Showing papers on "Band-stop filter published in 2010"
Book•
04 Jul 2010
TL;DR: In this paper, the authors propose a filter topology and damping scheme based on the radiation coupling between on-board filters and the power supply of a power supply, as well as a common mode component selection.
Abstract: Filtering. Graphical attentuation calculations. Conduction modes. Filter load impedance and measurement techniques. Filter source impedance. Power supply. Filter/supply interaction. Filter topologies and damping. Common mode component selection. Radiation coupling to on-board filters.
190 citations
TL;DR: In this paper, a planar circular slot antenna for UWB communications is presented, and the integration on this antenna of a notch filter, to reduce the possible interferences with the 5 GHz WLAN communications, has been discussed in detail.
Abstract: —The study of a planar circular slot antenna for Ultrawideband (UWB) communications is presented. The integration on this antenna of a notch filter, to reduce the possible interferences with the 5GHz WLAN communications, has been discussed in detail. Four different structures, achieved by etching a suitable pattern on the antenna circular stub, have been considered, and their features have been compared. The antenna with symmetrical and inverted-L cuts shows the best performance, and it has been therefore realized and fully characterized. It shows very good matching features over the UWB band, and notable rejection of the 5 GHz WLAN band.
128 citations
TL;DR: In this article, a single bandpass photonic microwave filter is proposed, which is based on optically filtering one of the sidebands of a phase-modulated optical carrier by means of the notch response of a silicon-on-insulator ring resonator.
Abstract: A novel tunable single bandpass photonic microwave filter is proposed. It is based on optically filtering one of the sidebands of a phase-modulated optical carrier by means of the notch response of a silicon-on-insulator ring resonator. The filter response can be tuned by changing the laser wavelength. Experimental results to prove the concept are provided.
118 citations
TL;DR: In this article, a compact planar tri-band bandpass filter with high selectivity is proposed, which employs two sets of resonators, i.e., stub-loaded resonators and half-wavelength resonators.
Abstract: This letter presents a compact planar tri-band bandpass filter with high selectivity. The proposed filter employs two sets of resonators, i.e., stub-loaded resonators and half-wavelength resonators. The former is designed to operate at the first and third passbands and the latter at the second passband. The passband frequencies can be conveniently tuned to desired values. One set of resonators is embedded in the other and thus the filter is compact in size. On each side of each passband, there is at least one transmission zero, resulting in high skirt selectivity. For validation, a demonstration filter is implemented. The design methodology and the experimental results are presented.
113 citations
TL;DR: In this paper, the authors present an introduction of recently developed techniques for the design and implementation of UWB bandpass filters, including single-layer and multilayer technologies, including MMR technique, hybrid microstrip/CPW technique, optimum short-circuited-stub technique, cascaded high-pass/low-pass filter technique and techniques that use EBG-loaded structures.
Abstract: This article presents an introduction of recently developed techniques for the design and implementation of UWB bandpass filters, including single-layer and multilayer technologies. Several techniques using single-layer technology were reported on, including the MMR technique, the hybrid microstrip/CPW technique, the optimum short-circuited-stub technique, the cascaded highpass/lowpass filter technique and techniques that use EBG-loaded structures.
100 citations
TL;DR: In this paper, a two-pole filter is proposed based on capacitively loaded folded-λ/2 resonators coupled to a microstrip line, and the filter analysis includes the effects of nonadjacent inter-resonator coupling.
Abstract: This paper presents a compact low-loss tunable X-band bandstop filter implemented on a quartz substrate using both miniature RF microelectromechanical systems (RF-MEMS) capacitive switches and GaAs varactors. The two-pole filter is based on capacitively loaded folded-λ/2 resonators that are coupled to a microstrip line, and the filter analysis includes the effects of nonadjacent inter-resonator coupling. The RF-MEMS filter tunes from 11.34 to 8.92 GHz with a - 20-dB rejection bandwidth of 1.18%-3.51% and a filter quality factor of 60-135. The GaAs varactor loaded filter tunes from 9.56 to 8.66 GHz with a - 20-dB bandwidth of 1.65%-2% and a filter quality factor of 55-90. Nonlinear measurements at the filter null with Δf = 1 MHz show that the RF-MEMS loaded filter results in > 25-dBm higher third-order intermodulation intercept point and P-1 dB compared with the varactor loaded filter. Both filters show high rejection levels ( > 24 dB) and low passband insertion loss ( <; 0.8 dB) from dc to the first spurious response at 19.5 GHz. The filter topology can be extended to higher order designs with an even number of poles.
97 citations
TL;DR: In this article, a hybrid resonant circuit is proposed, which is a combination of a shunt and series resonant circuits, which achieves a lower resonant frequency as compared to the single shunt circuit and series circuit.
Abstract: A hybrid resonant circuit is proposed in this paper. The circuit is a combination of a shunt resonant circuit and series resonant circuit. With this combination, lower resonant frequency is achieved as compared to the single shunt and series resonant circuits. As a result, a compact resonator with smaller size can be achieved as compared to the conventional quarter- and half-wave resonators. Besides the size reduction, the proposed resonant circuit is able to introduce a transmission zero to improve the stopband suppression in filter design. Based on this circuit, a very compact interdigital coupled microstrip resonator is proposed in this paper. The resonator achieves a small length of nearly 1/10 guided wavelength (?g), which has a length reduction of 63% as compared to the conventional uniform quarter-wave resonator. By using the proposed resonator, a second-order bandpass filter with a small size of 0.144?g × 0.128?g and a fourth-order bandpass filter with a size of 0.217?g × 0.1?g are built based on the standard filter synthesis methods. Both good performance and miniaturization are achieved for the proposed filters, and the expected transmission zeros are also observed. In addition to the small filters, the proposed resonator is suitable for miniaturized balun bandpass filters. A novel configuration for a balun bandpass filter is proposed based on the aforementioned resonators. A second-order balun bandpass filter with a size of 0.26?g × 0.145?g and afourth-order balun bandpass filter with a size of 0.213?g × 0.203?g are reported in this paper. Both balun filters achieve good filtering performance, as well as excellent amplitude and phase imbalances, which are less than 1 dB and 1° in the passband, respectively.
96 citations
TL;DR: In this article, a new type of compact wideband bandstop filter (BSF) with four transmission zero in the stopband is presented. And the proposed filter topology consists of a coupled line directional coupler connected in parallel to an interference transmission line.
Abstract: This work presents a new type of compact wideband bandstop filter (BSF) with four transmission zeros in the stopband. The proposed filter topology consists of a coupled line directional coupler connected in parallel to an interference transmission line. The filter characteristics can be easily controlled by the coupling factor of the coupled line coupler and the characteristic admittances of both the coupler and the transmission line. Design equations and curves are provided for the filter design. To validate the proposed topology, a compact microstrip BSF centered at 2.0 GHz with a measured 20 dB rejection bandwidth of 100% and sharp rejection characteristics is designed and built.
94 citations
TL;DR: In this paper, an asymmetric coupling strip is presented, which can be used in the ultra wideband (UWB) bandpass filter (BPF) to generate multiple notched bands within the passband.
Abstract: A novel asymmetric coupling strip is presented, which can be used in the ultra-wideband (UWB) bandpass filter (BPF) to generate multiple notched bands within the passband. The proposed structure can provide two main paths for the signals, which makes it possible to generate multiple transmission zeroes. The center frequencies and bandwidths of the notched bands can be controlled by tuning the structural parameters. The asymmetric coupling strip has been integrated into a circular disc resonator to construct a compact UWB BPF with multiple notched bands. The measured results agree with the predicted ones closely. These two notched bands centered at 4.3 and 8 GHz have 10-dB rejection fractional bandwidths of about 4.2% and 3.8%, respectively.
89 citations
TL;DR: In this article, a first-order voltage-mode all-pass filter with high-input and low-output impedances is described, which consists of only one grounded capacitor and one active element.
Abstract: A new circuit topology of first-order voltage-mode all-pass filter providing high-input and low-output impedances is described. The filter consists of only one grounded capacitor and one active element, namely VD-DIBA (Voltage Differencing-Differential Input Buffered Amplifier), with the possibility of electronically tuning the natural frequency. The filter is assembled from commercial integrated circuits, and the frequency responses measured are compared with the theoretical characteristics.
87 citations
TL;DR: In this article, a three-phase adaptive notch filtering approach for the extraction of harmonic and reactive current components for use in grid-connected converters is presented, which is applicable for a wide range of equipment like regenerative converters, distributed generation systems, as a basis for detection of the reference signals.
Abstract: This paper introduces a new three-phase adaptive notch filtering approach for the extraction of harmonic and reactive current components for use in grid-connected converters. The main function of this phase-locked loop-less method is to provide synchronized harmonic and reactive current components for control purposes. Moreover, this method is capable of detecting a selective order of harmonics. This feature is useful where elimination of certain harmonics is of concern. The theoretical analysis is presented and the performance of the method is experimentally evaluated. The methodology is applicable for a wide range of equipment like regenerative converters, distributed generation systems, as a basis for detection of the reference signals.
TL;DR: In this paper, a compact microstrip ultrawideband (UWB) bandpass filter (BPF) with a narrow notched band in the UWB passband is presented.
Abstract: A compact microstrip ultrawideband (UWB) bandpass filter (BPF) with a narrow notched band in the UWB passband is presented. The narrow notched band was introduced by using a new technique that involves embedding a parasitic coupled line to the UWB BPF in order to reject any undesired existing radio signal that may interfere with the determined UWB passband. The notched band can be easily generated and set at any desired frequency by varying the structural parameters of parasitic coupled line. The design is successfully realized in theory and verified by electromagnetic (EM) simulation and the experiment. This filter can be integrated in UWB radio systems and efficiently enhance the interference immunity from undesired signals such as wireless local area network (WLAN).
TL;DR: In this article, a compact ultra wideband (UWB) bandpass filter with an ultra narrow notched band is proposed using a hybrid microstrip and coplanar waveguide (CPW) structure.
Abstract: A compact ultra-wideband (UWB) bandpass filter with an ultra narrow notched band is proposed using a hybrid microstrip and coplanar waveguide (CPW) structure. The CPW detached-mode resonator (DMR) composed of a quarter-wavelength (?/4) nonuniform CPW resonator with a short-stub and a ?/4 single-mode CPW resonator (SMCR) can allocate three split frequencies at the lower end, middle, higher end of the UWB passband. The conventional broadside-coupled microstrip/CPW structure is introduced to improve the bandwidth enhancement around the split frequencies, which leads to good UWB operation. To avoid the interferences such as WLAN signals, the ?/4 meander slot-line structure embedded in the DMR is employed to obtain the notched band inside the UWB passband. The design is then verified by experiment. Good passband and stopband performances are achieved. Specifically, the fabricated filter has a 10 dB notched fractional bandwidth (FBW) of 2.06% at the notched center frequency of 5.80 GHz.
TL;DR: In this article, the theory of bandpass-to-bandstop reconfigurable filters is developed, and example filters are demonstrated, which could potentially be useful in dynamic, open spectrums, concurrent transmit-receive systems, and multimode antenna array applications.
Abstract: The theory of bandpass-to-bandstop reconfigurable filters is developed in this work, and example filters are demonstrated. Designs are developed that allow for reconfigurable response shape and independent bandwidths in the bandpass and bandstop modes of the filter. These capabilities could potentially be useful in dynamic, open spectrums, concurrent transmit-receive systems, and multimode antenna array applications. The demonstrated filters were fabricated using substrate integrated evanescent-mode cavity resonators. The resonators are tuned using deformation of a copper membrane induced by a piezoelectric actuator. In measurement, a 1.06% 3-dB bandwidth bandpass filter with 2.6-dB passband insertion loss was switched to a 0.82% 3-dB S11 bandwidth bandstop filter with 45 dB of isolation.
TL;DR: In this paper, an ultrawideband common-gate low noise amplifier with tunable interference rejection is presented, which embeds a tunable active notch filter to eliminate interferer at 5 GHz WLAN and employs a commongate input stage and dual-resonant loads for wideband implementation.
Abstract: An ultrawideband common-gate low noise amplifier with tunable interference rejection is presented. The proposed LNA embeds a tunable active notch filter to eliminate interferer at 5-GHz WLAN and employs a common-gate input stage and dual-resonant loads for wideband implementation. This LNA has been fabricated in a 0.18-?m CMOS process. The measured maximum power gain is 13.2 dB and noise figure is 4.5-6.2 dB with bandwidth of 3.1-10.6 GHz. The interferer rejection is 8.2 dB compared to the maximum gain and 7.6 dB noise figure at 5.2 GHz , respectively. The measured input P1dB is -11 dBm at 10.3 GHz. It consumes 12.8 mA from 1.8-V supply voltage.
TL;DR: In this paper, an adaptive notch filter (ANF) is proposed for real-time detection and extraction of individual harmonic and interharmonic components in a power signal with potentially time-varying characteristics.
Abstract: A method for real-time detection and extraction of individual harmonic and interharmonic components in a power signal with potentially time-varying characteristics is presented. The proposed method, which is based on the concept of adaptive notch filter (ANF), adaptively decomposes the measured power signal into its constituting components independent of where their frequencies are located. The algorithm provides instantaneous values of the various estimated frequency components in addition to the values of their frequencies, amplitudes, and phase angles. The structure and mathematical formulation of the proposed technique, including guidelines for its parameter tuning, are presented and its performance is studied in a variety of scenarios where the power signal attributes, such as fundamental frequency and amplitude, undergo variations over time. This study confirms the desirable transient and steady-state performances of the proposed method. Compared with its recently proposed counterpart, the proposed method of this paper obviates the need for using a phase-locked loop (PLL), and hence, offers a more simplified structure which makes it more attractive from an implementation point of view.
TL;DR: In this article, a microstrip lowpass filter with quasi-elliptic response is proposed, where a coupled capacitor between adjacent radial-shape patches is introduced in interdigital form.
Abstract: A compact microstrip lowpass filter with quasi-elliptic response is proposed. To achieve compact design, both symmetrically loaded radial-shape patches and meandered main transmission line are adopted. To realise the quasi-elliptic response and strengthen the roll-off sharpness for the filter, a coupled capacitor between adjacent radial-shape patches is introduced in interdigital form. Furthermore, the adoption of radial-shape patches and the interdigital structure can introduce both serial and parallel resonance in the circuit. Thus, a wide stopband with 7th harmonic suppression is achieved. A demonstration filter with 3 dB cutoff frequency at 1.18 GHz has been designed, fabricated and measured. Results show that a relative stopband bandwidth of 132.3 (referred to a suppression degree of 15 dB) is obtained while achieving a high figure-of-merit of 11543.
TL;DR: This study confirms the desirable transient and steady-state performances of the proposed algorithm, which is less sensitive to distortions such as harmonics and interharmonics and is not sensitive to unbalanced system conditions.
Abstract: An algorithm based on the concept of an adaptive notch filter is proposed for the frequency estimation of three-phase power signals. The algorithm permits direct estimation of frequency and its rate of change for power system signals. The proposed method uses the information of all three-phase signals together. The structure, mathematical formulation, and theoretical stability analysis of the proposed technique are presented, and its performance is studied in a variety of scenarios where three-phase power signal attributes such as frequency and amplitude undergo variations over time. This study confirms the desirable transient and steady-state performances of the proposed algorithm. In contrast to the conventional three-phase PLL-based frequency estimator, the proposed method is less sensitive to distortions such as harmonics and interharmonics and is not sensitive to unbalanced system conditions.
TL;DR: A complex adaptive notch filter is developed, for tracking single-sided tones immersed in background noise, which inherits useful properties from its real counterpart and is faster convergence and tracking than a gradient descent algorithm.
Abstract: A complex adaptive notch filter is developed, for tracking single-sided (a.k.a. analytic or complex) tones immersed in background noise. A complex all-pass based realization is pursued which inherits useful properties from its real counterpart: independent tuning of the notch frequency and attenuation bandwidth, easy realization of the complementary band-pass filter, unbiased frequency estimation, and faster convergence and tracking than a gradient descent algorithm.
TL;DR: Simulations verifying the effectiveness of the proposed Q-varying IIR notch filter are presented and it is compared with the performance of the traditional Q-constant filter using ECG signals with unwanted sinusoidal interference as a study case.
Abstract: In many measurement applications, it is required to have notch filters that simultaneously possess a very selective magnitude response (high quality factor Q) and a transient response of short duration. However, increasing the quality factor also increases the duration of the transient process in the filter after the action of the excitation. This paper presents a new concept of digital IIR notch filters, whose quality factor changes with time. Owing to a temporary change in the value of the quality factor, the transient can considerably be reduced. Simulations verifying the effectiveness of the proposed Q-varying IIR notch filter are presented and compared with the performance of the traditional Q-constant filter using ECG signals with unwanted sinusoidal interference as a study case.
Patent•
12 Mar 2010
TL;DR: In this article, a distance to PIM measurement circuit is made using a device such as an AWS transceiver that has separate transmit and receive bands, where a desired harmonic of a test PIM harmonic signal is selected outside the band of the band reject filter.
Abstract: A distance to PIM measurement circuit is made using a device such as an AWS transceiver that has separate transmit and receive bands. With a typical AWS transceiver placed in close proximity to a PCS transceiver, the AWS device will include a band reject filter to eliminate interference from the PCS signals. The PIM measurement circuit includes two frequency sources F 1 and F 2 that are provided through a combiner for characterization of the PIM circuit. To enable distance determination, an FM measurement is created by using an offset sweep generator attached to one of the two frequency sources. To avoid frequencies blocked by the band reject filter, a desired harmonic of a test PIM harmonic signal is selected outside the band of the band reject filter.
TL;DR: In this article, a novel approach to achieving frequency sextupling using a polarization modulator and a wavelength-fixed optical notch filter is proposed and experimentally demonstrated, which can be used to generate high-spectral-purity subterahertz wave signals using relatively low-frequency electrical and optical devices.
Abstract: Optical frequency multiplication based on electrooptical modulation is an effective way to generate high-spectral-purity and frequency-tunable subterahertz waves. The previously demonstrated frequency-doubling and quadrupling techniques based on a Mach-Zehnder modulator have a low multiplication factor and suffer from bias drift problem and residual chirp. In this paper, a novel approach to achieving frequency sextupling using a polarization modulator and a wavelength-fixed optical notch filter is proposed and experimentally demonstrated. The method is free from bias drift problem and residual chirp, which can be used to generate high-spectral-purity subterahertz wave signals using relatively low-frequency electrical and optical devices. By using a narrow-bandwidth fiber Bragg grating as a wavelength-fixed optical notch filter, a high-spectral-purity microwave signal tunable from 18 to 27.6 GHz is generated when a microwave drive signal from 3 to 4.6 GHz is applied to the polarization modulator. The phase noise of the generated signal is measured as low as -107.57 dBc/Hz at a 10-kHz offset frequency. By replacing the narrow-bandwidth notch filter by an optical interleaver, a subterahertz wave tunable from 66 to 114 GHz is generated when the drive signal is tuned from 11 to 19 GHz. The distribution of the generated signal over optical fiber is investigated. The results show that the quality of the distributed subterahertz wave signal is maintained after transmission over a 40-km standard single-mode fiber.
TL;DR: An eight-channel reconfigurable optical filter on a silicon chip with an embedded Mach-Zehnder arm coupling to a microring resonator that could potentially be useful in dense wavelength division multiplexing (DWDM) and radio frequency arbitrary waveform generation (RFAWG).
Abstract: We demonstrate an eight-channel reconfigurable optical filter on a silicon chip. It consists of cascaded microring resonators and integrated compact heaters. With an embedded Mach-Zehnder (MZ) arm coupling to a microring resonator, the important parameters of a filter such as center frequency, extinction ratio and bandwidth can be controlled simultaneously for purposes of filtering, routing and spectral shaping. Thus our device could potentially be useful in dense wavelength division multiplexing (DWDM) and radio frequency arbitrary waveform generation (RFAWG). Multichannel filter response was successfully tuned to match the International Telecommunication Unit (ITU) grid with 50, 100 and 200GHz in channel spacing. Programmable channel selectivity was demonstrated by heating the MZ arm, and continuous adjustment of through-port extinction ratio from 0dB to 27dB was achieved. Meanwhile, the 3dB bandwidth in the drop port changed from 0.12nm to 0.16nm. The device had an ultra-compact footprint (1200μm×100μm) excluding the metal leads and contact pads, making it suitable for large scale integration.
TL;DR: In this paper, a novel approach for designing dual-mode dual-band bandpass filters is proposed and experimentally studied by embedding a pair of slits in the square patch, the dualband response is realized and one transmission zero is introduced between the two passbands.
Abstract: A novel approach for designing dual-mode dual-band bandpass filters is proposed and experimentally studied By embedding a pair of slits in the square patch, the dual-band response is realized and one transmission zero is introduced between the two passbands Two degenerate modes are achieved by loading with a small square perturbation, which can be placed at the diagonal line There are three transmission zeros The slits control the first and third transmission zeros On the other hand, the right crossed slots control the first and the second transmission zeros
TL;DR: In this article, a tunable, substrate integrated, high Q bandpass-bandstop filter cascade is demonstrated that is capable of providing up to 100 dB of isolation between two dynamically selectable frequencies of interest.
Abstract: A tunable, substrate integrated, high Q bandpass-bandstop filter cascade is demonstrated that is capable of providing up to 100 dB of isolation between two dynamically selectable frequencies of interest. Evanescent-mode cavity filters are used in the cascade to allow high quality factors and wide tuning ranges. It is shown that it is theoretically possible to tune the cascade circuit's passband and transmission nulls independently over more than an octave in frequency while displaying good performance. General coupling matrix theory, ABCD matrix theory, and measurements are shown that describe the behavior of the filter cascade over the entire frequency tuning range. The high, dynamic isolation provided by cascade circuits has potential to be useful in concurrent transmit-receive systems, shared aperture systems, and spectral environments with strong co-site interference.
TL;DR: A number of novel filter designs that are specifically aimed at periodic signals are proposed that are optimal given the observed signal and thus signal adaptive, offer full parametrizations of periodic signals, and reduce to well-known designs in special cases.
Abstract: In this paper, we consider the problem of separating and enhancing periodic signals from single-channel noisy mixtures More specifically, the problem of designing filters for such tasks is treated We propose a number of novel filter designs that 1) are specifically aimed at periodic signals, 2) are optimal given the observed signal and thus signal adaptive, 3) offer full parametrizations of periodic signals, and 4) reduce to well-known designs in special cases The found filters can be used for a multitude of applications including processing of speech and audio signals Some illustrative signal examples demonstrating its superior properties as compared to other related filters are given and the properties of the various designs are analyzed using synthetic signals in Monte Carlo simulations
12 Apr 2010
TL;DR: In this article, a novel method for notch implementation in ultrawideband (UWB) bandpass filter (BPF) using open circuited metal lines embedded in a defected ground structure (DGS) is proposed.
Abstract: A novel method for notch implementation in ultrawideband (UWB) bandpass filter (BPF) using open circuited metal lines embedded in a defected ground structure (DGS) is proposed. Distinct from traditional notch implementation, the proposed method uses the additional metal lines with half waveguide length embedded in defected ground structure to produce additional notch band behavior based on the DGS bandpass behavior. Furthermore, the equivalent circuit model of the proposed UWB BPF with notch implementation is established for explaining the circuit behaviors more explicitly. In this way, the proposed circuit has a very small size, only amounting to 0.41 by 0.22 guided wavelength at the center frequency of 6.85 GHz. The experimental filter has a notch band frequency of 5.5 GHz, with two observable attenuation poles at 1.65 and 11.36 GHz, respectively. The measured BPF insertion loss is less than 1.0 dB throughout the passband of 3.1 to 10.6 GHz, and the variation of group delay is less than 0.2 ns in this band, except for the notched band.
TL;DR: In this paper, a tunable bandstop filter with the capability of controlling the shape of the frequency response is presented. Butterworth and Chebyshev response can also be tuned to have different center frequencies.
Abstract: 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.
TL;DR: In this article, the authors presented a tunable combline bandpass and bandstop filter using a dual-band circuit with wide passband and integrated narrow stopband and measured results showed that the bandwidth remained constant at 30 MHz as the filter was tuned from 3.22 GHz to 3.66 GHz.
Abstract: 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.
TL;DR: In this paper, a microstrip lowpass filter with an ultra-wide stopband is proposed to achieve wide stopband suppression and compact size, both symmetrically loaded resonant patches and meander transmission line are adopted.
Abstract: A compact microstrip lowpass filter with an ultra-wide stopband is proposed. To achieve wide stopband suppression and compact size, both symmetrically loaded resonant patches and meander transmission line are adopted. A demonstration filter with 3 dB cutoff frequency at 1.3 GHz has been designed, fabricated and measured. The proposed filter also exhibits a very wide stopband of 152%, and is able to suppress the eleventh-harmonic response together with a small size of 0.12λg × 0.071λg, where λg is the guided wavelength at 1.3 GHz.