Problems encountered in high-frequency surface-wave devices

Propagation loss and pattern resolution are well recognized as serious impediments to the realization of practical surface-wave devices at frequencies greater than 1 GHz. In addition, a number of lesser-known problems become critical. Both propagation loss and dispersion are strongly affected by the character of the substrate surface. Damage layers on LiNbO3 with a thickness of only a few tens of angstroms cause velocity dispersion of the order of 0.001 at 1 GHz. This dispersion introduces troublesome phase errors in surface-wave devices. Phase errors also result from the limited accuracy of electron-beam and interferometer-controlled pattern generators. Dynamic range is restricted by the occurrence of acoustic nonlinearities at relatively modest input powers. The magnitude of these effects can be estimated and, in many cases, special techniques are available for alleviating these problems and achieving successful high-frequency devices.