Filter Skirts Research Articles

Enhanced Harmonic Suppression for a Miniaturized Hairpin-Line Bandpass Filter with Meander Spurline

The design of a fourth-order centrally corrugated double-folded hairpin line bandpass filter with a broad stopband and enhanced selectivity is demonstrated in this article. Initially, a double-folded hairpin-line bandpass filter (DFHLBF) is designed from a fourth-order conventional hairpin-line bandpass filter (CHLBF), which is centred at 2.5 GHz and has a fractional bandwidth of 3%. This results in a 68% size reduction. With this folding mechanism, the filter's skirt characteristic is only enhanced at the upper passband edge, resulting in an attenuation level of 40 dB at 2.65 GHz. The capacitive loading has then been incorporated by periodic rectangular corrugations that have disturbed the folded arms. Because of the high capacitive coupling between the folded arms, a symmetrical passband with an attenuation level better than 40 dB at both edges has been observed. Besides, a size reduction of 14% than that for the DFHLBF has been achieved. However, because of the imbalance of the modal phase velocities in the inhomogeneous microstrip filter construction, the stopband's attenuation level climbs to 8 dB. Rectangular meander spurlines have been added between the connected arms of the neighbouring centrally corrugated cells of the filters as a way to lower the attenuation levels of the harmonics. This creates a slow-wave effect between the odd- and even-modes of the propagating signals. This results in an overall size reduction of 81% over the standard hairpin-line filter and an enlarged stopband of up to 4.36f0 with a rejection level of 42 dB.

Low-Loss Self-Packaged Ka-Band LTCC Filter Using Artificial Multimode SIW Resonator

In this brief, a low-loss self-packaged Ka-band LTCC filter is proposed based on an artificial multi-mode substrate integrated waveguide (SIW) resonator. Two ridges and two metal strips are tightly integrated in one SIW cavity to form the artificial quad-mode resonator. Due to the shielding of the SIW cavity, the resonator realizes a high Q factor, which contributes to an extremely low loss of the Ka-band filter. A fast design method for the bandpass filter based on an artificial multi-mode resonator is introduced. A simple approach to accurately extract all external Q factors for multiple resonant modes at the same time is also discussed. A pair of transmission zeros are generated to improve the filter skirt selectivity. For verification, a filter operating at 28 GHz is fabricated on the LTCC process. The measured result shows a low insertion loss of 0.8 dB, which is attracted in millimeter-wave applications.

Lamb Wave AlN Micromechanical Filters Integrated With On-chip Capacitors for RF Front-End Architectures

This paper reports on the implementation of an ultraminiature 140 MHz narrowband filter based on aluminum nitride Lamb wave resonators. Monolithically integrated with a pair of on-chip capacitors and cascaded with a pair of inductors, the filter is well matched to 50 ohm, showing a remarkably high performance. A low pass-band insertion loss of 2.78 dB and steep filter skirts are achieved. The form factor of the monolithic microelectromechanical systems filter is more than ten times smaller than its surface acoustic wave counterpart in the intermediate frequency band and it involves much simpler matching circuits.

Highly tunable microwave and millimeter wave filtering using photonic technology

The design for a photonic microwave filter tunable in both bandwidth and operating frequency is proposed and experimentally demonstrated. The circuit is based on a single sideband modulator used in conjunction with two or more transmission fiber Bragg gratings (FBGs) cascaded in series. It is demonstrated that the optical filtering characteristics of the FBGs are instrumental in defining the shape of the microwave filter, and the numerical modeling was used to optimize these characteristics. A multiphase-shift transmission FBG design is used to increase the dynamic range of the filter, control the filter ripple, and maximize the slope of the filter skirts. Initial measurements confirmed the design theory and demonstrated a working microwave filter with a bandwidth tunable from approximately 2 to 3.5 GHz and an 18 GHz operating frequency tuning range. Further work is required to refine the FBG manufacturing process and reduce the impact of fabrication errors.

Design and fabrication of aluminum nitride Lamb wave resonators towards high figure of merit for intermediate frequency filter applications

A design guideline for one-port aluminum nitride (AlN) Lamb wave resonators (LWRs) working at S0 mode with high performance is reported. A fabricated 252 MHz LWR, with an aperture of 200 μm, 12 fingers, and 1.5 μm thick AlN, is found to have a remarkably high figure of merit (FOM), which exhibits a high ratio of the resistance at parallel resonance (Rp) to the resistance at series resonance (Rs) of 1317 and a corresponding product of the effective coupling coefficient (k2eff) and quality factor (Q) exceeding 52. Consisting of such resonators, a 6-stage ladder filter with a low pass-band insertion loss (IL) of 4.5 dB and steep filter skirts is achieved, offering significant advantage of size savings.

공진기의 임피던스 변화에 근거한 비접촉 생체 신호 센서

본 논문에서는 공진기의 임피던스 변화에 근거한 생체 신호 센서를 제안한다. 제안된 생체 신호 센서는 호흡과 심장 박동 같은 생체 신호를 감지할 수 있고, 시스템은 공진기, 발진기, SAW 필터, 그리고 파워 감지기로 구성되어있다. 인체와 같은 유전체의 주기적인 움직임은 근거리 장 영역 안에서 공진기의 임피던스 변화를 야기하며, 따라서 공진기의 공진 주파수의 변화는 발진기의 발진 주파수 변화에 영향을 끼친다. 여기서 SAW 필터 저지대역의 가파른 주파수 응답특성은 작은 양의 주파수 편차를 큰 변화로 바꿀 수 있다. 기존의 센서의 감지 거리를 확장시키는 것을 목적으로 ISM 대역 870 MHz 대역에서 동작 시켰으며, 최대 거리 120 mm에서 호흡과 심장 박동신호의 검출을 확인하였다. In this paper, a vital signal sensor based on impedance variation of resonator is presented. Proposed vital signal sensor can detect the vital signal, such as respiration and heart-beat signal. System is composed of resonator, oscillator, surface acoustic wave (SAW) filter, and power detector. The cyclical movement of a dielectric such as a human body, causes the impedance variation of resonator within the near-field range. So oscillator's oscillation frequency variation is effected on resonator's resonant frequency. SAW filter's skirt characteristic of frequency response can be transformed a small amount of frequency deviation to a large variation. Aim to enhance the existing sensor detection range, proposed sensor operates in 870 MHz ISM band, and detect respiration and heart-beat signal at distance of 120 mm.

Pitch perception of concurrent harmonic tones with overlapping spectra

Fundamental frequency difference limens (F0DLs) were measured for a target harmonic complex tone with nominal fundamental frequency (F0) of 200 Hz, in the presence and absence of a harmonic masker with overlapping spectrum. The F0 of the masker was 0, ± 3, or ± 6 semitones relative to 200 Hz. The stimuli were bandpass filtered into three regions: 0-1000 Hz (low, L), 1600-2400 Hz (medium, M), and 2800-3600 Hz (high, H), and a background noise was used to mask combination tones and to limit the audibility of components falling on the filter skirts. The components of the target or masker started either in cosine or random phase. Generally, the effect of F0 difference between target and masker was small. For the target alone, F0DLs were larger for random than cosine phase for region H. For the target plus masker, F0DLs were larger when the target had random phase than cosine phase for regions M and H. F0DLs increased with increasing center frequency of the bandpass filter. Modeling using excitation patterns and "summary autocorrelation" and "stabilized auditory image" models suggested that use of temporal fine structure information can account for the small F0DLs obtained when harmonics are barely, if at all, resolved.

Synthesis and Design of a New Printed Filtering Antenna

Synthesis and design of a new printed filtering antenna is presented in this communication. For the requirements of efficient integration and simple fabrication, the co-design approach for the integration of filter and antenna is introduced. The printed inverted-L antenna and the parallel coupled microstrip line sections are used for example to illustrate the synthesis of a bandpass filtering antenna. The equivalent circuit model for the inverted-L antenna, which is mainly a series RLC circuit, is first established. The values of the corresponding circuit components are then extracted by comparing with the full-wave simulation results. The inverted-L antenna here performs not only a radiator but also the last resonator of the bandpass filter. A design procedure is given, which clearly indicates the steps from the filter specifications to the implementation. As an example, a 2.45 GHz third-order Chebyshev bandpass filter with 0.1 dB equal-ripple response is tackled. Without suffering more circuit area, the proposed structure provides good design accuracy and filter skirt selectivity as compared to the filter simple cascade with antenna and a bandpass filter of the same order. The measured results, including the return loss, total radiated power, and radiation gain versus frequency, agree well with the designed ones.

An alternative to the computational Speech Intelligibility Index estimates: Direct measurement of Rectangular Passband Intelligibilities.

The need for determining the relative intelligibility of passbands spanning the speech spectrum has been addressed by publications of the American National Standards Institute (ANSI). When the Articulation Index (AI) standard (ANSI, S3.5, 1969, R1986) was developed, available filters confounded passband and slope contributions. The AI procedure and its updated successor, the Speech Intelligibility Index (SII) standard (ANSI, S3.5, 1997, R2007), cancel slope contributions by using intelligibility scores for partially masked highpass and lowpass speech to calculate passband importance values; these values can be converted to passband intelligibility predictions using transfer functions. However, by using very high-order digital filtering, it is now possible to eliminate contributions from filter skirts and produce rectangular passbands. Employing the same commercial recording and the same one-octave passbands published in the SII standard (Table B.3), the present study compares Rectangular Passband Intelligibility (RPI) with SII estimates of intelligibility. The directly measured RPI differs from the computational SII predictions. Advantages resulting from direct measurement are discussed.

Thermal behavior of BAW filters at high RF power levels

The temperature increase of bulk acoustic wave filters at high RF power levels has been investigated. Self-heating due to power dissipation in the filter leads to a nonuniform frequency shift of the insertion loss. At the right filter skirt, self-heating is amplified by the negative temperature coefficient of frequency. We demonstrate that at high RF power levels, this can cause thermal instabilities resulting in an abrupt step in the insertion loss. A novel frequency transformation is introduced to describe the nonuniform frequency shift of the insertion loss as well as the thermal instabilities. A condition for the occurrence of thermal instabilities is derived. It is argued that because of this nonuniform frequency shift at high power levels, accelerated lifetime tests can overestimate the lifetime, if the stress frequency is not compensated for self-heating. Here, the frequency transformation is used to determine the stress frequencies at high RF power levels from low-power S-parameter measurements.

Is intelligibility of adjacent passbands hypoadditive or hyperadditive?

Based on their own findings and reports from other laboratories, H. Müsch and S. Buus [H. Müsch and S. Buus, J. Acoust. Soc. Am. 109, 2896–2909 (2001)] suggested that when heard together, the intelligibilities of adjacent passbands were hypoadditive, and those of disjoint passbands were hyperadditive. A subsequent study employed extremely high order far infrared filtering that had been shown to effectively eliminate contributions from transition band slopes [R. M. Warren, J. A. Bashford, Jr., and P. W. Lenz, J. Acoust. Soc. Am. 118, 3261–3266 (2005)]. That study measured the intelligibility for each of the 15 possible pairings of six one‐octave effectively rectangular passbands (3 dB/Hz filter skirts) that spanned the speech spectrum with center frequencies ranging from 0.25 to 8 kHz. Each pairing, whether contiguous or disjoint, exhibited hyperadditivity. The present study determined whether decreasing the filter skirts to 0.5 dB/Hz (considered quite steep by conventional standards) would produce the hypoadditivity reported in literature for adjacent bands. Results obtained support the hypothesis that redundancy introduced by overlapping transition band slopes could be responsible for the redundancy correction factor employed by some models for estimating intelligibility of paired adjacent passbands. [Work supported by NIH.]

Compact quasi-elliptic microstrip bandpass filter using terminated anti-parallel coupled-line

A compact quasi-elliptic microstrip bandpass filter with lower and upper stopband zeros is presented. The bandpass filter consists of terminated anti-parallel coupled-line and the stopband zero is generated and controlled by the reactive termination. In comparison to the traditional parallel coupled-line bandpass filter, the proposed filter achieves simultaneous size reduction and sharp filter skirt. The usefulness of the proposed filter is validated by a simultaneously miniature and selective quasi-elliptic bandpass filter centred at 2.4 GHz with 4.6% fractional bandwidth as well as two transmission zeros at 2 and 3.2 GHz.

The effect of smoothing filter slope and spectral frequency on temporal speech information

It is known that information contained within the filter skirts can provide cues important to speech intelligibility. However, the role of filter slope during temporal smoothing has received little attention. In experiment 1, smoothing filter slope angle was found to have a large effect on the intelligibility of sentences represented by three amplitude-modulated sinusoids. In experiment 2, the use of temporal cues above 16 Hz was examined across various regions of the spectrum. When increases in rate were presented to individual spectral bands, intelligibility only increased when presented in the higher spectral region. This result suggests a greater reliance on higher-rate cues in this region. However, intelligibility was greatest when these cues were distributed across the spectrum, indicating that their effective use is not restricted solely to this region.

Super UWB lowpass filter using open-circuited radial stubs

This paper presents a compact planar lowpass filter with super ultra-wideband (sUWB) passband and stopband for future possible sUWB radio system. The filter employs radial stubs to realize such sUWB passband and stopband and a sharp filter skirt performance. Design of the filter was based on electromagnetic simulation. The measured results of a 4-stage filter demonstrated the excellent filter performance: sUWB passband from DC to 22GHz with low insertion loss about 0.5dB at central frequency; sUWB stopband from 23 to 50GHz with attenuation larger than 35dB, which is the widest lowpass filter with widest stopband in the world, to the authors' best knowledge. The group delay over the passband is about 0.20ns and very flat. An sUWB bandpass filter with excellent bandpass and bandstop performance was also achieved and presented by integrating the developed sUWB losspass filter and an sUWB bandpass filter using broadside-coupled structure.

Auditory filter nonlinearity across frequency using simultaneous notched-noise masking

Psychoacoustic masking experiments have been widely used to investigate cochlear function in human listeners. Here we use simultaneous notched-noise masking experiments in normal hearing listeners to characterize the changes in auditory filter shape with stimulus level over the frequency range 0.25-6 kHz. At each frequency a range of fixed signal levels (30-70 dB SPL) and fixed masker levels (20-50 dB SPL spectrum level) are used in order to obtain accurate descriptions of the filter shapes in individual listeners. The notched-noise data for individual listeners are fitted with two filter shape models: a rounded exponential (roex) shape in which the filter skirt changes as a linear function of probe-tone level and the other, in which the gain of the tip filter relative to the filter tail changes as a function of signal level [Glasberg and Moore, J. Acoust. Soc. Am. 108, 2318-2328 (2000)]. The parameters for these fitted models are then described with a simple set of equations that quantify the changes in auditory filter shape across level and frequency. Both these models fitted the data equally well and both demonstrated increasing tip-tail gain as frequency increased.

A miniature 2.1-GHz low loss microstrip filter with independent electric and magnetic coupling

A miniature planar two-pole microstrip filter with independent electric and magnetic coupling has been developed at 2.1 GHz. The independent coupling allows separate control of two transmission zeroes and result in a sharp filter skirt. The two-pole filter occupies an area of 6.6/spl times/4.6 mm/sup 2/ (30 mm/sup 2/) on an /spl epsi//sub r/=10.2 substrate, and shows a 5% bandwidth (100 MHz) and an insertion loss of 1.4 dB. The filter unloaded Q is 150 at 2.1 GHz which is much better than compatible filters done in LTCC technology.

Optical narrow band filter without resonance's

This paper introduces an optical wave filter, which uses gratings at 45? or 135? inclined grating lines that avoid any resonance's. Therefore, many more options to form the filter shape exist. In general, the filter design can be traced to that of transversal filters (finite impulse response filter, FIR filter). Such an integrated optical wave filter is characterized by steep filter slopes and a narrow pass band (less then 01nm) combined with a high stop band attenuation (more than 40dB) and a linear phase response in the pass band. Compared to conventional Bragg grating filters, the inclined grating line filters can have a flatter pass band and steeper filter skirts related to the width of the pass band. In general, the filter's realization is possible using any optical material. In view of the excellent optical properties the semiconductor material system InP/InGaAsP is used for manufacturing the filter.

An Optical Wave Filter with 45° Inclined Grating Lines

This letter presents a novel integrated optical wave filter which can be realized in InP/InGaAsP, for example, in this device a definite shape of the filter function can be adjusted. The shape is characterized by steep filter slopes and a narrow pass band (down to 0.1 nm) combined with a high stop band attenuation (more than 40 dB), and a linear phase response in the pass band. Compared to conventional Bragg grating filters the inclined grating line filters can have a flatter pass band and steeper filter skirts related to the width of the pass band.

Photonic bandpass filters with high skirt selectivity and stopband attenuation

A new photonic signal processor topology that simultaneously achieves both a high-Q and a high skirt selectivity and stopband attenuation filter response is presented. It is based on a novel dual-cavity bandpass optical structure in which two pairs of active fiber Bragg grating cavities are used with an optical gain offset to control the poles and stopband attenuation characteristics of the filter. This concept enables a large improvement in the filter stopband attenuation, rejection bandwidth, and skirt selectivity to be realized. Measured results demonstrate both a narrow bandpass bandwidth of 0.4% of center frequency and a skirt selectivity factor of 16.6 for 40 dB rejection, which corresponds to a 6.5-fold improvement in comparison to conventional single cavity high-Q structures. To our knowledge, this is the best skirt selectivity reported for a photonic bandpass filter to date. The new photonic filter structure has been experimentally verified and excellent agreement between measured and predicted responses is shown.

Tl 2Ba 2CaCu 2O 8 thin film high frequency filters on 3 inch sapphire substrates

Modern communication systems require densely packed frequency channels in the expensive frequency bands. Therefore high temperature superconducting (HTS) high frequency filters are of increasing importance, taking advantage of their outstanding properties namely steep filter skirts, low insertion loss, and furthermore reduced mass and volume compared to conventional cavity or dielectric resonator systems. Within the framework of a German BMBF pilot project a HTS equiped satellite repeater will be developed to demonstrate the performance advantage of HTS. For that purpose we prepare filters on double-sided Tl 2Ba 2CaCu 2O 8 thin films on CeO 2 buffered 3 inch sapphire substrates. The HTS films are prepared in the two-step process by sputtering an amorphous thallium free precursor and following oxythallination. The critical temperature and spatial distribution of critical current density at 77 K, both measured by inductive techniques, show values above 100 K or 1 MA/cm 2, respectively. We use a dielectric resonator technique at 3.9 GHz and power levels up to some mT to determine the films surface resistance. We present measurements of input filters made from our double-sided 3 inch films.