Wideband Bandpass Filter Research Articles

A super-compact wideband bandpass filter using capacitor-loaded coupled lines

Abstract A wideband bandpass filter (BPF) using capacitor-loaded coupled lines is proposed with super-compact circuit size and very simple structure. By loading three lumped capacitors in parallel to three same pairs of coupled lines, three transmission poles and four transmission zeros can be achieved and they can be calculated by input admittance derivation. To verify the design, a wideband BPF prototype with center frequency at 1.34 GHz is fabricated, whose measured 3-dB fractional bandwidth is 98.5 % (0.68–2 GHz), in-band insertion loss is less than 0.5 dB, return loss is greater than 17.5 dB, and circuit size is only 0.24 λ g × 0.02 λ g (λ g: guided wavelength at the center frequency).

Design of highly selective balanced bandpass filter with wide differential-mode stopband and high common-mode suppression

A highly selective and wide stopband bandpass filter (BPF) with multiple transmission poles (TPs) and transmission zeros (TZs) has been proposed. The BPF employs a box-like coupling structure consisting of two half-wavelength resonators and a dual-mode open stub loaded resonator, enabling the generation of two TZs and four TPs. Three controllable TZs are obtained by adding an annular spiral open stub to the terminal of the input and output coupling lines, which significantly improves the selectivity of the BPF. To achieve a wide stopband characteristic, a wide stopband unit with three additional TZs is cascaded within the structure. A balanced BPF is realized by introducing a microstrip-slotline-microstrip balun structure to the input and output ports of the proposed BPF. Experimental results validate the feasibility of the proposed BPF and balanced BPF applied in 2.45 GHz ISM band. The introduction of eight TZs gives the BPF a 20 dB rectangular coefficient of 1.3 with an upper stopband exceeding than 12 GHz. The balanced BPF can achieve 40 dB of high common-mode(CM) suppression in the passband, while differential-mode (DM) transmission is close to the performance of the proposed BPF. The minimum insertion loss for BPF and balanced BPF is 0.8 dB and 1.3 dB, respectively.

Analysis and design of a wide stop‐band and high out‐of‐band suppression BPF

AbstractThis paper proposes a wide bandpass filter (BPF) with high out‐of‐band suppression and wide stop‐band characteristics. An interdigital coupled line structure loaded by a rectangular resonator ring is employed to generate three transmission poles in the pass‐band and an additional transmission zero (TZ) in the stop‐band, thereby achieving a wider pass‐band while enhancing stop‐band suppression. Compared to traditional coupled‐line structures, the structure mentioned in this paper offers significant advantages in designing filters with wide stop‐bands and high out‐of‐band suppression. Furthermore, open‐circuit T‐stub, and a pair of open‐circuit stub are used to generate multiple parasitic TZs at high frequencies, which is adopted to further expand the stop‐band range. Measurement results shows that the insertion loss of the BPF is of −2.86 dB within the range of 7.05–12.20 GHz. The stop‐band ranges from 13 to 48 GHz with an out‐of‐band suppression of −27 dB, especially when the out‐of‐band suppression is −40 dB, the stop‐band frequency range is 16.40–31.35 GHz.

Miniaturised high‐isolation K‐/Ka‐band diplexer with 3D antarafacial channel integration using vertical quasi‐coaxial matching network

AbstractA miniaturised high‐isolation K‐/Ka‐band diplexer with exceeding adjacent channels using 3D antarafacial channel integration and vertical‐quasi‐coaxial‐based matching network is proposed. For smaller size, lower loss and lower channel interference, the high‐order low‐pass filter for the K‐band channel and the four‐line‐interdigital‐coupled wideband bandpass filter for the Ka‐band channel are respectively designed on two low‐loss glass‐based substrates, and these two substrates are integrated on the two antarafacial surface of the mounting board. The vertical‐quasi‐coaxial (VQC) embedded in the mounting board is not only used as three‐dimensional (3D) interconnection of the two antarafacial channels but also designed as the constituent part of the matching/isolation network, and this can effectively decrease the impedance traction caused by the Ka‐band filter for the K‐band channel of the diplexer. In addition, four transmission zeros of the K‐band filter are designed at the whole passband of the Ka‐band channel to improve the isolation to the K‐band channel for guaranteeing the performance of the diplexer at the Ka‐band channel. Furthermore, working principle, design method and test solution of this proposed K‐/Ka‐band diplexer are well illustrated, and the high‐isolation (>40 dB) in very adjacent wideband channels at K‐band (18–23.5 GHz) and Ka‐band (25.8–31.6 GHz) is achieved within a tiny size of 9 × 4 × 0.87 mm.

Wideband filtering power dividers with/without notch band

AbstractLow loss and compact wideband filtering power dividers (WB‐FPDs) with/without notch band are proposed. The WB‐FPDs are designed using wideband bandpass filter based on asymmetric stepped‐impedance resonator (SIR). Parallel coupled microstrip lines are used to create both wideband filtering characteristic and two additional transmission poles. A notch band can be generated at upper passband edge by using open‐circuited stubs on the SIRs. The WB‐FPDs with/without notch band are successfully designed, fabricated, and tested. The wide passband is centered at 4 GHz with the fractional bandwidth (FBW) of 51.1%, while the notch band is at 5.56 GHz with the FBW of 3.1%. Good agreement between the simulated and measured results is observed.

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.

A systematic approach for the development of wide band band pass filters using resonators

In this paper, for the first time a novel and systematic approach is presented to construct a wideband Band Pass Filters (BPFs) with high selectivity and stopband response. Two BPFs (Filter I and Filter II) were built on a Taconic (TLX-9) substrate using semi-circular tapered coupled lines, Defected Microstrip Structures (DMSs), Defected Ground Structures (DGS), and Stepped Impedance Resonators (SIRs). The precision of the design procedure is confirmed through 3-D full wave Electro-Magnetic (EM) simulation software where two wideband filters were designed for L, S, and C-bands. Additionally, parametric analysis has been done to evaluate the performance of both wideband filters with key features such as return loss, insertion loss, Band Width (BW), selectivity, and stopband response. Even-odd mode analysis has been implemented using the ABCD matrix that acts as a source for mathematical analysis of Filter I. Eventually, two wideband filters have been fabricated and tested for their effectiveness, and the measured results of two wideband filters are in line with the simulated ones with slight deviations due to fabrication tolerances and connector losses. The prototyped Filter I functions as a bandpass in the frequency range of 2.4 GHz to 4.8 GHz with a maximum insertion loss of 0.85 dB and return loss of 19.5 dB thereby providing 64% Fractional Band Width (FBW). Near 19 dB rejection is observed in the lower and upper stopband regions with BW (stopbands) greater than 2 GHz. Moreover, Filter II is also fabricated and tested. The experimental return loss of 20 dB and insertion loss (maximum) of 0.73 dB over the passband (1.9 GHz to 3.4 GHz) were found with 0.7 Selectivity Factor (SF). More than 20 dB attenuation of stopbands (lower and upper) was achieved. Thus, the fabricated wideband BPFs operate in L, S, and C-bands for radars, satellite and long-distance radio communications, and military telemetry applications.

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.

Design of a compact filter integrated wideband and circularly polarized antenna array for K-band application

A compact filtering mechanism in the antenna system is required to avoid unwanted incoming electromagnetic waves in the working frequency band. A circularly polarized (CP), wideband, and high gain antenna array co-design with a wide bandpass filter (BPF) for a K-band satellite application at (17.7 to 21.2) GHz is studied in this paper. Antenna array elements with diagonal slots and BPF in the same frequency are compatible. For maximum radiation efficiency, the input impedance of the slotted 16 × 16 elements antenna array is matched to 50 Ω and equal to the output impedance of the BPF in the operating band. To implement the filtering concept, a co-design is modeled and simulated. The suggested wideband BPF and antenna array are integrated on a combined aperture, manufactured, and tested experimentally. Based on the results of the tests, it can be concluded that the suggested filtering antenna array is well matched (|S11| < −15 dB) throughout a wide frequency band of 17.7 GHz to 21.2 GHz. The final structure simulated and measured 3 dB axial ratio covers the functional spectrum with a maximum 25.3 dBi gain. High directive beams with a 20 dB cross-polarization suppression level in E & H planes are simulated and measured. Due to these advantages, the suggested antenna is an attractive option for use in K-band 3U satellite applications to minimize the requirement for extra filtering circuits in the RF system.

Abstract B008: Machine-learning enabled quantification of colocalized multiplex IHC signals with spectral overlap

Abstract Background: Immunohistochemistry (IHC) is the gold standard for detecting protein biomarkers in cancer. In breast cancer, several nuclear biomarkers are relevant for guiding treatment decisions, including estrogen receptor (ER) and progesterone receptor (PR), indicative of response to endocrine therapy, and the proliferation marker Ki67, indicative of response to CDK inhibition1. However, these nuclear markers are detected using chromogens that colocalize and spectrally overlap with hematoxylin (HTX), the standard nuclear counterstain for IHC. Thus, the accurate detection and quantification of nuclear antigens is challenging. To overcome this limitation of IHC-based biomarker assays, we developed a method to identify colocalized signals after staining with chromophores with spectral overlap. Methods: Multiplex IHC (mIHC) using primary antibodies against Ki67, PR, and ER was performed on a breast cancer tissue microarray (N=65 cores). Antigens were detected by dabsyl-, tamra-, and Cy5-conjugated secondary antibodies, respectively, and slides were counterstained with HTX. The cores were scanned with brightfield imaging (Aperio AT2 and 3DHistech microscopes). The same cores were imaged on a custom brightfield microscope using an LED light source and 10 nm wide band-pass filters at 405, 450, 520, 550, 589, 632 and 660 nm. Images were spectrally unmixed using absorption spectra of the different chromophores and the background estimated based on the images themselves and aligned with the brightfield images. Pathologist-trained individuals collected exhaustive manual annotations in regions of interest for each marker and HTX using unmixed channels. A convolutional neural network (CNN) was trained using the annotations for each marker and HTX and applied to the WSI. Predicted cell locations were aggregated across the four channels to obtain an exhaustive “super-annotation” co-expression map of the WSI. Super-annotations were then used to train a CNN to detect ER/PR/Ki67/HTX colocalization in the aligned RBG image of the same slide. Predictions from the super-annotation model were compared to ER/PR/Ki67/HTX detection done via HALO (Indica Labs). Results: Our multi-spectral imaging pipeline allowed for comprehensive annotations of all nuclei positive for at least one of the three markers or HTX. Using our super-annotation model, the count error of nuclei that are positive for HTX and one, two, or three markers was reduced by 7.8%, 6.4%, and 0.03%, respectively, compared to HALO. Conclusions: We have developed a method to identify colocalized antigens after mIHC using chromogens with spectral overlap. Related work to extend this approach to membranous biomarkers is ongoing and will enable additional novel analyses (e.g., describing the precise spatial organization of PD-L1+ tumor cells relative to CD8+ tumor-infiltrating lymphocytes). The approach that we describe here has great potential to facilitate the utilization of mIHC for the clinical detection of biomarkers in oncology.

The Singlet: Direct Synthesis of Pseudo-Elliptic Inline Filters With Frequency Variant Couplings

A general and direct synthesis of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{p}$</tex-math> </inline-formula> poles pseudo-elliptic inline filters having <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{p}$</tex-math> </inline-formula> purely real and/or imaginary frequency transmission zeros is presented. Using an appropriate model of the resonators (bandpass distributed or lumped element) and shifting the reference planes at the input and output of the filter network, a novel direct synthesis and realization of filters based on frequency variant coupling (inductive or capacitive) in the distributed domain is demonstrated for accurate modeling of narrow and broadband filters. First, a complete general synthesis procedure is described that allows for flexible or mixed topologies realizing transmission zeros anywhere on the frequency plane (including complex and infinite frequencies). Furthermore, by exploiting the power of modular design, a synthesis procedure that enables simultaneous extraction of reflection zero (a pole) and a transmission zero in the form of a symmetrical and physically realizable singlet as an elementary unit is showcased. The physical dimensions of the extracted singlets are independently determined in any chosen technology, and the overall filter is obtained by directly cascading the physical singlets. To validate this novel synthesis technique, three design examples are shown: a narrowband four-pole, four transmission zeros (fully canonical) filter from literature is synthesized and physically dimensioned, a wideband three-pole, three transmission zero (fully canonical) filter, and a broadband three-pole, one transmission zero, filter. In the first two examples, each of the singlet blocks was implemented in an overmoded rectangular waveguide cavity operating at the TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{201}$</tex-math> </inline-formula> mode coupled at the input and output to the fundamental nonresonating TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{10}$</tex-math> </inline-formula> mode. The third example was implemented in a re-entrant coaxial resonator operating at the fundamental mode. The simulation of the electromagnetic (EM) high-frequency structure simulator (HFSS) models of the overall example filters was in excellent agreement with the synthesized models, thereby validating the effectiveness of the proposed synthesis technique. Furthermore, the measured results of the fabricated wide bandpass filter showed close agreement with synthesis and EM model.

Compact wideband filter with wide stopband using transition-free spoof surface plasmon polaritons

In this article, a newly spoof surface plasmon polaritons (SSPPs) is proposed and used to design a compact wideband bandpass filter (BPF). Different from the traditional SSPP unit cell with one-shaped structure, the unit cell of the proposed SSPPs consists of an H-shaped slotline and a bilateral T-shaped slotline. Benefiting from the hybrid structure, no transition portion is needed for impedance matching in the design of the microwave filter, which highly reduces the horizontal size of the SSPPs-based filter. The transition structure of microstrip to slotline provides a capacitance with a highpass frequency response, which enables the realization of a passband by cooperating with the natural lowpass property of SSPPs. Also, the upper and lower cutoff frequencies of the proposed filter can be adjusted independently by the key parameters. Besides, a wide upper stopband can be obtained by properly designing the SSPPs unit cell and the microstrip to slotline structure. Finally, a well-designed BPF operated at 1.3–6.2 GHz and its upper stopband rejection reaching 20 GHz is fabricated and measured. The test results are in good agreement with the simulations, which verifies the feasibility of the proposed structure and design method.

Electromechanical interactions between cell membrane and nuclear envelope: Beyond the standard Schwan’s model of biological cells

We investigate little-appreciated features of the hierarchical core–shell (CS) models of the electrical, mechanical, and electromechanical interactions between the cell membrane (CM) and nuclear envelope (NE). We first consider a simple model of an individual cell based on a coupled resistor–capacitor (Schwan model (SM)) network and show that the CM, when exposed to ac electric fields, acts as a low pass filter while the NE acts as a wide and asymmetric bandpass filter. We provide a simplified calculation for characteristic time associated with the capacitive charging of the NE and parameterize its range of behavior. We furthermore observe several new features dealing with mechanical analogs of the SM based on elementary spring–damper combinations. The chief merit of these models is that they can predict creep compliance responses of an individual cell under static stress and their effective retardation time constants. Next, we use an alternative and a more accurate CS physical model solved by finite element simulations for which geometrical cell reshaping under electromechanical stress (electrodeformation (ED)) is included in a continuum approach with spatial resolution. We show that under an electric field excitation, the elongated nucleus scales differently compared to the electrodeformed cell.

A High-Temperature Superconducting Wideband Bandpass Filter at the L Band for Radio Astronomy

In order to ensure the normal operation of radio astronomy observations, an extremely sensitive receiver system needs to be equipped in front of the large radio telescope. An 8-pole wideband high-temperature superconducting (HTS) filter using a Coplanar Spiral Resonator Structure with a passband of 1160∼1670 MHz is developed to suppress strong radio interference. The filter is fabricated on a 36 mm × 14 mm YBCO HTS film, which is deposited on a 0.5 mm thick MgO substrate. The minimum insertion loss measured in the liquid nitrogen temperature region is 0.03 dB, and the first parasitic passband appears at 2600 MHz. The measured results are in good agreement with the simulations. The filter can be used in radio telescope receivers for the observation of neutral hydrogen and pulsars, as well as in high-sensitivity satellite navigation instruments.

Impact of holes in an interdigital parallel folded coupled line‐based wideband bandpass filter for X‐band applications

AbstractIn this paper, a study on the effects of strategically implemented holes in a miniaturized wideband bandpass filter (BPF) utilizing interdigital folded coupled lines is presented. First, the BPF is designed to produce the passband by introducing a fold in the coupled lines. The passband is centered at 9.3 GHz (X‐band), catering to radar applications. Coupled lines connected to a modified U‐shaped transmission line comprise the filter's design configuration. The novelty of the design resides in incorporating drilled holes along the coupled lines, which generate perturbations and resonant effects, resulting in enhanced impedance variations and improved filter performance. With the aid of electromagnetic analysis and simulation software, the coupled lines, U‐shaped transmission lines, and drilled hole diameters are all optimized. Vector Network Analyzer performs all the measurements and draws the comparisons. An increment of 22.58% is seen in return loss as it increases from −24 to −32 dB, and the insertion loss shows an increase of 16.74%. The proposed filter has been subjected to analytical study, simulation, and implementation, which have confirmed its exceptional return loss, favorable insertion loss, and compact dimensions. The research results make a valuable contribution to the development of miniaturized wideband BPFs, specifically focusing on their use in radar systems. In such systems, the ability to accurately and efficiently filter signals is paramount. The design insights and performance improvements presented in this study have significant implications for broader applications in microwave engineering and communication systems.

Design of substrate integrated-waveguide wide stopband bandpass filter for 5G applications

Design of substrate integrated-waveguide wide stopband bandpass filter for 5G applications

Design and performance evaluation of a novel metamaterial broadband THz filter for 6G applications

Terahertz (THz) radiation, which has applications in the imaging of objects, non-destructive testing, satellite communication, medical diagnostics, and biosensing, has generated a great deal of attention due to its remarkable properties. This paper proposes a novel broadband filter for THz applications. The main idea is to overcome the insertion loss and bandwidth issues by modeling a frequency-domain finite difference method and guided-mode resonance (GMR). The optimal design scheme of the wideband pass filter based on the circular resonant ring is discussed by comparing the transmission parameters under various parameters. This scheme overcomes the restriction of the narrow passband bandwidth of the prior THz filters and achieves approximately 3 dB bandwidth of 0.54 THz. The proposed THz filter paper also has the advantages of a straightforward structure, low processing costs, and ease of conformal with other structures, and it can be used for stealth fighters, new communication technology, and precise instruments. In addition, when compared to existing models, the suggested filter offers higher 3 dB BW operation, increased transmittance, low insertion loss, and stable performance at various oblique angles.

Spurious response suppression in wideband bandpass filters using chirality

A simple chiral medium is used to enhance the response of a conventional microstrip coupled line bandpass filter (BPF). The approach is applicable to both narrowband and wideband BPFs using the presented chiral topology. The topology is based on an ultra-subwavelength planar chiral particle that is utilized in the interface between two slabs of substrate. More specifically the medium realizes the suppression of the second spurious response of the filter at a large bandwidth, which enables its practical application in wideband coupled-line based BPFs. The effect of the chiral particles on the substrate's effective permittivity and on the phase velocities of the even and odd mode of two coupled transmission lines on top of the substrate structure is explicitly used in the design of the filter. The methodology is applicable to any coupled-line BPF order. Two wideband microstrip coupled-line prototype filters are designed, fabricated, and measured, one involving a substrate without particles and one involving the chiral substrate. Measurement results are in good agreement with the simulations. The chiral medium based filter results in a wide fractional bandwidth (FBW) of 81% for a 1 GHz center frequency and a measured suppression level of −60 dB.

Compact Wideband Groove Gap Waveguide Bandpass Filters Manufactured with 3D Printing and CNC Milling Techniques.

This paper presents for the first time a compact wideband bandpass filter in groove gap waveguide (GGW) technology. The structure is obtained by including metallic pins along the central part of the GGW bottom plate according to an n-order Chebyshev stepped impedance synthesis method. The bandpass response is achieved by combining the high-pass characteristic of the GGW and the low-pass behavior of the metallic pins, which act as impedance inverters. This simple structure together with the rigorous design technique allows for a reduction in the manufacturing complexity for the realization of high-performance filters. These capabilities are verified by designing a fifth-order GGW Chebyshev bandpass filter with a bandwidth BW = 3.7 GHz and return loss RL = 20 dB in the frequency range of the WR-75 standard, and by implementing it using computer numerical control (CNC) machining and three-dimensional (3D) printing techniques. Three prototypes have been manufactured: one using a computer numerical control (CNC) milling machine and two others by means of a stereolithography-based 3D printer and a photopolymer resin. One of the two resin-based prototypes has been metallized from a silver vacuum thermal evaporation deposition technique, while for the other a spray coating system has been used. The three prototypes have shown a good agreement between the measured and simulated S-parameters, with insertion losses better than IL = 1.2 dB. Reduced size and high-performance frequency responses with respect to other GGW bandpass filters were obtained. These wideband GGW filter prototypes could have a great potential for future emerging satellite communications systems.