This letter presents the development of a miniaturized and folded multisection quadrature hybrid for ultra-wideband (UWB) applications. For a size reduction, Stages 1, 2 and 3 are placed on the top of PCB, and Stages 5, 7 and 7 are placed on the bottom of PCB. The transition between top and bottom layers uses via transitions. Stage 4 is proposed with vertical via transitions and microstrip lines on the top and bottom sides of PCB, which is helpful for bandwidth increment and size reduction. The overall size of the proposed UWB hybrid is only 21 mm by 14 mm, and a size reduction of 50% is achieved compared with a planar multisection one. Performance comparisons are also implemented and discussed compared with a planar one.

In this paper, a novel low-cost, high gain dual-polarized antenna design with a suspended cylinder and a ground connected cylinder geometry is proposed. The design structure of the antenna is simple and fabricated with two cylinders, two shorting strips, and a circular ground plane. All these components are easily fabricated from a copper sheet of thickness 0.4 mm, and the antenna is fed by two coaxial probes at the orthogonal planes on the circumference of the cylinders. A prototype is designed, fabricated and measured. The measured results show that the prototype has -10 dB impedance bandwidth of 34.37% at port 1 & 34.21% at port 2. Broadside gain from port 1 is 10.2-10.4 dBi & port 2 is 10.25-10.52 dBi, which indicates that the antenna has flat gain over the impedance bandwidth, and isolation between the ports is more than 15 dB from 2.65-3.6 GHz and more than 20 dB from 2.75-3.55 GHz. The isolation of the proposed antenna is improved by shorting the suspended cylinder to the ground plane by two shorting strips. The resonance frequency and isolation peak are simultaneously tunable with varying the width of the shorting strips. The parameters of the antenna are optimized by using HFSS, and good agreement between the simulated and measured results is obtained. The proposed dual polarized antenna can be used for base station applications such as LTE (Long Term Evolution) and WiMAX (Worldwide Interoperability for Microwave Access).

In this paper, we present a hybrid system consisting of a novel design of a microstrip antenna that can be designed to resonate at various frequencies within the ultra-high frequency (UHF) band (e.g. 415 MHz, 905 MHz, and 1300 MHz), combined with a pair of high frequency (HF) coils (13.56 MHz). The system is designed to be fabricated on an FR4 substrate layer, and it provides a compact solution for simultaneous wireless power transfer (WPT) and multi-band wireless communication, to be utilized in implanted medical devices. The external antenna/coil combination (EX) will be located outside the body on the skin layer. The EX has 79.6 mm-diameter. The implanted hybrid combination (IM) has 31.5 mm diameter. The antenna is designed such that by varying the position of a shorting pin the resonance frequency can be switched among three frequencies; therefore, the same design can be used for various applications. The system was designed using numerical simulation tools, and then it was fabricated and measured. The design was optimized while the performance of the system was numerically simulated at various depths inside a layered body model. Furthermore, the insertion loss (S₂₁) and transmission efficiency (η) for both antenna and coil pairs at different depths were studied through simulation and measurements. The system provides a good solution for the combination of power transfer and multi-band data communication.

The scattering center extraction algorithm is a method to estimate the scattering center from the backscattered field. Superior scattering center extraction algorithms should be robust to noise, independent of the model order, and automatically and quickly operated. In this paper, we propose a novel super resolution scattering center extraction algorithm that satisfies the conditions mentioned above, which has been named the dimension reduced optimization problem (DROP). Using DROP, we determined a one-dimensional scattering center from a high resolution range profile and a two-dimensional scattering center from an inverse synthetic aperture radar image.

In this paper, the polarizations of single-feed crossed-dipole antennas loaded with different near-field resonant parasitic (NFRP) elements are investigated. The antennas are placed above a metallic reflector for a broadside radiation pattern. Meander line with an arrowhead-shaped ending is applied in all arms of the crossed-dipole and NFRP elements for the compactness. By adjusting the ending sizes of the NFRP element, the polarization of antenna can be right-hand circularly polarized (RHCP) - linearly polarized (LP) - left-hand circularly polarized (LHCP). For validation, two antennas with RHCP and LHCP performances are implemented and measured. The RHCP antenna yields a |S₁₁| < -10 dB bandwidth of 1.454-1.668 GHz (214 MHz) and a 3-dB axial ratio (AR) bandwidth of 1.525-1.585 GHz (60 MHz). The LHCP antenna yields a |S₁₁| < -10 dB bandwidth of 1.475-1.702 GHz (227 MHz) and a 3-dB AR bandwidth of 1.535-1.580 GHz (45 MHz). Moreover, both antennas yield a good broadside radiation with a gain of > 6.0 dBic and a radiation efficiency of > 65% across their operational bandwidth.

Thermal effects limit the gain, quality, and stability of high power fiber lasers and amplifiers. In this paper, different values of heat conductive coefficients at the core, the first and second clad with the complete form of the heat transfer equation are considered. A quartic equation was proposed to determine the temperature at the fiber laser surface. Using the surface temperature value, the temperature can be determined at the longitudinal and radial position of the double clad fiber laser. The different definitions of heat sources which were previously presented in articles is used to describe the heat generation at a double clad high pump power fiber laser condition. The results were compared to each other, and the percentage of each factor in heat generation was calculated.

A compact composite right/left-handed (CRLH) bandpass filter with wide out-of-band rejection, which utilizes a substrate integrated waveguide (SIW) and modified complementary split-ring resonators (CSRRs) is presented. By incorporating two sets of CSRRs resonators (the top and bottom CSRRs) into SIW cavity, the proposed filter obtains a high selectivity. Besides, the filter has the CRLH property, and no additional areas are required because of the structure of the top CSRRs and the gap between them. At the same time, two slots of etched units used in feeding lines are replaced to obtain a wide out-of-band rejection. Finally, the measured results show that the filter has a wide stopband with rejection over 20 dB up to 4.3 times of the center frequency, implying that the experimental results are in good agreement with simulated ones.

This paper describes a wideband transmitting adaptive digital beamforming (ADBF) scheme with nulls in the direction of interference. The scheme partitions the wideband transmit signal into independent sub-bands using an analysis filter bank behind each array element. In each channel, sub-band ADBF weight vector is computed based on the minimum variance criterion with multiple linear constraints to form the sub-band transmit beam. Finally, a wideband transmit adaptive beam is reconstructed through the synthesis filters. Theoretical analysis and simulation experiments show that this algorithm can form a wideband transmit beam with deep nulls, and the pointing direction of the null keeps unchanged regardless of frequency. The algorithm proposed in this paper has little computation load and is efficient to implement in engineering applications.

A three layered low profile dodecagon shaped band stop frequency selective surface (FSS) is presented in this paper for X band rejection applications. The three layers are placed in a manner which is complement to each other. The low profile three layered FSS with unit cell dimensions on the order of 0.2λ₀x0.2λ₀ (at lower center frequency of 8.2 GHz) with overall thickness of three layers including air gap of 5.2 mm is presented. For experimental verification, a three layered FSS has been fabricated and measured. Simulation results show that the designed three layered FSS can provide a stopband from 8 GHz to 12.5 GHz with two transmission zeros of 8.2 GHz and 10.2 GHz with a fractional bandwidth of 45%. The complete design and equivalent circuit model (ECM) of the three layered FSS are presented in this paper.

This paper describes the radio propagation measurement campaign in the sugarcane field representing a tall food grass characteristic which is one of the common types in outdoor agriculture environments. The measurement was conducted by using a channel sounder having a bandwidth of 45.6 MHz at 2.45 GHz with the aim at investigating the propagation channel characteristics which are useful in deploying of wireless sensor networks in the precision agriculture. By analogy to Ikegami model, the variation of path loss over the relative angles between the plant rows and the line-of-sight direction from the transmitter to the receiver is identified. Utilizing this knowledge, this work justifies the procedure of predicting the path loss at any point in the field by a few measurement efforts. Furthermore, the Rician K-factor and RMS delay spread are investigated in the vegetation depth shorter than 40 m. The result shows that the relationship between the Rician K-factor and its corresponding path loss value in each measurement point can be fitted with the log-linear line. This leads to the possibility of predicting K-factor at any points in the field. In addition, since the result of RMS delay spread is independent to the vegetation depth and the density of the plant, it is represented by the statistical model in which the Weibull distribution provides the best representation.

This paper presents single and dual notch ultra-wideband bandpass filters (UWB BPFs) to mitigate interference with coexisting wireless communication systems in ultra-wideband (UWB). The single and dual notch UWB BPF is developed by using signal interaction concept loaded with stub loaded resonator. The stub loaded resonator creates notches in the passband to avoid the interference with coexisting wireless communication systems. The notch frequency can be placed at the points of interest within passband by selecting a proper length of stub loaded resonator. Transmission zeros are introduced to enhance the selectivity of stopband. It presents UWB BPF with single notch at the frequency of 6.5 GHz and dual notch at the frequencies of 6.3 GHz and 8.0 GHz. The circuit size of proposed filters is 6 mm x 6 mm and 6 mm x 6 mm. The proposed filters exhibit good performance in terms of compact size, good fractional bandwidth and sharp selectivity. All the filters are simulated and fabricated on a Rogers R03010 substrate with relative permittivity of 10.2 and thickness of 1.28 mm. There is good agreement between simulated and measured results.

Ferrite toroids (or clamps) are widely used to reduce common-mode (CM) currents in power systems. The CM impedance of the ferrite depends on the frequency-dispersive permeability and permittivity of the ferrite, the geometry of the system, and the location of the ferrite in it. An analytical model was developed to predict the CM impedance of a wire harness above a return plane with a ferrite on it. The model is based on transmission line theory for a cable, a ferrite, and a return plane. The parameters of the model are calculated using a frequency-dependent quasistatic model for a ferrite toroid. This model accurately predicts the CM impedance of a mock harness within 3 dB up to 1 GHz. The proposed model is also applied to a real power system consisting of an inverter and a motor. Knowledge of the CM impedance of the system in the operating regime is critical to determining the impact of the ferrite on CM currents. The CM impedance is determined using the dual current clamp technique. The impact of the ferrite on the CM impedance and currents of the power inverter system was predicted within 3 dB, demonstrating the usefulness of the modelling approach for analysis of power systems.

Metasheets are ultra-thin sheets built from sub-wavelength resonators designed in order to achieve certain frequency-dependent transmission behaviour. A semi-analytical approach based on an equivalent circuit representation is proposed to calculate the microwave transmission through metasheets which consist of 2D periodic arrays of planar circular metal rings with and without substrate. The electromagnetic response of the metasheet can be controlled by changing the radius and periodicity of the circular rings. In the semi-analytical approach, the equations for impedances of the equivalent circuit are parameterized and fitted to match the values of transmission coefficients obtained by full-wave simulations at selected frequency points. Such an approach permits an optimization of the metasheet design with a very small number of full-wave numerical simulations. It is shown that the results of the semi-analytical approach match well with full-wave simulations and measurements within a reasonable range of radius and periodicity values.

The boundary element method is considered for solving scattering problems and is accelerated using the hierarchical matrix format. Thus, some matrix blocks chosen by geometrical criteria are approximated by low-rank matrices using a robust compression method. In this paper, we validate the use of the hybrid cross approximation which is quite new in this area, and we apply it to several examples. The validation is done on a conducting sphere, as well as less canonical objects such as the scattering by a rough (Weierstrass) surface or a plane.

In this paper, a novel HMSIW slot antenna combines a significant bandwidth enhancement and small footprint for inter-satellite communications at C-band. The designed antenna has the capability of achieving a reduction of size with nearly 50% in comparison to conventional SIWs. The results show that the proposed antenna has a bandwidth of 4%, an average gain of 5.8 dB, and the radiation efficiency of η = 93% at 5 GHz.

A polarization matched 2×2 radiating array for electronically steered phased array antenna is presented. The antenna array is a multi-layer structure consisting of four square microstrip patch elements grown on each substrate to provide wide band operation at S-band. Dual polarizations of radiated wave from the antenna array have been achieved by feeding the array in series fed mode through horizontal and vertical ports. Designed 2×2 S-band dual polarized series fed antenna has been optimized on finite element based ANSYS HFSS full wave solver. Controlling the amplitude of RF signal at input ports, the polarization can be matched to the target antenna polarization, hence antenna can work as polarization matched antenna. Gain of the developed antenna is 13 dBi, and the return loss is better than 10 dB over the frequency range of 2.3 to 2.5 GHz. This antenna can be used as radiating array for electronically steered phased array for S-band SOTM (SATCOM On The Move) application where the polarization of the antenna changes with movement of host platform.

A novel compact ultra-wideband (UWB) multiple input multiple output (MIMO) slot antenna with band notch characteristics is presented for portable wireless UWB applications. The antenna comprises co-planar waveguide feed (CPW) and two radiating monopoles oriented in orthogonal orientation for providing orthogonal radiation patterns. A Minkowski fractal parasitic stub along with a Minkowski fractal grounded stub has been placed at 45° between the monopoles to reduce the coupling between them which in turn establish high isolation between the radiators. An excellent band notch characteristic is obtained at 5.5 GHz by etching a modified E-shaped compact slot on the radiators. At the centre of notched band, the efficiency and gain of the antenna drop significantly which indicates a good interference suppression. Results show that the designed antenna meets -10 dB impedance bandwidth and -17 dB isolation throughout the entire operating band (3.1-12 GHz). Novelty of this design lies in improving isolation using compact fractal structures which occupy less space than conventional isolation mechanisms in MIMO structures. The simulated and measured results show that the proposed antenna is convenient for MIMO diversity systems.

High-order fractal characteristics of low-resolution radar echoes provide a supplementary description of the dynamic characteristics of the echo structure of a target, which provides a new way for the classification and recognition of targets with low-resolution radars. On basis of introducing the definition of high-order fractal statistic-lacunarity as well as its calculation method and the lacunarity characteristics of a target echo under additive fractal clutter background, this paper analyzes the characteristics of the lancunarity parameter variation of target echoes from a surveillance radar at a VHF band, and puts forward a classification method for aircraft based on the feature of the echo lacunarity scale change rate from the viewpoint of pattern recognition. The target classification experiments using real recorded echo data show that, as a high-order fractal characteristic parameter, the lacunarity scale change rate can be used as an effective feature for aircraft target classification and recognition, and the proposed method has good classification performance.

A concept of an experimental simulator for studying longitudinal magnetic waves in dielectric samples and its electrodynamic justification are presented. The simulator is intended to control impact power and frequencies of wave processes. The simulator is realized as a two-channel junction consisting of perpendicularly crossed infinite rectangular waveguides with slot coupling. The simulation process is based on cyclic mechanical displacements of dielectric samples along the longitudinal axis of the waveguide in a quasistationary magnetic field localized in the slot region.

A compact multiple input multiple output (MIMO) antenna with WLAN band-notch filtering function for portable wireless ultra-wideband (UWB) systems is proposed in this paper. The overall size of the antenna is 26 x 40 x 0.8 mm³, and it is fabricated on a low-cost FR4 substrate. The antenna comprises two identical planar monopole antenna elements, namely PM1 and PM2, which are fed by a 50-ohm coplanar waveguide. The PM1 and PM2 are positioned perpendicular to each other to minimize the mutual coupling between them. To further reduce the mutual coupling and to increase the impedance bandwidth, a long rectangular strip is protruded from the ground plane between the PM1 and PM2. To create the band-notch characteristics at WLAN band from 5 to 5.9 GHz, an inverted U-shaped slot is etched on the feed line. The simulated and measured results show that the proposed antenna achieves good impedance bandwidth (S₁₁ ≤ -10 dB) from 2.2 to 11.4 GHz and mutual coupling (S₂₁) of < -20 dB. The measured peak gain of 2.4 to 7.5 dBi and radiation efficiency above 90% are obtained except at notch band. The measured envelope correlation coefficient (ECC) of 0.008 in the whole operating band and omnidirectional radiation characteristics demonstrate that the proposed MIMO antenna is a suitable candidate for portable UWB systems.