Coupling-of-modes (COM) theory is applied to the analysis of low-loss SAW filters with single-phase unidirectional transducers (SPUDT’s). The filter response function is then derived from complex matrix “building block” relations for grating reflectors, IDT’s, and SAW transmission line sections. Experimental verification is illustrated for SO-MHz prototype filters with l-1.5-percent fractional bandwidths, fabricated on lithium niobate with up to ten IDT “rungs” in both input and output SPUDT’s. Insertion losses of as low as 2.6 dB could readily be obtained in such designs, which can be applied to either split-electrode or single-electrode IDT geometries.

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

A novel, 900-MHz SAW (surface acoustic wave) microstrip antenna-duplexer designed for use in European mobile radio systems is presented. The duplexer consists of a transmitter SAW filter, two receiver SAW filters, a low-noise receiver amplifier, and a duplexing microstrip circuit. A dual-track filter design using interdigital transducers for track coupling provides low insertion loss (5 dB), small passband ripple (+or-0.5 dB), high stopband rejection (50 dB), and small chip-size (TO-39 package). The filters were fabricated on 36 degrees -rotated YX-LiTaO/sub 3/ substrates with a photolithographic technique. Due to the design of the microstrip duplexer, the selectivity of the front end is enhanced by 15 dB. >

A 900 MHz SAW microstrip antenna-duplexer for mobile radio

Surface acoustic wave (SAW) filters using group-type unidirectional transducers on LiNb03 have been built with 5 dB loss and 0.01 dB in-band ripples. An impulse model is used to synthesize the transducers and calculate the values of the tuning elements for matching and phase shifting. The model agrees well with experimental results. Filters were tested at center frequencies of 360 and 650 MHz with fractional bandwidth of about 3%. The differences in filter characteristics for both Y-2 cut and 128 -rotated Y-X cut LiNbOJ are examined. By proper weighting of the transducers, proper fabrication control and careful choice of the matching elements, the insertion loss can be as low as 5 dB, the ripples as low as 0.01 dB (peak-to-peak) and the out-of-band-rejection as high as 40 dB.

Low-Loss, Low Ripple SAW Filters Using Group-Type Unidirectional Transducers

Low lossSAW filtershavebeen u sedina remarkable number of system applications The frequency ranoe for low loss devices has been from 30 MHz to 440 MHz 1 to 2 GHz devices can be manufactured using h igher resolution fabrication techniques Results fromunweighted, lithium niobate, and STcut Quartzdevices at 1233 FlHz are presented Weighting techniques for frequency sidelobe suppression are also discussed along with results from a 1233 MHz weighted ST-Quartz device

L-Band Low Loss SAW Filters

Low lossSAW filtershavebeen u sedina remarkable number of system applications. The frequency ranoe for low loss devices has been from 30 MHz to 440 MHz. 1 to 2 GHz devices can be manufactured using h igher resolution fabrication techniques. Results fromunweighted, lithium niobate, and STcut Quartzdevices at 1233 FlHz are presented. Weighting techniques for frequency sidelobe suppression are also discussed along with results from a 1233 MHz weighted ST-Quartz device.

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.

D.C. Malocha

Papers

Tuning of Group Type Unidirectional Transducers