Suspended Line Research Articles

A self‐packaged multilayer all‐metal integrated suspended slotline dual‐band filter

AbstractThis paper introduces a novel implementation technology for realizing dual‐band bandpass filtering responses using high‐ slotline resonators with self‐packaged multilayer configuration. The concept of a 3D slotline is introduced, which utilizes the innovative metal‐integrated suspended line (MISL) technology. This technology utilizes an all‐metal structure, effectively eliminating dielectric loss. Furthermore, the implementation of an encapsulated structure significantly reduces radiation loss in the slotlines. Thus, the factors are greatly improved. Based on MISL, a dual‐band bandpass filter with wideband responses and multiple transmission zeros was designed, fabricated, and tested based on 3D cascaded‐mode half‐wavelength resonators. The test results demonstrated a high level of consistency with the simulation results, confirming the high‐ characteristics of the proposed 3D slotlines.

A Miniaturized SISL Bandpass Filter Based on Deep Hole Drilling Capacitor

ABSTRACTIn this paper, a quasi‐lumped element‐based bandpass filter is implemented by substrate‐integrated suspended line (SISL) technology. To miniaturize the filter size, a deep hole drilling capacitor (DHDC) structure is proposed. The properties of DHDC are derived by parametric analysis and equivalent circuit analysis. Based on derived properties, a quasi‐lumped element bandpass filter using SISL technology is designed and fabricated. Experimental results demonstrate that the proposed bandpass filter achieves the center frequency of 1.48 GHz, with a fractional bandwidth of 50%. The minimum insertion loss within the passband is 0.96 dB, while the return loss exceeds 23.14 dB. The maximum out‐of‐band suppression is over −50 dB, and the filter size is only 0.172 λg × 0.062 λg.

Novel design and implementation of 3d packaged wideband bandpass filters

This study presents an innovative method for designing a 3D packaged wideband bandpass filter (BPF) by vertically integrating a high-pass filter (HPF) and a low-pass filter (LPF) using an air cavity and vertical interconnect accesses (VIAs). This integration enhances performance while significantly reducing system size. The fabricated BPF, constructed on multilayer substrates, achieves a passband from 2.175 to 4.2 GHz with less than 2.5 dB insertion loss and a return loss exceeding 10 dB. The design utilizes a partial substrate integrated suspended line (SISL) structure, enabling precise control over the equivalent dielectric constant and characteristic impedance to optimize insertion loss. The height of the air cavity, determined through theoretical analysis and S-parameter inversion, is critical for achieving optimal filter performance. The methodology allows for independent circuit designs on each layer, resulting in a 3D assembly. This refined approach makes it easier to produce compact bandpass and multi-band filters, simplifying circuit development and enabling scalable fabrication. This design is versatile across different frequency ranges, demonstrating significant practical and theoretical benefits.

A vertical transition for suspended line with two transition modes

In this article, we propose a substrate-integrated suspended line (SISL) vertical transition for chip packaging. The transition structure supports both counter-directional and co-directional modes for single-module packaging and vertical integration, respectively. Furthermore, the incorporation of an electromagnetic band gap (EBG) reduces the demands on substrate electrical contact and simplifies the assembly process. A transition structure was designed to convert SISL to a grounded coplanar waveguide (GCPW) to facilitate measurement. The overall structure can be implemented using cost-effective printed circuit board (PCB) technology. Two prototypes of this transition were designed and fabricated. In the frequency range of 12–18 GHz, corresponding to a fractional bandwidth of 40%, the measured return loss is better than 12 dB, while the insertion loss remains consistently below 2.2 dB.

Microwave plasma interaction in a printed transmission line for a power limiting application: from surface-wave-sustained to leaky-wave-sustained discharge

The coupling between a microwave signal and a plasma discharge in a suspended microstrip transmission line is analytically studied. Maxwell’s equations are solved in a 2D approximation to get the expressions of the electromagnetic field. The wave propagation in the guiding structure is first explored without plasma, and for several modes and frequencies. A unified characterization of the three different modes that can propagate at the interface between two dielectric media, namely the leaky waves, the pseudo-surface wave and the pure surface wave, is given in terms of of both wave vectors and electromagnetic field magnitude distribution. This analyze allow to conclude that the fundamental mode in this case is a pseudo-surface wave. Thereafter, we focus on the microwave propagation with a uniform plasma inside the guiding structure. In the non collisional limit, it appears that the plasma discharge is sustained by the so-called pure surface wave, whereas in the collisional limit, a leaky wave propagates along the plasma column. Finally, a non-uniform density profile is taken into account in the calculation. The numerical results obtained from the self-consistent simulation of the microwave-plasma coupling, in a previous work, are thus analyzed with the aid of the analytical formulas to identify the microwave coupling involved in our plasma-based microwave power limiter. The computed propagation constant from numerical data confirmed the type of coupling exhibited for a uniform electron density. Furthermore, we highlight the role of the dielectric slab, from which electromagnetic power transfer occurs into the plasma discharge.

A Ka-Band Two-Channel Two-Beam Receiver Based on a Substrate-Integrated Suspended Line

To realize the miniaturization and high performance for the key transceiver components of a phased array antenna, we proposed a two-channel two-beam receiver based on a substrate-integrated suspended-line (SISL). Multi-layer composite substrate printing circuit is used in the SISL structure to replace the metal cavity and passive circuits. The active components are placed in the air cavity in the SISL structure. The substrates forming the cavity are soldered together to ensure the hermetic seal and high performance. The SISL circuits have the advantage of low loss, low cost, light weight, self-packaging, and high inter-channel isolation. The proposed Ka-band two-channel two-beam receiver shows a gain of >28 dB, a noise figure of <2.6 dB, with functions of 6-bit phase shifting and attenuation.

Novel 6‐GHz/80.8% fractional bandwidth filtering power divider with ultra‐large coupling coefficient using air‐dielectric broadside‐coupled lines

AbstractIn the letter, a wideband filtering power divider (FPD) with ultra‐large coupling coefficient using air‐dielectric broadside‐coupled lines is proposed. The broadside‐coupled line and single transmission line are alternately connected to construct three resonators, which can be used for large bandwidth and high selectivity filtering. An improved substrate‐integrated suspended line (SISL) structure with two inner layers is developed. In the structure, the broadside coupling occurs by the air. The overall structure is implemented based on the low‐cost FR4 dielectric material. The designed FPD is simulated and fabricated. The results demonstrate its excellent performance, with center frequency of 6 GHz, a fractional bandwidth (FBW) of 80.8%, a maximum coupling coefficient of 0.84, an insertion loss of less than 0.29 dB, and an out‐of‐band rejection of more than 52 dB.

Contactless current measurement for suspended overhead lines using a magnetic field sensor array

AbstractIn this study, a long‐distance non‐contact current measurement method is proposed based on the non‐contact sensor array measurement technology, combined with a new current algorithm. The sensor array is a vertical array composed of three three‐axis magnetic field (MF) sensors that is placed on the ground plane below the measured overhead line. The proposed current algorithm can optimize the geometry of the overhead line using the spatial MF values measured by the sensor array and then the three‐phase currents can be calculated. To improve the accuracy of current measurement, the spatial MF model in the algorithm considers the influence of cable sag. It enables a more accurate coupling matrix between the measured overhead line and the sensor array to be established. Additionally, the current algorithm architecture is designed using a composite algorithm to more optimally obtain the best three‐phase current values. A scale‐down overhead‐line measurement system is developed to test the proposed current measurement method. The results show whether a cable sag exists when the three‐phase currents are approximately balanced, with errors less than 2.0%. Moreover, it can be determined whether cable sag exists when the three‐phase currents are unbalanced, with less than 3.4% errors.

Synthesis Design of In-Line Pseudoelliptic SISL Bandpass Filter Employing Non-Resonating Mode in Low-Loss Patch Resonators

This paper presents a novel type of patch resonator suitable for the design of high selectivity in-line pseudoelliptic bandpass filters (BPFs) based on a substrate-integrated suspended line (SISL) platform. The proposed structure is a rectangular patch resonator that allows the propagation of the fundamental mode and high order modes. By controlling the position of input and output feedlines, the proposed resonators can provide both a reflection and a transmission zero simultaneously. Thus, a pole-zero pair can be produced (behaving as a singlet). The position of poles and zeros can be fully controlled by varying the position and orientation of the feeding lines. To verify the proposed concept, a detailed study about the behavior of the patch singlet and a validated third-order filter BPF with three TZs ( canonical BPF) located in the lower and upper passband is presented in this brief. The measured results exhibit an extended stopband with rejection better than 58 dB in the lower passband and 40 dB in the upper passband. The tested return losses and insertion loss are better than -15.7 dB and 1.31 dB, respectively.

A wideband and self-packaged D-CRLH diplexer based on substrate-integrated suspended line

A wideband and self-packaged D-CRLH diplexer based on substrate-integrated suspended line

A compact differential branch‐line coupler using folded substrate integrated suspended parallel strip line

AbstractThis letter presents a compact fully differential branch‐line coupler. It is composed of folded substrate integrated suspended parallel strip line (SISPSL), which can generate slow‐wave effect and help reduce the circuit size. The used SISPSL type line is a fusion of double‐sided parallel‐strip line (DSPSL) and substrate integrated suspended line (SISL), which has the advantage of self‐packaging as compared with traditional DSPSL exposed to air. A DC to 30‐GHz differential transition from grounded coplanar waveguide (GCPW) to SISPSL is designed to test the SISPSL differential coupler. The implemented SISPSL branch‐line coupler has a compact size of 0.056 λg × 0.05 λg.

Design of Ka-Band SISL High Selectivity Bandpass Filter With Controllable Zeros

In this letter, high selectivity bandpass filters (BPFs) using folded stepped-impedance resonators (SIRs) are proposed based on substrate-integrated suspended line (SISL) platform. It is easy to change the position of transmission zeros (TZs) by controlling the strength of electric/magnetic coupling, separately. Also, the structure is compact with double-layer wiring and via holes. To validate the proposed method, two SIR electromagnetic coupling BPFs are implemented on FR-4 substrates. The rectangular coefficients (BW <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{20\, \text{dB}}}$</tex-math> </inline-formula> /BW <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{3\, \text{dB}}$</tex-math> </inline-formula> ) of the second-order and the fourth-order filters are only 2 and 1.3, respectively. In addition, air cavity, metal shielding wall, and substrate excavation methods also dramatically reduce the loss in substrates.

Slow‐wave substrate integrated suspended parallel strip line and its application to rat‐race coupler

AbstractThis paper presents a slow‐wave substrate integrated suspended parallel strip line (SW‐SISPSL) for the first time. The slow‐wave effect is produced by cascading high/low‐impedance SISPSL in the meander line configuration. Different from conventional single‐ended slow‐wave transmission lines, the proposed SW‐SISPSL supports differential signal transmission. The characteristic impedance and slow‐wave factor of the SW‐SISPSL are analyzed using equivalent circuit models. Using the proposed SW‐SISPSL and a SISPSL phase inverter, a very compact rat‐race coupler is implemented. The core circuit area of the slow‐wave rat‐race coupler is 0.083 λg × 0.089 λg, which is only 4.12% of the conventional topology.

Novel Miniaturized Self-Packaged Filters Based on Metasubstrate in SISL Platform

In this paper, a novel strategy is proposed to design miniaturized self-packaged filter based on the proposed metasubstrate in substrate integrated suspended line (SISL) platform. Multi-layer SISL and periodic metasubstrate structures contribute to the miniaturization and self-packaging of second-and fourth-order quarterwavelength hairpin filters, caused by the higher permittivity. The designed dumbbell-shaped metasubstrate shows a high relative permittivity of 15.4. The proposed FR4-based second/fourth-order filters with a reduced insertion loss of 1.13 dB/1.49 dB only show the miniaturized size of 0.26 λg ×0.19 λg and 0.27 λg ×0.32 λg, respectively. And the circuit areas of the above two designed filters with metasubstrate are reduced by 46% and 34%, compared with the cases without metasubstrate, successively.

Changes in shell height/shell length ratio of Pacific oyster &lt;i&gt;Crassostrea gigas&lt;/i&gt; under suspended line culture in Matoya Bay, Mie Prefecture, Japan

Changes in shell height/shell length ratio of Pacific oyster &lt;i&gt;Crassostrea gigas&lt;/i&gt; under suspended line culture in Matoya Bay, Mie Prefecture, Japan

A 220-GHz Balanced Frequency Tripler With Independently Biased Schottky Diodes

A 220-GHz balanced frequency tripler with independently biased diodes is presented. By introducing parallel coupled suspended lines in the circuit, an even mode signal is supported to propagate and excite the diode pair involved in the tripler in antiphase, thus the even harmonics are suppressed. By using two physically separated suspended lines, the diodes can be biased with different voltages and the circuit imbalance can be compensated. The presented tripler does not require any on-chip capacitor or discrete bias-tee, thus the circuit size and requirements on the circuit fabrication technology are greatly reduced. A prototype using a discrete diode and quartz substrate is fabricated, assembled, and measured. Measurement shows with 160–220-mW input power, a typical efficiency of 8% can be achieved, the average output power is 17 mW, and the 3-dB bandwidth covers the 212–228-GHz band. The output power can be improved by about 6.5% with an independent bias for each diode chip.

Compact wideband filtering Balun Based on SISL Technology

AbstractA new compact wideband filtering balun based on substrate-integrated suspended line technology is presented in this brief. The proposed device is composed of a λg/4 suspended stripline open-circuited stub, a λg/2 suspended stripline resonator, and a λg/2 suspended slotline resonator. These striplines and slotline are encapsulated in an electromagnetic (EM) shielding box consisting of air cavity, surrounding substrate layers, and metal layers to achieve EM shielding performance. By properly exciting the suspended stripline and slotline resonators, three transmission poles are generated to achieve high frequency selectively. The intrinsic 180∘ phase difference between the two output ports can be obtained by using the electric field distribution caused by the perpendicular coupling between the suspension stripline and the slotline resonator. The wideband passband is achieved with magnitude balance and out-of-phase properties. To validate our proposal, a wideband filtering balun operating at 2.56 GHz with fractional bandwidth of 65.6% is designed and fabricated.

High-Precision and Rapid Direct Laser Writing Using a Liquid Two-Photon Polymerization Initiator.

Two-photon polymerization based direct laser writing (DLW) is an emerging micronano 3D fabrication technology wherein two-photon initiators (TPIs) are a key component in photoresists. Upon exposure to a femtosecond laser, TPIs can trigger the polymerization reaction, leading to the solidification of photoresists. In other words, TPIs directly determine the rate of polymerization, physicochemical properties of polymers, and even the photolithography feature size. However, they generally exhibit extremely poor solubility in photoresist systems, severely inhibiting their application in DLW. To break through this bottleneck, we propose a strategy to prepare TPIs as liquids via molecular design. The maximum weight fraction of the as-prepared liquid TPI in photoresist significantly increases to 2.0 wt %, which is several times higher than that of commercial 7-diethylamino-3-thenoylcoumarin (DETC). Meanwhile, this liquid TPI also exhibits an excellent absorption cross section (64 GM), allowing it to absorb femtosecond laser efficiently and generate abundant active species to initiate polymerization. Remarkably, the respective minimum feature sizes of line arrays and suspended lines are 47 and 20 nm, which are comparable to that of the-state-of-the-art electron beam lithography. Besides, the liquid TPI can be utilized to fabricate various high-quality 3D microstructures and manufacture large-area 2D devices at a considerable writing speed (1.045 m s-1). Therefore, the liquid TPI would be one of the promising initiators for micronano fabrication technology and pave the way for future development of DLW.

A negative‐resistance oscillator using dual‐cavity based on SISL technology

AbstractThis article presents a low‐phase noise negative resistance oscillator using the dual‐cavity resonator (DCR) based on substrate integrated suspended line (SISL) technology. Two air cavities are stacked without increasing the footprint areas of the oscillator. A coupling hole is introduced to realize weak coupling between the two air cavities. The DCR can enhance the roll‐off of the equivalent resonator. The measured Q factor of the DCR is increased by 15% compared with the single cavity resonator. The measured phase noise of the designed oscillator is −135.32 dBc/Hz at 1 MHz offset from the carrier frequency of 12.44 GHz, and the measured FOM at 1 MHz offset is −204 dBc/Hz. Besides, the designed oscillator based on SISL technology has the advantages of low cost, compact size, and self‐packaging properties.

3-D SISL Feeding Network for 2-D Cavity-Backed Endfire Dipole Array at 24 GHz

This letter presents a 4×4 cavity-backed endfire dipole array with a novel feeding structure named as three-dimensional substrate integrated suspended line (SISL) feeding network (TSISLFN). Based on the SISL's structural superiority, air-filled substrate integrate waveguide (AF-SIW) can be vertically integrated with planar SISL in a self-packaged manner to form the TSISLFN. TSISLFN can be easily integrated with 2-D cavity-backed dipole array and the overall architecture can be realized through printed circuit board (PCB) technology. Then, the cost and weight of the whole structure are significantly reduced compared to the metal-waveguide counterpart. TSISLFN possess merits of self-packaging, low cost, and low loss. Both 2×2 and 4×4 cavity-backed endfire dipole arrays fed by TSISLFN are fabricated and measured. At 24.5 GHz, high efficiency of better than 91% and 79%, gain of 15.2 and 20.6 dBi are all obtained for the proposed 2×2 and 4×4 array respectively. Similar narrow beam widths in both E and H planes are also obtained.