Tunable Bandstop Filter Research Articles

Design of a Dual-Mode Tunable Wide-Bandstop Filter with Controllable Bandwidth

In this article, a compact dual-mode tunable wide bandstop filter with controllable bandwidth is presented. The proposed filter consists of an open-loop stepped-impedance resonator with a T open stub loaded. Varactor diodes Cv1 and Cv2 are loaded at two ends of the stepped-impedance resonator and the loaded T stub, respectively. By properly adjusting the capacitances Cv1 and Cv2 of the varactor diodes, the constant fractional bandwidth and constant absolute bandwidth can be achieved, respectively. A new dual-mode tunable wide bandstop filter with 61.0% constant fractional bandwidth and 2.0-GHz constant absolute bandwidth has been designed and fabricated to verify the validity of the proposed method. The measured results are in good agreement with the electromagnetic simulation.

Tunable Dual Band Filter with BST Capacitors

A tunable double band band-stop filter based on BST is presented. This configuration has a coplanar microstrip loaded with stepped impedance resonators. Ferroelectric BST parallel plate capacitors were loaded at the end of the stepped impedance resonators. When a DC voltage is applied to the BST capacitors, the change in capacitance shifts the resonance frequency of the stepped impedance transformers. The filters were designed with notch frequencies at 1.5 GHz and 3.5 GHz without loading them with BST capacitors. The filter circuits were simulated with Agilent ADS and were fabricated on FR-4 substrates. By loading the resonators with BST capacitors with no DC applied voltage, the first and second notch frequency shifts significantly. The first notch frequency can be tuned from 570 MHz to 781 MHz and the second notch frequency from 2.16 GHz to 2.55 GHz by applying the bias voltage of 5volts. The performance of the BST tuned filters were compared with filters tuned with p-n junction varactors.

Microstrip tunable bandstop filter with constant absolute bandwidth

This paper presents a novel designing approach for tunable bandstop filters (BSPs) with constant absolute bandwidth (CABW). A simple bandstop unit is introduced to design tunable BSPs. Through the analysis, the bandwidth and center frequency of the unit can be fully controlled. Furthermore, when the center frequency is tuned, the bandwidth can be kept constant by choosing proper loaded stub impedances. Then, profiting from this unique property, tunable filter designs with CABW are introduced. A compact cascade structure is adopted to satisfy the tuning requirement on J-inverter while designing tunable filters with CABW. For demonstration, second-order tunable BSP is designed, fabricated, and measured. The filter can be tuned from 1.55 to 2.21 GHz with CABW, a wide fractional tuning range up to 43%. High rejection levels are realized at the mid-stopband. The measurement shows good agreement with the simulation.

New opportunities in microwave electronics with ferromagnetic nanowires

A series of monolithic tunable microwave band-stop filters and phase shifters have been designed, fabricated, and characterized on arrays of ferromagnetic nanowires (FMNWs) constituted of Ni, Co, CoFeB, and NiFe alloy embedded in anodic alumina templates (AAO). The aim of the present investigation is to significantly boost the operating frequency of devices in very low applied magnetic field. The stop-band response can cover from 8 to 40 GHz with an applied magnetic field up to 5 kOe using these materials. In addition, we observed a substantial increase in frequency tunability (>110%) for Ni and NiFe alloy based filter. Frequency bandwidth/linewidth can be tuned with the proper choice of magnetic material, broad band for Co nanowires to narrow band for CoFeB nanowires. The amorphous nature of CoFeB reduces linewidth considerably and hence increases resonance absorption. It is also observed that the frequency linewidth (Δf) decreases with increasing applied magnetic field. The same filter can be used as a tunable phase shifter. For Ni nanowire based phase shifter, a maximum shift of 75°/cm at 4 kOe was observed.

Tunable low-pass MEMS filter using defected ground structures (DGS)

A tunable bandstop filter applying the micromachined technology is designed, simulated and fabricated. The filter is realized by incorporating defected ground structures structures with the micromachined switches. The surface micromachining fabrication process is employed on the high resistivity silicon substrate to fabricate the filter. The measured 3-dB cut-off frequency changes of the reconfigurable low-pass filter for four different states has been analyzed. The measured insertion loss is very lower in four tuning range of the filter. This work demonstrates the possibility of high-performance compact-size reconfigurable filters at mm-waves using multiple-contact micromachined switches. Simulated and measured results of the proposed filter show good agreements. The entire reconfigurable filter was realized in a small chip size of 1.2mm×1.5mm.

A Tunable Bandstop Filter Using Thin Film Barium-Strontium-Titanate Varactors

AbstractFerroelectric barium-strontium-titanate (BST) varactors are becoming extremely important particularly for frequency-agile RF and microwave circuits. Tunable bandstop filters are desired to eliminate unwanted signals for several communication systems. In this paper, a compact tunable bandstop filter (BSF) based on a single hairpin resonator, using ferroelectric BST varactors, is also presented. The frequency response of proposed BSF can be adjusted by increasing or decreasing the length, width, and space for the coupled line hairpin resonator. One pair of variable capacitors has been incorporated to the filter for tuning and miniaturization purposes. The notch frequency of BSF can be tuned from 705 MHz to 1.035 GHz with a tuning voltage of 6 Volts utilizing BST varactors.

CPW Tunable Band-Stop Filter Using Hybrid Resonator and Employing RF MEMS Capacitors

This paper presents a coplanar waveguide (CPW) tunable band-stop filter using hybrid resonator and employing RF microelectromechanical systems (MEMS) capacitors. The MEMS switches are used as varactors to tune the filter resonance frequency. Defected ground structures (DGSs) with MEMS switch is employed for filter unit to achieve miniaturization of filter structure. To accurately analyze the filter unit structure parameters, a hybrid resonance circuit is used as equivalent circuit and the relationship of MEMS switch and the transverse slot capacitance is analyzed. Hereby, a CPW tunable band-stop filter, cascaded periodically by DGS and MEMS switches, is fabricated on a glass substrate (er=3.78,tan δ = 0.0012). The filter has a midband retune loss of 2.3-2.8 dB and a tuning range of 35% from 8.5 to 12.3 GHz with a maximum dc voltage of 44 V. Finally, we propose a solution to achieve constant bandwidth when center frequency changes.

TUNABLE BAND-STOP PLASMONIC FILTER BASED ON SYMMETRICAL TOOTH-SHAPED WAVEGUIDE COUPLES

A simple plasmonic filter with symmetrical tooth-shaped waveguides is proposed and investigated by using finite element method. It is found that the structure with a single symmetrical tooth-shaped waveguide couple can realize a tunable band-stop filter. Attributed to cascaded symmetrical tooth-shaped waveguide couples, the structure can achieve a flat band-stop response with no intensity variation over the transmission spectrum. And the central wavelength of the stopband linearly increases with the simultaneous increasing of depths of waveguides. Moreover, reduced structure size can be achieved by controlling the dielectric constant of the medium.

Tunable Coplanar Wave Guide Band Stop Filters

A tunable band stop filter is designed in the frequency range of 0.5 GHz to 1 GHz and its performance is simulated with Agilent ADS. The filter is fabricated on FR-4 substrates. The BST parallel plate ferroelectric varactors are fabricated on sapphire substrates by MOD technique with Platinum Electrodes and ion-milling. The ferroelectric capacitors show a tunability over 50% within an applied DC bias of 5 V. The filter response was measured using Agilent Vector network analyzer. For the third order BST varactor tuned band stop filters, the notch frequency can be tuned from 480 MHz to 620 MHz by the application of 5 V tuning voltage with a maximum band attenuation of 20 dB.

NOVEL WIDEBAND TUNABLE RESONATOR AND THE APPLICATION TO FREQUENCY-AGILE BANDPASS AND BANDSTOP FILTERS

In this paper, a novel end-loaded resonator is investigated and applied to design tunable bandpass filter (BPF) and bandstop filter (BSF). The novelty of the resonator lies in that two varactors are added to the two ends of the resonator, and then its resonant frequency can be bi-directionally tuned. As a result, the theoretical frequency tuning range can be significantly extended to approximately double that of the conventional tunable resonator. For demonstration, the proposed resonator is applied to design tunable BPF and BSF. As expected, the tuning ranges are 52.4% and 53.5% for the BSF and BPF, respectively. Good agreements can be observed between the simulated and measured results.

Experimental studies of the surface plasmon polaritons waveguide filter in microwave band

Based on theoretical analysis, in this paper studied are the low pass and band stop filter effects of the μ-negative materials/double positive materials/μ-negative materials (MNG-DPS-MNG) surface plasmon polaritons waveguide with branch defect. The research results show that the defect is equivalent to a sub wavelength resonator. The central frequency of the band stop filter is determined by the resonator length and it is independent of the position where the resonator is located in the MNG region. The transmission dips of the waveguide are closely related to the coupling distance. So the filter characteristics of the surface plasmon polariton waveguide can be adjusted by changing the resonator length and number and the coupling distance. The experimental results are in good agreement with simulation results. These properties will have potential application value in the tunable single channel or multi-channel band stop filters.

Experimental research of the tunable magnetic plasmon polaritons waveguide filter in microwave band

Based on theoretical analysis, this paper studied experimentally the tunable low-pass, band-stop and band-pass filter effects of the MNG-DPS-MNG (μ-negative materials/double positive materials/μ-negative materials) magnetic plasmon polaritons waveguide. The research results show that the MNG-DPS-MNG waveguide without defect possesses the tunable low-pass filter characteristic. The waveguide with defect in the MNG region possesses the band-stop filter characteristic where the defect is equivalent to a sub wavelength cavity. And the waveguide with cavity in the DPS region possesses the band-pass filter characteristic. So the filter characteristics of the magnetic plasmon polaritons waveguide can be tuned by drawing into the resonators and changing the position and parameters of resonators. The experimental results are in good agreement with the simulation results. These properties will have potential application value in the tunable single channel or multi-channel filters.

A tunable band-stop filter using a metamaterial structure and MEMS bridges on a silicon substrate

A band-stop filter using a metamaterial structure (complementary U-shaped split resonator; CUSR) on a silicon substrate with a 13% tuning range is presented for Ka band applications. The metamaterial structure is used as a frequency-selective geometry on a coplanar waveguide (CPW) and tunability is achieved with the help of MEMS bridges. The rejection in the stop band is around 25 dB for the entire tuning range. A low insertion loss of 0.5 dB is obtained in the pass band. A simple electrical model of the proposed device and the design guidelines are presented. The filter is realized by a novel fabrication methodology involving the micromachining of two bonded silicon wafers and initial fabricated results are reported.

RF Tunable Bandstop Filters With Constant Bandwidth Based on a Doublet Configuration

This paper presents a novel approach to design RF tunable bandstop filters with constant absolute bandwidth. The filters are based on a doublet configuration which is attractive for high-order filter designs. In the doublet, two varactor-tuned resonators, arranged in a mirror-symmetrical manner, are coupled to a main transmission line. A novel coupling scheme is utilized between the resonators and the main line. Theoretical analysis indicates that, as the resonant frequency varies, the coupling coefficient within the fixed coupling region can be inherently changed to desirable values to meet the requirement of constant absolute bandwidth. Using the coupling scheme, constant absolute bandwidth can be obtained without extra circuits to control the coupling strengths. For demonstration, first-order and high-order filters are designed. Comparisons of experimental and simulated results are presented to verify the theoretical predications.

Extended Passband Bandstop Filter Cascade With Continuous 0.85–6.6-GHz Coverage

This paper presents a cascade of tunable bandstop filters with a wide spurious-free upper passband, which is completely spanned by the tuning range of the notch responses. A collection of resonators is shown to be able to provide bandstop filter responses over a 7.8 to 1 tuning range. By using spurious-free upper passband aperture-coupled cavity bandstop filters, multiple resonators, each with octave tuning, can cover a multioctave frequency range in a cascade. It is shown that the upper passband of this type of filter is limited by the reactance of the coupling apertures, which produce an unwanted in-band resonance unless designed properly. The details of this design process are explained and used to design a six-resonator bandstop filter cascade that is able to provide a bandstop filter response with up to 55 dB attenuation over the continuous band of 0.85-6.6 GHz. Through dynamic allocation of the cascade circuit's transmission zeros, one-, two-, three-, and four-pole bandstop filter responses of variable bandwidth can be realized over different frequency ranges, offering numerous bandwidth-attenuation level tradeoff combinations.

Lumped-Element Fully Tunable Bandstop Filters for Cognitive Radio Applications

This paper presents tunable lumped-element bandstop filters for the UHF-band cognitive radio systems. The two-pole filters are implemented using lumped elements with both single- and back-to-back silicon varactor diodes. The single diode filter tunes from 470 to 730 MHz with a 16-dB rejection bandwidth of 5 MHz and a filter quality factor of 52-65. The back-to-back diode filter tunes from 511 to 745 MHz, also with a 16-dB rejection bandwidth of 5 MHz and a quality factor of 68-75. Both filters show a low insertion loss of 0.3-0.4 dB. Nonlinear measurements at the filter null with Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> = 2 MHz show that the back-to-back diode filter results in 12-dBm higher third-order intermodulation intercept point than the single diode filter. A scaling series capacitor is used in the resonator arm of the back-to-back diode filter and allows a power handling of 25 dBm at the 16-dB rejection null. The cascaded response of two tunable filters is also presented for multiband rejection applications, or for a deeper rejection null (>;36 dB with 0.6-dB loss at 600 MHz). The topology can be easily extended to higher order filters and design equations are presented.

Tunable coplanar waveguide band-stop and band-pass filters based on open split ring resonators and open complementary split ring resonators

In this study, the authors show that open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs) can be loaded with varactor diodes in order to implement tunable filters in coplanar waveguide (CPW) technology. By loading a CPW with shunt-connected varactor-loaded OSRRs, a band-stop filter with tunable central frequency results. The electronically tunable band stop can be switched to a pass band by replacing the shunt resonators with varactor-loaded OCSRRs. To illustrate the possibilities of the approach, a tunable band-stop filter and a tunable band-pass filter have been designed and fabricated. The measured characteristics are in good agreement with the co-simulations (electric and electromagnetic) and with the circuit simulations of the electric model. The measured tuning range is roughly 120% for the stop-band structure (for varying voltages between 0 and 28 V) and over 30% for the band-pass filter (for varying voltages between 5 and 25 V).

Tunable Bandpass and Bandstop Filters Based on Dual-Band Combline Structures

New methods for the design of tunable combline bandpass and bandstop filters are presented. The first part of this paper presents a tunable bandstop filter designed using a dual-band circuit with wide passband and integrated narrow stopband. A prototype has been constructed and measured results shows that the bandwidth remained constant at 30 MHz as the filter was tuned from 3.22 GHz to 3.66 GHz. The second part of this paper presents a tunable bandpass filter designed using a dual-band circuit with both wide passband and stopband. The response corresponds to two narrow passbands, where the lower passband bandwidth and center frequency can be tuned. A prototype has been constructed and measured results demonstrate wide centre frequency tuning range and over 300% bandwidth tuning without the need for coupling adjustment.

Frequency Response Control in Frequency-Tunable Bandstop Filters

This letter presents a tunable bandstop filter with the capability of controlling the shape of the frequency response. The proposed filter structure can be tuned to have either a Butterworth or a Chebyshev response. The filter can also be tuned to have different center frequencies. Both the frequency response and the center frequency of the filter can be tuned by only adjusting the resonant frequency of each resonator without controlling inter-resonator coupling. Since the proposed filter structure has non-zero inter-resonator coupling, it can find its future application in reconfigurable filters which can be tuned to exhibit either a bandstop or a bandpass response.

Design and Analysis of a Novel Tunable Band-Stop Filter Using RF MEMS Technology

This paper presents a tunable band-stop filter within frequency ranges of 15-30 GHz, it used a novel method to turn the resonant frequency by micro-electromechanical systems (MEMS) switch and coplanar-waveguide (CPW) structures. The DC voltage is utilized to load RF-MEMS switch as source of the tunable cell’s power. The simulation obtained by HFSS and ADS tool shows that insertion loss is less than 1dB in pass-band and return loss is greater than 10 dB. The center frequency changes from 15.5 GHz to 26 GHz, which has 10.5 GHz adjustable range. The result shows good stop rejection and sharp roll off frequency and the extracted result from the circuit matches simulation result very well in this paper.