Low-loss SAW Research Articles

High-Steepness and Low-Loss SAW Filters With Fractional Bandwidth From 3.7% to 12.4% on a Monolithic X-Cut LiNbO3/SiO2/SiC Substrate

High-Steepness and Low-Loss SAW Filters With Fractional Bandwidth From 3.7% to 12.4% on a Monolithic X-Cut LiNbO₃/SiO₂/SiC Substrate

A Low-Loss Wideband SAW Filter With Low Drift Using Multilayered Structure

This research aims to overcome the tradeoff between bandwidth, temperature stability of frequency, and loss in surface acoustic wave filters. A novel multilayered structure, SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Cu-grating/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15^{\circ }~{Y}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /sapphire, is proposed. Resonators based on the multilayered structure are studied theoretically and experimentally. The results show that the multilayered structure can sufficiently suppress leaky wave and spurious responses, which significantly degrade the performance of devices based on conventional SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Cu-grating/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15^{\circ }~{Y}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> structure. Fabricated resonators exhibit high performance including low frequency drift, large coupling, and large quality factor. A multilayered structure filter is designed, fabricated, and measured, resulting in a flat and clean passband with a small minimum insertion loss of only 1.01 dB. A large 3-dB fractional bandwidth of 14.74% is achieved, as well as a low temperature coefficient of frequency of approximately −18 ppm/°C. This research proposes a useful solution for high-performance filters in fifth-generation networks.

Study of a Low Insertion Loss SAW Filter with SPUDT Structure Using YZ-LiNbO&lt;sub&gt;3&lt;/sub&gt;

To meet the demand for low insertion loss, we have studied a SAW filter with single phase unidirectional transducer (SPUDT) structure using piezoelectric materials YZ-LiNbO3. This article shows the simulation results of the SAW filter using Matlab software with the SAW velocity 3488m/s and electromechanical coupling constant 0.048. The theoretical center frequency is 72MHz and the 3dB bandwidth is 2.9MHz. The total frequency response of the entire SAW device is the product of the frequency response of the input transducer and the output transducer. It can be seen from the simulation results that the magnitude response and the linear phase response of interdigital transducer are consistent with the theoretical values and the minimum insertion loss reaches 5.43dB. So the low insertion loss SAW filter with SPUDT structure using YZ-LiNbO3 adapts the requirements of the radar, communications and other electronic systems.

1P3-3 Study on Low-Loss SAW Gas Sensor Consisting of Resonators with Large Spaces between IDTs and Reflectors(Poster Session)

1P3-3 Study on Low-Loss SAW Gas Sensor Consisting of Resonators with Large Spaces between IDTs and Reflectors(Poster Session)

Optimal Design of an RSPUDT-Based SAW Filter with Constant Group Delay

This paper describes the application of resonant single-phase unidirectional transducers (RSPUDTs) to the development of low-loss SAW filters with constant group delay in transition bands as well as in the passband. A low-loss SAW filter with constant group delay was designed and fabricated on a 128 degrees YX-LiNbO3 substrate. Experimental results were in good agreement with the design; the group delay deviation of 20 ns was realized over the range of +/-8 MHz at the center frequency of 512 MHz. The minimum insertion loss and -3 dB bandwidth were 4.3 dB and 8.5 MHz, respectively. The application of this technique is also extended to develop high-performance wideband filters employing quasi-slanted interdigital transducers.

Metal strip reflectivity and NSPUDT orientations in langanite, langasite, and gallium phosphate.

New materials of the trigonal 32 class have received much attention recently, due to their quartz-like temperature behavior and the promise of higher electromechanical coupling coefficients. The magnitude and phase of the reflection coefficient of the metal strips that form the SAW transducers and reflector structures is a critical parameter that allows proper device designs and optimal material surface orientation. This paper describes an investigation of the magnitude and phase of the SAW metal strip reflectivity in some new materials and along new orientations. The materials are langanite, langasite, and gallium phosphate. The results are presented as contour plots of the magnitude and phase of the reflection coefficient. In addition, the phase velocity, temperature coefficient of delay, electromechanical coupling coefficient, and power flow angle are given, thus allowing proper orientation selection for SAW device designs. The results presented highlight the reflection coefficient calculations in the selection of natural single-phase unidirectional transducer orientations (NSPUDT) for these new materials. As a result of the present work, reflection coefficient magnitudes five times larger than those of the well-known quartz NSPUDT orientation (Euler angles: 0 degrees 132.75 degrees 25 degrees) can be obtained with the new materials, for orientations where the optimum NSPUDT reflection coefficient phase criterion is met. The new materials discussed here provide an opportunity to design shorter- and higher-bandwidth devices due to: the increased electromechanical coupling coefficient; the higher reflection coefficient; and the lower phase velocities; while maintaining the excellent temperature insensitivity characteristic of quartz. The orientation regions suggested in this paper for the new materials are thus very promising for low-loss, high-performance consumer and communications SAW designs, such as NSPUDT filters, resonator-based filters, and other devices that can benefit from a high metal strip reflectivity.

A new design concept for low-loss SAW filters based on different-width split-finger SPUDT

A new design concept of a single-phase unidirectional transducer (SPUDT) has been investigated in this paper. The concept has been realized by using a newly developed different-width split-finger-SPUDT structure, in which the adjacent electrode fingers are given different widths. A symmetrical radiation conductance is obtained by adjusting the electrode finger positions. Computer simulations have confirmed that the electrical 1/Q factor and the directivity have a tradeoff relationship with regard to the finger-width ratio, depending on the metallization thickness used. From the simulation results, the optimum finger-width ratio for achieving a low insertion loss has been obtained. An experimental filter was constructed, which shows good performance, with the insertion loss improved by 1 dB when compared to a conventional electrode-width-controlled-SPUDT filter on an ST-cut quartz substrate.

Anomalous asymmetric acoustic radiationin low-loss SAW filters

The experimental discovery of a novel acoustic loss mechanism in SAW filters at RF frequencies is reported. The phenomenon is characterised by an unexpected spatial distribution of the surface-acoustic wave field. The observation and measurements were performed with a specially constructed scanning laser-interferometric probe. Current simulation methods and known phenomenological models applied to SAW resonators have no predictive ability to describe the discovered effect.

Super high electromechanical coupling and zero-temperature coefficient surface acoustic wave substrates in KNbO3 single crystal

This paper describes a super high electromechanical coupling SAW propagating on potassium ruobate (KNbO 3 ) substrate and its applications for low-loss, wide band and temperature stable SAW filters. KNbO 3 has large piezoelectric constants. We obtained the electromechanical coupling coefficient (K 2 ) of 0.53 for SAW in Y-cut X-propagating substrate theoretically and experimentally. It is about 10 times as large as that in LiNbO 3 . Moreover, we obtained a zero temperature characteristics around room temperature in rotated Y cut substrate. Experimental results of wide band SAW filters show low loss and temperature stable characteristics. The bandwidth is about 20% and insertion losses are less than 2∼6 dB.

SAW device applications of longitudinal leaky surface waves on lithium tetraborate.

The possibility of high frequency SAW device applications of longitudinal leaky surface waves (LLSW) on lithium tetraborate (Li2 B4O7; LBO) is investigated in this paper. An electrical equivalent circuit model (ECM) is extended in order to consider effects of bulk wave scattering for the LLSWs. The equivalent circuit parameters used in the extended ECM for designing the LLSW devices are directly determined from numerically calculated dispersion curves. For applications of the LLSW, high frequency SAW filters on LBO with the Euler angles (0&deg;, 47.3&deg;, 90&deg;) are demonstrated. As examples of the high frequency devices, 1.5 GHz and 1.2 GHz SAW filters using the mode are designed by using the extended ECM, and fabricated by using conventional patterning processes. One is for the filter of the global positioning system (GPS), another is for the 1.2 GHz band data transmission radio system in Japan. As a result, low loss SAW filters can be obtained easily without submicron fabrication techniques by using the LLSWs on LBO. Furthermore, the frequency response calculated by the extended ECM are in a good agreement with the experiments.

A low loss SAW matched filter under the compensation method of temperature deviations

A low loss SAW matched filter under the compensation method of temperature deviations

Design of mobile phone IIDT-type SAW filters with block-like distribution of transducers

Wide band low-loss SAW filters employing interdigitated interdigital transducers (IIDT's) and suitable for cellular radio applications are presented. After an investigation of the many design parameters that have to be taken into account, a new block-like distribution of transducers within the IIDT structure is studied in detail. This distribution leads to almost identical impedances at the filter input and output. An automatic optimization algorithm is also described. In particular, the finger numbers and the withdrawal weighting functions employed to increase the stopband rejection have been optimized by this algorithm. Filters fabricated on 36/spl deg/ rot Y, X-LiTaO/sub 3/ exhibit fractional bandwidths of up to 5.2% with passband ripples smaller than 1 dB at a center frequency of 500 MHz. The minimum insertion loss and the stopband rejection obtained were 1.8 and 23 dB, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Unidirectionality in dispersive SAW transducers

Low loss SAW filters can be built making use of unidirectionality and selfmatching of dispersive transducers. The origin of unidirectionality lies in internal reflections between electrodes. The calculated loss level may be as low as 0.08 dB in down chirp double dispersive IDT filters.

Low-loss SAW IF filters with new unidirectional IDTs used in digital mobile radios

A new type of unidirectional IDT having both excitation and reflection electrodes within each section of one wavelength (λ o ) was developed. High-performance SAW IF filters used in digital mobile radios with low insertion losses of 3.6 dB at 70 MHz and 3.8 dB at 250 MHz centre frequencies were realised using ST-cut quartz substrates

IIDT Type Low-Loss SAW Filters Using Withdrawal-Weighted Transducers

This paper describes a method of designing IIDT SAW filters with suppressed sidelobes and reduced insertion loss. The method employs withdrawal-weighted transducers which have almost the same frequency response in pass band and different trap-frequencies in stop bands. An 880 MHz filter was designed and fabricated according to the proposed method. The sidelobe suppression of 25 to 35 dB, the minimum insertion loss of 1.6 dB, and the 0.5 dB bandwidth of more than 20 MHz were realized.

Design of Phase Shifters for a Group Type Unidirectional Transducer

A group type unidirectional transducer (GUT) is useful for a low loss SAW filter. The four-port and two-port network expressions for the GUT are presented, and interaction between the inphase and quadrature ports is revealed analytically. The conditions for perfect unidirectivity are also described. The design procedures of the electrical phase shifters performing perfect unidirectivity are shown both in series and parallel configurations for any geometrical phase shift except π.

GHz-Range Unidirectional Low-Loss SAW Filters and Fine Lithography Technology

The frequency ranges for mobile telephone communication are now in 1 GHz and in the next stage will be in 2∼3 GHz. Various kinds of communication systems and signal processing systems also require high frequency devices, for example, the timing pick-up filter for the light wave communication must be one of 10 GHz. For these systems, low-loss and wide-band filters or temperature stable filters are required. In this paper, GHz range SAW IDT transducers and filters together with fine-lithography techniques are described.

Design of High-Frequency and Low-Loss SAW Filter Employing Multiple IDTs

This paper describes an accurate design method for the multi-IDTs type of SAW filters by equivalent circuit model analysis. Distances between IDTs are important design parameters to take account of mutual influence among all IDTs, especially in case of using single electrode transducers. Then, three-port admittance matrices of IDTs and two-port ones of SAW propagation paths are connected to compose a four-port admittance matrix. Iterative calculations of a four-port model are performed to determine numerous design parameters. Experimental results are in good agreement with calculation results. The experimental rejection level, however, is a little smaller than the calculated one because of electro-magnetic feed-through. Besides, the insertion loss is larger than the calculation in amount of two or three decibels.

Some new approaches to improved low-loss SAW bandpass filters

In recent years several new forms of low-loss SAW bandpass filter have been devised which are suitable for mass production. The letter describes a variety of modifications to these basic configurations which can lead to superior performance in various important respects, including increased fractional bandwidth and greater stopband rejection.

Low-loss SAW filters with 70 dB sidelobes using cascaded and weighted single-phase unidirectional transducers

Close-in sidelobe suppression was attained in low-loss SAW filters with single-phase unidirectional transducers (SPUDTs), by Dolph-Chebyshev weighting of the SPUDT rungs. Two such structures electrically cascaded in a 1.5% bandwidth filter yielded an overall 70 dB sidelobe level, with an insertion loss of only 8.5 dB.