Automatic computer-aided design of SAW filters using slanted finger interdigital transducers

This paper describes a design procedure for surface acoustic wave (SAW) filters using slanted finger interdigital transducers (SFIT) that are suitable for mid-band or wideband applications. The SFITs cannot represent the impulse response directly, in contrast to apodized IDTs. A design method for SFITs based on a building-block approach in the frequency domain is described. An automatic computer-aided design tool for SFIT filters has been achieved. The SFIT filters can be designed using a withdrawal weighting for stop-band responses, an aperture weighting for pass-band amplitude responses, and a distance weighting for pass-band phase responses. In addition, a SFIT pattern for photo mask can be automatically designed using this tool. Using this tool, an SFIT filter with a relative bandwidth of 15% was designed on an x-cut 112y-direction LiTaO(3) substrate.     

Design technique for nonlinear phase SAW filters using slanted finger interdigital transducers

This paper describes a useful design technique to achieve a nonlinear phase SAW filter using slanted finger interdigital transducers (SFITs) or tapered interdigital transducers which are suitable for wide-band filters in intermediate frequency stages. A required nonlinear phase response in the passband can be obtained by changing center-to-center distances between input and output SFITs along an axis perpendicular to the SAW propagation axis. The design is based on a building-block approach in the frequency domain. A nonlinear phase SAW filter with a center frequency of 70 MHz and a fractional bandwidth of about 10% is demonstrated on x-cut 112.2 degrees y-propagating LiTaO(3 ). Because the substrate has a power flow angle of 1.55 degrees, the SFIT pattern is tilted along that angle. Good agreement between theoretical and experimental results is obtained.     

Investigation of new low-loss and high-power SAW filters for reverse-frequency-allocated cellular radios

Japanese cellular radios employ reverse frequency-allocations of the transmitter and receiver frequency bands. A rather narrowband surface acoustic wave (SAW) transmitter prefilter and a new type of SAW low-loss and high-power transmitter final stage filter-dual configurations to previously developed US cellular radio system filter-have been developed. The dual configurations provide the stopbands for the filter at the lower side of the pass bands, which is a requirement for reverse frequency-allocation systems. Design procedures, including those for the piezoelectric substrates and the experimental results obtained for the filters of 1.5 dB low insertion-loss and over 30 dB stop band rejection at 920 MHz, are also presented. In addition, the frequency characteristics of the SAW antenna duplexer module used in Japanese new common carrier (NCC) systems are discussed.     

Tunable slotted ground structured bandstop filter with BST varactors

This paper presents an investigation of a tunable bandstop filter (BSF) using slotted ground structure. A kind of open loop slot resonator is used for the bandstop response and its characteristics according to various dimensions are considered to decide a proper shape for the final design. A barium-strontium-titanate (BST) varactor chip is deployed to tune each resonator and its location is determined by electromagnetic simulation for an optimum frequency tuning. A three-pole tunable BSF of this type is measured at the centre frequency from 4.5 to 5.5 GHz and its rejection is more than 20 dB at the stop band while the insertion loss at the pass band is less than 1.5 dB.     

Optimization of broadband withdrawal weighted interdigital transducers for high selective SAW filters

The problem under discussion is the design of highly selective broadband surface acoustic wave (SAW) interdigital transducers (IDT) with uniform electrodes. In most SAW filters, such transducers are used with apodized IDTs or instead of them. The proposed optimization algorithms are intended for improvement of IDT selectivity by means of a withdrawal weighting (WW) technique. Unlike the familiar methods of WW transducer optimization, these algorithms choose the best IDT structure on the basis of how well it meets the specifications, not in the time but in frequency domain directly. This approach is more effective for broadband WW transducers. A number of SAW filters have been designed using the described algorithms. Their experimental characteristics follow: bandwidths of 0.5 to 15%, stopband rejection of 40 to 50 dB, 3 dB/40 dB shape factors of 1.07 to 1.3.     

A third-order active-R filter with feedforward input signal

A realization of voltage-mode transfer functions with feedforward input signal for third-order active-R filter using an oprational amplifier has been presented. This filter is useful for high frequency operation, monolithic IC implementation and is easy to design. The single circuit gives three filter functions, low pass, high pass and band pass. This filter circuit can be used for differentQ and _f0 with high passband gain. This gives better stop band attenuation and sharper cut-off at the edge of the passband.     

Design of withdrawal-weighted SAW filters

Presents a new design algorithm for a withdrawal-weighted surface acoustic wave (SAW) transversal filter. The proposed algorithm is based on the effective transmission loss theory and a delta function model of a SAW transversal filter. The design process consists of three steps, which eventually determine eight geometrical design parameters for the filter in order to satisfy given performance specifications. First, the number of fingers in the input and output interdigital transducers (IDTs), plus their geometrical sizes is determined using the insertion loss specification. Second, the number and positions of the polarity reverses in the output IDT are determined using the bandwidth and ripple specifications. Third, the number and position for withdrawing and switching specific fingers in the output IDT and attached electrode area are determined to achieve the desired sidelobe level. The efficiency of the technique is illustrated using a sample design of an IF filter consisting of a uniform input IDT and withdrawal-weighted output IDT     

SAW filters including one-focus slanted finger interdigital transducers

The present paper describes a new filter type, slanted finger interdigital transducer (SFIT) that allows fast analysis as a precondition for fast optimization. Therefore, filter structure and analysis are especially suitable for optimizing unidirectional SFIT (USFIT) filters. For analysis, a SFIT filter is usually divided into many narrow channels. Every channel is considered to be a subfilter and is analyzed separately. Therefore, the total filter analysis is very time consuming. For reducing computing time, we suggest a one-focus structure. In contrast to conventional SFIT filters, not only the finger and gap widths but also the spaces between transducers of different channels differ by one and the same scaling factor. As a consequence, all prolonged finger edges of both transducers intersect in one point called focus. As a result, the parameters of all subfilters can be calculated from the parameters of only one subfilter by simple frequency scaling. Consequently, the total time for analysis is essentially reduced. However, one-focus SFIT filters with continuous finger edges show a deep minimum within the passband. This problem can be overcome by using stepped one-focus structures.     

SAW integrated modules for 800-MHz cellular radio portable telephones with new frequency allocations

Several technologies are developed to achieve broader band surface-acoustic-wave (SAW) filters for portable telephones used in an 800-MHz wideband (25-MHz) cellular radio system. The design and realization of a transmitter final stage filter (high-power filter) and a prefilter (high-performance filter) are examined from initial specification to final device operation. An insertion loss of less than 2 dB and a rejection level of more than 20 dB are achieved for the final stage filter, and less than 5 dB and more than 50 dB, respectively, are achieved for the prefilter. Two integrated SAW modules, an antenna duplexer and a high-power amplifier, that include the above SAW filters and satisfy almost all requirements for wideband cellular radio have been developed. Their physical dimensions are the same as those of previously developed 20-MHz models. New SAW electrode materials (Al+Ni, Al+Cu+Ni) have also been investigated to improve the power-handling characteristics of the transmitter final stage filter.     

A study of crosstalk effects on the packaged SAW by the FDTD method.

The purpose of this study is to estimate the complete crosstalk effects, including the package and the pads on the surface acoustic wave (SAW) substrate. The coupling influence from the SAW pattern is investigated by the full-wave approach. In order to combine the electromagnetic effects with the surface acoustic wave response, a new approach based on finite difference time domain (FDTD) with equivalent current source method is applied. The resistive voltage source model is carefully used to simulate the situations of measurement by the vector network analyzer more accurately. Two kinds of patterns of one-port SAW resonators with the same package structure and interdigital transducer (IDT) design are studied. From the simulated electromagnetic field distributions over the substrate, it can be seen that, as the pattern on the SAW substrate becomes closer, more input energy will be coupled directly to the parallel pads by crosstalk without filtering. This will lead to more coupling loss and, therefore, the insertion loss becomes universally lower by about 2 to 3 dB. Furthermore, it can be observed that the coupling interference from the SAW pattern is more serious than from the package in this case. Verification with the measurement results shows that our method is able to obtain good agreement and can be used to observe the influence from the SAW pattern that can seriously affect the performance of the SAW device.     

Study of crosstalk effects on the packaged SAW by the FDTD method

The purpose of this study is to estimate the complete crosstalk effects, including the package and the pads on the surface acoustic wave (SAW) substrate. The coupling influence from the SAW pattern is investigated by the full-wave approach. In order to combine the electromagnetic effects with the surface acoustic wave response, a new approach based on finite difference time domain (FDTD) with equivalent current source method is applied. The resistive voltage source model is carefully used to simulate the situations of measurement by the vector network analyzer more accurately. Two kinds of patterns of one-port SAW resonators with the same package structure and interdigital transducer (IDT) design are studied. From the simulated electromagnetic field distributions over the substrate, it can be seen that, as the pattern on the SAW substrate becomes closer, more input energy will be coupled directly to the parallel pads by crosstalk without filtering. This will lead to more coupling loss and therefore, the insertion loss becomes universally lower by about 2 to 3 dB. Furthermore, it can be observed that the coupling interference from the SAW pattern is more serious than from the package in this case. Verification with the measurement results shows that our method is able to obtain good agreement and can be used to observe the influence from the SAW pattern that can seriously affect the performance of the SAW device.     

A novel reflector-filter using a SAW waveguide directional coupler

The SAW waveguide technique was used to form a novel reflector-filter for the realization of compact IF filters in CDMA handsets. The reflector-filter design is an attractive technique to obtain characteristics with steep skirts in a short device length, because the SAW propagation path is folded and the frequency response is synthesized by utilizing both IDT and reflector responses. In this paper, we propose a new reflector-filter structure using a SAW waveguide directional coupler. For the implementation of the proposed reflector-filter, the key technology is the design of SAW waveguides. We have formed SAW waveguides using Al gratings loaded on the surface of the substrate. The pitch of the Al gratings has been chosen unequal to half the acoustical wavelength to avoid the occurrence of the gratings stopband at the filters passband position. Using the proposed reflector-filter structure, PCS-CDMA IF filters were fabricated on quartz substrates. The filter exhibited an insertion loss of 8.5 dB, a 5 dB bandwidth of 1.45 MHz, and a rejection of more than 33 dB at the center frequency +/-1.25 MHz with the package size of 4.8x9.1 mm (2). i.e., half the size of a conventional transversal filter was achieved using the proposed reflector-filter technique.     

Suppression of sidelobe levels for guided-wave acousto-optic tunable filters using weighted coupling

An analysis of guided-wave acousto-optic tunable filters (AOTFs) that employ simple acousto-optic (AO) weighted coupling techniques for sidelobe reduction and the calculated and experimental results from a specific example that involves only variation of the width of a surface acoustic wave (SAW) slot waveguide are presented. The calculations on single- and multi-stage AOTFs consisting of an optical channel waveguide and a SAW slot waveguide in LiNbO(3) substrate show that waveguide width weighting using generalized Hamming functions would provide significant improvement in sidelobe suppression. Calculated results together with the design, fabrication, and measured performance characteristics of a single-stage AOTF that utilizes a weighted-aperture SAW slot waveguide in YX-LiNbO(3) substrate at the optical wavelength of 1.55 mum and the acoustic center frequency of 175 MHz are reported. The measured sidelobe level is -13.6 dB and the measured FWHM bandwidth is 26 A, as compared to the theoretical values of -15.0 dB and 15 A, respectively. The RF drive power was measured to be 1.0 W at a mode-conversion efficiency of 100%     

SPUDT filters for the 2.45 GHz ISM band

Filters based on using single-phase, unidirectional transducers (SPUDT) consisting of lambda/4 and wider electrodes are presented. The design variants exploit the significant difference between the reflectivity of short-circuited lambda/4 electrodes and that of floating wide electrodes on 128 degree lithium niobate (LiNbO3). The surface acoustic wave (SAW) devices operating at 2.45 GHz have critical dimensions of about 0.3-0.4 microm, accessible to standard optical lithography. When matched, the fabricated SPUDT filters exhibit minimum insertion losses of 5.5-7.9 dB together with 3 dB passbands of 89-102 MHz. The majority of the insertion loss can be attributed to the attenuation on free surface and inside the grating, and to the resistivity of the electrodes.     

SAW ring filters with insertion loss of 1 dB

This paper presents low loss ring SAW filters on 49°YX, 64°YX, 128°YX LiNbO₃ with reflective multistrip couplers (RMSCs). Using the RMSCs with 3 electrodes per λ (λ is the SAW wavelength at the center frequency) and the self-matching approach, when the static capacitance of the IDT is compensated by the acoustic radiation susceptance, the ring filters have shown very low insertion loss of 0.8-1 dB, 3-dB fractional bandwidth of 2-5% with very low ripple of 0.1 dB, stopband attenuation over 50 dB at 10-33% offset from the center frequency of 45 MHz. In a 50 ohm system, 148, 164, 172 MHz ring filters on 128°YX for low power transceivers have provided an insertion loss of 1 dB, 1 dB bandwidth of 1.8-2 MHz, stopband attenuation over 55 dB at ±25 MHz offset from the center frequency. Two cascaded filters at 164.5 MHz have shown insertion losses below 3 dB and stopband attenuation over 90 dB at ±25 MHz, offset from the center frequency. The chip size is 5×4×0.7 mm     

新建立的衰减计量国家标准装置

为了满足大衰减量值的溯源，研制成功了新的PAS-1型衰减测量接收机和新的国家标准装置。文中论述了该标准装置的原理及特点，详细分析了它的不确定度。试验表明：该标准装置频带可扩展到18GHz，量程达100dB，在100dB量程的测量不确定度优于0．1dB，置信概率为95％。     

Pure shear horizontal SAW biosensor on langasite

The undetected introduction of pathogens into food or water supplies can produce grave consequences in terms of economic loss and human suffering. Sensitive and selective sensors capable of quickly detecting microbial pathogens are urgently needed to limit the effects of bioterrorist incidents, accidents, or pollution. Shear horizontal surface acoustic wave (SH SAW) devices provide an attractive platform for the design of microbial biosensors that function in liquid media, where Rayleigh-type modes are rapidly attenuated. This paper reports on an exploratory SH SAW delay line designed and fabricated on langasite, La3Ga5SiO14 (LGS), along the novel Euler propagation direction (0 degrees, 22 degrees, 90 degrees). A liquid chamber was fabricated and attached to the top surface, and the device was submitted to liquid and biochemical tests. Moderate (6 dB) additional attenuation of the transmission coefficient, /S21/, was consistently observed when the SH SAW delay line was assembled in the test fixture and submitted to the liquid tests, indicating that LGS is an attractive candidate for liquid sensing. Sensor selectivity can be achieved by integrating the LGS SH SAW delay line with a biochemical recognition layer. A test setup was implemented for the characterization of LGS SH SAW-based biosensors. The delay line response to biomolecule binding was shown by detection of sequential binding of proteins to the SH SAW device delay path. The biotinylated sensor was exposed sequentially to biotin-binding deglycosylated avidin, biotin-modified rabbit IgG, and goat anti-rabbit IgG antibody. As each protein was bound to the sensing surface, marked changes in the delay-line phase were recorded. The reported results demonstrate the capability of these devices to act as biochemical detectors in aqueous solutions, and this work represents the first effort using the novel material LGS in SAW-based biosensor technology.     

Sidelobe cancellation technique for achieving high rejection in SAW filters

A new technique called sidelobe cancellation technique (SCT) to achieve high stopband rejection in SAW filters is described, for varying requirements of shape factor and sidelobe levels, by using an eigenfunction approach. Cosine series functions with improved sidelobe levels are employed. Each design is characterized by the order of the cosine series and the number of functions used to obtain a particular shape factor and rejection. Limited trimming of shape factor also can be achieved in each design. The filters described here are compared with the Kaiser window filter and are found to be efficient. Measured response of a prototype SAW filter using the approach given in this paper is plotted, and it is in good agreement with the simulated response     

Viscoelastic properties of polymer films on surface acoustic wave organophosphorous vapor sensors

This work investigates the viscoelastic properties of the fluoropolyol (FPOL) polymer on the surface acoustic wave (SAW) organophosphorous vapor sensors. A complex shear modulus is used to express different polymer types (glassy, glassy-rubbery, and rubbery). The different polymer types leads to different propagating properties of SAW, such as attenuation change and velocity shift. Calculation results indicate that the glassy-rubbery film exhibits the highest sensitivity for detecting organophosphorous vapor. The thicker the glassy and glassy-rubbery film implies a higher sensitivity. Moreover, the SAW vapor sensor based on the rubbery film represents the response of acoustically thick layers which has a peak in attenuation with an increasing vapor adsorption. The selectivity factor between DMMP (10 ppm) and H₂O (40%RH) is so low that the selectivity of FPOL film towards water is ineffecient. However, the selectivity factor between ethanol (10 ppm) and DMMP (10 ppm) is as high as 2512, thus confirming that the selectivity of FPOL film towards ethanol is good. Therefore, a precise and dry humidity control in the sensors system with FPOL coating is required.