Center Frequency Of Passband Research Articles

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 broadband second-order bandpass frequency selective surface for microwave and millimeter wave application.

This paper presents a frequency selective surface (FSS) with a wideband second-order bandpass response in the dual-band of microwave and millimeter wave. The overall structure consists of three layers of metal pattern and two layers of thin dielectric substrate. The top and bottom metal layers have capacitive patches with integrated curled Jerusalem cross slot resonators, while the intermediate metal layer has an inductive grid structure with cross-shaped slot resonators. The incorporated slot resonators play a pivotal role in achieving the desired transmission poles or zeros, which enable a wideband second-order filtering response in the dual-band and a quick roll-off at the passband edges, increasing the efficacy of electromagnetic shielding. To fully investigate the structure's frequency response, an equivalent circuit model of the structure is created, spanning the complete frequency range of 5-50 GHz. Physical samples are created and measured to confirm the suggested approach's efficacy. The passband center frequencies of the FSS are found at f1 = 19.42 GHz and f2 = 42.78 GHz, and the - 3dB bandwidth is 4.34 GHz (17.25-21.59 GHz) and 8.54 GHz (38.51-47.05 GHz), respectively. The simulation results align well with the experimental data. The transmission response rapidly transitions from the passband to the stopband at the passband boundaries.

Multilayer circular SIW cavity differential bandpass filter with wide‐stopband characteristics

AbstractIn this paper, a compact differential bandpass filter with wide‐stopband is presented. The proposed differential filter is designed using two circular substrate‐integrated waveguide (SIW) cavities coupled through a pair of symmetric coupling slots. The filter operates in TM110 mode of the circular SIW cavity. The degenerate TM110 mode is shifted to higher frequency by the introduction of two pairs of perturbation vias. The center frequency of the differential passband can be tuned by changing different design parameters such as location of perturbation vias and length of the slotlines. As a proof of the proposed concept, a second‐order differential bandpass filter is designed, fabricated, and measured. The measured results are in good agreement with the electromagnetic‐simulated ones.

Non-Magnetic Non-reciprocal Bandpass Filter with Quasi-Elliptic Response and Tunable Center Frequency

This paper presents a detailed analytical numerical design methodology and experimental validation of non-magnetic non-reciprocal bandpass filter (NBPF) that exhibits a highly selective quasi-elliptic response in forward direction of propagation. By modulating resonators with progressive phase shift AC modulation signal, unidirectional RF signal propagation (|S21| ≠ |S12|) is achieved. Analytical spectral S-parameters of the proposed quasi-elliptic NBPF have been derived to gain insight nonreciprocal response. Furthermore, empirical relationships between modulation parameters and filter specifications have also been established through numerical simulations, allowing for simplified design process of the NBPF. By varying the resonant frequency of the resonators, a frequency reconfigurable transfer function can be achieved, providing center frequency tunability of NBPF. For experimental validation purposes, a prototype of microstrip line NBPF is designed and manufactured using three time-modulated resonators, which are implemented using transmission line loaded with varactor diodes. The passband frequency can be continuously tuned by changing DC-bias voltage of varactor diodes. The measurement results revealed that passband center frequency is tuned from 1.65 GHz to 1.95 GHz achieving at tuning ratio of 1.182:1, while maintaining the nonreciprocal behavior with two transmission zeros. For all tuning states, in-band minimum insertion loss in forward direction was measured between 3.20 and 4.8 dB, whereas isolation in reverse direction was measured up to 34.5 dB.

Generalised strategy for stabilising minimax-type variable bandpass filter

ABSTRACT This paper first develops a novel transformation-based strategy for guaranteeing the stability of recursive-type variable digital filters, and then presents a new type of functions called less-than-unity (LTU) functions required in performing stability-guaranteed parameter transformations (LTU transformations). The LTU transformations can be viewed as the generalised existing one. Based on the LTU transformations, a recursive bandpass filter with variable passband-width (PBW) is attained using the minimax criterion so that the stability is ensured. The recursive bandpass filter has continuously PBW and fixed passband centre frequency. To meet the stability condition of the recursive variable PBW bandpass filter (variable-PBW filter), the LTU parameter transformations are incorporated into the minimisation of the maximum amplitude-response error. It can be proved that incorporating the LTU transformations into the design process definitely produces a recursive variable-PBW filter whose stability is absolutely guaranteed. For verifying the ensured stability and demonstrating the high design accuracy, detailed computer simulations are included. The illustrative example verifies that the obtained variable-PBW filter not only has definitely ensured stability, but also its approximation accuracy is extremely high.

A Balanced BPF with Wide Bandwidth and Steep Selectivity Based on Slotline Stub Loaded Resonators (SSLRs)

A balanced bandpass filter (BPF) with a wide differential mode (DM) bandwidth and steep DM passband selectivity and high common-mode (CM) block based on slotline stub-loaded resonators (SSLRs) is designed in this brief. The proposed SSLR, which is composed of a half-wavelength slotline resonator and a shorted slot stub loaded at the symmetrical plane, is applied to achieve a broad DM passband with a center frequency at 5.1 GHz and a 3 dB bandwidth of 92%. Meanwhile, two transmission zeros (TZs) are introduced to realize a steep DM passband selectivity. The center frequency and bandwidth of the DM passband can be adjusted by changing the dimensions of SSLRs and the gaps between them. Meanwhile, one narrow notched band with a 3 dB bandwidth of 4.9% is realized by employing one coupled quarter-wavelength short-circuited stub at the input ports. In addition, the DM stopband with a rejection level of 10 dB can be extended to 20 GHz. The designed balanced broadband filter is stimulated by a U-shaped microstrip line to slotline transition structure, which can realize wideband a CM block with a high suppression level without influencing the DM one, and this can reduce the design complexity. In order to prove the idea, a balanced broadband filter is designed and measured. The predicted results of S parameters are compared with the measured ones, and a good agreement is achieved.

Dual-Band Frequency Selective Surface with Different Polarization Selectivity for Wireless Communication Application.

This article proposes a dual-band, frequency- and polarization-selective surface. Multiple resonant modes are introduced using the U-shaped resonator with a ground via to achieve dual-band responses and polarization selectivity. Two symmetrically grounded U-shaped resonators are coupled through electrically coupled apertures in a common ground, resulting in a passband with two transmission zeros per polarization. A general design flowchart and additional examples at the S, X, and K-bands are presented as well. A prototype at X-band is analyzed, fabricated, and measured, showing the passband center frequencies of 9.68 GHz and 10.73 GHz, factional bandwidths of 3.45% and 3.48%, and insertion losses of 0.9 dB and 1.1 dB, respectively. Due to the high selectivity, small frequency ratio, low profile, and stable performance under oblique incidence, the proposed designs have application potential in wireless communication systems.

Realization of a novel dual-band bandpass filter with coupled series gaps and stepped impedance complementary split ring resonators

In this article, a bandpass filter (BPF) is proposed by etching stepped impedance complementary split ring resonators (SICSRRs) pairs in parallel with series gaps on the top side of a coplanar waveguide (CPW). The Nicolson-Ross-Weir (NRW) method is used to analyze the left-handed (LH) behavior of the filter. The effects of the resonators parameters on the left-handed BPF are studied. The parameters and number of the resonators are adjusted properly to obtain the desired filter characteristics. Split ring resonators (SRRs) are magnetically coupled to the BPF to realize a novel left-handed dual-band bandpass filter. Besides, The dual-band filter is described by means of the lumped-element equivalent circuit model. Also, the quasi-static analysis is used to obtain the equations for the resonant frequencies of the resonators. The efficient electrical size of the dual-band filter is 0.51λg × 0.42λg where λg represents the guided wavelength at the first passband center frequency. The prototype of the compact dual-band BPF is fabricated and measured. The measured results reveal low insertion loss and high return loss at the passbands along with wide upper stopband attenuation. The measured result is in a good agreement with the corresponding simulation result.

High Performance Multiple Passband Substrate Integrated Plasmonic Filters

We proposed a new variety of substrate integrated plasmonic filters (SIPFs) with multiple passband characteristics based on the concept of spoof surface plasmon polaritons (SSPPs). By etching a periodic interdigital structure array on the top metal layer of substrate integrated waveguide (SIW), we can achieve high-efficiency microwave SSPP transmission with an insertion loss of 1 dB in the passband of 7.4-12.5 GHz, and a high rejection level of 27 dB in the rejection bands. By introducing antisymmetric C-ring resonators (ASCRs) in the filter structure, the passband number and bandwidth of the filter can be flexibly manipulated. To validate the proposed design, four SSPP filters prototypes are fabricated and tested, showing good filtering performances with a high transmission coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}21\mathbf {&gt;}-$ </tex-math></inline-formula> 1 dB) and low reflection coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}11\,\,\mathbf { &lt; } - $ </tex-math></inline-formula> 12 dB) in their passbands, and a high rejection level over 15 dB between them. By changing the geometric parameters of ASCR, the number of passbands can be increased from 1 to 3, and the passband center frequency and bandwidth can be engineered accordingly. The proposed SSPP filters with good multiple passband characteristics may have great potential applications in microwave wireless integrated plasmonic circuits and communication systems.

Compact Filtering Balun-Diplexer Using Coupled-Line-Loaded Hairpin Ring Resonator

A filtering balun-diplexer (FBD) with compact size and high channel isolation is proposed based on the dual-mode coupled-line-loaded hairpin ring resonator (C-HRR). The special features of C-HRR are presented and concluded. The out-of-phase current distribution of the C-HRR at the odd-mode resonant frequency is noticed and utilized in the balun design. By carefully arranging the resonant frequencies and coupling topology, the two channels of the FBD can share one common C-HRR to reduce the circuit size. The lower and higher channel filtering baluns are designed separately and integrated directly into the FBD without extra impedance matching network because of the low loading effect. For validation, an FBD is fabricated with circuit size of 0.24 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\lambda }_{\mathrm{ g}}\,\, {\times }\,\,0.14{\lambda }_{\mathrm{ g}}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\lambda }_{\mathrm{ g}}$ </tex-math></inline-formula> is the guide wavelength at the center frequency of the lower passband. The isolation between the lower and higher channels is greater than 39 dB with the common mode rejection better than 34 dB over the passbands.

Design and Synthesis of Reconfigurable Filtering Phase Shifter Using Optimization of Coupling Matrix

In this article, a design and synthesis method to realize filtering phase shifter with tunable insertion phase and passband center frequency is proposed. The filtering phase shifter is based on a circuit consisting of three resonators in a triplet topology. Coupling matrix analysis is employed to obtain the detailed relationship between the insertion phase and the amplitude response of the filter. Then, differential evolution (DE) algorithm-based optimization method is proposed to obtain the coupling matrix with an arbitrary prespecified insertion phase. The proposed optimization method can not only obtain the coupling matrix with desired insertion phase but also can align the phase slope of different phase states, resulting in a low-phase error over the filter passband. Furthermore, a method is proposed to extend the phase shift range to full 360° by switching the signs of specific terms in the coupling matrix, significantly simplifying the required optimization procedure. Finally, a filtering phase shifter using lumped elements is designed, fabricated, and measured to validate the design concept. The phase-shifting range of the circuit can achieve 360° with continuously reconfigurable center frequency covering from 650 to 860 MHz.

Miniature Dual-Band Absorptive Bandstop Filters With Improved Passband Performance

In this paper, a miniature dual-band absorptive bandstop filter (ABSF) design with improved lower passband performance is proposed. Specifically, a stepped-impedance short-circuited stub is introduced to a bridged-T coil-based dual-band ABSF design, such that the insertion loss around the desired passband center frequency can be largely reduced while the absorptive stopband performance remains intact. This also helps equalize the lower passband insertion loss response and achieve a flatter passband, which is especially advantageous when cascading multiple ABSFs for improving the stopband rejection or increasing the number of stopbands. Closed-form design formulas are established to facilitate the synthesis of proposed dual-band ABSF. As an example, a 4.8/9.6-GHz dual-band ABSF in GaAs is realized with a measured insertion loss within 0.85± 0.12 dB from dc to 2.6 GHz. The circuit size is only 1.6 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 1.84 mm, and the corresponding electrical size is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.013\lambda _{0} \times 0.015\lambda _{0}$ </tex-math></inline-formula> at the designated passband center frequency of 2.4 GHz. Application of the proposed dual-band ABSF for the passband performance improvement of cascaded ABSF designs is also demonstrated, and good performance is obtained.

Design of a compact quint-band bandpass filter using a symmetric dual-mode λ/4 resonator and a pair of inverted F-shaped resonators

In this paper, a compact quint-band microstrip bandpass filter (BPF) based on multiple mode resonating technology is proposed. It is composed of a symmetric dual-mode λ/4 resonator loaded with a shorted stub, two inverted F-shaped resonators, and two pairs of coupling configurations. To miniaturize the filter, the three resonators are bent and cross coupled together. Considering that the BPF has a symmetric structure, the even-odd mode analysis method is employed. On the basis of the simulation, the presented filter was fabricated by using a conventional PCB process with the substrate of Rogers RT/Duroid 5880. The measurement results are consistent well with the simulated data. The measured operating bands are centered at 1.8, 3.5, 4.5, 5.8 and 6.8 GHz, respectively, which are suitable for GSM, WiMAX, 5G, RFID and WiFi6 applications simultaneously. The measured in-band minimal return losses within five passbands are better than 15 dB. Furthermore, the filter exhibits a high selectivity with steep skirt property and the four band-to-band isolations among the five passbands are higher than 27 dB, and the out-of-band rejection is better than 25 dB. The filter’s total dimension occupies only 0.18λg × 0.15λg, where λg represents the free space wavelength corresponding to the center frequency of the lowest passband.

Compact UWB BPF With Broad Stopband Based on Loaded-Stub and C-Shape SIDGS Resonators

In this letter, two types of substrate-integrated defected ground structure (SIDGS) resonators (i.e., loaded-stub and C-shape resonators) are proposed for the ultra-wideband (UWB) bandpass filter (BPF) design. Coupled SIDGS resonators can generate four transmission poles to achieve the UWB response with low insertion loss in a compact size. Besides, the spurious cancellation with a broad stopband is achieved by mutual suppression of separated harmonics from the SIDGS resonators. In addition, the lowpass units (LPUs) embedded in the microstrip feed-lines are utilized to further improve the BPF stopband rejection. To verify the mechanism, a compact BPF operating at 6.85 GHz (i.e., the passband center frequency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{0}$ </tex-math></inline-formula> ) with 0.6-dB insertion loss and 3-dB fractional bandwidth (FBW) of 114% is implemented and fabricated. The measured stopband extends to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.7f_{0}$ </tex-math></inline-formula> with a rejection level more than 26 dB.

입사각 안정성을 갖는 밀리미터파 대역 주파수 선택적 레이돔 설계

In this study, a frequency-selective radome in the millimeter-wave band with excellent incident-angle stability is designed. The hybrid structure comprising the designed radome combines a multilayered composite material, which has a rectangular loop-type FSS (frequency selective surface) structure with frequency-selective transmission characteristics in the millimeter-wave band. It has a low transmission loss of ≤1 dB in the pass band and a high blocking characteristic of ≥10 dB in the X-band for polarization TE (transverse electric). Additionally, the TM (transverse magnetic) modes and incidence angles ranged from 0° to 50°. To confirm the design performance, a hybrid composite structure is fabricated and the transmission characteristics in the millimeter-wave band and X-band are measured using free-space measurement. The results confirm that the normal incident wave has a passband center frequency and stopband center frequency of 0.62 and 13.45 dB, respectively.

Semi‐circular mushroom resonator loaded substrate integrated waveguide cavity based compact triple‐band bandpass filter with high selectivity

Two cascaded semi-circular mushroom resonators (ScMRs) loaded to a circular substrate integrated waveguide (CSIW) is used to implement a triple-band bandpass filter of compact size and high selectivity with six transmission zeros (TZs). The ScMRs are coupled to each other along the linear edges of the metal patches and are loaded to the CSIW cavity. A distinctive modification in the schematic and the orientation of the loaded mushroom resonators is carried out along with the introduction of radial coupling slots into the CSIW cavity to generate the three passbands. The TM101 mode is responsible for the generation of first passband. The second and third passbands are formed due to the split odd and even modes of next higher order mode (TM201). An extracted pole is formed within the second passband that splits TM201 mode into odd and even modes. TM201 odd mode (TM201odd) and TM201 even mode (TM201even) are responsible for the generation of second and third passbands, respectively. Here, source-load coupling is employed within the proposed resonator to generate one TZ each at the lower stopband and upper stopband. Two cross-couplings of different modes between two loaded ScMRs are introduced to generate four transmission zeros (TZs) additionally to achieve high selectivity. The triple bandpass filter covering a compact volume of 0.0011 λg3 is fabricated and measured to validate the filter structure. The measured result agrees decently with the simulated one where the passband center frequencies (CFs) of first, second, and third passbands are measured at 1.9, 3.5, and 4.4 GHz with measured insertion losses of 1.5, 1.87, and 1.8 dB, respectively.

Miniaturized Wide-Angle Rasorber With a Wide Interabsorption High Transparent Bandpass Based on Multiple 2.5-D Resonators

A miniaturized high selectivityfrequency selective rasorber (FSR) with a wide interabsorption high transparent bandpass based on multiple 2.5-dimensional (2.5-D) resonators is investigated. The main contribution is the achievement of a wide and high transparent passband by combining the large inductance of parallel resonators (PRs) and cascading two 2.5-D PRs, which also provide the function of miniaturization. The 2.5-D PR is implemented by connecting the interdigitated capacitor and the metal meandered strip-line on both surfaces of a lossy layer through metalized vias. The inductor and capacitor values of 2.5-D PR can be individually adjusted to shift the passband's central frequency. The lossy element is realized by inserting two 2.5-D strip-type PRs at the center of each side of a meandered cross-dipole loaded with two resistive sheets on both sides. An equivalent circuit model is proposed to analyze its operating principle. The dimensions of the miniaturized element are 0.12 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> × 0.12 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> × 0.118 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> . While maintaining a good wide passband (−1dB relative bandwidth is 21.2%), the miniaturized FSR satisfies the characteristic of polarization insensitivity (TE and TM), and angular insensitivity (up to 45°). A prototype of miniaturized FSR has been manufactured and measured, showing a reasonable agreement with simulations.

Miniaturized high selectivity bandpass filter based on hairpin two-conductor stripline resonators

A resonator based bandpass filter miniature design formed by two U-shaped metal strip conductors located at different sides of a suspended dielectric substrate is developed. In each conductor one end is grounded to the screen and the other is free. A resonators are connected in pairs with overlapping sections of strip conductors, it leads not only to the reduction in the dimensions of the device, but also to the increase in its selectivity due to transmission zeros near the passband. The prospects of the proposed design are proved by the measured characteristics of the 6th-order filter made on a substrate with the relative permittivity er = 80 (TBNS-ceramic) and the thickness of 0.5 mm. The filter passband central frequency f0 = 150 MHz, and the fractional bandwidth Δf/f0 = 25 %, while the size of the device is only 42 × 20 × 8.25 мм3 (0.02λ0 × 0.01λ0 × 0.005λ0, where λ0 is the wavelength at the center frequency f0). The filter has high slope steepness and a wide stopband, which extends up to the frequency of 3f0 at the level of –50 dB.

A quint mode fractal architecture based resonator and its efficacy in the design of multiband bandpass filters

This paper presents a new approach to design multiband bandpass filters (BPF) using multimode resonator topology inspired from Bamileke fractal architecture in the form of fractal shaped resonator. The proposed resonator architecture exhibits quint mode resonance behavior where resonance frequencies are determined using ABCD matrix. It offers flexibility in terms of choosing passband center frequencies precisely. Initially a second order dual band BPF is presented by suppressing higher order modes using asymmetric feed line. The same structure is used further to implement a triband and a quad band BPF where the input/output coupling circuit is modified to extract the higher order modes. Two stub loaded resonators are also embedded to improve the passband selectivity and to improve upper stopband characteristics. The design guidelines are demonstrated through the external quality factor (Qe) and coupling coefficient (k) synthesis approach. The developed filters are fabricated and measured to verify the predicted and simulated results. A close agreement is observed between them. The fabricated multiband BPFs has a very compact size, less insertion loss and good return loss profile.

Dual‐band bandpass to bandstop switchable filter with independently tunable center frequency and bandwidth

AbstractThis article presents a dual‐band bandpass (BP) to bandstop (BS) switchable filter with independently tunable center frequency and bandwidth. Two different length half‐wavelength resonators are coupled with two separate coupling lines. Each resonator consists of a varactor‐loaded stub at the center to tune the even mode frequencies, whereas two identical varactors are connected at the ends to tune odd and even mode frequencies simultaneously. The center frequency of the first passband is tuned from 1.03 to 1.4 GHz with constant fractional bandwidth (CFBW) of 3.4%, and second passband from 1.35 to 1.74 GHz with CFBW of 2%. BP to BS switching is achieved by connecting a p‐i‐n diode between input and output feedlines.