Abstract :
Summary form only given, as follows. A number of approaches have been investigated or suggested which can delay and process microwave signals by using electromagnetic, acoustic and magnetic propagation in materials. Some of these approaches will be summarized and their capabilities and limitations will be discussed. Delay, delay variation, bandwidth, dispersion and attenuation will be considered, including their dependence on the available coherent of materials. Optical approaches involving coherent Brillouin scattering will be included in the discussion.