Wide Stopband Research Articles

A ridged waveguide filter design with ultra-wideband and harmonic suppression

In this paper, a new structure for wide-band rectangular waveguide bandpass filters with distinguished harmonic suppression is presented. The filter is realized by using ridged waveguides in both resonant cavities and coupling windows and a metal plate, which performs like a low-pass filter and makes it arduous to form parasitic passbands. According to the field analysis and out-of-band response, the ridge structure can expand pass bandwidth and obtain a wide stopband by harmonic suppression. The filter is designed to perform a passband of 67% fractional bandwidth at center frequency at 75 GHz. The harmonic suppression of the design is increased from 1.5 times to 3.6 times the center frequency of the filter with 20 dB suppression levels. Finally, the measurement results validate the proposed design.

Noise-insulating structures based on supercells and chirped lattices enhanced via tuning of local coupling

Acoustic metamaterials and phononic crystals have proven themselves to be highly promising for the development of next-level noise-mitigation systems. One of the main challenges limiting the implementation of such structures is a typically narrow operational frequency range. In this work, we consider a periodic system consisting of locally coupled Helmholtz resonators and demonstrate that positions and widths of stop-bands can be adjusted via tuning of the coupling strength. Several approaches are developed, including the introduction of the chirped structures, supercells, or resonators with enhanced intrinsic losses. We numerically and experimentally demonstrate that tuning of local coupling leads to a merging of stop-bands, resulting in broadband noise-insulation within the operational range covering about 3.5 octaves. This property is linked to band structures of the associated infinitely periodic structures and discussed in terms of band-gap engineering. The low filling factor of the unit cells also suggests that the considered structures can be ventilated, which is demonstrated numerically.

A compact dual‐band bandpass filter based on coupled stub‐loaded square ring resonators by using transversal signal‐interaction concepts

AbstractIn this paper, a novel dual‐band wideband bandpass filter (BPF) based on transversal signal‐interaction concepts with a wide upper stopband is proposed and investigated. The designed specification of two passbands can be managed and satisfied based on the independent controllable fractional bandwidth of the two passbands and the centered frequencies. The centered frequencies of dual‐band BPF are, respectively, 0.79 GHz (ƒ1) and 1.24 GHz (ƒ2) with 3 dB fraction bandwidths of 26.54% and 11.3%. Two transmission paths consisting of coupled stub‐loaded square ring resonators and anti‐coupled shorted lines are used to realize signal cancellation of multiple transmission path signal transmission from Port 1 to Port 2. Eleven transmission zeros (TZs) modify harmonic suppression up to 10 ƒ1 with stopband rejection higher than 15 dB. Butterworth lumped notch network and step impedance resonator (SIR) are also utilized to improve the selectivity and harmonic suppression. A compact filter with a circuit size of 0.08λg × 0.08λg is implemented and tested. Good agreement between simulation and measured results verifies the reliability of the designing scheme.

High-entropy processed high quality and low-temperature cofired LiMgPO4-based dielectric ceramics for low-loss packaged millimeter-wave filters

In this work, we successfully integrated the high-entropy concept into LiMgPO4-based ceramics by strategically substituting Mg2+ with various divalent ions. Through a low-temperature solid-phase reaction method, a series of high-entropy LiMg0.9R0.1PO4 (R = Ni, NiCo, NiCoZn, NiCoZnCu, NiCoZnCuMn) ceramics were prepared successfully, and their MW dielectric properties were found to be heavily influenced by the ionic character, lattice energy, bond energy, entropy, ion radius disorder, and electronegativity of chemical bonds. Remarkably, LiMg0.9(Ni0.2Co0.2Zn0.2Cu0.2Mn0.2)0.1PO4 (LM5RP) ceramics exhibited exceptional MW dielectric properties (εr = 7.43, τf = − 27.6 ppm/°C, and Q × f = 83,216 GHz@13 GHz and 105,889 GHz@28 GHz) when sintered at an extraordinarily low temperature of 900 °C for 2 h. To demonstrate the real-world applicability of the LM5RP high-entropy ceramic, we designed and fabricated a state-of-the-art millimeter-wave (mmWave) filter, operating at 28 GHz, using low-temperature co-fired ceramic (LTCC) packaging technology. The filter exhibited unparalleled performance, featuring a low insertion loss (0.9 dB) and wide stopband suppression (> 17 dB @ 2.14 f0). These groundbreaking findings underscore the immense potential of high-entropy ceramics in revolutionizing advanced MW applications, particularly in the domain of B5G/6 G mmWave communication systems.

Polarization-insensitive compact frequency selective surface with higher angular stability for GSM applications

This article proposes a highly compact, angularly stable, and polarization-insensitive frequency selective surface (FSS) based bandstop filter geometry for shielding electromagnetic (EM) radiations across the GSM band. Each of the unit cells (having dimensions of 10 mm × 10 mm) is made of convoluted meander patterns, which are orthogonally printed on both sides of a dielectric substrate to design this highly compact FSS (the unit cell size is 0.029λ0· 0.029λ0, where λ0 corresponds to the resonance frequency). The metallic pattern on the top layer of the substrate selectively reflects the EM wave for one particular polarization around 890 MHz but transmits the orthogonally polarized wave. In contrast, the pattern printed on the bottom layer behaves oppositely (allowing one polarization and reflecting other polarization), thereby the overall structure exhibiting a bandstop filter response with a 3-dB stop bandwidth ranging from 800 MHz to 960 MHz under dual polarizations. In addition, the geometry exhibits a high angularly stable response till 80° angle of incidence under both transverse electric (TE) mode and transverse magnetic (TM) mode. Good agreement is also observed between the simulated and measured responses for various cases.

A dual-band bandpass filter based on hybrid ESPPs-SIW structure with ultra-wide upper stopband suppression

In this paper, a new bandwidth-controllable dual-band bandpass filter (BPF) based on hybrid effective surface plasmon polaritons (ESPPs) and substrate integrated waveguide (SIW) structure is presented. It consists of three parts, where a dual-band filtering part is realized by a two-layer SIW and an air cavity located on the top of SIW, and two traditional SSPPs low-pass filtering parts are introduced for wide stopband suppression. According to effective-medium theory and structural dispersion, different widths and relative permittivities of the SIW and air cavity are used to provide flexible cutoff frequencies of the ESPPs-SIW structure, thus exhibiting independently controllable bandwidth. The simulation results reveal that the presented dual-band BPF has outstanding filtering performance and ultra-wide upper stopband suppression level. The upper stopband can be extended up to 21.4 GHz (8.5f 0) with a suppression level of −20 dB, where f 0 is the center frequency of the first passband (i.e., 2.52 GHz). The measurement results are in good agreement with the simulation results, which verifies the correctness of our design concept and method.

A miniaturized on‐chip BPF with low insertion loss and wide stopband based on integrated passive device technology

AbstractIn this study, a novel bandpass filter (BPF) characterized by low insertion loss (IL) and the presence of two transmission zeros (TZs) based on integrated passive device (IPD) technology is introduced. The design incorporates a low‐pass filter and a high‐pass filter which both exhibit strong out‐of‐band suppression performance. The control structure for TZs is constructed by cascading the inductance and capacitance components. The TZ controlling structure primarily generates TZs at high frequencies, resulting in a further bandwidth enhancement in the stopband. The lumped circuit of the proposed BPF is first constructed, and rigorous design formulas are provided to assist in constructing the proposed design. After schematic optimization, the second step involves layout optimization and simulation based on the specific IPD process. Experimental results mounted on a printed circuit board demonstrate that the bandwidth spans from 3.3 to 4.2 GHz with an IL of only 2.0 dB at the center frequency. Additionally, this BPF achieves impressive sideband suppression, exceeding 18 dB in the 0–1.7 GHz range and 30 dB in the 9–15 GHz range. Remarkably, the BPF is exceptionally compact with only 0.5 mm × 1.0 mm (0.006λc × 0.012λc). The proposed BPF exhibits outstanding performance with minimal IL and extensive sideband suppression at such a compact size based on the IPD technology.

Metal Mesh Metasurfaces as Dual-Band Bandpass Filters for Terahertz Frequencies

In the paper, we propose a new strategy to design of metal mesh filters (MMFs) based on spatial symmetry analysis of bound states in the continuum(BICs) and manipulating and control with resonances, when BICs transformed to the resonances due to spatial perturbations in the MMF structure. The design of a dual-band polarization-insensitive terahertz bandpass filter with wide upper stopband characteristics using a single conducting layer patterned with rectangular holes is presented. The transmission response of the MMF with two poles is obtained to realize dual-band characteristics and three zeros to suppress the stopband. The proposed design has achieved broadband bandpass transmission characteristics under both TE and TM polarizations with canter frequencies at 0.516THz and 0.734THz and 3dB bandwidths of 25% and 17%, respectively, and upper stopband from 0.887THz to 1.6THz with over 10dB suppression.

Compact microstrip lowpass filter with wide stopband and sharp transition band using radial stub resonator

This study introduces a compact microstrip lowpass filter that offers a wide stopband and a low transition band. The couple radial stubs are designed for having sharp roll-off. The filter has a −3 dB cut off frequency of 1.6 GHz, with a transition band ranging from 1.6 to 1.7 GHz with attenuation levels of −3 dB and −20 dB, respectively. To ensure a wide stopband, the filter utilizes bended transmission lines with stepped impedance suppressing cells, resulting in a stopband attenuation of 20 dB from 1.7 to 28 GHz. The insertion loss in the passband is less than 0.1 dB, and the overall size of the filter is 0.127 × 0.087 λg2.

Analysis and design of compact dual-mode bandpass filter based on modified CSRR with wide stopband for 5G sub-6 GHz mobile communications

In this paper, a dual-mode bandpass filter with a wide stopband based on modified complementary split-ring resonators for 5G sub-6 GHz mobile communications is presented. The non-magnetic resonant particle known as a complimentary split ring resonator is used with a host microstrip line with a series gap in order to obtain a bandpass response. Since a complementary split-ring resonator provides a narrow passband, a T-slot has been introduced in the middle of this resonator to obtain dual-mode behavior with controllable bandwidth. Moreover, a pair of stubs are added to the host microstrip line in order to achieve a wide stopband with good out-of-band rejection. The proposed resonator is analyzed, and a bandpass filter is designed to operate at 3.6 GHz to cover the 5G band from 3.4 to 3.8 GHz. The results show that the filter has a low insertion loss, good return loss, and a wide stopband up to 9 GHz with a compact size since its resonator offers a size of 0.1 λ g × 0.14 λ g where λ g is the guided wavelength at 3.6 GHz.

A novel modified complementary metamaterial resonator based dual-band bandpass quasi-elliptic filter using half-mode SIW cavity with wide stopband rejection for wireless communication applications

This article presents a novel dual-band metamaterial bandpass quasi-elliptic filter (DBBPF) for wireless communication applications, addressing the critical need for compact, high-performance multi-band filters in modern systems. The proposed filter leverages substrate-integrated waveguide cavity (SIWC) technology combined with innovative complementary metamaterial resonators to achieve significant miniaturization while maintaining excellent electrical performance. The filter’s design incorporates four complementary resonators of modified rectangular shape (CMSRR) on the metalized top face, generating targeted operating bands below the SIW cutoff frequency. To control their resonances, the size of each CMSRR is optimized for electrical dimensions of just 0.154 λ0× 0.115 λ0× 0.028 λ0. We present a comprehensive analysis of both full mode (FMSIWC) and half mode (HMSIWC) configurations, demonstrating dual-bandpass behavior with central frequencies at 5.79 and 9.82 GHz for FMSIWC, and 5.72 and 9.74 GHz for HMSIWC. The electromagnetic behavior of the basic cell of the filter is analyzed based on the frequency characteristics of its permittivity and permeability. A parametric study according to the location of the metamaterial resonators in the filter is conducted to have the optimized dimensions. Additionally, the confinement of the electric field in the two filter configurations is discussed to better understand their behavior. The fabricated HMSIWC filter, implemented on an FR4-Epoxy substrate measuring only 54.60 × 25.75 × 1.5875 mm3, achieves remarkable miniaturization while maintaining desired performance characteristics. Experimental results validate the simulated performance, demonstrating excellent agreement for both configurations. Key performance metrics include fractional bandwidths of 3.77 and 6.98 %, and insertion losses of 1.33 dB and 2.14 dB for the two passbands in the HMSIWC design. This work advances the state-of-the-art SIW filter design by combining half-mode techniques with optimized CMSRR structures, resulting in a compact, high-performance dual-band filter. The proposed DBBPF’s simple design and small form factor make it an ideal candidate for integration into various wireless communication systems, particularly where space constraints are critical.

Beam-steerable filtering patch antenna with wide-stopband suppression and stable radiation characteristics

A method of designing beam-steerable patch antennas with wide stopband suppression is proposed in this article. The wide stopband suppression characteristic is realized by designing suitable parallel coupled lines and open-circuited stubs. The beam steering characteristic is achieved by using a driven patch and two pairs of metal walls vertically placed on both sides of the driven antenna. By controlling the different states of the switching PIN diodes loaded between metal walls, the stable beam steering characteristic can be obtained over the entire operating bandwidth. An experimental antenna is designed and manufactured to validate the approach. The beam steering angles of the simulation and measurement results are ±30°. Moreover, in the three proposed operating states, the out-of-band suppression from 2.6 GHz to 10 GHz is more than 16 dB. The proposed antenna can achieve the characteristic of both wide stopband suppression and beam steering. In addition, the proposed antenna is able to maintain good impedance characteristics during beam steering and maintain stable beam over the entire operating bandwidth.

Compact transversal signal-interaction wideband bandpass filter with multiple transmission zeros and wide stopband

In this paper, a compact wideband bandpass filter with multiple transmission zeros and a wide upper stopband is proposed based on the transversal signal-interaction concept. The filter has two transmission paths for signals to travel from the input port to the output port. The wideband bandpass filter is designed with a center frequency of 4.29 GHz (f0) and a 3-dB fractional bandwidth of 71.3 %. Six transmission zeros from 0 GHz to 4.2 f0 can be achieved due to the superposition of signals of the two transmission paths and the virtual short effect of open stub. The designed and fabricated wideband bandpass filter is of minimum insertion loss of 0.3 dB, group delay in the passband below 1.1 ns, and upper-sideband rejection up to 18 GHz (4.2 f0). Additionally, the proposed filter possesses compact size, and the overall circuit only occupies 0.23 λg × 0.15 λg (λg is the guide wave length of 50 Ohm microstrip line at 4.29 GHz). Measurement and simulation results are in good agreement.

Distributed Bragg reflector based ASE noise removal pump wavelength filters for futuristic chip-scale quantum photonic circuits

This article reports a novel design of a compact tunable resonance filter with a highly extinguished and ultra-broad out-of-band rejection for on-chip amplified spontaneous noise suppression from pump lasers highly demanding for generating pure/entangled photon pairs via χ(3) process in a CMOS compatible silicon photonics technology platform. The proposed device is designed with two identically apodized distributed grating structures for guided Fabry-Perot resonant transmissions in a silicon-on-insulator rib waveguide structure. The device design parameters are optimized by theoretical simulation for a low insertion loss singly-resonant transmission peak at a desired wavelength. We observed that a device length of as low as ∼ 35 µm exhibits a rejection band as large as ∼ 60 nm with an extinction of ∼ 40 dB with respect to the resonant wavelength peak at λ r ∼ 1550 nm (FWHM ∼ 80 pm, IL ∼ 2 dB). The experimental results have been shown to be closely matching to our theoretical simulation and modeling results in terms of its stop bandwidth and resonance wavelength for noise suppressed pump laser wavelength filtering. As expected from the theoretical prediction, the trend pertaining to the trade-off between passive insertion loss and Q-value of the resonances has been observed depending on the device parameters. The thermo-optic tuning characteristics of resonant wavelengths have been obtained by integrating microheaters. The resonance peak could be tuned at a rate of 96 pm per mW of consumed thermal power. Noise associated with an amplified pump wavelength (λ P ∼ 1550 nm) has been shown to be suppressed (∼ 40-dB), up to the detector noise floor.

Super compact and ultra-wideband bandpass filter with three band notches using triple-mode stepped impedance resonator and defected ground structure

A super-compact ultra-wideband (UWB) microstrip band-pass filter (BPF) with triple-notched bands and wide stopband is proposed in this paper. The super-compactness of the proposed filter is achieved by integrating the modified SCRLH-TL UWB-BPF and backbone-shaped defected ground structure (DGS). The equivalent LC circuit models of the DGS and the modified SCRLH-TL UWB-BPF with the DGS are analyzed to validate their numerical simulation results. To introduce the triple notched-bands to mitigate the interference the two triple-mode SIRs are designed and loaded on the modified UWB-BPF without increasing the circuit size. The proposed filter was fabricated by using a conventional PCB process with the substrate of FR4. The measured 3-dB passband ranges from 2.8 through 10.2 GHz with the fractional bandwidth (FBW) of about 114%. The triple-notched bands with attenuation of more than 15 dB are measured at 4.4, 5.3 and 8.2 GHz, respectively. The filter exhibits a high selectivity with steep skirt property and has a wide upper stopband with an out-of-band rejection of −10 dB at 11.8−20 GHz. Its total dimension, including the rectangular substrate with feed lines, occupies only 16mm × 8 mm.

A simple miniaturized sub‐6‐GHz bandpass filter with wide upper stopband in gallium arsenide‐based integrated passive device process

AbstractA very compact three‐pole bandpass filter with wide upper stopband is proposed and implemented by gallium arsenide integrated passive device technology. By organizing inductor and capacitor in parallel with an LC series network, a dual‐frequency bandstop structure is constructed in the first step to achieve transmission zeros (TZs). Then, the lowpass capacitor network and highpass inductor network are wisely cascaded with the bandstop structure, thus to the realization of three‐pole bandpass filter with a wide upper stopband. Based on the even‐/odd‐mode analysis, theoretical equations for the in‐band resonances and out‐of‐band TZs are given. Then, one filter prototype centered at 4.4 GHz with 3‐dB fractional bandwidth of 45.5% is designed, fabricated, and measured. Both simulated and measured results indicate that the proposed filter exhibits a wide stopband rejection of 25 dB from 6.4 to 22.8 GHz as well as a very compact size about 0.026λg × 0.031λg.

Compact IPD bandpass filter with wide upper stopband based on modified topology for 5G applications

AbstractA compact bandpass filter (BPF) with wide stopband performance is proposed and implemented on Si‐based integrated passive device (IPD) technology. A modified topology consisting of a novel Pi‐section and two capacitors are introduced in this BPF. The Pi‐section topology can achieve a band‐pass performance and generate four transmission zeros out‐of‐band. These two capacitors can improve the in‐band matching and also widen the stopband. The proposed BPF with a compact size of 1.0 mm × 0.5 mm × 0.3 mm is fabricated using Si IPD technology and measured by on‐wafer probing. It shows that the insertion loss is less than 1.75 dB, the return loss is better than 18 dB in the 5G band, and the upper stopband suppression level is better than 17.5 dB up to 18 GHz. The simulated and measured results of the proposed BPF are in reasonably good agreement.

Design of single layer bowtie wide band-stop frequency selective surface with angular stability for C-band applications

This paper presents the design and analysis of a single-layer wide band-stop frequency selective surface (FSS) tailored for C-band applications. The proposed FSS design employs a modified bow-tie unit cell structure that enhances band stop characteristics, resulting in improved performance compared to traditional FSS geometry. The design process involves numerical simulations and optimization techniques to achieve the desired frequency response. A modified bowtie element with FR4 substrate comprises the proposed FSS which exhibits a resonant frequency of 6.0 GHz with a wide bandwidth of 4.84–6.96 GHz (35.93 %) and act as a band stop filter. The FSS is analyzed in terms of its transmission coefficients, providing insight into its filtering properties. In addition, parametric studies of the unit cells are done. Furthermore, the angular stability of the proposed FSS is simulated with incident waves at various angles between 0° to 60° for both TE and TM modes. The proposed FSS presents C-band applications of WLAN, ISM/WiMAX, satellite communications, radar systems, shielding and communication devices, also enhancing filtering capabilities and system performance. The simulation results are well correlated with measurement results.

Impact of Grating Duty-Cycle Randomness on DFB Laser Performance

The duty-cycle randomness (DCR) of the Bragg grating of the distributed feedback (DFB) lasers introduced by the fabrication process is inevitable, even with state-of-the-art technologies such as electron beam lithography and dry or wet etching.This work investigates the impact of grating DCR on DFB laser performance through numerical simulations. The result reveals that such randomness causes a reduction in the side mode suppression ratio (SMSR), and deteriorates the noise characteristics, i.e., broadens the linewidth and increases the relative intensity noise (RIN). With the grating DCR, the effective grating coupling coefficient decreases as evidenced by the reduced Bragg stopband width. However, the longitudinal spatial hole burning (LSHB) effect in the DFB lasers can somewhat be diminished by the grating DCR. The seriousness of these effects depends on different grating structures and their coupling strengths. Our simulation shows that a degradation of 17 dB can be brought to the SMSR of the uniform grating DFB lasers with their duty cycles taking a deviation of ±25% in a uniformly distributed random fashion. It also broadens the linewidth of the quarter-wavelength phase-shifted DFB lasers by more than 2.5 folds. The impact of this effect on the RIN is moderate—less than 2%. All the performance deteriorations can partially be attributed to the effective reduction in the grating coupling coefficient of around 20% by such a DCR.

Terahertz dual-band bandpass filter based on spoof surface plasmon polaritons with wide upper stopband suppression

In this paper, a terahertz (THz) dual-band bandpass filter based on spoof surface plasmon polaritons (SSPPs) with wide upper stopband suppression is proposed. The filter utilizes two types of SSPP unit cells loaded on a double-sided quasi-SSPPs transmission line to achieve dual-band filtering responses and wide upper stopband suppression simultaneously. The performance and bandwidth of the filter's passbands can be adjusted by modifying the SSPP unit cells within the dual-band filtering part. The detailed design method is provided to enhance understanding of the operating principle of the presented filter. The simulation results of the designed THz filter demonstrate its excellent dual-band filtering performance. It features a wide stopband spanning from 0.91 to 1.45 THz with |S21| < -35 dB. To validate the proposed approach, a microwave filter with a similar design is implemented. Finally, the simulated and measured S-parameter responses of the filter are provided for comparison and evaluation.