4. Areas of application. Outlook

Since the development of microwave-grade substrates and the advent of CAD software that includes open-line modeling, more and more microwave circuit designs have been based on planar transmission lines. Although the modes transported by these structures are more complex than those transported by homogeneous guiding structures, they offer clear advantages in terms of :

• size and weight;

• ease of production in the case of engraved lines;

• miniaturization;

• ease of insertion of active components;

• cost when large production runs are involved.