Planar Quasi-Optical Circuit Technology

Recent advances in planar integrated circuit configurations implementing the quasi-optical concepts and functions accompanied by several groups in the U. S. are summarized. As the frequency of operation is increased toward millimeter-waves and beyond, new circuit configurations are needed to meet a specific challenge. After a brief historical review of quasi-optical mixers, more recent efforts in developing the active quasi-optical planar integrated circuits and components are described. This circuit configuration can exploit the maximum capability of active devices which exhibits ever decreasing performance as the frequency is increased. Simplicity of the circuit and greater flexibility of design can make this technology attractive also at lower microwave frequencies where cost effectiveness is often more emphasized rather than overall performance. Examples include quasi-optical oscillators, power combiners and second harmonic generators.