudes, longitudes and equatorial anomaly regions are used to forecast the 10th day TEC values of each of these stations. The performance of the model is assessed by comparing the statistical parameters such as Standard Deviation (SD) and Mean Square Deviation (MSD). The forecasted results are very encouraging. For all the considered five stations, forecasting is better for post sunset time than day time. Also, the results indicate that SD and MSD values are comparatively more for Trivandrum (near geomagnetic equator) and Ahmedabad (near the crest of the equatorial anomaly region). These results indicate that the proposed model is useful for forecasting of GPS signal delay both for civil aviation and strategic applications.

This paper presents a wide-angle polarization independent triple-band absorber based on a metamaterial structure for microwave frequency applications. The designed absorber structure is the combination of two resonators (resonator-I and resonator-II). The proposed absorber is ultra-thin in thickness (0.012λo at lowest resonance frequency and 0.027λo at highest resonance frequency). The proposed absorber structure offers three absorption bands with peak absorptivities of 99.95%, 95.32% and 99.47% at 4.48, 5.34 and 10.43 GHz, respectively. Additionally, it also offers the full width at half maximum (FWHM) bandwidth of 167.2 MHz (4.40 - 4.56 GHz), 178.1 MHz (5.25 - 5.43 GHz) and 393.8 MHz (10.24 - 10.63 GHz), respectively. The metamaterial property of the designed absorber structure has been discussed by using dispersion diagram plot. The designed absorber structure exhibits wide-angle absorption at various oblique incidence angle for both TM and TE polarizations. The absorption mechanism of the designed absorber structure has been analyzed through electric field and surface current distribution plots. The input impedance of the designed absorber (375.67 Ω at 4.48 GHz and 346.73 Ω at 10.43 GHz), nearly matches the free space impedance. The proposed absorber structure is fabricated and measured. Simulated and measured results are in good agreement with each other.

In this paper we present an approach to reduce the cavity resonant edge effects in printed circuit boards (PCBs) and semiconductor packages. Power supply noise, in the form of fast changing currents (di/dt), traverses the power-return paths of PCBs and semiconductor packages using power vias. The cavity effects produce considerable level of noise along the edges of PCB and integrated circuit (IC) package power planes due to signal coupling between vias and reflection from PCB edges with transient currents. The cavity effects also amplify the electromagnetic radiation from PCB edges, which are major sources of EMI/EMC problems in electronic devices. By using absorbing material and decoupling capacitors (de-caps) on power distribution networks (PDNs), we observe considerable mitigation in impedance noise, signal noise and electromagnetic interference/compatibility (EMI/EMC) issues caused by the cavity effects. In particular, simulation results show notable reduction of upper peak (anti-resonant) impedance noise and reduction in radiated emissions by as much as 20 dB. This article presents a comparative case-study using various models (Section 3) and report on their effectiveness to reduce the cavity effects. The models are listed as (1) "Original" model, (2) "Absorbing material along the edge" model, (3) "MURATA based De-cap only" model and (4) "Absorbing material along the edge w/ De-cap" model. The used capacitance ranges between 0.1 μF and 22 μF. The ESR and ESL range between 2 mOhm-20 mOhm and 238 pH-368 pH, respectively. Conclusively, we learn by adding absorbing material along the PCB edges with a few decoupling capacitors. The PDN impedance noise is improved, and EMI issues in PCBs and semiconductor packages suppress the cavity effects.

In this letter, two different types of band-notch UWB-MIMO antennas are presented. the filtering effect can be achieved by integrating slot resonators to a UWB antenna. Both of the proposed antennas have very compact size and are smaller than most of the other band-notch UWB-MIMO antennas. The ultra-wideband is achieved by etching stepped slots on the ground. The band-notch characteristic can greatly reduce the potential interference between the UWB and WIMAX/WLAN system. Our proposed antennas can also possess a wide bandwidth from 3.3 GHz to 11 GHz with |S11| < -10 dB. Some effective measures have been taken and illustrated to reduce the isolation. Measurements demonstrate that the mutual coupling between the antenna elements is good enough for a MIMO system. Their stable radiation patterns are simulated, designed and measured successfully. The good performance and compact size make the antennas good candidates for UWB applications.

A Ku-band bandpass frequency selective surface (FSS) with high selectivity and miniaturization is proposed in this paper. We use two metallic strips and one slot to design the frequency selective surface structure which contains both electrical and magnetic couplings. A metallic via is introduced in the FSS element for miniaturization. With the via inserted at the end of the metallic strip, the FSS unit size is reduced to half compared to that without via inserted. To investigate the operating principle of the slot-coupled FSS, an equivalent-circuit model is given and analysed using the odd- and even-mode method. The constructed out-of-phase signal path causes two transmission zeros (TZs) near the skirts of the narrow pass band, thereby enhancing the selectivity. A prototype of the proposed FSS operating at 16GHz is fabricated and measured. The measured results agree well with the full-wave and circuit simulation results, thus verifying the FSS design.

Numerical dispersion is the main error source of the finite-difference time-domain (FDTD) method. In this paper, an optimized piecewise linear recursive convolution (PLRC) FDTD method with low numerical dispersion is presented first time for electromagnetic-wave propagation in anisotropic magnetized plasma. An optimized difference item which can achieve better approximation to the partial differential operator from transform domain is induced in this algorithm which decreases numerical dispersion. The item can be regarded as adding a correcting coefficient to conventional central difference format. And it is easy for programming and implementation. Numerical examples of electromagnetic pulse wave propagating in plasma demonstrate that the proposed optimized PLRC-FDTD method can not only reduce the numerical dispersion, but also improve precision, saving computational memory and computational time compared with the conventional PLRC-FDTD method. Same accuracy can be achieved when the spatial mesh size for the optimized PLRC-FDTD method is 2 times coarser as that in the conventional PLRC-FDTD method, corresponding to the computation time consumed in the optimized method is only 1/2 as that in the conventional one.

This article contains derivation of propagation factors and Fourier series for harmonically time varying, traveling electromagnetic fields in a plate and a laminate with rectangular cross sections, isotropic materials and infinite length. Different and quite general fields are taken into account on all boundaries. Choices of boundary conditions and continuity conditions are discussed. Certain combinations of types of boundary conditions make the derivation possible for a laminate. Comparisons are made between results of Fourier series and finite element calculations.

5G new spectrum radio access should support data rates exceeding 10 Gbps in most of its applications. An Ultra Wide Band (UWB) Ultra-high data rate Wilkinson power divider up to 6.9 Gbps for 5G new spectrum and CAR applications is presented in this paper. The step by step design procedure, optimization and implementation of this Wilkinson power divider in 20-30 GHz are completely done to achieve the optimum performance. The final fabrication results show the average of -14 dB of input matching, -20 dB of isolation of isolated Ports, -4.2 dB of coupling in output ports (considering 2 SMA connectors and transitions in each path), and linear phase variation of outputs in the whole bandwidth of 20-30 GHz. During the design procedure, a new and very useful coaxial to microstrip transition in K-band is designed, analyzed, developed and fabricated to achieve the best results. Also a complete study of time domain analysis with ultra-high data rate signal is presented to minimize the total reflection coefficient caused by the partial reflections from several discontinuities. To complete and validate the final fabricated Wilkinson power divider in ultra-high data rate application in 5G new spectrum, the extracted results of UWB-IR impulse radio with modulated ultra-high data rate signal up to 7 Gbps and in 20-30 GHz bandwidth is completely done. The measured results show that this fabricated Wilkinson power divider can handle a periodic modulated signal up to 7 Gbps which are valuable results for many applications in 5G and CAR systems.

In this paper, a compact MIMO antenna with improved isolation is proposed. Elliptical slots and an SRR like structure are employed to improve the isolation. The proposed MIMO antenna structure consists of two semi-circular radiators attached to a rectangular monopole which are mirror images of each other with edge to edge spacing of 0.125 λ₀, where λ₀ is the free space wavelength corresponding to the lowest operating frequency of the structure. Two square steps are added to the above semi-circular monopole to increase the effective path length to cover the lower frequencies. Thereafter, a semi-annular ring slot is introduced, and square steps above the semi-circular monopole are modified to curved steps to further improve the impedance bandwidth of the antenna. The mutual coupling over the wideband is reduced by placing elliptical slots and SRR like structure in the ground plane. The proposed antenna has impedance bandwidth of 2.1- 12 GHz with |S₂₁| < -20 dB over the entire frequency range. The antenna is designed and fabricated on an FR-4 substrate having overall dimensions of 38 mm × 33.4 mm× 1.6 mm. The measured results show a good correlation with the simulated ones. The envelope correlation coefficient (ECC) of the antenna is less than 0.02 over the entire band. The proposed MIMO antenna is an appropriate candidate for 3G, 4G, Wi-Fi, Bluetooth and UWB applications.

The mutual coupling between very low frequency (VLF) antenna elements is an important factor affecting the radiation performance of umbrella antenna arrays. This study evaluates the factors influencing the mutual coupling between the elements of an umbrella antenna array. We develop a mutual coupling analysis method for calculating the input impedances of a VLF antenna based on the impedance effect of mutual coupling. The radiation resistance of the VLF umbrella antenna can be obtained using numeric integral from Method of Moments (MoM) solution. Using the FEKO simulation software, a model of a trideco-tower umbrella antenna array is established. The electrical parameters of the VLF umbrella antenna array on inhomogeneous ground are calculated for both single and dual feeding modes. The impedance characteristics of the umbrella antenna arrays are also simulated for different array inter-element spacings on homogeneous ground. Representative numerical results are reported and discussed to assess the mutual coupling effect of the proposed method in comparison with full-wave simulations.