Propagation loss in electrostatically variable SAW delay lines

Variations in SAW time delay due to an applied dc electric field has been suggested as a means for achieving the phase shift needed for each radiating element in phased-array antennas. Important device parameters are: (1) insertion loss and, (2) sensitivity of delay change to dc terminal voltage. These parameters can be in competition, in that device modifications intended to improve one parameter may make the other worse. These parameters are considered for the normal-field configuration, and for the in-plane configuration in which both dc electrodes are on the same surface as the SAW. The in-plane configuration can have high-voltage sensitivity if the electrodes are close together, but diffraction loss for this case is found to be large for long path lengths. Methods for limiting diffraction loss without reducing voltage sensitivity are investigated.