Cross-coupling Paths Research Articles

Mechanistic Facets of the Competition between Cross-Coupling and Homocoupling in Supporting Ligand-Free Iron-Mediated Aryl–Aryl Bond Formations

In the context of cross-coupling chemistry, the competition between the cross-coupling path itself and the oxidative homocoupling of the nucleophile is a classic issue. In that case, the electrophilic partner acts as a sacrificial oxidant. We investigate in this report the factors governing the cross- versus homocoupling distribution using aryl nucleophiles ArMgBr and (hetero)aryl electrophiles Ar′Cl in the presence of an iron catalyst. When electron-deficient electrophiles are used, a key transient heteroleptic [Ar2Ar′FeII]− complex is formed. DFT calculations show that an asynchronous two-electron reductive elimination follows, which governs the selective evolution of the system toward either a cross- or homocoupling product. Proficiency of the cross-coupling reductive elimination strongly depends on both π-accepting and σ-donating effects of the FeII-ligated Ar′ ring. The reactivity trends discussed in this article rely on two-electron elementary steps, which are in contrast with the usually described tendencies in iron-mediated oxidative homocouplings which involve single-electron transfers. The results are probed by paramagnetic 1H NMR spectroscopy, experimental kinetics data, and DFT calculations.

Atomically Dispersed Pt-N3C1 Sites Enabling Efficient and Selective Electrocatalytic C-C Bond Cleavage in Lignin Models under Ambient Conditions.

Selective cleavage of C-C linkages is the key and a challenge for lignin degradation to harvest value-added aromatic compounds. To this end, electrocatalytic oxidation presents a promising technique by virtue of mild reaction conditions and strong sustainability. However, the existing electrocatalysts (traditional bulk metal and metal oxides) for C-C bond oxidative cleavage suffer from poor selectivity and low product yields. We show for the first time that atomically dispersed Pt-N3C1 sites planted on nitrogen-doped carbon nanotubes (Pt1/N-CNTs), constructed via a stepwise polymerization-carbonization-electrostatic adsorption strategy, are highly active and selective toward Cα-Cβ bond cleavage in β-O-4 model compounds under ambient conditions. Pt1/N-CNTs exhibits 99% substrate conversion with 81% yield of benzaldehyde, which is exceptional and unprecedented compared with previously reported electrocatalysts. Moreover, Pt1/N-CNTs using only 0.41 wt % Pt achieved a much higher benzaldehyde yield than those of the state-of-the-art bulk Pt electrode (100 wt % Pt) and commercial Pt/C catalyst (20 wt % Pt). Systematic experimental investigation together with density functional theory (DFT) calculation suggests that the superior performance of Pt1/N-CNTs arises from the atomically dispersed Pt-N3C1 sites facilitating the formation of a key Cβ radical intermediate, further inducing a radical/radical cross-coupling path to break the Cα-Cβ bond. This work opens up opportunities in lignin valorization via a green and sustainable electrochemical route with ultralow noble metal usage.

3-D Printed Dual-Band Filter Based on Spherical Dual-Mode Cavity

A new dual-band bandpass filter (BPF) is designed and fabricated based on a pair of spherical dual-mode resonant cavities using 3-D printing technology. By elaborately introducing three-type metallic posts into each cavity to perturb the degenerated TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> modes in a reasonable way, a dual-band coupling topology is developed in the design accordingly. Owing to the cross-coupling paths in the designed topology, two transmission zeros (TZs) are successfully introduced between the passbands, bringing out a high band-to-band isolation. Even more, TZs can also be generated by creating additional internal coupling paths to the presented dual-band coupling topology. Besides, the spherical cavity provides a higher quality factor and wider stopband, compared to that of a square or cylindrical cavity. To validate the design concept, a dual-band BPF prototype, operating at 12.0 and 12.5 GHz with respective bandwidths of 120 and 240 MHz, is implemented by 3-D printing process. The measured results exhibit good agreement with the simulated ones, showing more than 20-dB return losses and 20-dB dual-band isolation.

Compact high-isolation self-diplexing antenna based on SIW for C-band applications

ABSTRACTThis paper presents a novel compact high-isolation cavity-backed inverted U-shaped slot antenna using substrate-integrated waveguide (SIW) for C-band applications. The SIW cavity is loaded by an inverted U-shaped slot that produces two fictitious aperture for radiation at two distinct frequency bands and to exhibit self-diplexing antenna (SDA) characteristics. Two orthogonal microstrip feed lines are applied for excitation of fundamental mode () and two degenerated modes ( and ). The perturbation of these modes due to slot loading allows to achieve size miniaturization. Compared with conventional SIW cavity without slot, the proposed SDA allows a size reduction of 56%. High isolation is achieved due to the transmission zeros produced by these modes and orthogonal feed lines. This isolation is further improved (>40.5 and >32.8 dB) due to off-centered input ports that creates very weak cross-coupling path between them. The resonating frequencies of the proposed SDA can be designed individually. Finally, an SDA working at 4.29 and 7.52 GHz is fabricated for validation of simulated performances. The measured gains of the fabricated SDA are 5.38 and 5.82 dBi at the resonating frequencies of 4.29 and 7.52 GHz, respectively. A good consistency is found between measured and simulated results.

Third‐order complex delta‐sigma modulator with arbitrary poles and zeros placement

A third-order complex delta-sigma modulation (CDSM) structure with cross-coupling paths is proposed and analysed. Although the conventional CDSM can reduce circuits complexity in digital transmitter systems, it suffers from other shortcomings like increasing algorithm complexity. This structure imports cross-coupling paths both at output and interstage, which realises decorrelation between zeros and poles. The advantage is that complex zeros can be arbitrarily placed, and thus, the reconfigurable digital wireless transmitter application can be satisfied; and the poles are not affected by zeros placement, which improves the flatness of signal transfer function.

New negative coupling structure and its application on substrate integrated waveguide bandpass filters

To design cross-coupled substrate integrated waveguide (SIW) bandpass filters (BPFs) with high performance, a new negative coupling structure is proposed, which is constructed by two coupled lines with shorted ends. The negative coupling structure is analyzed in detail. The stracture which can realize both relatively weak and strong negative coupling strength. The optimization method based on characteristic polynomials and reference zeros and poles of scattering parameters is realized for the filter design. To verify the proposed negative coupling structure, two fourth-order cross-coupled SIW BPFs with the center frequency of 10 GHz based on the optimized coupling matrixes are designed. The first one has a normalized bandwidth of 3% with a negative coupling in one cross-coupling path to illustrate the realization of weak negative coupling strength, and the second one has a normalized bandwidth of 8% with a negative coupling in one main coupling path to illustrate the realization of strong negative coupling strength. Finally, the two BPFs are fabricated and measured. Simulation and measurement results are in good agreement, which demonstrates the feasibility of the proposed negative coupling structure and its application on cross-coupled SIW filters with high performance. The influence of weak disperse cross coupling on locations of transmission zeros is also discussed.

Generalised Chebyshev function bandpass filters in box‐like topologies based on the properties of dual‐mode loop microstrip resonator

A new class of compact microstrip bandpass filters in doublet topology based on a dual-mode loop microstrip resonator with controllable locations of input/output feeding lines is presented and researched. Filters with up to five poles are proposed and researched. Diagonal cross-coupling path in box-like topology can be introduced to produce a finite transmission zero (TZ) with controllable position. Some design examples are provided to illustrate the performances of the proposed two-, three-, four- and five-pole filters with controllable TZs. A three-pole and a five-pole filters were fabricated and measured. Good agreement is achieved between the simulated and the measured results.

SIW bandpass filters in modified box‐section scheme with bypass/constant/frequency‐dependent coupling in diagonal cross‐coupling path

Here, three fourth-order bandpass filters (BPFs) in modified box-section schemes using substrate integrated waveguide (SIW) are proposed and researched. The proposed filters are based on a conventional box-section structure with considering bypass/constant/frequency-dependent coupling (FDC) in the diagonal cross-coupling path to construct new filtering responses. Based on the different type of the cross-coupling path, the frequency response of each proposed structure is analysed and presented, which indicates that the proposed filters have flexible response in terms of finite transmission zeros (FTZs). The proposed filters can realise generalised Chebyshev responses with one/two/three FTZs at arbitrary positions. Moreover, one FTZ may be produced by using bypass coupling and direct inductive coupling window to improve lower stopband performance, which is verified by a coupling matrix. For the demonstration, three quasi-elliptic response filters were designed, fabricated, and measured. Good agreement is achieved between simulated and measured results.

Substrate Integrated Waveguide Bandpass Filters in Box-Like Topology With Bypass and Direct Couplings in Diagonal Cross-Coupling Path

Substrate integrated waveguide (SIW) bandpass filters in box-like topology based on combining single- and dual-mode cavities are presented. Two coupled TE101-mode-based cavities are coupled to one square-shaped dual-mode (modes TE102 and TE201) cavity to realize the box-like coupling scheme in which bypass and direct couplings can provide the diagonal cross-coupling path. Based on the characteristics of dual-mode SIW and multiple energy flow paths, the superior design flexibility in terms of TZ positioning has been realized and demonstrated. Finally, two asymmetrical response SIW filters with two lower TZs, a quasi-elliptic SIW filter with three TZs and a filter with linear-phase response are simulated, fabricated, and measured to demonstrate and verify the proposed structure.

Filtering Antenna With High Selectivity Using Multiple Coupling Paths From Source/Load to Resonators

This communication presents a filtering antenna with high selectivity using multiple coupling path from source/load to resonators. The high selectivity of the filtering antenna’s boresight gain response is achieved by a novel coupling scheme, which induces additional coupling between source/load and nonadjacent resonators to construct cross coupling paths. Thanks to the extra cross-coupling paths, the filtering antenna can generate a maximum of N radiation nulls with N resonators. Besides, a resonator using a combination of open-ended stub and short-ended stub is adopted to construct this novel coupling scheme more easily. For demonstration, a three-order filtering stacked patch antenna with a center frequency of 2.3 GHz and a fractional bandwidth of 15.2% is fabricated. Two independently controllable radiation nulls are located at 1.97 and 2.61 GHz. Unidirectional radiation patterns have been achieved with cross polarization lower than −20 dB and back lobes lower than −18 dB.

Tri-band cross-coupling bandpass filter with rectangular defected ground structure array

A tri-band cross-coupling bandpass filter (BPF) with rectangular defected ground structure (DGS) array is proposed in this paper. Cross-coupling paths comprised of five resonators are employed to achieve general Chebyshev filtering frequency responses. Besides changing gaps among resonators, a novel rectangular DGS array is proposed to exactly meet coupling coefficients for specific demands for different passband in multi-band BPF. The centre frequency of the tri-band filter that is selected at 2.4, 3.4, 5.5 GHz are for LTE, Bluetooth, WiMAX and WLAN. The 3 dB bandwidth of the three passbands are 5, 3.23 and 3.45%, respectively, meanwhile, more transmission zeros are generated, leading to enhanced selectivity and high out of band isolation. The proposed tri-band filter is completed with a few simple calculations and several brief processes. Measured results of the fabricated filter demonstrate the theory prediction and proposed method well.

Ultra‐compact highly selective quasi‐elliptic filters based on combining dual‐mode SIW and coplanar waveguides in a single cavity

Two bandpass filters (BPFs) are implemented on a single dual-mode square-shaped substrate-integrated waveguide (SIW) cavity with two etched coplanar waveguides. The proposed BPFs can achieve two transmission zeros (TZs) using dual modes in the SIW cavity (i.e. TE102 and TE201) with non-resonating mode (i.e. fundamental TE101), which provides a direct input-to-output coupling. Moreover, the positions of the two TZs can be tuned by changing the positions of input and output ports. Moreover, an extra TZ with controllable position is also achieved by using controllable electric and magnetic mixed coupling; and the TZ also can be split into two TZs for the mixed cross-coupling paths. The BPFs with the controllable TZs improve the selectivity and out-of-band rejection. The designed BPFs have a centre frequency of 5.8 GHz. The measured results agree with the simulated ones.

Digital Complex Delta–Sigma Modulators With Highly Configurable Notches for Multi-Standard Coexistence in Wireless Transmitters

This paper presents a complex delta–sigma modulator (CDSM) designed for integration in a digital transmitter chain targeting multi-standard coexistence with nearby receivers. The use of a DSM has the advantage of increased performance in terms of signal-to-noise-ratio in the band of interest. However, the resulting out-of-band noise becomes an issue for multi-standard coexistence, thus increasing the complexity of the subsequent filtering stage. This constraint could be relaxed in the DSM stage, by placing a complex zero near the frequency band, where a low noise level is needed. This is achieved by cross coupling the in-phase (I) and quadrature (Q) channels, thus obtaining a CDSM. A review of known design methods for CDSM revealed limitations regarding the poles/zeros optimization, and the configurability of the complex zeros placement. The proposed architecture introduces two additional cross couplings from the I and Q quantizers outputs in order to decorrelate the zeros placement and the poles optimization problem. Hence, the improved CDSM can be implemented using existing optimization tools, which reduces considerably the number of iterations and the computational effort. In addition, the resulting modulator can target different coexistence scenarios without the need of redesign, unlike other known methods. Simulation results show a noise level reduction of approximately 20–30-dB near specific frequency bands by the proposed CDSM scheme with respect to standard DSM. Finally, we show an efficient coarse/fine configurability mechanism, which is obtained when introducing additional delays in the cross-coupling paths.

Quantum-optical description of losses in ring resonators based on field-operator transformations

In this work we examine loss in ring resonator networks from an "operator valued phasor addition" approach (or OVPA approach) which considers the multiple transmission and cross coupling paths of a quantum field traversing a ring resonator coupled to one or two external waveguide buses. We demonstrate the consistency of our approach by the preservation of the operator commutation relation of the out-coupled bus mode. We compare our results to those obtained from the conventional quantum Langevin approach which introduces noise operators in addition to the quantum Heisenberg equations in order to preserve commutation relations in the presence of loss. It is shown that the two expressions agree in the neighborhood of a cavity resonance where the Langevin approach is applicable, whereas the operator valued phasor addition expression we derive is more general, remaining valid far from resonances.

Synthesis and Implementation of LTCC Bandpass Filter With Harmonic Suppression

In this paper, we utilize the coupling matrices to design a compact low-temperature cofired ceramic (LTCC) bandpass filter with wide stopband and high selectivity. One coupling matrix at the fundamental frequency is synthesized to obtain required passband responses. The other one at the third harmonic is manipulated to realize wide stopband. Two transmission zeros are appointed at both sides of the passband to enhance the skirt selectivity. They are generated by multiple cross-coupling paths, which are easy to realize in the multilayer LTCC structure. To reduce the circuit size, two coupled quarter-wavelength resonators are folded vertically and horizontally on different layers. An experimental filter is designed for verification. High skirt selectivity and wide stopband are observed in the measurement. Due to the LTCC techniques, the proposed circuit has a compact size of $2~\text {mm}\times 1.7~\text {mm}\times 2$ mm or $0.042\lambda _{g}\times 0.035\lambda _{g}\times 0.042\lambda _{g}$ . It is suitable for system-in-package applications.

Dual-mode substrate integrated hexagonal cavity (SIHC) filter with uncoaxial feeding structure

Novel uncoaxial dual-mode substrate integrated hexagonal cavity (SIHC) filters are presented for high selectivity application. The SIHC filters with uncoaxial feeding structure can add two extra coupling paths to their topologies: one is a source–load coupling path, and the other is a non-physical higher order modes cross-coupling path. Under the circumstances, the proposed filter can generate up to three transmission zeros (TZs) for improving stopband performance. Meanwhile, the numbers and the locations of TZs can be controlled conveniently by tuning the uncoaxial feeding structure. Accordingly, the filter not only has good selectivity due to flexible TZs, but also has a small size by virtue of its single-cavity structure. Two experimental filters at the same central frequency of 10 GHz but with different fractional bandwidths of 2 and 5% and numbers of TZs from 2 to 3 are designed, fabricated, and measured to validate the proposed structure. The measured results agree well with the simulated ones, with their good performance just as pedicted.

A zero phase error tracking based path precompensation method for high-speed machining

Contour error due to the dynamic characteristics of feed system has a great influence on machining accuracy, in high-speed machining. In this paper, a new path precompensation method is proposed using zero phase error tracking control algorithm to improve the contouring accuracy for multiaxis machining with large feed rates. In this method, the outputs are predicted with the identified position-loop models of feed systems, and a contour error calculator is designed to calculate contour error in each sample instance using the predicted output and reference input. In order to compensate the contour error resulting from the dynamic tracking error of feed systems, the contour error vector is decomposed orthogonally and the compensation components for individual axis are calculated using zero phase error tracking control algorithm. Simulations showed that contour errors can be significantly improved with small compensation using the new path precompensation method for linear, circular, and parabola contours. Experimental results showed that the new method can reduce contour error significantly and achieve a better compensation compared with zero phase error tracking control and cross-coupled path pre-compensation.

Extended Noise Shaping in Sigma-Delta Modulator Using Cross-Coupled Paths

In this paper, combined with time-interleaving, noise coupling is used to achieve considerable improvement in the performance of sigma-delta modulator. Two types of noise-coupling, unextended and extended coupling, are presented for $N$ -path architecture based on first-order sigma-delta modulator which can enhance the effective order of noise shaping without significant overhead. In the general condition, the optimum coupling matrices are obtained analytically to achieve the desired noise shaping. It is also shown that the proposed $N$ -path first-order sigma-delta modulator provides $(2N-1)$ th-order noise shaping. However, the unextended coupling provides $N$ th-order. To verify the proposed method, the macro-level simulations show that third-order and fifth-order noise shaping were achieved in two-path and three-path first-order sigma-delta modulators with extended noise coupling, respectively. Likewise, the ADS software's simulation result of the switched-capacitor circuit implementation confirms the effectiveness of the proposed method.

Miniaturized Mixed Electric and Magnetic Coupling Bandpass Filter Based on Interdigital Resonator

By integrating the interdigital structure into a conventional open-loop resonator, a compact mixed electric and magnetic coupling bandpass filter is designed and fabricated for the first time. Due to the high intensity inner coupling capacitor, which is generated by interdigital lines, not only did the size of the filter sharply decrease, but the electric field was strengthened. Therefore, by properly adjusting the ratio of electric and magnetic coupling, the transmission zeros very close to the passband is obtained readily. Based on mixed electric and magnetic coupling, a fourth-order bandpass filter with multiple transmission zeros is realized without requiring either a cross-coupled path or source-load coupling. For design purposes, the equivalent-circuit model is also derived and verified. Advantages of this filter include its miniaturized size of only 0.06λ0 × 0.045λ0, its sharp cutoff slope, as well as the tiny discrepancies between simulation and measurement.

Two New Electric Coupling Structures for Double Folded Substrate Integrated Waveguide Cavity Filters with Transmission Zeros

Two electric coupling structures for double folded substrate integrated waveguide (DFSIW) cavity filters are presented in this article. The coupling strength can be easily tuned, and the coupling mechanism is investigated. With electric coupling realized by the proposed structures in the main path and magnetic coupling by a conventional coupling structure in the cross coupling path, an X-band cross-coupled filter is designed, which possesses a transmission zero on either side of the passband. A prototype of the filter is fabricated to validate the predicted frequency response, and the measured results agree with the simulated ones. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1815–1818, 2013