This study proposes a differential-fed microstrip antenna, which is characterized with an ultra-wideband of 120% (3-12 GHz), improved radiation patterns, stable gains, and compact size. Two symmetrical trapezoid shaped slots and four triangle-cut corners on the ground are used to improve the impedance matching over the UWB frequency band. To clarify the improved radiation characteristics, the simulated radiation patterns of the proposed antenna are compared with the conventional single-ended feed UWB antennas. The measured results show that, in the entire frequency band, the designed antenna exhibits a stable radiation patterns and the gain variation is less than 2 dB. Furthermore, the polarization purity are increased compared with the conventional ones, especially in the high frequency band.

Soil density is one of the important parameters to be investigated in civil, geological and agricultural works. Unfortunately, the challenging issue is found on the suitable model in determining accurately the soil density. In this article, a new soil density model based on radio-wave surface reflection method is presented. The development of the model is based on result analysis collected from the experiment. Then, comparisons with related theoretical models, Hallikainen and Topp, are performed. The experiment is performed by using a vector network analyzer (VNA) that generates radar signal and recording return loss (S₁₁) from a horn antenna. In the analysis, two new proposed soil density models have shown good agreement for soil density from 1.1 g/cm³ to 1.7 g/cm³ for sand and silty sand samples. This is verified when the model able to predict real samples as the one used in the experiment and result shows a very small relative error within 0.05% and 6.87%. Additionally, spectrograms in real time were produced in this study in order to observe more on the soil density. By using the proposed developed models, soil density estimation can be easily determined with minimal data input such as soil type, return loss and reflection coefficient by using regular radio-wave devices.

Phase shifters are the key components of phased array systems which provide a low-profile solution for Ka-band satellite communications. In the transmitting mode, it is crucial for the phased array antenna system to meet the standard radiation masks, and any imperfections of phase shifters can yield into radiation mask violation. In this paper, we present the analytical approach to model the non-linear phase-frequency characteristics of Resonance-Based phase shifters, which constitute one of the most widely used class of phase shifters for Ka-band satellite communications. Furthermore, it has been investigated how the phase-frequency response non-linearity affects the phased array radiation patterns, gain, and the beam pointing direction. The simulation results show that, depending on the phase shifter phase-frequency response profile, the radiation mask satisfaction is an important factor in determining the system bandwidth.

This article presents the Wave Concept Iterative Procedure, an efficient method for characterization of substrate integrated Non-Radiative Dielectric passive circuits based on wave concept formulation and its iterative solution. WCIP simulations are compared to measurements and Finite Element Method simulations. A good agreement is achieved with computation time saving.

Three-dimensional Finite-Difference in Time-Domain method is applied to simulate Low Frequency antennas in the presence of natural environments. All antennas are made up of wires set down on a square shaped ground plane and their dimensions depend on the wavelength of the source. Both monopole and inverted L antennas are considered in this paper. The antenna systems are computed in the presence of two examples of natural elements: a large forest and then on the top of a hill. The main aim of this paper is to show the effects of these environments on the properties of the antennas and on the efficiency of the ground wave excitation. The outcome of these investigations shows a power ratio enhancement of several decibels when the two kinds of antenna described in this paper are located on the top of a hill. On the other hand, the effects of a large forest depend on the geometry of the antenna. It doesn't affect the radiation of a quarter-wave monopole antenna, on the contrary losses disrupt radiation when an inverted L antenna is built in the middle of a large forest.

A new dual-band dual-sense circularly polarized (CP) slot antenna is designed in this paper. The proposed antenna is composed of a rectangle patch and a modified ground plane. By opening a U-shaped open-slot and loading a vertical stub to the ground plane, a dual-sense CP performance is achieved for two frequency bands. A bevel is cut on the patch to improve the impedance matching. The antenna is fabricated on a low-cost FR4 substrate and fed by a coplanar waveguide (CPW) structure. The antenna has been investigated numerically, and a prototype was experimentally measured. Experimental results show that the measured 10-dB return loss impedance bandwidths are 18.3% (2.72-3.27 GHz) for the lower band and 23.7% (4.65-5.90 GHz) for the upper band, and the measured 3-dB axial ratio (AR) bandwidths for the lower and upper bands can be up to 28.4% (2.48-3.30 GHz) and 26.3% (4.63-6.03 GHz), respectively.

In this paper, a wideband differential phase shifter has been analyzed and designed using Genetic Algorithm (GA). The differential phase shifter consists of two fixed main lines of length λ/2, and parallel open and short stubs of length λ/8, which are shunted at the edge points of the main lines, respectively. With the application of GA, an impedance match and minimum phase deviation for the desired phase shift over a wide frequency band are obtained. In order to verify the optimum results, simulation experiments are made and a 45° phase shifter is fabricated and measured. The phase shifter exhibits an impedance bandwidth (|S₁₁|<-10 dB) and a consistent 45° (±2°) phase difference bandwidth around 66%.

We report the experimental measurements of weak light signal at 1550 nm wavelength with a high-quality factor microwave coplanar waveguide (CPW) resonators. The quality factor of this niobium λ/4 CPW resonator is measured as Q = 7.4×10⁵ at ultra-low temperature (20 mK). With this device, we developed a technique to implement the proper fiber-resonator coupling, and realized the desirable weak light detection at telecommunication wavelength with 35 pW resolution by probing the shift of resonance frequency (f₀). We found that the resonator shift increases with the increasing light power (from 11.7 pW to 9.77 nW), similar to the effects of increasing the system temperature (from 20 mK to 800 mK). The observed blue shifts of f₀ (with the increasing of either the temperature and the applied light powers) are thoroughly deviated from the usual Mattis-Bardeen theory prediction, and could be explained by the effects relating to the two-level system existed on surface of the CPW device.

A simple method for designing a triple-mode bandpass filter is presented in this paper. Triple-mode is achieved by using half-mode substrate integrated waveguide (HMSIW) cavity.Three perturbation metal vias were introduced for shifting resonant modes.The resonant frequencies of these modes can be adjusted by the location and the diameter of perturbation vias properly. In order to improve the out-of-band rejection, the CPW-to-SIW transition was added. A triple-mode HMSIW filter with the center frequency of 13 GHz was designed and fabricated. The measured fractional bandwidth is 35% with a transmission zero located at 20.4 GHz. Good agreement is observed between simulation and measurement.

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.