Showing papers on "Band-stop filter published in 2005"

Generation and distribution of a wide-band continuously tunable millimeter-wave signal with an optical external modulation technique

Abstract: A new technique to generate and distribute a wide-band continuously tunable millimeter-wave signal using an optical external modulator and a wavelength-fixed optical notch filter is proposed. The optical intensity modulator is biased to suppress the odd-order optical sidebands. The wavelength-fixed optical notch filter is then used to filter out the optical carrier. Two second-order optical sidebands are obtained at the output of the notch filter. A millimeter-wave signal that has four times the frequency of the microwave drive signal is generated by beating the two second-order optical sidebands at a photodetector. Since no tunable optical filter is used, the system is easy to implement. A system using an LiNbO/sub 3/ intensity modulator and a fiber Bragg grating filter is built. A stable and high spectral purity millimeter-wave signal tunable from 32 to 50 GHz is obtained by tuning the microwave drive signal from 8 to 12.5 GHz. The integrity of the generated millimeter-wave signal is maintained after transmission over a 25-km standard single-mode fiber. Theoretical analysis on the harmonic suppression with different modulation depths and filter attenuations is also discussed.

An ultrawideband bandpass filter using broadside-coupled microstrip-coplanar waveguide structure

Abstract: This paper presented an ultra-wideband (UWB) bandpass filter using broadside-coupled microstrip-coplanar waveguide structure. The filter consists of a microstrip line coupled to a coplanar waveguide (CPW) that was fabricated on the ground of the microstrip line. The proposed filter has been simulated, fabricated and measured for UWB system. The measured results demonstrated the UWB properties from 3.0 GHz to 10.63 GHz (-10 dB bandwidth) and the potential to be wider. A threesection filter shown insertion loss at central frequency is about 0.32 dB and very flat over the whole band. The group delay, which is important to an impulse radio UWB system, is about 0.42 ns over the most central band and less than 0.95 ns over the whole band. The filter also exhibited a good performance outside the band, both at low frequency end (to meet FCC limit) and high frequency end higher than 18 GHz with insertion loss larger than 30 dB.

Tunable combline filter with continuous control of center frequency and bandwidth

Abstract: A new combline filter structure with a continuous tunability for both the center frequency and bandwidth is presented in this paper. The passband-width tunability is achieved by placing variable coupling reducers between the filter resonators. The coupling reducers, operating as bandwidth control subnetworks, are designed as detuned resonators made up of a line segment ending in a variable capacitor. The proposed filter structure is experimentally validated with the design, construction in suspended stripline technology, and characterization of a low-cost filter prototype for terrestrial digital video broadcasting receivers operating in the UHF band (470-862 MHz). Other relevant factors, such as the intermodulation distortion produced by the varactors used to control the bandwidth electronically or the power-handling performance of the constructed filter, are also discussed. The reconfigurable filter module described in this paper is very suitable for the design of flexible multifunction receiver subsystems simultaneously supporting signals with a different bandwidth.

Microwave filters with improved stopband based on sub-wavelength resonators

Abstract: The main aim of this paper is to demonstrate the potentiality of sub-wavelength resonators, namely, split-ring resonators, complementary split-ring resonators, and related structures to the suppression of undesired spurious bands in microwave filters, a key aspect to improve their rejection bandwidths. The main relevant characteristics of the cited resonators are their dimensions (which can be much smaller than signal wavelength at resonance) and their high-Q factor. This allows us to design stopband structures with significant rejection levels, few stages, and small dimensions, which can be integrated within the filter active region. By this means, no extra area is added to the device, while the passband of interest is virtually unaltered. A wide variety of bandpass filters, implemented in both coplanar-waveguide and microstrip technologies, have been designed and fabricated by the authors. The characterization of these devices points out the efficiency of the proposed approach to improve filter responses with harmonic rejection levels near 40 dB in some cases. It is also important to highlight that the conventional design methodology for the filters holds. For certain configurations, the presence of the resonators slightly lowers the phase velocity at the frequencies of interest with the added advantage of some level of reduction in device dimensions.

Design of microstrip bandpass filters with multiorder spurious-mode suppression

Abstract: This paper proposes a bandpass filter design method for suppressing spurious responses in the stopband by choosing the constitutive resonators with the same fundamental frequency, but staggered higher order resonant frequencies. The design concept is demonstrated by a four-pole parallel-coupled Chebyshev bandpass filter and a compact four-pole cross-coupled elliptic-type bandpass filter. Each filter is composed of four different stepped-impedance resonators (SIRs) for which a general design guideline has been provided in order to have the same fundamental frequency and different spurious frequencies by proper adjusting the impedance and length ratios of the SIR. Being based on knowledge of the coupling coefficients and following the traditional design procedure, the resultant filter structures are simple and easy to synthesize. The measured results are in good agreement with the simulated predictions, showing that better than -30-dB rejection levels in the stopband up to 5.4f/sub 0/ and 8.2f/sub 0/ are achieved by the Chebyshev and quasi-elliptic filters, respectively.

Compact microstrip bandstop filter using open stub and spurline

Abstract: A compact wideband high-rejection microstrip bandstop filter (BSF) is presented This filter combines two traditional BSFs: open-stub filter and spurline filter Due to the inherently compact characteristics of the spurline, the proposed filter shows a better rejection performance than open-stub BSF without increasing the circuit size From 37 to 54 GHz, the proposed BSF has a rejection of better than 20 dB and the maximum rejection level of 61 dB Application of this BSF to suppress the second harmonic of an open-loop ring bandpass filter is also investigated with a 40-dB suppression improvement achieved

Compact and wideband microstrip bandstop filter

Abstract: A novel one-section bandstop filter (BSF), which possesses the characteristics of compact size, wide bandwidth, and low insertion loss is proposed and fabricated. This bandstop filter was constructed by using single quarter-wavelength resonator with one section of anti-coupled lines with short circuits at one end. The attenuation-pole characteristics of this type of bandstop filters are investigated through TEM transmission-line model. Design procedures are clearly presented. The 3-dB bandwidth of the first stopband and insertion loss of the first passband of this BSF is from 2.3 GHz to 9.5 GHz and below 0.3 dB, respectively. There is good agreement between the simulated and experimental results.

Direct-coupled microwave filters with single and dual stopbands

Abstract: This paper presents new ideas for the design and implementation of microwave filters with single and dual stopbands. They can be realized with waveguide, coaxial, dielectric resonators, or in a planar technology. The new methods represent an advance over present methods in that the resonators are direct coupled, thus avoiding the need for transmission line phase lengths between resonator stubs that tend to degrade performance due to their dispersion and are difficult to adjust during tuning. Three bandstop (BS) configurations are presented. The first will accommodate even or odd characteristics and also asymmetric responses, although some negative or diagonal cross-couplings will be needed. The second resembles the cul-de-sac configuration for bandpass filters and needs no diagonal or negative couplings even for asymmetric characteristics. The third is an application of the cul-de-sac synthesis technique to dual-band bandstop (DBBS) filters. All these BS designs are very similar to regular bandpass filters in their design and realization. The design of a DBBS filter is presented and compared with an equivalent bandpass filter to demonstrate its advantages. Finally, the simulated and measured results of a fourth-degree BS filter design in the novel cul-de-sac configuration are presented.

Fractal-shaped microstrip coupled-line bandpass filters for suppression of second harmonic

Abstract: In this paper, microstrip coupled-line bandpass filters using a Koch fractal shape are proposed for the first time. These filters are fabricated on a liquid crystal polymer (LCP) substrate for Ku-band. Conventional microstrip coupled-line filters are very popular for RF front ends because they can be fabricated easily. However, their large second harmonic causes the shape of the passband to be asymmetric in the upper band and it worsens the skirt properties. By proper design, the second harmonic of fractal filters can be significantly suppressed through the use of fractal shapes. In this paper, using LCP, the maximum harmonic suppression was almost 42 dB. This type of filter can be used to suppress the second harmonic without any additional devices and regardless of the substrate.

Compact, frequency-agile, absorptive bandstop filters

Abstract: Two absorptive bandstop filter circuit topologies are introduced. The preferred topology is analyzed and its advantages over traditional approaches quantified. A corresponding varactor-tuned microstrip absorptive bandstop filter is described and its unique ability to maintain its attenuation while tuning across a broad frequency range using only resonant frequency tuning is demonstrated.

An integrated LMS adaptive filter of TX leakage for CDMA receiver front ends

Abstract: The theory and practical implementation of a continuous-time LMS adaptive filter of the TX leakage in CDMA receivers are described. The filter works by injecting a matched out-of-phase copy of the TX leakage into the LNA output. It requires a reference signal coupled from the TX chain, whose I and Q components are appropriately scaled to generate the matched copy. The scale factors are the results of the correlation between the filter output signal and the I/Q components of the reference signal. The filter was designed as part of a 0.25-/spl mu/m CMOS cellular-band receiver. The effect of the DC offsets in the correlators on the TX leakage rejection ratio (TXRR) was minimized by using the sign-data variant of the LMS algorithm and by increasing the gain of the correlating multipliers. The loop stability margin was improved by swapping the I and Q reference inputs of the scaling multipliers. Without a significant group delay of the TX leakage relative to the reference signal, the filter achieved the maximum TXRR of 28 dB, which was limited by the reference signal coupling. The group delay introduced by the SAW duplexer reduced the minimum TXRR to 10.8 dB. The filter degraded the LNA noise factor and gain by 1.3 dB and 1.7 dB, respectively.

Investigation of phase-modulator-based all-optical bandpass microwave filter

Abstract: Theoretical analysis and experimental implementation of an all-optical bandpass microwave filter are presented. Bandpass filtering is implemented using an electrooptic phase modulator combined with a dispersive device to eliminate the baseband resonance of a typical low-pass filter. In addition to bandpass operation, the proposed filter also provides an improved mainlobe-to-sidelobe ratio (MSR) and a reduced mainlobe bandwidth compared with those of the conventional microwave filters with windowing. A four-tap bandpass microwave filter with a 3-dB mainlobe bandwidth of 2.65 GHz and an MSR of 30 dB is demonstrated. The filter performances, including the reconfigurability, tunability, and the dynamic range, are also discussed.

Band reject filters

Abstract: Acoustic resonators such as surface acoustic wave (SAW) devices and thin film bulk acoustic resonators (FBAR) can be configured to produce a band reject filter. Such a filter overcomes the insertion loss and power handling limitations of conventional band pass configurations and as such can be used in power amplifier and duplexer applications.

Oximeter ambient light cancellation

Abstract: A pulse oximeter method and apparatus which provides (1) a notch filter at a distance between a modulation frequency and a common multiple of commonly used power line frequencies (50, 60, 100 and 120) and also (2) a demodulation frequency greater than a highest pulse rate of a person and lower than any harmonic of 50, 60, 100 or 120 Hz, to filter ambient light interference, while choosing an optimum demodulation frequency that avoids interference from the notch filter or from harmonics of the line interference. Also, ambient light for any low frequency interference, such as power line interference, is measured both before and after each of the light emitter wavelengths and the average of the ambient light is then subtracted from the detected signal.

System for limiting loudspeaker displacement

Abstract: Loudspeakers can be damaged by high drive signals. One reason for this damage is an excess vibration displacement of the coil-diaphragm assembly. This invention describes a novel method for limiting this displacement by a signal processor. In the present invention, a low frequency shelving and notch filter is used to attenuate low frequencies according to a prediction of the loudspeaker displacement. A novel method for calculating coefficient values for a digital implementation of the low frequency shelving and notch filter according to the predicted displacement is described.

MEMS-actuated microdisk resonators with variable power coupling ratios

Abstract: A novel tunable microdisk resonator with microelectromechanical-system (MEMS)-actuated deformable waveguides is demonstrated for the first time. The deformable waveguide enables us to continuously vary the power coupling ratio of the microdisks. A laterally coupled device with a quality factor of 7700 is fabricated on silicon-on-insulator substrate. An optical notch filter with variable attenuation at the resonant wavelength is successfully demonstrated, with an extinction ratio of 9 dB. The MEMS-actuated tunable microdisk is a basic building block for many dynamic wavelength-division-multiplexing circuits.

Estimation of Power System Frequency Using Adaptive Notch Filter

Abstract: An algorithm based on the concept of adaptive notch filter (ANF) is proposed for estimation of power system frequency. The ANF is a second-order notch filter that is further furnished with a nonlinear differential equation to update the frequency. Performance of the algorithm is compared with that of a newly introduced algorithm which is based on using an enhanced phase-locked loop (PLL) system. Unlike the PLL-based frequency estimator, the proposed algorithm does not employ voltage-controlled oscillator (VCO). This makes its structure much simpler for implementations. Transient response of the proposed estimator is faster than the PLL-based estimator. Computer simulations are presented to highlight the usefulness of this approach in estimating near nominal and off nominal power system frequency

A CMOS Continuous-Time Low-Pass Notch Filter for EEG Systems

Abstract: A CMOS OTA-C low-pass notch filter for EEG application is described. The pass-band covers four bands of brain wave and provides more than 65 dB attenuation for the 50 Hz power line interference. The OTA works in the weak inversion region and a low transconductance of 3 nA/V is achieved. The low transconductance enables using small capacitors in the OTA-C filter so that the filter is suitable for the multi-channel EEG integrated circuits. The measured results show the good performance of the filter for filtering the noise in acquired EEG signals.

Miniaturized dual-mode bandpass filter with harmonic control

Abstract: This letter presents a miniaturized dual-mode microstrip bandpass filter with the right crossed slots. The right crossed slots perturb and reduce the fundamental resonant frequency, but the second resonance is not affected. Therefore, the second resonance will be effectively higher than 2f/sub o/, where f/sub o/ is the fundamental frequency. Since the fundamental frequency is lower, the bandpass filter is smaller than the conventional filter. The proposed filter shows a 4.4% fractional bandwidth at 1.595GHz with a return loss of better than 10dB and an insertion loss of less than 2.5dB, while the second passband is located around 2.88f/sub o/= 4.6GHz. Compared with the conventional square patch filter, the proposed filter also shows a 58% size reduction.

A Frequency Selective Filter for Short-Length Time Series

Abstract: An effective and easy-to-implement frequency filter is proposed, obtained by convolving a raised-cosine window with the ideal rectangular filter response function. Three other filters, Hodrick--Prescott, Baxter--King, and Christiano--Fitzgerald, are thoroughly reviewed. A bandpass version of the Hodrick--Prescott filter is also introduced and used. The behavior of the windowed filter is compared to the others through their frequency responses and by applying them to both quarterly and monthly artificial, known-structure series and real macroeconomic data. The windowed filter has almost no leakage and is better than the others at eliminating high-frequency components. Its response in the passband is significantly flatter, and its behavior at low frequencies ensures a better removal of undesired long-term components. These improvements are particularly evident when working with short-length time series, which are common in macroeconomics. The proposed filter is stationary and symmetric, therefore, it induces no phase-shift. It uses all the information contained in the input data and stationarizes series integrated up to order two. It thus proves to be a good candidate for extracting frequency-defined series components.

Tapered dual-plane compact electromagnetic bandgap microstrip filter structures

Abstract: In this paper, the designs of two novel tapered dual-plane compact electromagnetic bandgap (C-EBG) microstrip filter structures are presented. With the dual-plane configuration, the proposed structure displays an ultrawide stopband with high attenuation within a small circuit area. Chebyshev distribution is adopted to eliminate ripples in the passband caused by the periodicity of the EBG structure. This gives rise to a compact EBG structure that exhibits excellent transmission and rejection characteristics in the passband and the stopband, respectively. The proposed structures are implemented and the measurement results are found to be in good agreement with the simulation results, verifying the excellent stopband and passband performance obtained using the proposed configuration. These novel structures are easy to fabricate and are promising structures that have wide applications for compact and high performance circuit component designs in microwave circuits.

Miniaturized parallel coupled-line bandpass filter with spurious-response suppression

Abstract: A novel miniaturized parallel coupled-line bandpass filter with suppression of second and third harmonic frequencies is demonstrated in this paper. This new filter is based on the capacitive termination on the conventional parallel coupled line to achieve size minimization, while the spurious responses are eliminated by the over-coupling approach. These features offer the classical parallel coupled-line bandpass filter simultaneous compactness and wide stopband performance. The simulations and measurements of a 900-MHz prototype bandpass filter are presented. The measured results agree well with the simulation. Compared with the conventional parallel coupled-line bandpass filter, the measured second and third spurious responses are suppressed to -64 and -55 dB, respectively. In addition, the circuitry size of the prototype filter can be reduced up to 25%.

Tunable wideband microwave band-stop and band-pass filters using YIG/GGG-GaAs layer structures

Abstract: Magnetically tunable wideband microwave bandstop and bandpass filters using ferromagnetic resonance absorption in yttrium iron garnet/gadolinium gallium garnet-gallium arsenide (YIG/GGG-GaAs) layer structures are reported. The measured characteristics of the bandstop filter, with nonuniform bias magnetic field distribution along the YIG/GGG film, shows a large absorption bandwidth of 1900 MHz at the stopband center frequency of 11.0 GHz, average peak absorption of 13 dB, and an out-of-stopband insertion loss of 1.5 dB. The measured characteristics of the bandpass filter at the passband center frequency of 7.1 GHz demonstrates a 3-dB bandwidth of 1450 MHz, out-of-band rejection of 33 dB, and an insertion loss of 1.5 dB. A good agreement between the experimental results and the simulation results based on a lumped element equivalent circuit modeling of YIG bandstop filters has been achieved.

Image-rejection CMOS low-noise amplifier design optimization techniques

Abstract: This paper reviews and analyzes two reported image-rejection (IR) low-noise amplifier (LNA) design techniques based on CMOS technology, i.e., the second-order active notch filer and third-order passive notch filter. The analyses and discussions are based on the quality factor of filters and the ability of the frequency control. As the solution to deal with the suitable on-chip filter, this paper proposes a new notch-filter topology that can overcome the limitations of the two previous reported studies. In addition, the LNA design method satisfying the power-cons-trained simultaneous noise and input matching, as well as the linearity optimization conditions is introduced. By using the proposed notch filter and proposed design methodology, an IR LNA used in the superheterodyne architecture is implemented. The proposed IR LNA, designed based on 0.18-mum CMOS technology with total current dissipation of 4 mA under 3-V supply voltage, is optimized for a 5.25-GHz wireless local area network with IF frequency of 500-MHz applications. The measurement results show 20.5-dB power gain, lower than 1.5-dB noise figure, -5-dBm input-referred third-order intercept point and an IR of 26 dB

Periodically nonuniform coupled microstrip-line filters with harmonic suppression using transmission zero reallocation

Abstract: In this paper, the two-port periodically nonuniform coupled microstrip line with finite length is thoroughly studied as an equivalent J-inverter network for microstrip bandpass filters with harmonic suppression. Extracted J-inverter susceptance is exhibited to vary up and down versus frequency with the null or transmission zero when the coupled length becomes half-wavelength. This transmission zero can be adjusted by varying the periodicity and/or slit depth to suppress the first spurious harmonic passband of the filter. Firstly, two one-stage bandpass filters with wide and narrow bandwidths are designed to assure the first-harmonic passband is fully suppressed as illustrated in theory and experiment. Secondly, a three-stage bandpass filter with harmonic suppression is designed optimally. The predicted S-parameters are found in good agreement with the measured values, at least 40-dB insertion loss, at the point where the first-harmonic passband is achieved.

Microstrip dual-mode band reject filter

Abstract: Novel microstrip dual-mode band reject filters using triangular patch resonators are investigated. It is shown that with simple circuit topologies highly selective notch filters can be realized. Full-wave electromagnetic (EM) simulations and circuit modeling are performed in order to understand the operation of this type of filter. Two demonstrators, i.e. single-patch and double-patch dual-mode band reject filters are presented with simulated and measured results.

Miniaturized cross-coupled filter with second and third spurious responses suppression

Abstract: Novel miniaturized cross-coupled filter with second and third spurious responses suppression is proposed. This new filter structure is incorporated with the stepped-impedance resonator, which is beneficial for size diminution, and a proposed compact harmonic suppression cell that exhibits photonic bandgap (PBG) characteristics. When compared with a conventional cross-coupled filter, the proposed square stepped-impedance cross-coupled filter acquires more than 8% size reduction and spurious responses suppression simultaneously. Furthermore, the proposed filter performance shows almost 60-dB attenuation improvement to both second and third spurious frequencies.

CPW band-stop filter using unloaded and loaded EBG structures

Abstract: Two different structures of unloaded and loaded electromagnetic bandgaps (EBG) are proposed. The models of the unloaded and loaded unit structures are derived by equivalent circuit approach and full-wave electromagnetic simulation is used for extracting the values of the lumped elements in the circuit. A band-stop filter (BSF) has been designed with flat response at a selected frequency by cascading the unit EBG structures. The EBG filter is fabricated on high resistivity silicon substrate employing a microelectromechanical systems (MEMS) surface micromachining process. The measurement results for the loaded EBG reveals a 20 dB stop-band with a bandwidth of 13.2 GHz. The lower and the higher pass-band insertion losses are less than 2 dB and 4.5 dB, respectively. EBG band-stop filters fabricated by the MEMS process have immense potential to be integrated with CMOS devices owing to compactness and low cost.

All-optical microwave bandpass filters implemented in a radio-over-fiber link

Abstract: An all-optical microwave bandpass filter implemented in a radio-over-fiber (RoF) link is proposed and demonstrated. The filter consists of an optical phase modulator, a length of high birefringence (Hi-Bi) fiber, a 25-km singlemode fiber and a narrow linewidth laser source. Different time delays are achieved when the two orthogonal polarization modes are traveling along the Hi-Bi fiber. The baseband resonance is eliminated by use of the optical phase modulator in combination with the 25-km single-mode fiber serving as a dispersive device. The proposed filter is immune to optical interference because of the orthogonality of the two polarization modes. A two-tap all-optical microwave bandpass filter with a null-to-null bandwidth of 8.7 GHz and a notch rejection level greater than 30 dB implemented in the 25-km RoF link is demonstrated.

Method of making high performance optical edge and notch filters and resulting products

Abstract: High performance optical edge and notch filters and methods of making the same are disclosed. The multi-layer, thin-film optical edge filters have an edge steepness greater than about 0.8% as measured by dividing (a) the edge width from the 50% transmission wavelength to the optical density 6 (“OD6”) wavelength by (b) the 50% transmission wavelength. The optical edge filters also have an average transmission above about 95%. The notch filters exhibit a blocking of OD>6, very high transmission (>90%) outside the notch(es), and a narrow notch bandwidth comparable to that of holographic notch filters. The methods for making such filters accurately determine when deposition of each layer of the filter should terminate.