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.