Folded Substrate Integrated Waveguide Research Articles

Compact wide‐stopband bandpass filter using FSIW‐patch triple‐mode resonator

AbstractIn this study, the compact third‐order filter with wide stopband is proposed, and it is based on the folded substrate integrated waveguide (FSIW)‐patch resonator. The embedded semicircular patch with two etched slots is integrated into the closed dual‐mode FSIW, so the miniaturized single‐cavity triple‐mode resonator with electromagnetic (EM) shielding and high quality can be achieved. In addition, the slots can reduce transverse electricity (TE)101 and TE201 on FSIW, while the other higher‐order modes of FSIW remain unchanged, then the wide stopband can be realized, and the stopband can be further widened by designing the feeding position to suppress higher‐order modes. Then, this filter based on hybrid FSIW modes has compact size, wide stopband, and good EM shielding. Finally, a prototype with 3‐dB fractional bandwidth of 8.4% is designed at 5.87 GHz (f0), and its insertion loss is only 1.16 dB. The upper‐stopband attenuation is better than 23 dB extended to 3.08f0. It occupies only 0.18λg2, where λg is the guided wavelength at f0.

A Design Method to Realize Manufacture-Friendly Millimeter-Wave Folded Substrate Integrated Waveguide Bandpass Filters

A design method for manufacture-friendly millimeter-wave (mm-Wave) folded substrate integrated waveguide (FSIW) bandpass filters (BPFs) is proposed in this brief. Based on conventional magnetic post-wall iris structure, etched parallel rectangular slots and an incompletely folded structure are introduced to serve as internal coupling structures. A design method is proposed to achieve lower fabrication errors and reduce the sensitivity to them by optimizing the coupling structures, thus, increasing the performance robustness. Then, an FSIW BPF based on the multilayer printed circuit board (PCB) is designed at Ka-band using the proposed method, and a conventional FSIW BPF is also designed as a reference. Both the two FSIW BPFs are fabricated, measured, and compared to confirm the effectiveness of the proposed method. The designed BPF using the proposed method exhibits a higher simulation-to-fabrication performance accuracy compared to the regular one, thus, should be a promising candidate for mm-wave applications.

Broadband and compact folded substrate integrated waveguide phase shifter and its application to 180° directional coupler

Abstract In this paper, a broadband, low insertion loss, and compact folded substrate integrated waveguide (FSIW) phase shifter is proposed for the first time. By loading the complementary split-ring resonators (CSRRs) on the middle metal layer of the FSIW, a closed-type slow-wave transmission line (TL) is obtained, which can provide a wideband phase shift (39%) compared with the equal-length fast-wave one. The enclosed structure of the CSRR-loaded FSIW prevents the CSRRs from radiation as suffered in the previous reported CSRR-loaded TLs, resulting in a low insertion loss. This feature greatly reduces the amplitude imbalance between the main line and the reference line of the phase shifter. In addition, no transition structure is required between the FSIWs with and without CSRRs for broadband impedance matching, which makes the phase shifter more compact and easier to integrate with other FSIW devices. To validate the performance of the proposed phase shifter and to illustrate its ease integration, a novel FSIW 180° directional coupler that consists of an FSIW 90° coupler and an FSIW 90° phase shifter is designed, fabricated, and measured. The measured results agree well with the simulated data.

T-type folded SIW-based leaky-wave antennas with wide scanning angle and low cross-polarization

Abstract In this paper, a leaky-wave antenna (LWA) with wide scanning angle and low cross-polarization is proposed based on a T-type folded substrate-integrated waveguide (FSIW). Transverse slots with a sinusoidal distribution pattern are etched on the surface of the FSIW so that transmission lines with slow-wave characteristics can excite and radiate −1 order harmonics. The length of the transverse slot affects the dispersion characteristics of the transmission line, and the sinusoidal modulation period controls the operating range of the LWA. In the frequency range of 8.3–15 GHz, the proposed LWA achieves a wide scanning ranging from backward −42° to forward +68° continuously. The cross-polarization of the beam is also kept at less than −30 dB during this scanning. A prototype is fabricated and measured to confirm the design, and the measured results show an agreement with the simulated one.

Analysis of Narrow Slot Loading on a Half Guided Wavelength Folded Substrate Integrated Waveguide

In this paper, effects due to variation in positioning, width and length of a narrow slot loaded on central metal septum of a half guided wavelength Folded Substrate Integrated Waveguide (FSIW) segment is presented. The study shows that the most significant effect is due to variation in slot length. It was observed that the slot loading can be used both for slow wave structure and filter depending on the length of the slot. The smaller lengths of the slot provide the slow wave effect, whereas the longer lengths result in filtering effect. Both the phenomena are explained with the help of field diagrams for different propagating modes and extracted equivalent circuit for the Slot Loaded Folded Substrate Integrated Waveguide (SFSIW) segment. This study will help in deciding the dimensions of the slot as per application. The measured scattering parameters of the fabricated structure are compared with the simulated results obtained from the HFSS and the circuit simulator in ADS and are in good agreement.

A novel feeding technique for folded substrate integrated waveguide

In this paper a novel feeding technique is presented using transition between microstrip-line segment and folded substrate integrated waveguide (FSIW), which provides very low insertion loss over wide frequency band and can be used for signal feeding in FSIW based waveguides and components. Concept of simultaneous transformation in mode and impedance by tapering central metal septum and removing upper ground plane precisely above the tapering over the transition section is used to design the novel transitions. The presented design procedures are applied on transitions for FSIW transmission lines operating in different frequency bands from C to K band. The concept is explained in detail with an example for transitions designed for FSIW operating in Ku band. All the designed structures are simulated using HFSS software. The designed FSIW with the transitions operating in Ku band is fabricated and the measured results are compared with simulated results and are found in good agreement. Dimensions of transitions designed for FSIWs operating in other frequency bands are tabulated.

A Folded Substrate Integrated Waveguide Re-Entrant Cavity for Full Characterization of Magneto-Dielectric Powder Materials

In this study, a folded substrate integrated waveguide (FSIW) re-entrant cavity sensor (RECS) is proposed for full characterization of magnetic-dielectric powder materials. In the re-entrant cavity, the electric field (E-field) and magnetic field (H-field) are localized at two different regions for detecting complex permittivity and complex permeability independently. Due to the extremely weak H-field in the high-intensity E-field region of the re-entrant cavity, the impact of the high magnetic loss of magneto-dielectric (MD) materials on the permittivity measurement is ignored, which simplifies the algorithm for extracting the complex permittivity. The simulated results demonstrate a good electromagnetic separation performance of the FSIW RECS, characterized by the very low cross-sensitivity-ratios ${S}_{\textit {fm}2}{/}{S}_{\textit {fe}}$ of 0.0289 and ${S}_{\textit {Qm}2}{/}{S}_{\textit {Qe}}$ of 0.0035. Folding technology is used to enhance the sensitivity for extracting the complex permittivity and realize the miniaturization of the designed sensor. To accurately characterize the MD materials with the high magnetic loss tangent up to 0.7, the weak-coupling feeding method is employed to improve the Q-factor of this sensor, and magnetic loss tangent is taken into account in the extraction of the real part of the permeability. The prototype of the FSIW RECS was fabricated and experimentally verified by measuring the complex permittivity and permeability of several powder materials. The measured relative permittivity and permeability of powder samples are in good agreement with the referred ones, and the corresponding maximum relative errors are 3.79% and 4.44%, respectively.

Folded Substrate Integrated Waveguide Based Multiband Filter for Wi-Fi6E Application

This paper presents the design and development of a multiband filter using folded substrate integrated waveguide (FSIW) for the Wi-Fi 6E application. The emerging network standard IEEE802.11ax also known as Wi-Fi 6E is the next generation of Wi-Fi, which includes an additional frequency band at 6 GHz and provides improvements over 802.11ac (Wi-Fi 5). The designed filter is based on modification of the impedance of the FSIW structure introducing longitudinal as well as transverse slots. The equivalent circuit of the slot loaded structure is derived and simulated results using ADS are compared with the simulated results of the structure using HFSS as well as with the measured results. The measured results and simulated results using HFSS and ADS show the good agreement. The size of the designed structure is 0.31λg × 0.15λg and shows insertion loss less than 0.8 dB over the desired frequency bands.

A novel wideband bandpass filter based on CSRR‐loaded substrate integrated folded waveguide

A novel wideband bandpass filter based on folded substrate integrated waveguide (FSIW) is presented in the article. Five square complementary split-ring resonators (CSRRs) are etched in the middle layer of the FSIW. By adjusting the physical size of the CSRR structure, the resonant frequency of the CSRRs can be tuned at the same time and the stopband performance can be changed. As transverse electromagnetic (TEM) mode can be transmitted in the stripline, FSIW excited by stripline shows wider passband than that excited by microstrip line directly. To achieve perfect impedance matching, two microstrip lines to stripline transitions are added in two ports of the filter. The proposed bandpass filter exhibits compact size, high selectivity, good stopband rejection, lower radiation loss, and wideband performances. The measured results show that the fractional bandwidth of the filter is about 35.5%. The measured return loss is better than 15 dB from 4.84 GHz to 6.90 GHz, and the insertion loss is less than 1.2 dB. The comparison between the simulated results and the measured ones validate the possibility of the technology that combines the FSIW and CSRR.

Design of miniaturized high selectivity folded substrate integrated waveguide band pass filter with Koch fractal

ABSTRACTThis paper proposes the design of a novel double folded substrate integrated waveguide (FSIW) band pass filter (BPF) based on Koch space-filling curve (SFC). The folded SIW filter is incorporated with first and second iteration levels of Koch curve on central conducting layer. A prototype of second iteration Koch fractal FSIW BPF has been fabricated using substrate having dielectric constant 2.55 and thickness 0.508 mm for each layer and then tested. The fabricated second order filter has merits of compact size (0.204 λ02), high roll off rate (82.2 dB/GHz) and low insertion loss (<0.85 dB) in the X band.

Low-Loss Spoof Surface Plasmon Polariton Based on Folded Substrate Integrated Waveguide

Spoof surface plasmon polariton (SSPP) features highly confined field confinement and subwavelength operational scale. However, at the low-frequency region, SSPP usually suffers from a poorly confined field, and a relatively large loss resulted from the mode conversion. Folded substrate integrated waveguide (FSIW) is a compact version of substrate integrated waveguide. However, FSIW suffers from a large guided wavelength and hence is not preferred for compact antennas. In this letter, we propose a combination of FSIW and SSPP, which has the benefits of both FSIW and SSPP. Compared with the pure SSPP, FSIW–SSPP significantly improves the field confinement and transmission loss at the low-frequency region due to the closed structure. At the same time, FSIW–SSPP reduces the guided wavelength by 67% due to the slow-wave feature of SSPP. A prototype of FSIW–SSPP was fabricated and measured. The simulated and measured results validate the expected performance. This new structure has potential applications in the antenna miniaturization.

Folded Substrate-Integrated Waveguide Band-Pass Post Filter

This letter presents a novel concept of band-pass filter realized with metal posts in folded substrate-integrated waveguide (FSIW) technology, together with an efficient specific design procedure. As a first step, it is shown that a particular dimension of the middle vane in the FSIW yields an equivalence to a dielectric-loaded unfolded rectangular waveguide. This equivalence is investigated by comparing the modal dispersion characteristics in both folded and unfolded structures. A direct comparison of the posts placed in the FSIW and in the equivalent unfolded waveguide then further confirms their similar characteristics. As a result, the classical mode-matching method (MMM), straightforwardly applied in the equivalent unfolded structure, can be used to efficiently design a post filter in FSIW technology. For illustration, the method is applied to realize a $5^{th}$ -order Chebyshev band-pass post FSIW filter with a center frequency of 7GHz and a fractional bandwidth of 5.71%. The viability and efficiency of the design approach is successfully validated by finite-element simulations and measurements.

Variational Analysis of Folded Substrate-Integrated Waveguides

An accurate numerical solution describing the propagation behavior of two types of folded substrate-integrated waveguide (FSIW) is demonstrated in this letter. The computation is based on a variational method which can be carried out efficiently by solving the stationary equation corresponding to each type of FSIW. The approach can be extended to solve various folded structures, i.e., with different gap positions, where the layers are made of substrates with different thicknesses and material properties.

Dual-Band Ring Coupler Based on the Composite Right/Left-Handed Folded Substrate-Integrated Waveguide

In this letter, a dual-band ring coupler based on the folded substrate-integrated waveguide (FSIW) is proposed. The artificial structure, the composite right/left-handed (CRLH) transmission lines were implemented in the FSIW by loading the interdigital capacitors in the middle metallic layer to generate a left-handed passband region below the cutoff frequency of the ordinary waveguide ${\rm TE}_{10}$ mode for coupler miniaturization. The FSIW is the folded counterpart of the substrate-integrated waveguide (SIW) and thus can prevent the CRLH transmission lines from radiation loss by shielding the interdigital capacitors in the waveguide. Besides, the FSIW-based coupler is able to eliminate the electromagnetic interference (noise) with adjacent objects and lend itself to multilayer circuit integration. A ring coupler that operates at 4.3 and 7.6 GHz was developed and experimentally verified. To the best of the authors' knowledge, it is the first time that a dual-band rat-race was implemented and reported based on the CRLH-FSIW structure.

Folded Substrate Integrated Waveguide Based Composite Right/Left-Handed Transmission Line and Its Application to Partial $H$-Plane Filters

Composite right/left-handed (CRLH) transmission line structures based on the folded substrate integrated waveguide (FSIW) are presented and discussed in this paper. This FSIW-based CRLH (FSIW-CRLH) transmission line exhibits much lower cut-off frequencies as compared to the ordinary FSIW of the same footprint, and furthermore, it requires only one-half width of the conventional substrate integrated waveguide (SIW) based CRLH (SIW-CRLH) transmission lines while possessing the same dispersion characteristics. In addition, the proposed structure offers the advantage of a high quality factor for preventing the guided-wave circuits from radiation as suffered in the previous open CRLH transmission line structures when operated in the fast-wave region. All of the aforementioned properties lend the proposed FSIW-based CRLH transmission lines best suited to miniaturized and guided-wave microwave applications. In this paper, a comprehensive study on the FSIW-CRLH transmission structures is conducted by means of its dispersion relation and Bloch impedance. In addition, two partial <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -plane filters are implemented here to demonstrate the capabilities of miniaturization and high quality factor based on the proposed FSIW-CRLH structures. The resultant filters are shown to have about 80% size reduction as compared to the conventional FSIW filters, and 59% size reduction as compared to the SIW-CRLH filters. To the best of our knowledge, it is the first time that the partial <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -plane filters are implemented utilizing both the dispersion behavior of the CRLH transmission structures and the structural benefits of the FSIW configuration.

NOVEL COMPOSITE RIGHT/LEFT-HANDED LEAKY-WAVE ANTENNAS BASED ON THE FOLDED SUBSTRATE-INTEGRATED-WAVEGUIDE STRUCTURES

In this paper, novel composite right/left-handed (CRLH) leaky-wave antennas based on folded substrate-integrated-waveguide (FSIW) structures are proposed. The proposed leaky-wave antennas were realized by periodically loading the radiating slots on the top metallization of the FSIW-based CRLH transmission lines. The structural advantages of the FSIW combined with the unique dispersion characteristics of the CRLH transmission line enable the proposed leaky-wave antennas to present continuous beam-scanning capability from backflre to endflre directions, occupy smaller footprint size, and provide more design ∞exibility than the conventional CRLH leaky-wave antennas. Two of such CRLH leaky-wave antennas were developed. In addition to the continuous beam scanning, it is found that the radiation e-ciency and polarization of the FSIW-based leaky- wave antennas can be easily tuned by means of the slot size and slot orientation, respectively, indicating their potential for versatile applications. Calculated and experimental results are presented and compared. A good agreement is obtained. To the best of our knowledge, it is the flrst time that the leaky-wave antenna exploits both of the dispersion behavior of the CRLH transmission lines and the structural beneflts of the FSIW conflguration.

A Novel Multilayer Partial H-Plane Filter Implemented With Folded Substrate Integrated Waveguide (FSIW)

A novel multilayer partial H-plane filter is proposed using folded substrate integrated waveguide (FSIW) and fabricated based on a standard LTCC technology. Evanescent SIW sections are utilized to form coupling structures, and no additional via-holes are introduced except those composing the filter boundaries, with its tolerance sensitivity reduced. The measured and simulated S-parameters of the filter samples are presented to show their superior performance, and good agreements are achieved between them.

A folded substrate integrated waveguide cavity filter using novel negative coupling

AbstractThis article presents a cross‐coupled folded substrate integrated waveguide (FSIW) cavity bandpass filter. A novel type of negative coupling between FSIW cavities has been investigated and demonstrated. A prototype of four‐pole FSIW cavity bandpass filter has been designed, fabricated with multilayer standard printed circuit board process. The filter has good selectivity which is demonstrated by the measured results, indicating 7.5% bandwidth and more than 14‐dB return loss, with good agreement obtained when compared with the simulated ones. In addition, the rejection band of this filter is quite wide, implying good harmonic rejection. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 866–871, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24181

Narrow‐slot bandpass filter based on folded substrate‐integrated waveguide with wide out‐of‐band rejection

AbstractThe folded substrate‐integrated waveguide (FSIW) takes the advantages of more compact size and higher integration than the conventional SIW structures, probably resulting in a very compact design. One simple narrow‐slot bandpass filter is thus proposed and implemented to demonstrate the superiority of FSIW structure. The design strategies of the bandpass filter are introduced. One prototype with three narrow slots in the middle layer of FSIW is fabricated to demonstrate the validity of the proposed design. For the sake of measurement, one back‐to‐back stripline transition is also designed. The measured results are in good agreement with the HFSS‐simulated results, which indicates that the bandwidth is about 15%; the insertion loss is less than 1.5 dB. In addition, the rejection band of this filter is quite wide, implying very good harmonic rejection. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1155–1159, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23327

COMPACT FOLDED SUBSTRATE INTEGRATED WAVEGUIDE CAVITIES AND BANDPASS FILTER

In this paper, a folded substrate integrated waveguide (FSIW) cavity is analyzed theoretically. Formulae for the determination of the dimensions of the FSIW cavity have been deduced. To verify the proposed formulae, simulated results are compared with the results of the formulae and good agreement has been observed between them. An example filter working at 8 GHz is designed and fabricated. Good agreement between the simulated and the measured results has been obtained. Result shows the advantage of wide out-of-band rejection and compact size.