Gunter Dr. Müller

A new low loss SAW filter structure with extremely wide bandwidth for mobile communication systems

The authors present a low-loss surface-acoustic-wave (SAW) filter with a dual-track configuration which is characterized by a novel arrangement of interdigital transducers (IDTs) and reflectors in each acoustic track as well as a special electrical connection of the IDTs. Broadband filter characteristics can easily be achieved by using chirped components. The inherently good stopband rejection of the new structure has been further improved by applying proper weighting techniques to the IDTs and reflectors. A filter with a relative bandwidth of 10% and a center frequency of 200 MHz has been designed by means of a novel synthesis method. The filter has been fabricated on 128 degrees Y-X LiNbO/sub 3/. A minimum insertion loss of 4 dB, a small passband ripple of about 1 dB, and a stopband rejection of better than 35 dB were measured. Excellent agreement between simulation and measurement has been found.<<ETX>>

Design of a low loss SAW reflector filter with extremely wide bandwidth for mobile communication systems

The design and performance of a low-loss surface acoustic wave (SAW) reflector filter are presented. The structure is a dual-track configuration incorporating two interdigital transducers (IDTs) and reflectors in each track. Extremely wide bandwidth can be obtained if chirped IDTs and reflectors are used. From the theoretical conditions for low-loss operation of the reflector filter, a design rule for the distances between the chirped components and for their lengths is derived. Because the transfer function of the filter is predominantly determined by the reflectors, a new synthesis method for chirped reflectors has been developed. For the design of the reflectors, phase-weighting and finger-width-weighting techniques were used to reduce passband distortions and improve the shape factor and stopband rejection. The filter has been fabricated on 128 degrees YX-LiNbO/sub 3/. The center frequency and fractional bandwidth are 200 MHz and 100%, respectively, the minimum insertion loss is 4 dB, a passband ripple is about 1 dB, and the stopband rejection is better than 35 dB. >

A novel SAW filter for IF-filtering in DECT systems

We have developed an improved SAW filter for IF-filtering in DECT systems. The filter is a two track reflector filter using EWC-SPUDTs as in- and output-IDTs and reflectors in the center of each track The propagation path of the SAW is folded in order to make better use of the total chip length. A similar configuration with identical reflectors in the tracks is known in literature, however, we used different reflectors in the tracks and this way we could improve the filter performance and especially the stop band attenuation considerably. The SPUDTs are withdrawal weighted, for the reflector design we used an electrode width weighting technique. The filter fits into a very small QCC10 package (9.1/spl times/7.1/spl times/1.8 mm/sup 3/) and has high performance so that it can be used in a DECT base-station, too. The substrate is LiTaO/sub 3/, X112.2Y, the center frequency is 110.59 MHz, the minimum IL is 8 dB typically, the 3-dB-bandwidth is 1.1 MHz and the stopband attenuation is better than 40 dB.

Experimental determination of the complete scattering matrix of SAW reflectors by a new deembedding method

We present a new measuring method which is capable of determining the complete scattering matrix of a surface acoustic wave (SAW) 180° reflector. Additional to the reflector to be investigated only one interdigital transducer (IDT) has to be designed for SAW excitation. These two elements have to be combined in several different arrangements. Exclusively electrical measurements with a commonly used network analyzer are necessary. From these measurements the acoustical two-port description can be evaluated using a deembedding method which will be described. Furthermore, error estimations have been worked out allowing for the assessment of the results. Experimental results demonstrate the feasibility of our procedure

Extended phased array model for the calculation of mechanical bulk wave excitation in SAW reflectors

A new model for mechanical conversion of surface acoustic waves (SAWs) into bulk acoustic waves (BAWs) in SAW reflectors is presented. It is based on the far field computation of a bulk wave source distribution. These sources are derived from a one-dimensional P-Matrix formalism, which is known to be an accurate description of SAW propagation under metallic gratings. The model takes into account the anisotropy of the piezoelectric substrate and is not restricted to a specific acoustic wave type. Furthermore, arbitrary reflector geometries can be considered allowing for the modeling of finger width-weighted, position-weighted and chirped reflectors which are increasingly used in low loss SAW filters. By the use of our model, for the first time bulk wave losses at harmonic stop band frequencies can be predicted and characterized.<<ETX>>