Wide Stopband Research Articles

10–14GHz and 14–18GHz Interdigital Planar Bandpass Filters for Frequency Multiplexer

This paper presents the design of two wideband bandpass filters (BPF) operating in the 10–14 GHz and 14–18 GHz ranges for a five port 1-18GHz frequency multiplexer. The 10–14 GHz BPF utilises an interdigital array of resonators with asymmetrical widths and is combined with a low-pass filter for wide stopband characteristics. Sharp attenuation in the stop bands is achieved by including quarter wavelength open stubs. The 14–18 GHz BPF incorporates three interdigital resonators with a modified middle resonator, introducing a variable gap width for improved impedance matching. Open-circuited stubs and a bandstop filter further enhance attenuation in the stop bands. Equivalent circuit models accompany both filters. Both filters exhibit excellent performance, as evidenced by the reflection coefficients below −12 dB within their respective frequency ranges. The insertion loss remains below 2.5 dB throughout the passband, indicating efficient signal transmission. Moreover, the group delay for both filters is less than 0.8 ns, indicating minimal signal delay. These results demonstrate the high-quality characteristics of the designed filters, making them suitable for a wide range of applications requiring efficient signal filtering and multiplexing.

Optically transparent and angularly stable broad‐stopband frequency selective surface for millimeter wave electromagnetic interference mitigation

AbstractAn optically transparent and angularly stable frequency selective surface (FSS) with a broad stopband is introduced for addressing millimeter wave (mmW) electromagnetic interference. The unique FSS unit cell pattern incorporates a cross patch with Y‐shaped branches, effectively broadening the bandwidth and enhancing the angular stability. Utilizing transparent conductive indium tin oxide deposited on both sides of a glass substrate enables the FSS to reflect and absorb electromagnetic waves. Consequently, the proposed FSS exhibits an exceptionally wide stopband ranging from 18.7 to 40.2 GHz, featuring an insertion loss of 14 dB and maintaining stable angular response up to 60° for both transverse electric and transverse magnetic polarizations. Moreover, an equivalent circuit model is developed to characterize the stopband behavior of the FSS. Finally, measurements conducted on a physical prototype of the proposed FSS validate its effectiveness, showing good agreement with the simulation results.

A New Compact Wideband Filter Based on a Coupled Stepped Impedance Resonator.

A new compact wideband filter is introduced to address the requirements of recent communication and radar systems. The filter is based on a quarter-wavelength short-circuit coupled stepped impedance resonator (SIR). The analytical solution shows that the suggested SIR resonator provides a compact size and a wide stopband response, which are essential features in many wireless communication systems. The analytical results also reveal that increasing the impedance ratio of the SIR extends the stopband by increasing the first spurious response and reducing its total length. A compact two-coupled short-circuit SIR filter is designed at 1.23 GHz. The design approach is validated using an ideal transmission line modeling analysis and electromagnetic simulation using CST Microwave Studio 2021. The proposed structure is shown to be flexible, allowing the achievement of a relative bandwidth as low as 5% and as high as 50%. A four-resonator filter is designed by cascading two stages of the designed two-coupled short-circuit SIR filter, which are coupled through a quarter-wavelength line. The simulation results illustrate that the suggested structure can be used to design a filter with any number of resonators. The filter is implemented using a high-resolution LPKF laser machine on Rogers RT/duroid 6010.2LM material with a thickness of 0.635 mm. From the measurements, the bandwidth is found to be 390 MHz and centered at 1325 MHz (29.4% relative bandwidth) and the insertion loss is 1.3 dB. The simulation and experimental results verify the proposed approach and indicate the potential of this component in meeting the design requirements of next-generation microwave circuits related to flexibility and size-compactness.

A Wilkinson power divider with harmonic suppression through low-pass filter for GSM and LTE applications

Conventional Wilkinson power dividers (WPDs) perform satisfactorily near the intended operation frequency. Nonetheless, these WPDs demonstrate subpar performance in the stopband and necessitate a significant physical space. To enhance the existing level of advancement and in order to improve on the current state-of-the-art, a modified WPD is designed and fabricated, demonstrating a significant improvement in stopband and superior isolation between output ports. To improve the stopband and suppress unwanted harmonics, a low-pass filter (LPF) structure is placed in the both branches of the conventional WPD. The proposed modified WPD depicts a wide stopband bandwidth (fSB > 17.25 GHz) from 2.75 to over 20 GHz with an attenuation level of 20 dB, suppressing 2nd to 11th harmonics. According to measured results, the input return loss (|S11|), insertion loss (|S21|) and output isolation (|S32|) at f = 1.8 GHz are better than 33 dB, 3.2 dB and 21 dB, respectively. Indeed, the proposed modified WPD exhibits a magnitude imbalance of 0.00018, a phase imbalance of 1.25 degrees and a group delay of 0.5 ns. The proposed WPD depicts a compact size of 35 mm × 25 mm (0.38 λg × 0.27 λg), where λg is the guided wavelength at f = 1.8 GHz. There is a good agreement between the simulated and measured results. According to the obtained results, the proposed modified WPD shows a desirable performance for modern LTE and GSM communication applications.

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.

A Quad-Band Highly Selective Frequency Selective Surface with Ultra-Wideband Rejection.

In this paper, a highly selective quad-band frequency selective surface (FSS) with ultra-wideband rejection is presented. The proposed FSS structure was developed by cascading five metallic layers by three thin dielectric substrates. The five metallic layers are composed of two bent slot layers, two metallic square rings, and a metal patch. The dimensions of the unit cell are 0.13λ0× 0.13λ0× 0.18λ0 (λ0 is the free-space wavelength at the first operating frequency). The proposed structure achieves four transmission bands and has two wide stop-bands located at 1 to 5.5 GHz and 14 to 40 GHz, with a suppressed transmission coefficient below -20 dB. In order to verify the simulation results, an FSS prototype was fabricated and measured. It can be observed that the measured results are in favorable agreement with the simulation results. Its multiple narrow passbands and highly selective and ultra-wideband rejection properties ensure that our design can play a significant role in narrowband antennas, spatial filters, and many other fields.

Broadband balanced filter with high common-mode suppression and wide stopband based on SIW and SSPP

Broadband balanced filter with high common-mode suppression and wide stopband based on SIW and SSPP

Design of Compact GaAs-Based On-Chip Filter and Duplexer With High Selectivity and Wide Stopband

Design of Compact GaAs-Based On-Chip Filter and Duplexer With High Selectivity and 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.

Packaged 5G Filter with Miniaturization and Wide Stopband Based on Shielded Stripline Resonator

Packaged 5G Filter with Miniaturization and Wide Stopband Based on Shielded Stripline Resonator

Miniaturized High-Selectivity Bandpass Filter with Wide Stopband Based on Through-Glass-Via IPD Technology

Miniaturized High-Selectivity Bandpass Filter with Wide Stopband Based on Through-Glass-Via IPD Technology

High-Selectivity FSS with Wide Stopbands for EMI Suppression in Wireless Power Transfer Systems

High-Selectivity FSS with Wide Stopbands for EMI Suppression in Wireless Power Transfer Systems

Frequency and bandwidth modulation of a wide band-stop metamaterial for EMI shielding applications

In this paper, a µ-near-zero wide band-stop metamaterial (MM) shield is conducted for electromagnetic interference (EMI) shielding purposes in the C- and X-band. The proposed design intends to employ a shared MM structure to serve two distinct microwave bands with extended shielding bandwidth. The proposed structure consists of metal strip coupled four identical quartiles based unique mirror symmetric resonator and designed on a low-loss Rogers 5880 substrate within a compact physical dimension of 7.5 mm × 7.5 mm × 1.575 mm. The speciality of the proposed MM is its wide band-stop functionality with maximum shielding bandwidth and effectiveness of 4.33 GHz and 66.6 dB, respectively. Moreover, four shorting metal strips among adjacent quartiles can control the shielding spectrum from C-band to X-band with an outstanding band-stop enhancement capability of 170.63 %, which significantly outperforms the existing MMs. Therefore, the proposed MM structure can be utilized for two distinct wide frequency spectrums shielding by introducing simple shorting metallic strips. The electromagnetic radiation shielding phenomena are also explained using surface current and electric and magnetic field distribution. The proposed MM prototypes are fabricated and experimentally verified with numerical results. The promising shielding performance of the developed MM demonstrates the potentiality for shielding undesired electromagnetic radiation.

A Miniaturized Bandpass Filter with Wideband and High Stopband Rejection Using LTCC Technology

This paper designs an L-band wide stopband bandpass filter by applying low-temperature cofired ceramic (LTCC) technology to the global positioning system (GPS) frequency band. Taking the Chebyshev filter as a prototype, an equivalent collector element (capacitive and inductor) structure is adopted to fully use the three-dimensional package structure of LTCC to reduce the filter size. The filter is integrated into an eight-layer LTCC dielectric, and the series–parallel connection of the collector elements in the resonance unit is utilized to produce out-of-band transmission zeros, while the input and output ports’ capacitance is adjusted to control the bandwidth. Harmonic suppression is achieved by cascading two new compact stopband filters, while the size increase is insignificant due to LTCC technology. The simulation results are as follows: the center frequency is 1.575 GHz, 1 dB relative bandwidth is 6.3%, insertion loss in the passband is as slight as 1.6 dB, return loss is better than 30 dB, rejection bandwidth up to 16 GHz is more than 44 dB, and the volume of the whole filter is 6.2 × 3.7 × 0.78 mm3.

Miniaturised wideband bandpass filter with good selectivity based on 3D heterogeneous integrated passive device technology

AbstractThe miniaturised wideband filter with good frequency selectivity and wide stopband is proposed, which is based on three‐dimensional (3D) heterogeneous integrated passive device technology. The proposed sixth‐order wideband bandpass filter is based on the magnetic‐coupling‐loaded highpass‐lowpass lumped topology and implemented by the 3D heterogeneous integration process, integrating GaAs‐based and Glass‐based micro‐nano‐scale processes together. Then, lumped inductors are designed in the Glass substrate with low dielectric loss tangent and realised by a three‐dimensional spiral structure. Therefore, the inductors have high quality factors and small sizes. The lumped capacitors are designed using the GaAs thin film process. Finally, a prototype with a 3‐dB fractional bandwidth of 42% is designed and fabricated at 3.875 GHz (f0). The upper‐stopband attenuation higher than 30 dB is extended to more than 5.15f0. It occupies only 0.014 × 0.018 λ02 (1.1 × 1.42 mm2), where λ0 is the free‐space wavelength at f0.

(Invited) Applications of Electrochemistry Toward Blue/Green and SWIR-Wavelength VCSELs

Unlike the more established edge-emitting lasers (EELs) with a horizontal Fabry-Perot (FB) cavity, VCSELs have a vertical cavity with highly reflective top and bottom mirrors sandwiching the active region. This design enables wafer-level testing, one- and two-dimensional arrayed integration, and scalability for low- and high-power applications. VCSELs are poised to surpass EELs as a more versatile and intelligent option for semiconductor lasers in the future.Currently commercially available VCSELs only cover the red to near-infrared (NIR) range of 700-1100nm, whereas EELs offer products across a wide spectral range. The optimal active regions for blue and short-wavelength infrared (SWIR) spectra are only supported on GaN and InP substrates, respectively. Lattice-matched, epitaxial mirrors compatible with these two substrates remain major challenges. As a solution, we propose the use of electrochemistry to engineer the refractive index of the material. The innovation is based on the recognition that nanoporous (NP) semiconductor layers can be considered a nanocomposite with nanoscale voids of air uniformly dispersed in a single-crystalline semiconductor, thus rendering a unique way to control the effective optical index with a tunability that is typically un-attainable through epitaxy.We have studied the electrochemistry of semiconductors for applications in photonics, beginning with GaN and most recently with InP. In both material systems, we have discovered a selective porosification process based on the doping concentration. Due to the doping selectivity in EC etching, layers with high doping concentration will be converted to low index nanoporous material with an unprecedented tunability in the refractive index depending on the porosity. Meanwhile, the lightly doped layers remain intact. As a result, highly reflective mirrors were fabricated on GaN and InP substrates with wide stopbands. In this talk, we will provide latest updates in the VCSEL performances in the blue/green and long-wavelength region.

Millimeter‐wave filtenna for 5G application with multiple controllable radiation nulls and wide stopband

AbstractA filtenna (filtering antenna) for the fifth generation (5G) mobile communications in millimeter‐wave (mmWave) band is proposed in this paper. The filtenna is fed by a probe, and two radiation nulls are generated at the upper sideband based on the stacked‐patches structure. Then, two shorting pins loaded on the driven patch are introduced, which then result in the third radiation null. An “X‐character” shape radiation loop is added therefore, the fourth radiation null can be generated. Besides, the fifth radiation null at around 34 GHz is generated by adding four parasitic strips on the top radiation patch. The measured −10 dB impedance bandwidth of the filtenna is from 23.07 to 30.99 GHz. The average gain of the antenna is larger than 5.5 dBi, and the stopband suppression can reach 14 dB with a wide stopband. With the merits of low profile, wide stopband, and stable radiation, the proposed filtenna can be a good candidate for 5G mmWave applications.

Stepped Impedance Optimum Short-Circuited Stub 1–6 GHz and 6–10 GHz Bandpass Filters for Multi-standard Radio

This article presents two ultra-broadband bandpass filter (BPF) designs for multi-standard applications, operating from 1–6 GHz and 6–10 GHz, with wide stopband characteristics. 1–6 GHz BPF (Filter 1) is based on the circuit model for an optimum distributed bandpass filter consisting of 3 shunt short-circuited stubs separated by non-redundant unit elements. By varying the length ratio between the unit elements and stubs and introducing stepped impedance in the unit elements, a 143% fractional bandwidth (FBW) is achieved, which is 20% higher than that obtained through the conventional optimum shunt short-circuited stub method. In addition, a stepped impedance elliptic lowpass filter was cascaded to achieve wide stopband characteristics from 7 GHz to 20 GHz. Filter 2 (6–10 GHz) is constructed by cascading a shunt short-circuited stub optimum high pass filter having a stepped impedance unit element with a stepped impedance low pass filter. The analytical model, transmission line equivalent circuit model, and full wave electromagnetic simulated model are presented along with the measured results. The measured in-band return loss of Filter 1 and Filter 2 is >12 dB, and the measured insertion loss is < 2 dB. The measured group delay of Filter 1 and Filter 2 is <0.8 ns.

Polarization-Insensitive and Oblique Incident Angle Stable Miniaturized Conformal FSS for 28/38 GHz mm-Wave Band 5G EMI Shielding Applications

This letter presents a miniaturized conformal dual-band mm-wave frequency selective surface (FSS) for fifth-generation (5G) electromagnetic interference (EMI) shielding applications. Two back-to-back resonators are separated with a 0.254 mm thin dielectric substrate. The proposed FSS exhibits two wide stopbands (S21<-10 dB) in the mm-wave 5G frequency spectrum. The stopband bandwidths (BW) are 42.8% at 28 GHz and 24.2% at 38 GHz. The periodicity of the unit cell is 0.26 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength of the lower stopband. The key features of the proposed FSS include a miniaturized unit cell structure for 28 GHz and 38 GHz frequency bands with a high oblique incident angle (OIA) stable filter behavior up to 60°. The proposed FSS also features polarization insensitivity and conformality. The simulated and measured results show good agreement for EMI shielding applications.

High-Gain Third-Order Filtering Patch Antenna Array With Two Radiation Nulls Using Cross-Radiation

A compact third-order filtering antenna array with high gain and two controllable radiation nulls is proposed. The antenna consists of one narrow patch in the center fed by the coaxial port and four wide patches placed around it. Four shortend stub-loaded resonators are capacitively coupled between the center patch and the outer patches, which makes the radiated Efields of the center patch and the outer patches in-phase at the center frequency of the passband to realize the high gain and outof-phase at the low and high stopbands to introduce a pair of radiation nulls. The working principle of the filtering antenna array can be explained by the coupled-resonator network. Finally, a filtering antenna array centered at 3.5 GHz with a fractional bandwidth of 4.26%, a high maximum gain of 12.2 dBi, high out-of-band selectivity, and wide stopband is designed, fabricated, and measured.