In this paper, a novel compact ring resonator based bandpass filter with a second harmonic rejection capability is proposed. The proposed bandpass filter uses a stepped-impedance open stubs and a stepped-impedance ring resonator at feeding lines. Stepped-impedance open stubs are used to obtain a better rejection level in the second harmonic-frequency band. Ring resonator's radius is calculated by examining and solving the eigenvalue equation of the ring resonator. Firstly, Sierpinski second order curve is used to achieve size reduction of about 66 % and 71 % compared to conventional microstrip ring bandpass filter inner and outer areas, respectively. Sierpinski curve is chosen because of its symmetry and its suitability for orthogonal feeding lines and open stubs incorporation without using any additional space. Referring to resonant rejection value, the proposed first Sierpinski structure -15 dB simulated fractional bandwidth is 5.6 % at 1.505 GHz and with rejection of -0.16 dB. Transmission zeros at 2.25 GHz and 3.78 GHz are obtained. Secondly, stepped-impedance open stubs are added to the resonator ports to add another transmission zero at 3.84 GHz. At 2.9 GHz, second harmonic band, the proposed structure achieves rejection of - 6.7 dB instead of -1.7 dB for the conventional one. The proposed structure -15 dB simulated fractional bandwidth is 3 % at 1.42 GHz. Innovation is achieved by the simplicity of inserting the transmission zeros, controlling zeros rejection values, incorporating stubs and orthogonal feeding lines in the same resonator area and reasonable power capability of the proposed structure. The proposed bandpass filter's prototype is fabricated using FR4 material, and a good agreement is found between simulated and measured results for return loss and rejection values. The proposed structure is very suitable for L-band applications.

A circular slotted elliptical patch antenna with an elliptical notch in ground for L-band and S-band application is presented. The proposed antenna consists of an elliptical patch with a circular notch on the top layer of a substrate, and a wide elliptical slot and an elliptical notch with two symmetrical slots on the bottom layer of the same substrate. The proposed antenna was fabricated on an FR-4 substrate (tan(δ) = 0.02, ε_r = 4.3) with the thickness of 1.6 mm, and it was excited by coaxial feed joined with microstrip line through via. The proposed antenna exhibited the bandwidth of 110.28% from 1.2 GHz to 4.15 GHz for |S₁₁|. Surface current distribution and radiation pattern at resonating frequencies 1.71, 2.28, 3.03 and 3.84 GHz were analyzed. Evolution of the antenna and effect of parameters were also studied to know the behavior of the antenna.

In this paper, a novel M-shaped UWB Vivaldi array antenna is presented. First of all, a simple M-shaped UWB Vivaldi antenna is designed, and its properties of return loss, radiation pattern, VSWR, gain, etc. are analyzed. An array of M-shaped UWB antenna is simulated and designed after the successful implementation of the simple UWB Vivaldi antenna. The designed antenna has operating frequency from 3.25 GHz to 8.85 GHz covering 5.6 GHz bandwidth. The antenna has flat gain over entire frequency range. The proposed antenna is fabricated on a commercially available FR-4 substrate having relative permittivity of 4.4 and height of 1 mm. The proposed antenna has wide band and good flat gain over entire frequency range. The proposed antenna can be used in next generation wireless communication because of its efficiency, gain and wide bandwidth.

We investigate thermal noise mechanisms and present analytical expressions of the noise power spectral density at high frequencies (HF) in Silicon-on-insulator (SOI) MOSFETs. The developed HF noise model of RF T-gate body contact (TB) SOI MOSFET for 0.13-μm SOI CMOS technology accounts for the mechanisms of 1) channel thermal noise; 2) induced gate noise; 3) substrate resistance noise and 4) gate resistance thermal noise. The extraction method of modeling parameter utilized by Y-parameter analysis on the proposed small-signal equivalent circuit is demonstrated in this paper. Excellent agreement between simulated and measured noise data is obtained at different temperatures.

Artificial magnetic conductor (AMC) is a periodic structure with in-phase reflection, which can be used in dual-polarization dipole antenna to reduce profile height. In this study, a low-profile dual-polarized dipole antenna with an AMC reflector is proposed by improving the AMC structure. The antenna consists of a pair of orthogonal planar dipoles with U-shaped slots, two T-shaped feeding lines, and an AMC reflector. The overall height is 0.132λ_{2.2 GHz}. Experimental results show that the proposed antenna has a wider bandwidth than other antennas of the same type. The impedance bandwidth of this antenna is 52.3% (1.65 GHz to 2.81 GHz), and the proposed antenna also has the advantages of low profile, high port isolation (<-30 dB), and low cross polarization (<-27 dB). These features can meet the current needs of the telecommunications industry.

In this communication, a dual-sense dual-polarized hybrid rectangular dielectric resonator antenna (RDRA) is explored. Two leading aims of the present article include: (i) to obtain dual-polarization characteristics i.e. the combination of linear and circular polarizations; (ii) to achieve quad-band features by using the concept of hybrid antenna. Modified printed line is used to excite dual radiating modes in RDRA i.e. TE^x_δ11 and TE^y_1δ1. In order to authenticate the proposed radiator, archetype of the proposed antenna is fabricated and tested. Good accord is established between measured and simulated outcomes. The proposed radiator is operated over four different frequency bands i.e. 1.81 GHz-2.06 GHz, 2.37 GHz --2.7 GHz, 3.35 GHz -- 4.4 GHz, and 4.62 GHz -- 5.62 GHz. Left Hand Circularly Polarized (LHCP) and Right Hand Circularly Polarized (RHCP) waves are obtained form 4.1-4.39 GHz and 4.78-5.2 GHz respectively. All these properties of the proposed radiator make it appropriate for 3G/WLAN/WiMAX applications.

The paper presents the application of a hybrid neuro-fuzzy model for the analysis and synthesis of a square multiband Sierpinski carpet fractal antenna. For the analysis model, the antenna geometrical parameters were taken as the input, and the resonant frequencies were obtained as the output while for the synthesis model, the resonant frequencies were taken as the input, and geometrical parameters were obtained as the output. Also, a model was trained to obtain the return loss characteristics for the given set of geometrical parameters. The developed model was validated by comparing the resonant frequencies and radiation patterns of the simulated and fabricated antennas.

Grounding grid is responsible for driving lightning and short circuit currents into ground. Faults in substation grounding grid can lead to significant rise in surface potential and ultimately loss to power system and operators. This paper proposes a novel technique based on derivative method to diagnose breakpoints in grounding grid. Derivative of surface magnetic flux density on circle results in peak at conductor's location. Once a conductor is broken the flow of current and surface magnetic field ceases, which is recognized by the absence of peak at corresponding conductor's location. The use of circle even enables this method for diagnosing diagonal branch. Furthermore, the method is analyzed for soil of different resistivities and monolayer and multilayer soils. Simulation results show that the proposed method is feasible for breakpoint diagnosis of grounding grid without excavation.

A highly efficient Doherty power amplifier (DPA) using shunted reactive load is designed to achieve wideband operation. For enhanced back-off efficiency over the whole bandwidth, a modified load modulation network (LMN), which employs a shunted reactive load at the combining point, was firstly designed to enlarge the effective load impedance of the carrier amplifier at low and high frequencies. Then, the two-point matching approach was employed to design the carrier and peaking output matching networks, which can eliminate the use of offset lines and simplify the LMN. Measurement results show that the designed DPA can deliver an efficiency of 48%-61% at 6 dB back-off power over the frequency band of 2.2-2.9 GHz. For a 20 MHz LTE modulated signal, an average efficiency of higher than 55% can be achieved at an average output power of 37 dBm, while the adjacent channel leakage ratio is below -49 dBc after linearization.

A broadband circularly polarized cross-shaped slot antenna with a parasitic cross-shaped patch and an improved feedline is proposed for wireless applications between 3-6 GHz. In order to achieve a wide axial ratio bandwidth that is totally enclosed within a wide impedance bandwidth, a wide cross slot in the ground plane and an L-shaped strip attached to the lower section of the feedline are employed. This design presents a technique for achieving an axial ratio (AR) bandwidth for a single fed antenna that is wider than most of the single fed slot antennas that currently exist. The proposed antenna with a compact size of 30 mm × 30 mm × 1.6 mm is fabricated and measured. A measured broadside 3 dB axial ratio bandwidth of 68.7% (3.1-6.35 GHz) within a measured impedance bandwidth of 84.1% (2.61-6.4 GHz) for S₁₁ < -10 dB is obtained. A measured peak gain of 3.8 dBi is obtained within the axial ratio bandwidth. The obtained results show that the antenna can be used for wireless devices that operate in the 3.3-3.8 GHz and 5.15-5.35/5.725-5.825 GHz (specified by IEEE 802.11a) bands for wireless standard technologies.

A novel rat-race coupler with wide adjustable range of power-dividing ratio and uncrossed input/output ports is presented by using coupling adjustable trans-directional (TRD) coupled lines, parallel coupled lines and a 180° phase shifting line. Wide adjustable range of power-dividing ratios is accomplished by varying the coupling of the TRD coupled lines. Moreover, with the combination of the TRD coupled lines and parallel coupled lines, the input and output ports of the rat-race coupler are uncrossed. The structure of the proposed rat-race coupler is analyzed, and the design equations are derived. As an example to validate the feature of the proposed rat-race coupler, a prototype operating at 1.6 GHz is devised, fabricated and measured. The measured results show that the designed coupler has a wide adjustable range (-7 ~ 15 dB) of power dividing ratio with a controlled voltage range of 3.5 to 13.5 V. 

This work proposes a radio-frequency interference (RFI) noise suppression filter with low noise generation for a power trace. This is based on a quarter-wavelength open-stub resonator (QWOSR) in a multilayered high-speed digital PCB (printed circuit board). RFI noise with frequencies at 2.4 GHz and 5 GHz is considered. The proposed filter structure is a four-layer PCB. The low noise generation includes the following schemes. The trace of the QWOSR is a stripline on the third layer. Four ground vias are added adjacent to the QWOSR via, which is short. Electromagnetic (EM) radiation noise, plan cavity resonance, ground bounce noise (GBN), and peak noise on insertion loss (|S₂₁|) are all reduced. The electric field distributions are elucidated to understand the effect of cavity resonance on the insertion loss (|S₂₁|) values of the proposed filter structure. The proposed filter structure significantly reduces the time-domain ground bounce and power noise whose frequency is equal or close to the center frequency of filter. Finally, favorable comparisons between simulated and measured results confirm the excellent low noise generation performance of the proposed filter structure.

This paper studies the application of vortex wave with orbital angular momentum (OAM) in the radar. The vortex waves can have eigenstates or modes with different integer topological charges, which are orthogonal to each other. The eigenstates with topological charges of 0, -1 and 1 were utilized in this paper. The radar transmitted the pulse with topological charge of 0 and received echoes with topological charges of 0, -1 and 1. The receiver can process the signals received by these orthogonal modes to obtain the azimuth and elevation angles of the two targets in a same range gate. Compared with the traditional mono-pulse radar only with sum beam and difference beam, this vortex-wave-based radar can track two targets in principle. This is meaningful for the application of the vortex wave.

This paper presents a numerical study of microwave scattering and emission from a foam-covered ocean surface. The foam layer is modeled as an inhomogeneous layer with randomly rough air-foam and foam-seawater boundaries. Kelvin's Tetrakaidecahedron structure is selected as the skeleton for simulating the air bubbles in the foam layer. The electromagnetic characteristics of the foam layer, including absorption and scattering coefficients for both vertical and horizontal polarizations, are calculated using a multilevel volume UV fast algorithm to accelerate the numerical computation of three dimensional Maxwell's equations. The surface scattering at air-foam and foam-seawater interfaces is determined using the integral equation model (IEM). The microwave emission from the foam-covered ocean surface, which accounts for multiple incoherent interactions within the foam layer and between the foam and interfaces, is modeled using the vector radiative transfer approach and numerically solved using the matrix doubling method. The model analyses of volume scattering and absorption of the foam layer reveal that the volume scattering coefficient of a foam layer increases with increasing water fraction at all selected frequencies, and its polarization dependence is negligible at a water fraction less than 2%. At 10.8 GHz and 18 GHz, the H-polarized scattering coe±cient is smaller than the V-polarized scattering coefficient for a larger water fraction; the opposite occurs at 36.5 GHz, at which V polarized scattering is weaker compared to H-polarized scattering. The model analyses of emission from a foam-covered ocean surface reveal that the emissivities at all selected operating frequencies have similar dependencies with water fraction and frequency, and they exhibit different sensitivities to water fractions. Moreover, the emissivities at high operating frequencies exhibit higher sensitivities to water fractions than the lower ones.

Based on the complex analysis of the Lossy Transmission Line Theory, which involves the result of a Generalized Smith Chart, a new version of the last one arises when trying to characterize the wave impedance along the Transmission Line by means of analytical complex functions. Among these functions, the complex logarithm of the reflection coefficient leads to the logarithmic-reflexion coefficient-plane and its parameterized version, the Logarithmic Generalized Smith Chart. This plane is specially useful for characterizing the Transmission Line along its extension. To validate these results, some examples will be presented providing physical interpretations to the behaviour of a lossy TL and pointing out some practical applications.

In this paper a method for a fast synthesis of planar, maximally thinned and steerable arrays is proposed and tested on several benchmarks available in literature. The method optimizes simultaneously the weight coefficients and sensor positions of a planar array without using global optimization schemes, properly exploiting convex optimization based algorithms. The resulting arrays are able to radiate a steerable beam pattern, satisfying a prescribed power mask and avoid to constraint the fitting of any a priori assigned reference field pattern. Although such a method takes into account the general case of sparse arrays, this letter is focused on the case of thinned arrays as a special case of sparse ones, since the initial grid to thin on has only half-wavelength distances. Such a feature allows a faster synthesis than in the general case of sparse arrays.

The modulational instability of a lower hybrid wave is investigated in a dusty plasma slab by developing a non-local theory of this four wave parametric interaction process. The immersed dust grains modify the dispersion relation and growth rate expression of low frequency unstable mode. A numerical analysis shows that the frequencies and growth rate of unstable mode is higher in dusty plasma than that in without dust grains. The growth rate of the unstable mode is proportional to pump amplitude and has strong dependence on pump frequency.

Digital manufacturing, or 3D printing, is a rapidly emerging technology that enables novel designs that incorporate complex geometries and even multiple materials. In electromagnetics and circuits, 3D printing allows the dielectrics to take on new and profound functionality. This paper introduces negative uniaxial metamaterials (NUMs) which are birefringent structures that can be used to manipulate electromagnetic fields at a very small scale. The NUMs presented here are composed of alternating layers of two different dielectrics. The physics of the NUMs are explained and simple analytical equations for the effective dielectric tensor are derived. Using these equations, the NUMs are optimized for strength of anisotropy and for space stretching derived from transformation optics. The analytical equations are validated through rigorous simulations and by laboratory measurements. Three NUMs where manufactured using 3D printing where each exhibited anisotropy in a different orientation for measurement purposes. All of the data from the analytical equations, simulations, and experiments are in excellent agreement confirming that the physics of the NUMs is well understood and that NUMs can be designed quickly and easily using just the analytical equations.

In this paper, radio wave propagation over irregular terrain is investigated in 200-600 MHz (VHF/UHF band). Measured results are compared with different path loss models such as Fresnel knife edge diffraction and uniform theory of diffraction (UTD). It is shown that, for low antenna heights, using a combination of the two-ray path loss model and knife-edge diffraction, great improvement in path loss prediction accuracy is achieved. The derived model is aimed to effectively predict path loss for near-ground and short-range communication applications.

A novel design for radar cross section (RCS) reduction of a bilateral Vivaldi antenna is presented. The method for RCS reduction is based on the wave-guiding characteristic of the substrate integrated waveguide (SIW) structure, which guides the incident energy to the lateral side of antenna plane. The bistatic RCS is controlled under the premise of reducing the monostatic RCS. Compared with the reference antenna, a significant monostatic RCS reduction is achieved over a wide frequency band ranging from 5 GHz to 12 GHz, and a remarkable monostatic RCS reduction at 7 GHz is as much as 34.73 dB without obvious radiation performance degradation. To verify the proposed strategy, prototypes of the reference and proposed antennas have been fabricated and measured. Good agreements between the simulated and measured results demonstrate that the proposed method preserves the radiation performances well and achieves an outstanding wideband RCS reduction.