Possible design procedure for low-loss 180 degrees reflecting arrays in SAW devices

Medium-loss SAW filters with synthesized characteristics

Medium-loss surface acoustic wave (SAW) filters based on the in-line dot array structure are reported. This configuration is very amenable to device synthesis, potentially to specifications comparable to conventional high-loss designs. The design procedure fully allows for multiple reflections within the reflecting arrays and can handle chirps. The devices have achieved up to 0.2-dB RMS passband ripple and 32-dB rejection after direct coupling and multistrip coupler (MSC) reflection are removed. Passband loss (6-8 dB) could be reduced if transducer and MSC loss (3 dB) can be improved. The devices also have sharp cutoffs, and fairly uniform input and output impedances in the pass and transition bands. The reflectors chosen for the reflecting arrays are thin metal dots. The results of computation and experimental verification of dot reflectivity and velocity change for the particular size of dots and dot pattern used are given. The device design, and the measured results are discussed.

Phase correction of SAW ILRACs and RACs using Langmuir-Blodgett films

A novel method of adjusting surface-acoustic-wave (SAW) velocity in reflective array pulse compressors (RACs), including in-line devices (ILRACs) and hence correcting fabrication errors, is described. The velocity change is effected by depositing Langmuir-Blodgett films (LBFs) on the surface of the device. An accurate, stepped thickness profile can be created, enabling position-dependent velocity errors to be corrected. Experimental results for the velocity perturbation per LBF layer are first given together with data on temperature, humidity and age dependence. This is followed by the theory required to calculate the necessary thickness profile, including retrofitting to existing devices and allowing for the limitation to positive integer numbers of layers. Finally, experimental results are presented. In one device, simulated compressed pulse sidelobe levels are reduced by 19 dB.

Addendum to 'Possible design procedure for low-loss 180 degrees reflecting arrays in SAW devices' (Jan 88 57-60)

The original paper (ibid., vol.35, no.1, p.57-60, 1988) describes how multiple reflections can be allowed for in SAW reflecting arrays. Comments are now made on the error in frequency response due to truncation of the array to finite length, and on multiple transits between transducers via the array.

Correction factor for low-loss 180 degrees reflecting linear chirp arrays in SAW devices

Low-loss, 180 degrees -reflecting linear chirps with constant or slowly varying weighting and large time-bandwidth product are analyzed. Multiple reflections are fully taken into account, giving a universal correction factor as a function of array parameters. This should enable such chirps to be designed without making iterations. Surface acoustic-wave (SAW) device layouts making use of the 180 degrees arrays are suggested.