Microwave materials have advanced to a new level over the past 10 to 15 years. Many years ago, only one material was available to RF and microwave designers. That material was a woven Teflon fiberglass material that came in only one thickness, and was used for every application, regardless of the frequency ranges, power levels, or loss requirements that were called out. Today, there are many types of materials with a variety of parameters, so materials can be custom fitted to just about any application. With a variety of materials available, there is no excuse for using the same material for every application. No one should rely on a pet material for all designs. The mind-set "We've always used this material, why not use it again?" or "This material worked great for our last job, so we might as well use it again; why take chances?" does not work today. There is no excuse for not having a working circuit, provided that the right design procedures are used, if the time is spent choosing the proper material for the application at hand.

Microwave materials are special types of materials. These materials are an integral part of the circuits they support, not like the low-frequency and digital circuit boards (those with low data rates), where the only functions are to support components and get current from one point to another. The microwave material is actually a part of the circuit that is being designed. This was shown briefly in Chapter 1,...