Ultra-wide Stopband Research Articles

Ultra-wide stopband polarization narrow band filter combining optical Tamm state engineering and grating structure

Ultra-wide stopband polarization narrow band filter combining optical Tamm state engineering and grating structure

Dual-band dual-truncated R-slot loaded monopole patch antenna using a single-layer bandstop FSS reflector for gain enhancement

New reflector structure (RS) based on ultra-wide stopband single-layer frequency selective structure (FSS) for mid-band sub-6 GHz 5G applications is designed. The proposed RS is arranged into array of 7 × 7-unit cell of FSS elements for antenna gain and front-to-back ratio enhancement. The single antenna element of volume 30 × 20 × 1.6 (in mm3) consists of a dual-quarter-circular truncated edge-fed rectangular slot (R-slot) loaded rectangular patch (R-patch) antenna with degraded ground structure (DGS) to operate at 3.6 GHz mid-band sub-6 GHz 5G and 5.8 GHz WBAN band. The proposed unit cell FSS element, the RS of volume 55.5 × 55.5 × 13.2 (in mm3) and the associated antenna are designed on lossy thin FR-4 substrate material and investigated numerically using commercial computer simulation technology microwave studio (CST-MS) software. The studied dual-structure based RS made with array of single-layer FSS and monopole R-patch antenna is fabricated and measured. The measured impedance bandwidth (IBW) of 48.28% (3.06–4.85 GHz) and 86.20% (5–10 GHz), peak gain of 5.36 and 7.45 dBi, radiation efficiency of 67.11% and 80.16%, and front-to-back ratio of 12.23 dB and 22.84 dB are achieved at the resonant frequencies 3.5 and 5.8 GHz respectively. The FSS reflector associated with the dual-band monopole R-patch antenna performances are in good agreement with the portable wireless applications requirements.

Wideband bandpass filter with ultra-wide stopband based on cross-shaped parallel coupled lines

A broadband out-of-band rejection capability and multiple transmission zeros of wideband bandpass filter are proposed and validated in this article, which employ quadruple anti-parallel coupled-line structures to form a novel cross-shaped resonator planar topology. The centered frequency of the single wideband bandpass filter designed for verification is located at 2.4 GHz (f 0) with a fractional bandwidth of 50%. The interaction of crossed multiple anti-coupled lines with a lowpass-loaded fan constitutes the wideband with nine transmission zeros in the 5 f 0 frequency range for improved suppression extending to 26.5 GHz (10.7 f 0) with a suppression level of 12.5 dB. Moreover, the designed prototype filter is implemented and tested with a measured minimum insertion loss of 0.9 dB. Good agreement between the measured and simulated results is attained to successfully validate the correctness of the proposed design approach.

Novel bow-shaped local resonance acoustic metamaterials with ultra-wide low-frequency stopband: design, modeling, and testing

This paper proposes a novel bow-spring local resonance (LR) structure featuring an exceptionally wide low-frequency stopband. Unlike traditional methods reliant on heavy mass or stiffness adjustments, this structure effectively manipulates and amplifies the dynamic characteristics of negative stiffness solely by designing parameter values for the bow-spring set. Through finite element method analysis, an ultra-wide stopband ranging from 91 to 570 Hz is achieved within the LR structure. Further modification of the connection pattern with a perforated plate extends the upper edge to 686 Hz while reducing the lower edge to 76 Hz. Most notably, within the novel bow-spring LR structure, a stopband width of 610 Hz is attained, resulting in a gap-mid gap ratio of 160.1%. The numerical and experimental results demonstrate good agreement. These findings offer a new perspective and guidelines for developing LR structures with ultra-wide low-frequency stopbands, potentially finding applications in the field of low-frequency vibration and noise reduction.

Narrow bandpass filter with ultra-wide stopband in a hybrid metal-optical Tamm state structure

Narrow bandpass filters (NBPF) play an important role in quantum communications, optical biometrics and other fields. However, traditional narrow bandpass filters have limited stopband capabilities. Here, an ultrawide stopband narrow bandpass filter is realized by combining a metal layer with a distributed Bragg reflector (DBR) structure to simultaneously excite the upper and lower Tamm plasma polarization (TP) modes. Numerical simulations show that the transmittance of the filter exceeds 94 % at a wavelength of 1.55 μm with a full width at half maximum (FWHM) of 8 nm. In addition, the addition of metal layer Ge reduces the electric field intensity of the lower DBR structure, effectively reducing the side peak, making the filter stopband range reach 1 μm–20 μm, which is 32 times that of traditional NBPF. Our research results provide a method to obtain narrow-band optical signals from ultra-broad and strong background noise, which facilitates the field of quantum communication.

Multilayer circular substrate-integrated waveguide cavity band-pass filters with ultrawide stopband characteristics

AbstractThis paper presents a methodology to design band-pass filters having ultrawide stopband characteristics using multilayer circular substrate-integrated waveguide (SIW) cavities. The orthogonal microstrip feedlines are used as input and output ports that are present at the top and bottom layers, while the middle layers are used to couple the SIW cavities. Higher-order spurious modes of the circular SIW cavity are suppressed by using orthogonal feeding mechanism and properly adjusting the arc-shaped slots between the cavities. To validate the present approach, two filters (second- and fourth-order) have been designed and fabricated and their characteristics are measured. The second-order filter exhibits a stopband rejection below 25 dB up to nearly 5.07f0, while the fourth-order filter has a stopband characteristic of nearly 5.05f0 with 20 dB rejection. The filters allow only TM010 mode propagation and attenuate the higher-order spurious modes of the cavity.

Compact bandpass filter with ultra-wide stopband based on spoof surface plasmon polaritons for sub-6G application

In this paper, a newly ring-shaped spoof surface plasmon polaritons (SSPPs) structure is proposed for the construction of bandpass filter (BPF) with combing the short-circuited stubs (SCSs). Compared with the conventional rectangular-shaped SSPPs unit, the proposed ring-shaped SSPPs unit has a relative lower cutoff frequency at the same periodic unit size. Moreover, the high-order modes of the ring-shaped SSPPs unit at different height are disperse distribution, which allows it to realize wide stopband suppression. The lower and upper cutoff frequencies of the passband can be respective controlled by structural parameters of SCSs and SSPPs unit. By properly adjusting the height of SSPPs units in conversion parts, a balanced performance between the passband and ultra-wide stopband suppression can be achieved. For verification, a BPF with the frequency from 2 GHz to 5 GHz for Sub-6G application and the stopband reaching 30 GHz is designed. The experimental show that the measured results agree well with the simulated results, validating the proposed structure and design method. The fabricated filter only occupies 1.13λg × 0.23λg, exhibits the advantage of compact size.

Switchable and optically transparent ultrawide stopband frequency selective surface for electromagnetic shielding

In view of the fact that high-frequency electromagnetic waves mainly enter buildings through windows and glass doors, switchable optically-transparent shielding with broad stopband is increasingly needed. Herein, a novel design for a switchable and optically transparent frequency selective surface (FSS) with ultrawide-stopband is presented in this study. The structure consists of a polymethyl methacrylate (PMMA) layer sandwiched between polydimethylsiloxane (PDMS) layers which contain liquid metal microchannels arranged in an orthogonal Ω-shaped configuration. The mobility of the liquid metal can switch the FSS response from an all-pass to an ultrawide bandstop behavior. The proposed FSS achieves a rejection bandwidth of 18.1 GHz, covering P, L, S, C, X and Ku bands, while maintaining a transparency of 81% and high angular stability up to 80°, regardless of polarization. Furthermore, the mechanism behind the ultrawide stopband and high angular stability is explored through an analysis of reflection and absorption for both TE polarization and TM polarization. Experimental validation under both normal and oblique incidence demonstrates the ultrawide-stopband performance of the fabricated FSS.

Mode Control of Slotline Resonator and Its Application to the Design of Balanced BPF with Ultra-wide Stopband

Mode Control of Slotline Resonator and Its Application to the Design of Balanced BPF with Ultra-wide Stopband

Reflective nonlinear optical limiter design based on coupled Tamm plasmon polaritons and optical Kerr effect

With the increasing applications of high-power lasers in fields such as laser fabrication, laser measurement, laser therapy and scientific research, there is an increasing demand for high-performance nonlinear optical limiters (NOLs) to protect human eyes and optical sensitive elements. Here we propose a brand-new approach to design a reflective NOL with an ultra-wide stop band based on coupled Tamm plasmon polaritons (TPPs) and optical Kerr effect. The NOL permits the transmission of weak signal light at the desired wavelength while effectively blocking potentially harmful or accidentally intense lasers at the same wavelength to avoid damage to sensitive optical elements or human eyes. The design can be optimized for the desired operating wavelength and threshold intensity by using different dielectric layers. In a proof-of-concept design, taking the 1064 nm laser as an example, we design a NOL capable of dynamically adjusting its transmission in response to laser intensity. The NOL has a high transmission of 85.21 % at weak light (intensity less than 0.20 MW/cm2), and the transmission can be rapidly reduced to 1.39 % when the incident light intensity increases to 60.37 MW/cm2. Furthermore, the broad stop band effectively safeguards the limiter from potential damage caused by intense light at different wavelengths. Our proposed limiter exhibits an exceptionally wide stop band range spanning from 0.5 ∼ 20 µm, nearly 30 times broader than conventional reflective NOLs. The proposed NOL design scheme provides a new promising method to design an excellent reflective NOL at the desired wavelength.

Design and analysis of highly selective ultrawide stopband lowpass filter using lumped and distributed equivalent circuit models

AbstractAn ultrawide stopband lowpass filter is reported using three stepped impedance resonators with high selectivity. The filter extends the stopband frequency range and attenuation, and two quarter‐wave open stubs and three circular ground slots are introduced. The lumped and distributed equivalent models are derived and analyzed. The corresponding results are validated experimentally in a fabricated prototype. The prototype lowpass filter has a 3 dB cutoff frequency (fc) of 2.9 GHz, and the stopband is extended up to 35 GHz (12.07fc), with an attenuation level better than 20 dB throughout. The passband‐to‐stopband transition (3 dB–20 dB) bandwidth is 0.18 GHz, and the roll‐off factor is 135 dB/GHz at 30 dB. The insertion loss is 0.3 dB at 1.6 GHz. The normalized circuit size of the proposed filter with respect to the guided wavelength is 0.04.

Metamaterial inspired electromagnetic bandgap filter for ultra-wide stopband screening devices of electromagnetic interference

Presented here is a reactively loaded microstrip transmission line that exhibit an ultra-wide bandgap. The reactive loading is periodically distributed along the transmission line, which is electromagnetically coupled. The reactive load consists of a circular shaped patch which is converted to a metamaterial structure by embedded on it two concentric slit-rings. The patch is connected to the ground plane with a via-hole. The resulting structure exhibits electromagnetic bandgap (EBG) properties. The size and gap between the slit-rings dictate the magnitude of the reactive loading. The structure was first theoretically modelled to gain insight of the characterizing parameters. The equivalent circuit was verified using a full-wave 3D electromagnetic (EM) solver. The measured results show the proposed EBG structure has a highly sharp 3-dB skirt and a very wide bandgap, which is substantially larger than any EBG structure reported to date. The bandgap rejection of the single EBG unit-cell is better than − 30 dB, and the five element EBG unit-cell is better than − 90 dB. The innovation can be used in various applications such as biomedical applications that are requiring sharp roll-off rates and high stopband rejection thus enabling efficient use of the EM spectrum. This can reduce guard band and thereby increase the channel capacity of wireless systems.

Stacked lightweight metasurfaces for wider stopband in X-K band

Frequency selective surfaces printed on optically transparent, large-area, flexible plastic sheets are studied for their passband and stopband characteristics when present as single-layer, two-layer and three-layer stacks. The unit cell design, its size, spacing and thickness on the substrate enable the single layer metasurface to yield a stopband width of 4.46 GHz (corresponding to 34.80%), when the center frequency is at 12.83 GHz in simulation and 12.86 GHz in measurement. On stacking identical surfaces as two-layer and three-layer configurations with suitable displacements both within the surface plane and perpendicular to the surface plane, the structural geometry of the unit cell gets varied leading to an ultra-wide stopband of 8.96 GHz in the range from 12.16 GHz to 21.11 GHz which covers X to K band. This leads to a wider stopband width of 43.60% for two-layer stack and 48.10% for three-layer stack with no in-plane shift. This is further enhanced to 65.50% with suitable shift within the plane of the stacked design. The three-layer stacked structure is ultra-thin with a thickness of 0.012 λ0. The single layer as well as all the three stacked structures have stopband characteristics that are invariant to incidence angle variation up to 750.

Performance analysis of frequency selective reflectors based on rectangular loop pair for wideband applications

This paper presents performance analysis of single layered bandstop frequency selective surfaces (FSSs) for C-band and ultra-wideband (UWB) frequency ranges respectively. These FSSs are based on polarization dependent (PD) single rectangular loop pair (RLP). RLP arrays in square and rectangular grids are developed and simulated to evaluate signal rejection and reflection for incident transverse electric (TE) and transverse magnetic (TM) waves. Further, orthogonal patterns are printed back-to-back (BTB) on dielectric substrate to study wave propagation and effect on wave polarization. Non-linearities in the reflection phase of BTB arrays are then mitigated by printing orthogonal FSS arrays on the same side of the dielectric substrate. The equivalent circuit models (ECMs) of these FSSs are also presented to predict their transmission characteristics. Later, two FSSs with wideband and ultra-wideband rejection capability are developed and experiments are carried out. The array of merged RLP arranged in square grid exhibits stopband from 4.5 GHz to 8.4 GHz with polarization independence (PI) and it is angularly stable while merged array of RLP arranged in rectangular grid exhibit ultra-wide stopband from 2.3 GHz to 11.5 GHz but it is not angularly stable. The measured transmission responses of all FSSs proposed here are close to simulated results.

Dual-Band Power Divider With Wide Passbands and Wide Harmonic Suppression Utilizing Multi-Mode T-Stub Loaded Slotline Resonators

This brief proposes a novel dual-wideband slotline power divider (DWSPD) with ultrawide stopband, which is suitable for the multi-band wireless communication system application. The proposed DWSPD is mainly constructed with two multi-mode T-stub loaded slotline resonators (MTSRs), four folded slotline structures (FSSs), four microstrip-slotline transitions and two isolation resistors. The MTSR can generate four transmission poles (TPs), which forms two wide passbands. Furthermore, the FSS contributes to four additional transmission zeros (TZs), which enhances the harmonic suppression. The fabricated DWSPD demonstrates the 3-dB fractional bandwidths of 45.3% @2.25 GHz and 47.1% @4.37 GHz and the stopband with a suppression more than 18 dB @ up to 40 GHz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$17.8~f_{01}$ </tex-math></inline-formula> ). To the best of the author’s knowledge, the 3-dB FBWs and stopband achieve the best among the existing dual-band filtering power dividers (DBFPDs).

Ultrawide Stopband Superconducting Filters With Multiple Harmonics Suppression

Multiple harmonics are suppressed by reduced external couplings and a symmetrical layout. The reduced external couplings are implemented by employing dual-hairpin resonators that simultaneously cancel the electric and magnetic fields. The symmetrical layout is utilized to additionally eliminate the spurious modes of substructure resonators. For validation, an eight-order superconducting filter incorporating two groups of stagger-tuned dual-hairpin resonators is designed and fabricated. The filter demonstrates excellent harmonic rejection suppressing six harmonics, extending the stopband to 17.4 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> with a rejection of 60 dB, highlighting straightforward synthesis and compact size (0.206 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> × 0.046 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.</sub>

The Design and Investigation of the Low-Pass Filter with High Selectivity and Ultra-Wide Stopband

In this work, an ultra-wide stopband low-pass filter (LPF) is proposed using tapered step impedance resonators. The distributed equivalent of the proposed step impedance LPF is extracted, analyzed, and legitimated with simulated and fabricated results. The fabricated prototype has a 3 dB cut-off frequency (fc) of 2.92 GHz and an ultra-wide stop band extended up to 25.7 GHz (8.8fc) with an attenuation level of >20 dB. The transition bandwidth (from 3 to 20 dB) is 0.20 GHz and the roll-off factor is 112 dB/GHz (a reference to 30 dB). The passband insertion loss is 0.32 dB at 1.5 GHz and the normalized circuit size of the filter is 0.055.

Design of a modified hairpin bandpass filter using embedded radial stubs featuring ultrawide stopband

The analysis and design of a microstrip bandpass filter featuring an ultrawide stopband are presented and investigated in this paper. In this filter, single radial stubs are exploited in combination with a regular hairpin structure to achieve suppression of harmonic responses of the filter passband up to 10f0. The passband of the filter remains almost intact compared to the conventional hairpin filter. A 3rd-order BPF with a central frequency of 2 GHz and a bandwidth of 44% is designed and the simulation results are verified with the measurement results. The proposed filter shows more than 32 dB rejection from 3 GHz to 20 GHz in S21 and the measured passband insertion loss is 1.3 dB. The filter structure is simple, without the need for defected ground structures, multilayers, lumped elements, and even vias. The proposed filter can be in demand anywhere easy fabrication, low cost, ultrawide stopband together with a good rejection level are considered crucial.

A Frequency Independently Tunable Dual-Band Bandpass Filter With Large Frequency Ratio and Ultra-Wide Stopband

To meet the demand for simultaneously supporting the microwave and millimeter-wave technologies in emerging industrial wireless systems, research on dual-band components with a large frequency ratio has been conducted recently. However, it is challenging to implement independent frequency tunability on bandpass filters with both compactness and high performance. This article presents a dual-band bandpass filter with a large frequency ratio, independently tunable frequencies, and an ultrawide stopband. This is achieved by artfully incorporating a harmonic-controllable varactor-loaded microstrip BPF and a wide-stopband dielectric-loaded cavity BPF with the bandgap-embedded aperture coupling mechanism. Extremely compact size can be achieved without additional filtering elements. Two pairs of transmission zeros can be allocated beside two passbands for good selectivity due to the separate path and cross-coupling in the resonators. For validation, a prototype is designed, fabricated and measured. It can provide two independent tunable frequency ranges (3.22–3.52 GHz and 25–27.06 GHz), exhibiting a large frequency ratio up to 8.3. Mid-band suppression better than 20 dB and ultra-wide stopband up to 32.5 GHz with 20 dB suppression level are achieved. Low insertion loss and good selectivity can also be observed.

Wideband-Filtering Switches With Ultra-Wide Stopband Using P-I-N Diodes Loaded on Slotline

This paper presents a new design method for the microwave switch, which uses p-i-n diodes loaded on slotline. A single-pole single-throw (SPST) switch based on the microstrip-slotline-microstrip (M-S-M) transition with non-uniform loading structures is first designed to validate our design approach, which controls the on and off states of the switch by applying different voltages to the diodes. Then a single-pole double-throw (SPDT) switch using p-i-n diodes loaded on slotline T-junction is proposed, which achieves great high-pass response of ON-state channel and 20 dB OFF-state suppression (OSS) within dc to 4.64 GHz. To overcome the poor selectivity of two switches, transmission zeros need to be introduced to achieve band-pass response. Therefore, the slotline of the M-S-M transition is loaded with gradient length short stubs to bring in multiple transmission zeros and achieve SPST/SPDT wideband-filtering switches with ultra-wide stopband. Finally, the proposed filtering switches are fabricated and measured. The measurement results show that the SPDT filtering switch not only provides the expected band-pass response and wide stopband from 4 to 43.5 GHz of ON-state channel, but also has 22.8 dB rejection of OFF-state channel, and the 20.8 dB port-to-port isolation from dc to 43.5 GHz.