Low-loss SAW Filters 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

Study of a Low Insertion Loss SAW Filter with SPUDT Structure Using YZ-LiNbO<sub>3</sub>

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.

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.

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°, 47.3°, 90°) 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.

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.

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.

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.

Analysis and Design of Low-Loss SAW Filters Using Single-Phase Unidirectional Transducers

Analysis and Design of Low-Loss SAW Filters Using Single-Phase Unidirectional Transducers

New low-loss broadband SAW filter using unidirectional IDTs with U-shaped MSCs

A new low-loss broadband SAW filter is presented. A new configuration using one pair of electrically connected IDTs with an optimum number of fingers, as well as unidirectional IDTs with U-shaped MSCs, is described. Experimental results with bandwidth as wide as 10% and loss as low as 3 dB are achieved. Very accurate computer-aided design of a low-loss filter with MSCs is obtained.

Erratum: 1.03 GHz operation of a low-loss SAW filter using 3-phase unidirectional transducers with thin dielectric layered feed electrodes

Erratum: 1.03 GHz operation of a low-loss SAW filter using 3-phase unidirectional transducers with thin dielectric layered feed electrodes

New low-loss SAW filter using internal floating electrode reflection types of single-phase unidirectional transducer

A new single-phase unidirectional transducer utilising the difference between excitation and reflection positions caused by the floating electrodes of open and short metal strips inserted into the interdigital transducer within a half wavelength is described.

Low-loss SAW filter using internal reflection types of single-phase unidirectional transducer

A new single-phase unidirectional transducer utilising the difference between excitation and reflection positions caused by the change of the electromechanical coupling coefficient within a half or one wavelength is described.

New phase-shifting technique for group-type unidirectional transducers used in surface-acoustic-wave filters

The letter reports a novel method of phase shifting useful in the group type of unidirectional transducers used for the design of low-loss SAW filters. This technique utilises the thin-film capacitance present between the newly described configuration of the feed-electrode layers as an essential element of the required phase shifter. The stray capacitance existing between the feed electrodes is used to advantage. The theoretical and experimental results of one of the filters fabricated are presented.

1.03 GHz operation of a low-loss SAW filter using 3-phase unidirectional transducers with thin dielectric layered feed electrodes

Successful working of a 3-phase unidirectional transducer (TPUDT) SAW filter at 1.03 GHz, without using any airgap crossovers, is reported in the letter. A thin-film capacitance existing between the feed electrodes of the transducers is used to advantage, as an essential element of the required phaseshifting network. The minimum insertion loss is found to be 2.0 dB. The filter is believed to have wide applications in the present and future communication systems requiring low-loss bandpass filtering.