Group-type Unidirectional Transducer Research Articles

Cascading formulas for identical transducer P-matrices

Formulas are derived for the P-matrix of a cascade of identical acoustic transducers, in terms of the P-matrix of one elementary transducer. The derivation makes no assumptions other than reciprocity and the validity of the P-matrix description. Consequently, the results are valid for a wide range of cases, such as simple SAW gratings or group-type single-phase unidirectional transducers (SPUDT's), where each element is a transducer plus grating. The formulas are used to derive a general relation for the directivity of a SPUDT in terms of the directivity of one period.

Narrow‐gap and multiphase interdigital transducer using anodic oxidation

AbstractA method of fabricating a narrow‐gap interdigital transducer and of a multilevel interconnection using anodic oxidation is discussed, which is a key technology for SAW devices with high performance. This process can cope with the two problems of its high‐frequency application and fabrication of an advanced electrode structure. As an example, this method is applied to a group‐type unidirectional transducer (GUDT). The process for a high‐frequency performance by having a narrow‐gap structure and no loss without meander‐line electrodes is proposed.A prototype filter with GUDT has been fabricated by using this method and a good result of an insertion loss of 2 dB at a center frequency of 700 MHz was obtained. This result has confirmed that GUDT is useful for low loss and with very small ripple where no meander‐line electrode is used. The present method has demonstrated its high applicability.

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.

Directivity of group-type single phase unidirectional SAW transducers

It is shown that the centre-frequency directivity for a SPUDT comprising conventional transducers alternating with reflecting gratings is determined simply by the grating reflection coefficient. This applies if the transducers and gratings are varied to weight the device. If the grating strips are all identical the directivity is proportional to the total number of grating strips. >

Sampling effect of distributed reflector arrays within a single-phase unidirectional SAW transducer

A noteworthy feature of the group-type single-phase unidirectional transducer is that it can permit wideband low-loss surface-acoustic-wave (SAW) comb filter operation. This is shown to be due to the sampling imposed by the distributed reflector gratings. The capability is illustrated theoretically and experimentally for a 65-MHz comb filter on 128 degrees Y-X lithium niobate, with 5 comb modes of 585-kHz bandwidth each, together with 2.6-dB minimum insertion loss and overall 50% fractional bandwidth.

A low-loss SAW-TV-IF filter with an extended impedance matching range

A novel low-loss SAW (surface acoustic wave) filter for an intermediate frequency (IF) circuit in a color TV receiver has been developed. It consists of an apodized bidirectional and an unapodized group-type unidirectional transducer. The unidirectional transducer is designed to use different numbers of finger pairs in sending and reflecting electrodes for extension of the impedance-matching range. A thin-film capacitor for use as a phase shifter is monolithically fabricated on a 128 degrees Y-X LiNbO(3) substrate. A low insertion loss (11.3 dB) and impedance matching without adjustment are achieved at the same time without increasing the device chip size or number of electrical parts.

Surface Wave Reflection from Metal-Strips and Transducers

Various contributions to the surface wave reflection, viz., piezo-shorting, mass and stress loading and electrical regeneration, are treated appropriately for the estimation of overall reflection from metallic strips and transducers. The effect of mass loading is studied for metal strips deposited on YZ LiNbO3 and ST-X quartz substrates. A simple theory is developed which predicts zero reflection for an open aluminium strip and short gold strip on YZ LiNbO3 for specific values of metallisation ratio. The theory also describes the reflection process in ordinary bi-directional and group type unidirectional transducers. Experimental results obtained on YZ LiNbO3 substrate are in close agreement with the theoretical predictions. The theory may prove to be useful in the design of SAW transversal and resonator filters.

A New Unidirectional SAW Transducer with a Simplified External Network

A group-type unidirectional SAW transducer with new electrode constitution and new phase shifter has been developed. It is designed to have non-quadratic geometrical phase difference between sending and reflecting electrodes and the electrodes have different finger pairs. In addition, the phase shifter is constituted by only one capacitor and is fabricated on the same piezoelectric substrate. Consequently, inductors of the external network can be reduced. Furthermore, as suppression of backward response is more optimal, the transducer eliminates any adjustment with low loss and low ripple.

Wide-Band and Low-Loss Unidirectional SAW Filter

An improved group-type unidirectional SAW transducer has been proposed which reduces the geometrical phase difference between sending and reflecting electrodes. A 90° phase shifter delays the phase of the reflection side electrodes. In consequence, both the wider frequency band width for triple transit suppression and low insertion loss can be achieved.

Scattering Parameters of Interdigital and Group Type Unidirectional Saw Transducers

In this paper, the frequency dependence of scattering parameters of simple bidirectional transducers and group-type unidirectional transducers have been studied using cross-field model equivalent circuit. The analytical expressions for scattering parameters developed are simple for the purpose of computation. The scattering parameters were also measured experimentally for transducers fabricated on Y-cut, Z-propagating LiNbO3 substrate. The experimental curves of the different scattering parameters versus frequency agree generally with the theoretical curves.

Novel realisation of an automatic transmit-receive switch and two bandpass filters by a single SAW filter

In the letter we describe and demonstrate a completely new application of SAW filters in present-day communication systems to realise a kind of transmit-receive switch (TRS). The TRS using the SAW filter works well up to expectations, replacing the required two bandpass filters and an antenna directional coupler. To do this the undesired reverse propagation sidelobe (higher) of a group-type unidirectional transducer (GUDT) has been used to advantage. The theoretical and experimental results are found to be in one-to-one correspondence.

Improved feed network for group-type unidirectional transducers

In the letter we propose a phasing and matching network for group-type unidirectional transducers (GT-UDTs) which takes into account the electroacoustic interactions between the two phases of the GT-UDT. In comparison with analogous feed circuits from the literature, this network represents an improvement as far as the reduction of the residual fluctuations in the passband frequency response of a GT-UDT device is concerned.

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.

Group-type Unidirectional Acoustic Surface Wave Filters Using Distance Weighting Techniques

We earlier proposed distance weighting techniques which have better characteristics than apotization techniques. The distance weighting technique works best for reducing weighting and diffraction loss. A group-type of unidirectional transducer also has low loss characteristics. In this paper we investigate a low loss filter combining the distance weighting techniques and group-type unidirectional transducer.

GHz Band SAW Filter Using Group-Type Unidirectional Transducer

Gigahertz frequency surface acoustic wave (SAW) filters using group-type unidirectional transducers on LiNb03 (128O rotated Y-cut, X-propagation) are investigated. Unfavorable effects caused by stray capacities are analyzed through the equivalent circuit, and an index for design procedure is obtained. The fabrication of the filters is carried out by use of polymethyl metharcylate @MA) resist and electron- beam exposure. The insertion loss is 10 dB at 1.025 GHz in 50 S2 sys- tem. Moreover, by improvement of the pattern arrangement, a fiter having a 7-dB insertion loss and 0.2dB ripple for 1.23 GHz is obtained.

Experimental Results on SAW Filters with One Bidirectional and Two Unidirectional Transducers

SAW band pass filters were examined, in which three-transducer configurations consisting of one bidirectional transducer for an input and two group-type unidirectional transducers for an output are employed. The configuration has advantages, such as easy design for frequency responses, a low insertion loss and easy fabrication. Experiments were carried out using ceramic and LiNbO3 substrates. An insertion loss of 6.5 dB and ripples of group delay less than 100 nsec were obtained, showing that the configuration can be applied to a TV-intermediate-frequency filter with a high performance. It has been found that the good results are due not only to the directivity of the unidirectional transducers, but also to the inherent properties of the three-transducer configurations. Therefore, the improvements of the matching circuit and the phase shifters will result in better performance.

Tuning of Group Type Unidirectional Transducers

Abstroct-A simple tuning network is presented for tuning of group type unidirectional transducers. The method of tuning described uses a maximum of two elements and in special cases requires only a siigle external element. Experimental results for a filter having a 6.3dB insertion loss and a triple transit echo suppressed -44 dB using the described method verifies the analysis.