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In this letter, an ultrawideband (UWB) bandpass Wilkinson power divider (WPD) is introduced. By using filter synthesis theory and proposed optimization algorithm, all the S-parameters (S 11 , S 21 = S 31 , S 22 = S 33 and S 32 ) of the proposed topology could provide an equal-ripple response, and their equal-ripple level and bandwidth can be controlled, respectively. For verification purposes, a prototype UWB WPD has been simulated, fabricated, and measured. The measured and simulated results are matched reasonably well.

In this brief, a tunable Wilkinson power divider (WPD) with port match and isolation is proposed based on a reconfigurable compact structure. The reconfigurable unit is composed of one varactor cascaded by a transmission line (TL) with specific characteristic impedance and electrical length. Each unit can be alternately connected with two cascaded varactors to constitute a T-type structure, where the operating frequency can be selected by providing proper bias voltages for the three varactors. By adjusting the characteristic impedance and electrical length of the transmission line in each unit, the continuous tuning range can be easily extended to exceed 120% tunability. The reconfigurable units can also be flexibly configured to work in designated discrete tuning range as well. An experimental reconfigurable WPD with wide continuous tuning range of 0.96-1.73 GHz (57.3% tunability) is designed and fabricated. The measured results show that more than −20dB return losses and isolations can be realized in the entire tuning range.

A compact optical polarization converter (PC) based on slot waveguide has been proposed in this study. Utilizing the high refractive index contrast between a Si waveguide and SiO2 cladding on the silicon-on-insulator platform, the light beam can be strongly confined in a slot waveguide structure. The proposed PC consists of a square waveguide and an L-shape cover waveguide. Since the overall structure is symmetrically distributed along the axis rotated 45-degree from the horizontal direction, the optical axis of this PC lies in the direction with equi-angle from two orthogonally polarized modes of the input and output ends, which leads to a high polarization conversion efficiency (PCE). 3D FDTD simulation results illustrate that a TE-to-TM mode conversion is achieved with a device length of 8.2 µm, and the PCE exceeds 99.8%. The structural tolerance and wavelength dependence of the PC have also been discussed in detail.

In this paper, a parallel transmission-line transformer with complex terminal loads is introduced for dual-frequency design. Through analyzing the different cases of complex terminal loads conditions, there are four different mapping patterns of designable regions on the Electrical Length-Electrical Length ( EL-EL ) plane. By adding an extra vertical Frequency Ratio ( FR ) axis, a novel 3D cube can be created on the FR-EL-EL coordinate system, then the designable ranges of frequency ratio can be easily drawn in this 3D cube. Therefore, the visible 3D mapping approach is newly reported for matching the complex terminal load of parallel transmission-line transformer at two different frequencies. For the certain pattern, a clearly boundary could be drawn to distinguish the designable and undesignable ranges. For verification, two examples are designed, fabricated and measured. Simulated and measured results are matched very well.

With improved isolation performance, a wideband bandpass power divider is newly reported. Four transmission zeros of $S_{22}$ and $S_{23}$ can be got, and the amplitude of both $S_{22}$ and $S_{23}$ can be controlled below −20 dB by adding an extra isolation resistor. The mathematical conditions are presented, the several design examples are listed, and the S-parameters of different cases are compared. For verification, a wideband power divider is shown with $\text{FBW} =78\%$ at $f_{0}=2.5\ \text{GHz}$ .

A synthesis theory of ultra-wideband (UWB) bandpass (BP) transformer with short-circuited stubs is proposed in this paper. Based on the short-circuited stub number and their positions, six combination topologies are presented when the transmission line (TL) section is fixed to 4. Although analyzing the characteristic functions of these six combination topologies, the same theoretical Chebyshev transfer function can be summarized. Therefore, by selecting different short-circuited stub number and their positions, we can make a flexible choice of the filtering transformer pattern and keep the Chebyshev response at the same time. Finally, by using the proposed transformer, a UWB BP type Wilkinson power divider can be easily designed. In order to match the numbers and frequencies of output ports reflection zeroes ( $S_{22} =0$ )/isolation zeroes ( $S_{32} = 0$ ) with those of input port reflection zeroes ( $S_{11} =0$ ), one extra TL and one isolation resistor are newly added in the power divider design. One experimental circuit is fabricated, and its measured frequency response verified well the proposed design theory and method.

Extended Smith chart concept is proposed to enable advanced graphical interpretation of devices containing complex properties. This methodology is based on the Smith chart concept, and makes it easy to deal with devices containing signal sources, nonlinearity, very high Q factors and negative resistances. It is difficult or even not possible to treat those devices by conventional design methodologies with the Smith chart. The point of this proposal is to introduce a bilinear transform with a coordinate rotation as a pre-process, and 3 dimensional use of that Smith chart plane for the graphical treatment. To demonstrate the effective usage of this methodology, an interpretation and an analysis of the oscillator, especially in terms of the phase noise, are provided.

A wideband bandpass filter using coupled lines with sharp roll-off shirts is proposed in this paper. Seven transmission poles within the passband and high out-band rejection performance can be realized through even-and oddmode input impedance calculations. For demonstration, a wideband bandpass filter prototype centered at 1.5 GHz with high-stopband rejection is designed and fabricated. Good agreement between the simulations and measurements validates the design idea.

In this paper, a modified double-layered metallic photonic crystal (MPhC) structure is proposed for designing microwave planar devices. The modified MPhC is implemented by inserting a thin air layer into a traditional planar MPhC consisting of a periodic metallic post-array sandwiched by a parallel plate waveguide. As examples, a point-defect resonator based on the modified MPhC is implemented by eliminating one or several metallic posts. It can be found that the resonant frequencies of the novel cavities can be tuned by changing the thickness of the air-gap. To validate the proposed structure, an air-gap inserted point-defect-cavity is investigated. Moreover, a BPF (bandpass filter) is designed using the proposed MPhC cavities.

In this paper, a Wilkinson power divider with dual coupled lines and open stubs is presented for dual-band application. Two coupled lines with different even and odd-mode characteristic impedances are inserted between input and output ports to compact the circuit size. An open stub pair is connected to the input port to provide a compensation. The lumped isolation resistor is connected between the two coupled lines. Based on the even- and odd-mode analysis, parameters are newly derived and summarized. The experimental results are also presented to verify the design.

A compact modified N-way Wilkinson power divider with complex isolation units is presented in this paper, where the complex isolation units are bridged between output ports. Through analyzing the equivalent circuit, the design equations of the proposed N-way power divider are summarized in detail. Several design examples are also given and compared. Finally, a three-way power divider ( $N=31$ ) is fabricated for proving the proposed theory, and the measured results meet the simulation results very well.

By analyzing the equivalent circuit of coupled line section, three potential isolation resistor positions are investigated for Wilkinson power divider application in this letter. Design equations of Wilkinson power divider with multi-isolation resistors are newly derived in closed-form. After optimization, five designable cases (Case I~V) with one isolation resistor are summarized and compared in details. Finally, one circuit (Case IV) is selected, fabricated and measured. Measured and simulated results are matched very well. The purpose to investigate the multi-isolation resistance position could be quite useful to improve the isolation performance of multi-way or multi-section power divider topologies.

A single-polarization single-mode (SPSM) photonic crystal fiber (PCF) based on double-hole unit core is proposed in this paper for application to cross-talk free polarization splitter (PS). Birefringence of the PCF is obtained by adopting double-hole unit cells into the core to destroy its symmetry. With an appropriate cladding hole size, single x- or y-polarized PCF can be achieved by arranging the double-hole unit in the core along the x- or y-axis, respectively. Moreover, our proposed SPSM PCF has the potential to be applied to consist a cross-talk free PS. The simulation result by employing a vectorial finite element beam propagation method (FE-BPM) demonstrates that an arbitrary polarized incident light can be completely separated into two orthogonal single-polarized components through the PS. The structural tolerance and wavelength dependence of the PS have also been discussed in detail.

Novel microwave high-Q point-defect-cavity (PDC) resonators based on metallic photonic crystals (M-PhCs) are experimentally studied. After the illustration of the band structure of M-PhCs, the first two resonant modes of a PDC are computed by supper-cell methods. The results show that the Q-value of M-PhC PDCs is almost the same as that of the traditional waveguide cavity resonators. Moreover, the PDC is then fabricated and experimentally measured. The measured resonant frequencies and Q-factors are compared with the calculated ones to validate our computation and show the property of the proposed PDC.

Using first-principles calculations, we predict the existence of two dimensional (2D) pentagonal ZnO 2 (penta-ZnO 2 ) sheet and confirm that penta-ZnO 2 is dynamically and mechanically stable. Due to its unique atomic configuration, penta-ZnO 2 has intrinsic negative Possion's ratio, contrary to the most existing materials. Furthermore, Penta-ZnO 2 is much more flexible than graphene-like ZnO and penta-graphene in elasticity. Using the Heyd-Scuseria-Ernzerhof (HSE06) functional, the calculated indirect energy band gap is 4.53 eV, which is corresponding with optical gap (4.54 eV). More interesting, in the visible range of light, we find that penta-ZnO 2 has very low reflectance (0.0035%). Together with the expected zero absorption below the band gap, the light transmittance of penta-ZnO 2 is almost 100% in a broad spectral range. Our study demonstrates that penta-ZnO 2 possesses unique stable structure and promising mechanical, electronic and optical properties, which offers great potential in a wide range of applications in optoelectronics. Especially, the high flexibility and high light transmission make the penta-ZnO 2 to be a promising candidate for transparent electrodes.

The H2O molecule dissociation on the alkali-earth (Ba and Mg) or transition-metal (Ti)-embedded nitrogen-doped graphene was studied systematically using first-principles calculation. The metal-embedded nitrogen-doped graphene (MN4-graphene) (M = Ba, Mg and Ti) membranes are good candidates for single-atom catalysts (SACs), because the single metal atom can be strongly trapped in the divacancy of the MN4-graphene membranes and exists in the isolated form. The significant activation of the reactant H2O molecule was observed. The binding energy of the first H atom of H2O molecule adsorbed on the MN4-graphene (M = Ba, Mg and Ti) membranes are 2.88 eV, 3.11 eV and 0.75 eV respectively, which are notable smaller than that 6.01 eV for free H2O molecule. Thus, the TiN4-graphene membrane can remarkably decrease the potential barrier of H atom dissociated from H2O molecule, which is a very promising SAC candidate for molecular dissociator. Our report comes as a first report towards the demonstration of the MN4-graphene membranes for the H2O molecule dissociation.

The adsorption of H 2 CO molecule on pristine and transition metal (Ti and V) doped graphene samples were investigated via a first-principles approach based on density functional theory. The most stable adsorption geometry, energy and charge transfer of H 2 CO molecule on pristine and doped graphene are discussed respectively. We have found that Ti and V dopant atoms can significantly enhance the interaction between H 2 CO molecule and graphene. The calculated net electron transfers, electronic density difference images and densities of states give the evidence that the H 2 CO molecules stay on Ti (or V) – doped graphene by chemisorption. After H 2 CO adsorption, there are significant changes in electronic structure near the Fermi level, for both two systems of Ti and V doped graphene. This indicates distinct changes of electron transport properties. We have also found that H 2 CO molecule has a larger absorption energy on V-doped graphene (1.939 eV) compared with Ti-doped graphene (1.120 eV). It is shown that the Ti-doped graphene has enough binding energy, adequate changes in electronic structure and reasonable short recovery time 10 −3 s, making it a promising candidate for detecting formaldehyde gas.

Herein, an isolated hydrogen atom absorbed on penta-graphene (PG) was predicted to induce magnetic moments and tune the electronic properties of penta-graphene and was systematically studied using first-principles calculations. The adsorption energy and formation energy calculations suggest that magnetic penta-graphene (M-PG) and weak magnetic penta-graphene (WM-PG) of hydrogen-absorbed PG systems are energetically the most favorable states among the possible hydrogen-absorbed configurations. The hydrogen atom adsorbed on the PG sheet can effectively tune the electronic properties of PG and change it from a semiconductor to half-metallic. In the M-PG system, this spin-polarized state is essentially localized on the three-fold coordinated C atoms in the first layer opposite to that where the hydrogen atom is chemisorbed. Through changing the bond angle and bond length of the adsorbed hydrogen atom on the PG system, we can remarkably increase the magnetic moment of the hydrogen-absorbed PG system by 137 times. This would allow us to design a magnetic nanoswitch to manipulate the magnetic state of PG. We also obtained the scanning tunneling microscopy (STM) images for future experimental identification. Our findings show that the hydrogen atom absorbed on the PG system will have exciting applications in magnetic storage technology and next-generation electronic and spintronic nanodevices.

In this paper, we demonstrate new electrode pattern on rear side of p-type bifacial passivated emitter and rear cells (bifacial-PERC) solar cells for reducing series resistance loss caused by the aluminum grid lines. Cell efficiency of bifacial PERC is enhanced by rear Al grids add multi bus-bar (MBB) or grid segments interconnection. The high J sc and FF value of the PERC+ using local grid with MBB as rear electrodes which increases the J sc by 0.5 mA/cm2 and FF by 2.58 % compare to the PERC+ without rear MBB. The high Jsc and FF value of the PERC+ using local grid with vertical line segments as rear electrodes which increases the J sc by 0.34 mA/cm2 and FF by 3.6 % compare to the PERC+ without vertical line segments. In contrast to the PERC cell, the bifacial PERC cell using localized Al grid on rear side and with thicker back surface field (BSF).

A design approach of single-/dual-band Wilkinson power dividers with single/two section transmission line transformers is summarized in this letter. Normally, two section transmission line transformer is well-known topology, which is not only used for single-band design application with compact circuit size and harmonics suppression, but also for dual-band circuit in other circuit topologies, such as Wilkinson power divider application. In this paper, several kinds of topologies could be summarized to a general topology with the same design equations and mathematical constraints. It is quite useful to understand the relationship among these topologies, meanwhile, it is also helpful for further circuit improvement.

A conventional metallic photonic crystal (M-PhC) point-defect-cavities(PDC) can be realized by removing a rod from the periodical structure. Therefore, to keep the periodicity, the resonant frequency of such cavity is difficult to be changed. In this paper, a novel class of PDCs is constructed by putting a metallic/dielectric rod at the center of the cavity. By changing the radius of the central rod, the resonant frequency can be easily-tuned. After the calculation of band structure of a square-lattice PhC for TE/TM modes, the resonant-frequencies the cavity are calculated and illustrated. Finally, a PDC-based filter is designed to show its potential applications in microwave regime.

2,4,6-Tris(pyridin-4-yl)-1,3,5-triazine (tpt), as an organic molecule with an electron-deficient nature, has attracted considerable interest because of its photoinduced electron transfer from neutral organic molecules to form stable anionic radicals. This makes it an excellent candidate as an organic linker in the construction of photochromic complexes. Such a photochromic three-dimensional (3D) metal–organic framework (MOF) has been prepared using this ligand. Crystallization of tpt with Cd(NO3)2·4H2O in an N,N-dimethylacetamide–methanol mixed-solvent system under solvothermal conditions afforded the 3D MOF poly[[bis(nitrato-κ2 O,O′)cadmium(II)]-μ3-2,4,6-tris(pyridin-4-yl)-1,3,5-triazine-κ3 N 2:N 4:N 6], [Cd(NO3)2(C18H12N6)] n , which was characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis and single-crystal X-ray diffraction. The X-ray diffraction crystal structure analysis reveals that the asymmetric unit contains one independent CdII cation, one tpt ligand and two coordinated NO3 − anions. The CdII cations are connected by tpt ligands to generate a 3D framework. The single framework leaves voids that are filled by mutual interpenetration of three independent equivalent frameworks in a fourfold interpenetrating architecture. The compound shows a good thermal stability and exhibits a reversible photochromic behaviour, which may originate from the photoinduced electron-transfer generation of radicals in the tpt ligand.

In this study, a novel polarization converter (PC) based on square lattice photonic crystal fiber (PCF) is proposed and analyzed. For each square unit in the cladding, two identical circular air holes are arranged symmetrically along the y = x axis. With the simple configuration structure, numerical simulations using the FDTD analysis demonstrate that the PC has a strong polarization conversion efficiency (PCE) of 99.4% with a device length of 53 μ m, and the extinction ratio is −21.8 dB. Considering the current PCF fabrication technology, the structural tolerances of circular hole size and hole position have been discussed in detail. Moreover, it is expected that over the 1.2∼1.7 μ m wavelength range, the PCE can be designed to be better than 99% and the corresponding extinction ratio is better than - 20 dB .

This paper presents a systematic synthesis procedure for M-PhC(Metallic Photonic Crystal) BPFs(bandpass filters) in THz regime based on M-matrix scheme. M-PhC point-defect cavities with a centrally-loaded-rod are used to design the filters. As an example, a 5th-order Chebyshev-type filter based on an inline structure is designed. The simulation results of the synthesized filter agree well with the theoretical ones, which validates the proposed filter structure and the design scheme.

In this study, a polarization rotator (PR) with a simple structure distribution based on square lattice photonic crystal fiber (PCF) has been proposed. The unit cell in the cladding is designed of two circular air holes that are distributed along the diagonal. Simulation result illustrates that a polarization conversion efficiency of 99.4% is obtained with a device length of 53:2 μm at wavelength of 1:55 μm. Additionally, the structural tolerance and wavelength dependence of the proposed PR are also discussed in detail.

In this paper, a compact tunable Wilkinson power divider is presented with a simple structure. T-type structure replaced a quarter-wave transmission line for compact circuit and tunable function, where T-type structure only includes three varactors and one stub. Design parameters are newly derived from even- and odd-mode analysis. Both characteristic impedance and its electrical length of the stubs could determine a tuning frequency range independently. Therefore, by selecting these two different parameters, various tuning frequency ranges can be realized. One experimental circuit was fabricated, and measured results show a good tuning range with good Wilkinson power divider performance.

A wideband bandpass filter (BPF) composed of two cascaded single-short-circuited-stub-loaded parallel-coupled-lines (SSCSL-PCLs) and two short-circuited shunt stubs at ports are theoretical investigated for the first time. The synthesis formulae of the BPF are derived based on the equi-ripple filtering function. As an example, a wideband BPF with a fractional bandwidth (FBW) of 33% is synthesized. The designed filter is then simulated, fabricated and measured. The good agreement validates the effectiveness of the newly proposed filter structure and the corresponding synthesis technique.

To accurately design wideband filters composed of three-coupled-lines, an improved equivalent circuit is derived by taking the cross-coupling between non-adjacent lines into consideration. Since the cross-coupling between non-adjacent lines is also dependent on the coupling between adjacent lines, conventional synthesis techniques cannot be used directly. Instead, an improved synthesis scheme based on successive iterations is proposed to synthesise the filters. As examples, two 2-stage microstrip three-coupled-line filters [bandwidth: 2.67–5.33 GHz (fractional bandwidth: 67%)] with a reversed connection sequence are synthesised, simulated, and experimentally realised to validate the proposed theory. The frequency responses of the designed filters using the authors’ new model and synthesis theory compare well with those by simulation and experiment, whereas an error of about 17% is found in bandwidth if the authors use the conventional model that neglecting the cross-coupling between non-adjacent lines. In addition, the asymmetric property of the three-line unit is revealed.

Background: Cardiovascular diseases (CVDs) are commonly comorbid with depression and vice versa. Polyunsaturated fatty acids (PUFAs) have been suggested to mediate in CVDs and depression in cross-sectional and observational studies. With the patients of CVDs, we investigated the role of depression on the effect of PUFAs. Methods: Forty-four patients with CVDs were recruited and assessed with Hamilton depression rating scale (HAMD). Patients’ CVDs markers were measured by electrocardiogram and their red blood cell (RBC) samples were collected for PUFAs analyses. Results: The data of 44 subjects were analyzed; where 10 participants (23%) with CVDs had moderate or severe depression, defined by a HAMD score more than 19 points. The moderate depression group had lower docosahexaenoic acid (DHA), omega-3 (N3) and omega-6(N6) to N3 (N6/N3) ratio than non-depression group (HAMD score less than 8), while no differences between the 2 groups in terms of corrected QT (QTc) intervals and high sensitivity C-reactive protein (hsCRP) levels. Furthermore, when we analyzed the data with an inclusion of a more heterogeneous depression group, where HAMD score is greater than or equal to 10 (mild depression group, N = 24), the differences in PUFAs levels between the 2 groups disappear. Secondary analysis of the moderate depression group showed a positive correlation between DHA, N3 PUFAs, and N6/N3 ratio and total HAMD scores, a positive correlation between N3 PUFAs and QTc intervals in non-depression group. Conclusion: Moderate depression group of patients with CVDs had lower levels of DHA, N3, and N6/N3 ratio than non-depression group, while both groups had no differences in QTc and hsCRP. On the other hand, the differences in PUFAs levels disappear in the mild depression group after inclusion of patients with CVDs with greater heterogeneity of depression. Hence, the role of N3 PUFAs is implicated in depression of patients with CVDs if the depression status is more strictly defined.

As a non-destructive measurement technique, flanged-open-ended-coaxial-probe-based measurement technique has been attracting a lot of interests in the simultaneous measurement of the complex EM-parameters (i.e. complex permittivity and permeability) of high loss materials. Since at least two complex reflection coefficients under different experimental setting must be obtained to extract two complex parameters simultaneously, in this paper, we proposes a new method, named “Two-Probes-Method”. Two reflections are obtained by using two different coaxial probes. The broadband frequency-swept measurements/simulations are then conducted on two absorbing materials using APC-7 and 3.5mm coaxial probes. The experimental results agree with the reference data, which validates the feasibility and effectiveness of this proposed technique. It should be noted that the proposed method is applicable for in-situ/nondestructive measurements.

The paper presents a novel bandpass-to-all-stop switchable wideband filter composed of short-ended stubs and modified parallel-coupled-lines, as well as the corresponding synthesis/design scheme. By changing the end-states of the stubs, the bandpass or all-stop state can be realized and switched. To synthesize the two-filter-states simultaneously, firstly, the synthesis equations system for the bandpass state of the filter is derived based on Chebyshev characteristics. It can be found that, for the proposed structure, there will be a degree of freedom in filter synthesis. Accordingly, the equation used to estimate the insertion loss(IL) of the filter in all-stop state is added to the synthesis equations system, so that the two states of the switchable filter can be therefore theoretically synthesized. An example filter is then designed and confirmed in stripline line by simulation. A good agreement between the numerical experimental results and theoretical ones validates the proposed filter structure and corresponding design scheme.

A conventional metallic photonic crystal (M-PhC) point-defect-cavities(PDC) can be realized by removing a rod from the periodical structure. Therefore, to keep the periodicity, the resonant frequencies of such cavities are difficult to be changed. In this paper, an extended study on a recently-proposed novel PDC constructed by putting a metallic/dielectric rod at the center of the cavity will be conducted with an emphasis on the properties of the higher-order modes and a reconfigurable structure with a replaceable centrally-loaded-metal-rod. Since the Qs of the higher-modes are 2-times higher than the fundamental modes, they have great potentials to be used in MMW, SMMW and even in THz bands, while the new PDCs structure has a great potential to realize a reconfigurable devices. After illustration of band structure of a square-lattice PhC for TE/TM modes, the first 3-modes of the cavity are investigated by the numerical technique. A good agreement between the experimental results and simulated ones validates our computation and show its properties.

An improved equivalent circuit of a parallel-coupled three-line section is derived for the design of wideband filter. Compared with the conventional model, the cross-coupling between nonadjacent lines is taken into consideration and shows a better accuracy. A wideband filter composed of three-line sections is then synthesized using the new equivalent circuit. The simulation and measurement results agree well with the theoretical ones, which validates the new model as well as the synthesis method. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2392–2395, 2014