Feng Xu

Bio: Feng Xu is an academic researcher from Nanjing University of Posts and Telecommunications. The author has contributed to research in topics: Coplanar waveguide & Dipole antenna. The author has an hindex of 3, co-authored 10 publications receiving 21 citations.

A planar magic-T based on folded substrate integrated waveguide

Abstract: In this paper, a novel planar magic-T using H-plane folded substrate integrated waveguide (FSIW) and E-plane substrate integrated waveguide (SIW) power dividers without narrowband slotline-to-SIW transition is proposed. Due to the symmetrical field in the FSIW, two equal in-phase outputs are achieved. The signal applied to the difference SIW port, is split by the middle metal ground into two out-of-phase signals. And a novel way to excite folded substrate integrated waveguide (FSIW) is utilized in order to obtain a broader bandwidth in the proposed magic-T. If the edge of the middle metal layer is designed properly, the bandwidth will be further extended. From 6.65GHz to 9.73GHz (fractional bandwidth 37.6%), the return loss is below −15dB and the amplitude and phase imbalances are less than 0.1dB and 1o, respectively. The measured results are in good agreement with the simulated results.

A compact bandpass filter with SIW triangular cavities

Abstract: In this paper, a compact bandpass cross-coupled substrate integrated waveguide (SIW) filter with transmission zero is proposed. Using three triangular cavities as basic elements, a bandpass filter is designed and fabricated on a single-layer substrate with the standard printed circuit boards (PCB) process. This structure gives full expression to the advantages of compact SIW triangular cavity. Not only the compact structure, but also the inverse feedback is the characteristic of the bandpass filter. The cross-coupled technique makes a sharper transition performance at the upper sideband and a great promotion to out-band.

A novel UWB bandpass filter based on double interdigital structure

Abstract: In this paper, a novel ultra-wideband (UWB) filter with double interdigital structures and periodic slow wave structures is proposed. By using these structures, the performance of the microstrip bandpass filter has been improved significantly. The slow wave structures are constructed by the periodic fishbone structures and the ground etching periodic square holes. This novel filter is very compact and has a wide passband of 5.4GHz from 2.4GHz to 7.8GHz and the fractional bandwidth is about 106%. The simulation results and measurement data have verified the proposed UWB filter.

An improved coplanar waveguide to slotline transition for multi-layer circuit structures

Abstract: A novel transition from coplanar waveguide (CPW) to slotline is presented in this paper, which utilizes conduct vias and metal strips to connect two ground planes of CPW instead of air bridges. The metal strips which connect the two ground planes in the back of CPW are used to suppress the reflected slotline mode in order to reduce the return loss and enlarge the bandwidth. The CPW stub used as a phase shifter converts the CPW mode to slotline mode. Due to the absence of the air bridges in the component structure, the transition can be integrated on a multilayered microwave and millimeter-wave circuits. Compared to other transitions, the proposed transition has the advantages of higher compactness, simpler fabrication, lower radiation and lower cost. The simulation results and measurement data have verified the proposed transition.

A Broadband Microstrip-to-Folded Substrate Integrated Waveguide Transition and In-phase Power Divider

Abstract: In this paper, a novel microstrip-to-FSIW (folded substrate integrated waveguide) is proposed, which has a lot of good performances such as low return loss and insertion loss from 6GHz to 13.8GHz. The field in FSIW has been studied before and is folded in H plane for TE10 mode. The field in the underneath substrate is similar to microstrip and the whole field in FSIW is similar to stripline so that the proposed transition can be realized by using stripline. In order to reduce the radiation loss, the stripline is shielded by two rows of conduct holes to constrain the field. What is more, an inductive metal via hole is positioned on the interface of stripline and FSIW to obtain better impedance matching in a broader bandwidth. There are some other types of transitions shown in this paper for comparison and an in-phase power divider is shown. The measured results are in good agreement with the simulated results.

Analysis and design of efficient passive components for the millimeter-wave and THz bands

Abstract: This thesis tackles issues of particular interest regarding analysis and design of passive components at the mm-wave and Terahertz (THz) bands. Innovative analysis techniques and modeling of complex structures, design procedures, and practical implementation of advanced passive devices are presented. The first part of the thesis is dedicated to THz passive components. These days, THz technology suffers from the lack of suitable waveguiding structures since both, metals and dielectric, are lossy at THz frequencies. This implies that neither conventional closed metallic structures used at microwave frequencies, nor dielectric waveguides used in the optical regime, are adequate solutions. Among a variety of new proposals, the Single Wire Waveguide (SWW) stands out due to its low attenuation and dispersion. However, this surface waveguide presents difficult excitation and strong radiation on bends. A Dielectric-Coated Single Wire Waveguide (DCSWW) can be used to alleviate these problems, but advantages of the SWW are lost and new problems arise. Until now, literature has not given proper solution to radiation on bends and, on the other hand, rigorous characterization of these waveguides lacks these days. This thesis provides, for the first time, a complete modal analysis of both waveguides, appropriated for THz frequencies. This analysis is later applied to solve the problem of radiation on bends. Several structures and design procedures to alleviate radiation losses are presented and experimentally validated. The second part of the thesis is dedicated to mm-wave passive components. These days, when implementing passive components to operate at such small, millimetric wavelengths, to ensure proper metallic contact and alignment between parts results challenging. In addition, dielectric absorption becomes significant at mm-wave frequencies. Consequently, conventional hollow metallic waveguides and planar transmission lines present high attenuation so that new topologies are being considered. Gap Waveguides (GWs), based on a periodic structure introducing an Electromagnetic Bandgap effect, result very suitable since they do not require metallic contacts and avoid dielectric losses. However, although GWs have great potential, several issues prevent GW technology from becoming consolidated and universally used. On the one hand, the topological complexity of GWs difficulties the design process since full-wave simulations are time-costly and there is a lack of appropriate analysis methods and suitable synthesis procedures. On the other hand, benefits of using GWs instead of conventional structures are required to be more clearly evidenced with high-performance GW components and proper comparatives with conventional structures. This thesis introduces several efficient analysis methods, models, and synthesis techniques that will allow engineers without significant background in GWs to straightforwardly implement GW devices. In addition, several high-performance narrow-band filters operating at Ka-band and V-band, as well as a rigorous comparative with rectangular waveguide topology, are presented.

A W-band miniature power divider based on E-faced-folded magic-T junction

Abstract: A novel design of W-band power divider using E-faced-folded waveguide magic-T junction to realize the miniaturization is proposed in this paper. A stepped regular triangular prism and the stepped impedance transformer are utilized in order to obtain excellent performance. Besides, the performance of the E-faced-folded magic-T power divider is also improved by using short planes. The measured results show that the insertion loss of the power divider is better than 0.6dB and the return loss is better than 15dB. The measured average E-H isolation is better than 30dB from 92GHz to 100GHz range.

Triangular substrate integrated waveguide resonant cavity dual-mode band-pass filter

Abstract: The invention discloses a triangular substrate integrated waveguide resonant cavity dual-mode bandpass filter based on different wave ports. A resonant cavity is in the shape of an isosceles triangle,the top angle of which is 120 degrees. The dual-mode bandpass filter comprises three structures: the two wave ports are in the two side edges of the isosceles triangle respectively; the two wave ports are arranged in the bottom edge of the triangle; and one wave port is arranged in one side edge of the triangle and the other wave port is arranged in the bottom edge of the triangle. Two microstriplines are connected with the resonant cavity; and four metal through holes are arranged between the two microstrip lines to serve as interference columns, and thus a complete resonant cavity is formed. The four metal through holes are introduced to serve as the interference columns for the first time, so that resonant frequency of a fundamental mode is changed to a higher frequency, while resonant frequency of a first higher-order mode keeps basically unchanged, and the dual-mode bandpass filter is formed. The dual-mode bandpass filter is simple in structure, easy to process and good in performance, and lays a foundation for future study of a more compact dual-mode filter.

Filter-divider based on quarter-mode substrate integrated waveguide circular cavities

Abstract: The invention discloses a filter-divider based on quarter-mode substrate integrated waveguide circular cavities; the filter-divider is formed by combining two quarter-mode substrate integrated waveguide circular cavities through signal input microstrip lines; the quarter-mode substrate integrated waveguide circular cavities are acquired by segmenting a substrate integrated waveguide circular cavity along any two mutually perpendicular magnetic walls, each quarter-mode substrate integrated waveguide circular cavity is provided with a signal input microstrip line and a signal output microstrip line respectively along its two right-angle side, and a field mode disturbance hole and a parasitic passband inhibition mode disturbance hole are arranged in each quarter-mode substrate integrated waveguide circular cavity; a signal input from the signal input end enters the two quarter-mode substrate integrated waveguide circular cavities, and the signal filtered and divided is output from the signal output ends of the two signal output microstrip lines. The size of the filter-divider is reduced significantly; with a filter and a divider combined, the filter-divider forms a high-integrity multifunctional passive device suitable for filtering and power dividing in a microwave and millimeter wave communication system local oscillator.

Compact cross‐coupled filters based on isosceles right triangular and equilateral triangular SIW cavities

Abstract: Two kinds of classical triangular metric resonant cavities including the isosceles right triangular and equilateral triangular metric cavities are investigated carefully. A comprehensive and rigorous derivation process of these two resonant cavities is proposed. Based on this, the mode function and the transverse field components for the modes in the triangular substrate-integrated waveguide (SIW) cavities can be provided. Then the resonant frequency of both kinds of triangular SIW cavities can be calculated. Combined it with the coupling matrix, a fourth-degree filter implemented of isosceles right triangular SIW cavities and a sixth-degree filter formed by equilateral triangular SIW cavities are designed, fabricated and measured in detail. The measured results are in line with the simulated ones. The frequency responses of both filters show a pair of transmission zeroes at each side of the pass band due to the cross-coupling structure. It also verifies the validity of the derivation in this study. Compared with the rectangular and circular resonant ones, the construct of the triangular cavity has the advantage of much more compact. Besides, the proposed filters based on the triangular cavity also have their own advantages of low cost, good selectivity and easy integration with other planar circuits.