Graphene is increasingly being used in the design of electromagnetic devices. The resistivity of graphene can be adjusted via chemical potential tuning, which truly benefits the implementation of tunable and reconfigurable devices. This paper investigates the switch-like attribute of parasitic graphene surface used in a dipole operating at 0.39 THz. Further, a novel orbital angular moment (OAM) generator with radiation reconfiguration is proposed. Spiral beams carrying variety of OAM modes can be produced easily using the generator.

The electromagnetic force acting on a Rayleigh particle placed in a rectangular waveguide is studied. The particle is excited using the lowest order TE₁₀ mode. It is determined that the particle is laterally trapped at the high intensity region of the electric field and either pushed away from or pulled toward the light source. This push-pull phenomenon depends on whether the frequency of the light wave is above or below the cutoff frequency (i.e. the particle can be pushed or pulled by tuning the frequency). While conventional optical tweezers rely on a balance of scattering and gradient force in the propagation direction, the phenomenon predicted here switches between the two forces near the lowest cutoff in a waveguide.

In this paper, three commonly used on-ground antenna types (loop, monopole and planar inverted-F antenna) are compared in the scope of wireless body area networks (WBAN) for on-body communications at 2.45 GHz. The bandwidth of the antennas can be enhanced by placing them towards the edge or the corner of the small ground plane (25 × 35 mm²) which has, as a consequence, detrimental effects on radiation characteristics that motivates the examination of the impact of feeding location for on-body propagation in detail. The present study quantifies the trade-off between on-body efficiency, the gain in the direction tangential to the surface, applicability to launch creeping waves and bandwidth potential of the different antenna types with various feeding locations. The simulated channel gain |S₁₁| around tissue-equivalent numerical phantoms is compared to an analytical WBAN path loss model.

This work addresses the low-pass equivalent behavioral modeling of radio frequency (RF) power amplifiers (PAs) for modern wireless communication systems. Similar to a previous approach, here the PA behavioral modeling is based on two independent real-valued feed-forward artificial neural networks (ANNs). A careful analysis is first presented to show that the nonlinear training algorithm for the previous ANN-based approach can be easily trapped into local minima, especially for the ANN that estimates the polar angle component of a complex-valued signal. Then, a modified ANNbased model is proposed to eliminate the local minimum problem, in this way significantly improving the modeling accuracy. Indeed, in the proposed model the two real-valued ANNs are responsible for estimating the in-phase and quadrature components of a complex-valued base-band signal. When applied to the behavioral modeling of a GaN HEMT class AB PA, the proposed ANN-based model reduces normalized mean-square error (NMSE) by up to 2.2 dB, in comparison with the previous ANN-based model having an equal number of network parameters.

In this paper a compact planar dual-mode metamaterial (MTM) antenna using rectangular type complementary split ring resonator (CSRR) is proposed. It is observed that an increase in series capacitance tends to decrease resonant frequency at which n = 1 mode is obtained in the proposed antenna. Zeroth order mode (ZOR) is obtained by means of rectangular type CSRR, tends to provide the miniaturized area. Dispersion relations are shown in order to characterize the metamaterial behavior by extracting the equivalent circuit parameters. The resonant frequency of the antenna is 2.14 GHz with input reflection coefficient up to -45 dB. The electrical size of the proposed MTM antenna is 0.321λ₀ × 0.285λ₀ × 0.011λ₀. ZOR mode is observed at 1.15 GHz although the proposed antenna is operated at 2.14 GHz. Furthermore, it achieves simulated antenna gain of 2.60 dB with 70% radiation efficiency. In order to verify the simulation results of antenna, a prototype is fabricated and measured.

In the paper presented here the optimization of Halbach arrays as storage media for mechanical potential energy is investigated with numerical simulations using FEMM and analytical calculations using the Maxwell stress tensor. Two opposing Halbach arrays form a ``magnetic spring'' and mechanical potential energy is stored when this structure is compressed. It is here seen that the wavelength of the magnetization in the material and the dimensions greatly in fluence the stored energy density. A clear region of maximum is identified which leads to important conclusions on how the material should be employed. The suggested approach for storing energy have advantages and approximately 250 kJ/m³ can be reached. The main drawback is the large prize of rare earth metals such as Neodymium.

A novel planar dual-band microstrip power divider is proposed in this paper. The circuit is composed of two sections of transmission line, short-circuited stub line and planar resistor, which can provide high isolation and good amplitude balance simultaneously at two frequencies. The closed-form equations are derived,and the design procedures of dual-band power divider are given. To Certify the validity, a proposed power divider was fabricated and measured at 950 MHz and 2200 MHz which might be applied to M and CDMA systems. Both theoretical and simulated results are given, which are in good agreement with the measured results.

In this paper, we propose a new retrieval technique to estimate the dielectric permittivity of the sub-soil materials of a stratified structure. The core of the retrieval procedure is a proper electromagnetic circuit model representing the realistic stratified media as a cascade of transmission line segments. Exploiting the analogies between the electrical parameters of the transmission line segments and the constitutive parameters of the materials of the multilayer structure, the propagation of the Ground Penetrating Radar (GPR) signal is equivalently represented as a pair of voltage and current waves propagating in the transmission line network. The effectiveness of the proposed retrieval technique is confirmed by proper experimental results. In particular, the retrieved electromagnetic parameters of the sub-soil materials are found to be consistent with the ones obtained by a direct characterization of the same materials. These results suggest that the proposed method can be successfully applied to the material characterization able to monitor several macroscopic properties of sub-soil materials.

A novel dual-band bandpass filter based on shorted rectangular patch resonator is proposed and experimentally studied. The resonant modes and frequencies of the shorted rectangular patch resonator are analyzed. Based on miniature structure of the new resonator, a novel dual-band bandpass filter with good out-of-band performance is designed for demonstration. The experimental results agree well with numerical simulations.

A broadband artificial material based on meander-line (ML) structures is proposed for enhancing the gain of printed end-fire antennas. The ML based material with an effective index of refraction greater than 1 behaves as a dielectric lens in improving the directivity of an end-fire antenna. The electric field intensity distribution can be changed by the material, resulting in a more directional emission. Simulated results indicate extending the length or width of the material can lead to more significant gain enhancement without destroying the impedance bandwidth of the antenna. Three printed end-fire antennas with and without material loading are fabricated and measured. The measurements show that end-fire antennas loaded with two and four rows of ML structures can obtain gain increments of 0.6-3.6 dB and 1.2-5.7 dB, respectively, and that the radiation patterns are narrowed in both E- and H-planes over the whole operating band (6-11.5 GHz).

The present paper analyses and documents the merits of incorporating fractal design in microstrip antenna intended to be mounted on and integrated into the design of smart vehicles. A novel design is proposed for a compact tri-band hexagonal microstrip antenna to be integrated with the body of a smart vehicle for short range communication purpose in an Intelligent Transport System (ITS). This antenna can be used at 1.575 GHz of GPS L1 band for vehicle to roadside communication, at 3.71 GHz of mobile WiMAX band (IEEE 802.16e-2005) for blind spot detection and at 5.9 GHz of DSRC band (IEEE 802.11p) for vehicle to vehicle communication. At 3.71 GHz, the two major lobes of the antenna radiation beam, tilted by 35° on both sides from its broadside direction, help the vehicle to detect blind spots efficiently. The largest dimension of the proposed antenna corresponds to the lowest resonating frequency, 1.575 GHz. Compared to the conventional hexagonal patch, the modified Sierpinski fractal proposed herein reduces the overall area, at 1.575 GHz, by 75%, with 5.2 dBi gain. In comparison with other popular fractals, the proposed fractal structure achieves demonstrably better antenna miniaturization. When the antenna is mounted on the vehicle, considered an electromagnetically larger object, the simulated and on-vehicle experimental results show antenna gains of more than 5.5 dBi at 1.575 GHz, 8 dBi at 3.71 GHz and 9 dBi at 5.9 GHz in the desired direction with negligible amount of electromagnetic interference inside the car.

A novel 180˚ out-of-phase power divider with complex-source to complex-load impedance transformation and high power-handling capability is proposed in this paper. It is composed of three double-sided parallel-strip lines (DSPSLs), a conduct plane in the middle as common ground, and two resistors for heat sinking and high isolation. Based on the rigorous odd- and even-mode analytical methods, closed-form design equations about electrical parameters are obtained. To demonstrate our design theory, a practical three-layer out-of-phase power divider is designed, simulated and measured. The measured results show that the return losses |S_ii| (i=1, 2, and 3) are all larger than 17 dB. The insertion loss |S₂₁| (|S₃₁|) is 3.6 dB (3.7 dB). The isolation |S₂₃| is -24 dB, and the output phase difference is -177˚ at the operating frequency. Good agreements between the simulated and measured results verify our design theory.

A novel, compact wideband bandpass filter based on an improved quad-mode resonator is proposed in this paper. Due to the usage of a coupled-line section, the resonator has a quad-mode behavior. The resonant frequencies can be tuned by regulating not only the electrical lengths, but also the characteristic impedances. Owing to the symmetry of the construction, even- and odd-mode analysis is utilized to analyze the proposed resonator. Finally, a wideband bandpass filter with 88% (2.1 to 5.4 GHz) relative bandwidth is designed, fabricated, and measured. The measured results are in good agreement with the simulated ones, which demonstrates the feasibility of the design approach.

We have studied dynamics of a periodic X-band Gunn oscillator (GO) forced by microwave chaotic signals through numerical simulation and by hardware experiment. The chaos used as forcing signal is generated in a periodically driven non-oscillatory GO. Numerical simulation results indicate that the forced periodic GO becomes chaotic for a moderate strength of forcing chaos. The generated chaos in driven GO is found to become phase or general synchronized to the forcing chaos depending on strength of the latter one. Hardware experiments are performed in X-band of microwave frequency. It shows generation of chaos in driven GO due to forcing. Moreover, synchronization between forcing and generated chaos is indirectly verified.

A novel printed antenna with a slotted patch and a defected ground structure (DGS) for dual-band operation is presented. By inserting an I-shaped slot into the patch and defecting the ground plane, triple-mode resonance for achieving dual operation bands, especially an extremely wide bandwidth for the higher band, can be excited. The measured bandwidths are 100 MHz (2.38-2.49 GHz) and 2.94 GHz (3.4-6.34 GHz) for the lower and upper bands, respectively, which agree well with the simulation. The experimental average gains across the two operating bands are 1.0 and 3.9 dBi, respectively, with typical radiation patterns for a patch antenna having a defective ground. The proposed antenna with a compact size of only 22×25 mm² sufficiently covers performance requirement of the 2.4/5.2/5.8 GHz WLAN and the 3.5/5.5 GHz WiMAX operation systems.

A broadband rectifying circuit with high microwave-direct current (mw-dc) conversion efficiency is designed based on the voltage doubling circuit. The rectifying circuit consists of a broadband match network, a capacitance, a diode, a dc-pass filter formed by three fan-shaped stubs and a resistive load. The measured results show a maximum mw-dc conversion efficiency of 78.3% at 2.45 GHz centre frequency on a 900 Ω load. When the input power is 15 dBm, the bandwidth of efficiencies higher than 50% is about 57% (1.65 GHz-3.05 GHz). The simulated results agree with the measured ones. The rectifying circuit has the characteristics of simple structure and easy integration, which can be applied in the microwave power transmission systems.

A dual-band circularly-polarized microstrip antenna is proposed, and the antenna for GPS is designed. The radiation characteristics of the dual-band circular polarization are achieved by installing one pair of L-shaped slits at all edges of the square patch. The impedance matching in the dual band is tuned by an L-probe feed. The proposed antenna is effective and useful in the design for dual-band circularly-polarized operation.

This paper presents a broadband hexa-band dual-polarized loop antenna for mobile communications. Two orthogonal one-wavelength-perimeter modes of a rectangular loop are excited by two orthogonal feedings. One mode for vertical polarization is excited by a circular monopole, and the other mode for horizontal polarization is excited by a slot-coupled microstrip line. By optimizing the antenna structure and the orthogonal feedings, the orthogonal polarizations can be achieved in a wide bandwidth with high ports isolation. The overall size of the proposed antenna is only 58×53 mm² (0.43λ₀×0.39λ₀, λ₀ is the free-space wavelength at 2.2 GHz). A prototype of the proposed antenna is built and tested. The measured bandwidth with reflection coefficient less than -10 dB is 61.4% (1.65-3 GHz) for both orthogonal polarizations, covering the DCS, PCS, UMTS, WLAN, LTE 2300, and LTE 2500 operation. The measured ports isolation is better than 28 dB over the entire band. In addition, the radiation patterns, gains and diversity performance are also discussed.

This paper presents the design of an asymmetrical Doherty power amplifier (DPA) with improved linearity and efficiency performance. Resonator-type drain bias networks, providing high impedances at the carrier frequency and low impedances with small variation at the envelope frequency, are introduced to reduce the DPA's memory effects when transmitting wideband signals. The general criteria for DPA design are summarized, and the approach to obtain optimum fundamental and harmonic impedances is proposed to achieve back-off efficiency enhancement. For experimental validation, the asymmetrical DPA is designed and implemented using two identical GaN HEMTs. Measured with continuous wave (CW), the proposed DPA delivers a saturation power greater than 49.3 dBm from 3400 to 3600 MHz, along with high drain efficiency of over 62% and 48% at peak and 8-dB back-off power, respectively. Driven with 100-MHz LTE-advanced signals, the adjacent channel leakage ratio (ACLR) asymmetry of the DPA at 20-MHz offset is lower than 1-dB. After digital predistortion (DPD) linearization, the proposed DPA achieves an ACLR of better than -48 dBc at an average output power about 41 dBm and the drain efficiency over 45% across the frequency band.

We characterize the alpha power and chirped types of refractive index profile planar slab waveguide in terms of TE/TM mode study, waveguide dispersion study, mode profile properties, power confinement factor and universal b-V graph. Our own developed finite element method has been efficiently applied to analyze the symmetric planar slab waveguide having a complicated refractive index profile. There is a requirement for a high accuracy of numerical technique to analyze the arbitrary refractive index waveguide, as at some frequency the TE and TM modes are smeared on each other, and it is difficult to distinguish them while analyzing. This paper successfully demonstrates the different TE/TM modes supported by the waveguide with respect to alpha-power and linearly chirped types of refractive index profile. The main contribution of our work is to identify the TE/TM mode numerically for a complex refractive index planar slab waveguide and to characterize them in terms of their performance parameters. Then we apply the mode propagation concept to estimate the propagation phenomena in alpha-power and chirped types of refractive index profile waveguide. All the results presented in this paper are simulated in MATLAB only. Our study reveals that waveguide dispersion and number of allowed guided modes are small while for the case of triangular index profile followed by chirped profile and maximum for step index profile case. Hence triangular and chirped types of refractive index profile waveguide seem to be more efficient for long haul optical communication systems.