A novel compact ultra-wideband (UWB) in-phase multilayer slotline power divider with high isolation is presented as a complement in slotline power divider field. The new structure proposed in this paper overcomes the shortcoming that power divider based on slotline almost cannot obtain high isolation between output ports. Based on the equivalent-circuit of microstrip-to-slotline transition and the method of odd-mode and even-mode analysis, the designing expressions of the proposed compact power divider have been obtained. The simulated and measured results have shown good agreement, and both of which have also shown that all the ports of the novel compact in-phase power divider have good impedance matching, and shown high isolation between the output ports over the band 3.4 GHz-12 GHz.

Enhancement of the reflection bands in ultraviolet region by using one-dimensional multi quantum well (MQW) photonic crystal (PC) structure has been investigated theoretically. The proposed structure is composed of three MgF₂/SrTiO₃ MQWs. The range of reflection band is investigated from the reflectance spectra of the one-dimensional MQW photonic crystal structure obtained by Transfer Matrix Method (TMM). From the numerical analysis it is observed that a range of reflection band for a single MQW PC is very narrow though it increases as the thickness of layers increases. But when three MQWs of MgF₂/SrTiO₃ are used we get much enlarged reflection band covering the range 119.8 nm-311.3 nm (reflectivity > 99%) with bandwidth 191.5 nm, for normal incidence. Further, we see that when the angle of incidence is increased, the width of reflection band increases in case of TE wave with a decrease for TM wave, because this omnidirectional reflection (ODR) band is very much narrow in UV region. We have computed ODR band upto incidence angle 50˚ for single as well as combined MQW PC. Analyzing the reflectance curve for incidence angle up to 50˚ for both TE and TM polarizations we find that by applying the combine MQW PC, omnidirectional reflection band increases significantly in comparison to single MQW structure. The proposed MQW photonic crystal structure is very useful in designing ultraviolet shielding for drugs, ultraviolet reflector for protecting damage of DNA and in skin diseases especially for skin cancer.

In this paper, we theoretically study the phase treatment of reflected waves in one-dimensional Fibonacci photonic quasicrystals composed of nano-scale fullerene and semiconductor layers. The dependence of the phase shift of reflected waves for TE mode and TM mode on the wavelength and incident angle is calculated by using the theoretical model based on the transfer matrix method in the infrared wavelength region. In the band gaps of supposed structures, it is found that the phase shift of reflected wave changes more slowly than within the transmission band gaps. Furthermore, the phase shift decreases with the incident angle increasing for TE mode, and increases with the incident angle increasing for TM mode. Also, for the supposed structures it is found that there is a band gap which is insensitive to the order of the Fibonacci sequence. These structures open a promising way to fabricate subwavelength tunable phase compensators, very compact wave plates and phase-sensitive interferometry for TE and TM waves.

The existing robust narrowband beamformers based on probability-constrained optimization have an excellent performance as compared to several state-of-the-art robust beamforming algorithms. However, they always assume that the steering vector errors are small enough. Without this assumption, we extend the probability-constrained approach to a wideband beamformer. In addition, a novel robust wideband beamformer with frequency invariance constraints is proposed by introducing the response variation (RV) element. Our problems can be reformulated in a convex form as the iterative second order cone programming (SOCP) problem and solved effectively using well-established interior point method. Compared with existing robust wideband beamformers, a more efficient control over the beamformer's response against the steering vector errors is achieved with an improved output signal-to-interference-plus-noise ratio (SINR).

A novel compact two-element MIMO (Multiple Input Multiple Output) antenna system operating from 6.1-7.8 GHz is proposed for wireless applications. The developed antenna system resonates at 6.8 GHz frequency, giving an impedance bandwidth of 25% (based on S₁₁<-10 dB). An efficient technique is proposed to reduce the mutual coupling developed in the antenna system by employing a simple microstrip patch element in between the antennas. Using the proposed method, the mutual coupling is reduced to around -33 dB at the resonant frequency and maintaining the overall mutual coupling less than -20 dB in the operating band. The experimental models are developed for both the MIMO systems i.e. without and with patch element between the antennas and the results are compared with simulated results. Also, Enveloped Correlation Coefficient (ECC) between the two antennas is calculated and compared.

A low-profile wideband circularly polarized aperture stacked patch (ASP) antenna without air dielectric layers is presented. The new circular ASP antenna, which is fed by two orthogonal dual-offset lines through an asymmetric crossed slot, delivers a wide bandwidth of 80% for the 10-dB return loss and similar input impedance characteristics for the two ports. Then, a novel broadband 90° hybrid feed network is employed to achieve good impedance matching, balanced power splitting and consistent 90° (±9°) phase shifting across the wide operating band. The two unbalanced feed lines are connected to the respective ports of the feed network comprising a three-section Wilkinson power divider and a broadband 90° phase shifter. It is found that the proposed antenna can achieve a measured impedance bandwidth of 91.3% (2.44-6.54 GHz), a measured 3-dB axial ratio (AR) bandwidth of 86.4% (2.5-6.3 GHz), and a measured gain bandwidth of 60.9% from 3.2 to 6.0 GHz for the gain >4 dBic. In addition, a comparison between the proposed wideband CP antenna and related wideband CP and ASP antennas in the literature is made.

We propose a technique for enhancing the angular resolution of a flat-base Luneburg lens antenna to enable it to detect multiple targets with arbitrary scattering cross-sections that are located in angular proximity. The technique involves measuring the electric field distribution on the flat plane of the Luneburg lens antenna, operating in the receive mode, at a specified number of positions, and correlating these distributions with the known distributions derived from the field distributions in the measurement plane generated by single target at different look angles. We show that the proposed approach can achieve enhanced resolution than the basis of the beam-width of the Luneburg lens antenna, and it is capable of distinguishing between two targets with different scattering cross-sections that have an angular separation as small as 1˚ for a Luneburg lens with 6.35λ aperture size, for Signal-to-Noise Ratio (SNR) better than 20 dB.

A new compact antenna with the capability of covering Ultra Wide Band (UWB) Communication is presented. The size of the antenna is 22×24 mm². Moreover, the proposed antenna has been successfully fabricated and measured, showing broadband matched impedance (~149%, 2.1 up to more than 14.3 GHz, VSWR ≤ 2). Also the antenna has dual band rejected characteristic on WLAN and WiMAX bands. Frequency and time domain performances of the antenna such as fidelity factor are examined at the end of the paper.

In this letter, a dual-band Multiple Input Multiple Output (MIMO) antenna system with high isolation is presented. This design consists of two dual-band monopole antennas and neutralizing transmission line. For each antenna element, the operating frequency band covers from 2.4 GHz to 2.6 GHz and 5.2 GHz to 6 GHz. To improve the isolation between these two antenna elements spacing only 0.1225 λ₀ at 2.45 GHz, a neutralization decoupling transmission line is introduced. The measured return loss results of these two antennas are better than 10-dB in operating frequency band. The measured isolation between the two antennas is better than 15 dB. The envelope correlation coefficient (ECC) is smaller than 0.01 of whole operating frequency band. The peak gain of this design is better than 2 dBi in operating bands. This configuration can be applied for Wireless local area network (WLAN) and Bluetooth (BT) communication system.

This paper discusses the problem of choosing an appropriate direction of the test dipole used in linear sampling for the 2-dimensional inverse scattering problem of the transverse electric case. In particular, we propose two approaches, one purely mathematical and the other based on the physics theory of multipole expansion of the scattered magnetic field. It is shown that though the approaches are drawn from different perspectives, they perform similarly and show reasonable reconstruction for several interesting and difficult to reconstruct dielectric scatterers.

In this paper, a new electrically small metamaterial-inspired monopole antenna is presented. The antenna consists of a simple square-shaped coplanar waveguide (CPW-fed) monopole with an embedded complementary split ring resonator (CSRR). It operates at three distinct frequency ranges with central frequencies around 2.45, 4.2, and 5.8 GHz, exhibiting low return loss and uniform radiation patterns, making it a perfect candidate for modern wireless applications. Furthermore, using this antenna as a primary unit to construct two different 2×2 MIMO system configurations, we achieve systematic minimization of mutual coupling between the radiation elements around 2.45 GHz, using additional single negative (SNG) metamaterial inspired resonators. Mutual coupling is reduced by as much as 27 dB at the aforementioned frequency. The simulated and measured results of all the fabricated antennas are in good agreement.

Here the hollow vortex Gaussian beam is described by the exact solution of the Maxwell equations. By means of the method of the vectorial angular spectrum, analytical expressions of the electromagnetic fields of a hollow vortex Gaussian beam propagating in free space are derived. By using the electromagnetic fields of a hollow vortex Gaussian beam beyond the paraxial approximation, one can calculate the orbital angular momentum density distribution of a hollow vortex Gaussian beam in free space. The overall transverse components of the orbital angular momentum of a hollow vortex Gaussian beam are equal to zero. Therefore, the influences of the topological charge, beam order, Gaussian waist size, and linearly polarized angle on the distribution of longitudinal component of the orbital angular momentum density of a hollow vortex Gaussian beam are numerically demonstrated in the reference plane. The outcome is useful to optical trapping, optical guiding, and optical manipulation using the hollow vortex Gaussian beams.

In this paper, we present the design of a metamaterial based microstrip patch antenna, optimized for bandwidth and multiple frequency operations. A Criss-Cross structure has been proposed. This shape is inspired by the famous Jerusalem Cross. The theory and design formulas to calculate various parameters of the proposed antenna have been presented. The software analysis of the proposed unit cell structure has been validated experimentally thus giving negative response of ε and μ. Following this, a metamaterial-based-microstrip-patch-antenna is designed. A detailed comparative study is conducted exploring the response of the designed patch made of metamaterial and that of the conventional patch. Finally, antenna parameters such as gain, bandwidth, radiation pattern and multiple frequency responses are investigated and optimised and presented in tables and response-graphs. It is also observed that the physical dimension of the metamaterial based patch antenna is smaller than its conventional counterpart operating at the same fundamental frequency. The response of the patch antenna has also been verified experimentally. The challenging part was to develop metamaterial based on some signature structures and techniques that would offer advantage in terms of bandwidth and multiple frequency operation, which is demonstrated in this paper. The unique shape proposed in this paper gives improvement in bandwidth without reducing the gain of the antenna.

Some microobjects can concentrate an incoming incident plane wave and create the socalled photonic nanojets. These highly focused emerging beams have a high intensity and can be used in applications such as microscopy, beam manipulation and imaging. In this article, it is shown that an adequate choice of geometric shape and material can lead to an improvement of the electric field enhancement capability of nanojets by a factor of 40%.

A coax-feed low profile dual-polarized circular patch antenna with ±45˚ polarization is presented. The antenna consists of a dual-polarized circular patch excited by two coax-lines and an AMC reflector. By using the AMC reflector as the ground plane of the patch antenna, the profile of the antenna is reduced to λ/8 of the operation frequency, which is much lower than that of the conventional dual-polarized patch antenna. The experimental results show that the proposed design obtains a wide bandwidth (2.12-2.77 GHz) and a high isolation (>35 dB) over the entire band. In addition, the front-back radio of the antenna is improved significantly by using the AMC reflector. The wide bandwidth, low-profile and high front-to-back ratio make the antenna a good candidate as a base station antenna for WLAN, WiMAX and LTE applications.

A dual-beam frequency scann ing microstrip antenna is proposed in this letter. The wellknown characteristic of the conventional leaky wave antenna is the beam scanning with operating frequency variation. Here, four slots are applied on the ground plane of the conventional leaky wave antenna structure to obtain the dual-beam frequency scanning characteristic. According the results, it shows that this work with relatively simple structure radiating not only in upper half-plane, but also in lower half-plane. The upper half-plane main lobe scans from 356˚ (-4˚) to 24˚ (scanning region is 28˚). Meanwhile, the lower half-plane main lobe scans form 190˚ (-170˚) to 161˚ (scanning region is 29˚). The 7-dB return loss bandwidth is 600 MHz from 3.4 GHz to 4 GHz. In addition, the measured average antenna gain is about 5.3 dBi in the operating frequency.

Wireless power transmision has been analytically studied in near-field coupling systems based on the small-antenna and near-field approximations, and in microwave power beaming systems based on the far-field approximation. This paper attempts to provide a general solution based on full-wave analysis to wireless power transmission between two circular loops. The solution applies to arbitrary transmit and receive loop radii, transmission range, orientation and alignment of the loops, and dielectric properties in a homogeneous isotropic medium. The power link is modeled as a two-port network and the efficiency based on simultaneous conjugate matching is used as the performance metric. The self and mutual admittances are analytically solved by expressing the current on the loops in Fourier series and the fields in vector spherical wave functions, and by the use of vector addition theorem to relate the coupling between the loops. The general solution is then applied to draw new insights such as the optimal carrier frequency between symmetric loops and impact of higher order modes on the power transfer efficiency between asymmetric loops.

It is well known tha the conventional edge element method in solving vector Maxwell's eigenvalue problem will lead to the presence of nonphysical zero eigenvalues. This paper uses the mixed finite element method to suppress the presence of these nonphysical zero eigenvalues for 2D vector Maxwell's eigenvalue problem in anisotropic media. We introduce a Lagrangian multiplier to deal with the constraint of divergence-free condition. Our method is based on employing the first-order edge element basis functions to expand the electric field and linear nodal element basis functions to expand the Lagrangian multiplier. Our numerical experiments show that this method can successfully remove all nonphysical zero and nonzero eigenvalues. We verify that when the cavity has a connected perfect electric boundary, then there is no physical zero eigenvalue. Otherwise, the number of physical zero eigenvalues is one less than the number of disconnected perfect electric boundaries.

By the transfer matrix approach we numerically study the electromagnetic properties (narrow peak positions) of the transmission spectra for microspheres coated by a multilayered stack with the generalized Cantor structure (fractal). As opposed to the standard Cantor system with removed γ/3 [γ=1] section we consider here the solid stack with Si/SiO2 layers at general γ value. In such a solid composition the SiO2 layers replace the empty Cantor sections and the parameter γ acquires meaning of a specific control parameter. At successive generations the central layers (in blocks of the spherical stack) acquire a progressive decreased width that leads to generation of the radially inhomogeneous defects. We show that the wave phase interference in such a fractal pattern leads to formation of very narrow electromagnetic transmittance resonances that can be used in modern optoelectronics.

In this letter, a reflectarray antenna based on the folded stepped impedance resonator (SIR) patch-slot configuration with variable size is presented. A novel frequency selective surface (FSS) in the reflectarray as a ground plane for reducing radar cross section (RCS) level is applied. The FSS is based on the folded SIR configuration. Two prime-focus 15 × 15 reflectarray antennas backed on the folded SIR FSS ground and a conventional ground are designed and manufactured. The radiation performance of a reflectarray element backed either by a solid ground plane or a band-stop FSS structure is compared. The measured results demonstrate that the radiation pattern and gain of the FSS-backed reflectarray are almost same to its counterpart backed by a conventional ground plane at the operating band of 11.5 GHz. The RCS is effectively reduced in the out of this band when compared with the reflectarray with a solid metal ground plane of the same dimension.