Why FR-4 Is Often Inadequate for RF Design

There are times when designers want to use FR-4 for RF and microwave circuit designs. After all, it is less expensive than other materials, like Rogers 4350, and much less expensive than reinforced PTFE composite boards such as Rogers RT/Duroid 5870. However, sometimes it is necessary to spend the money for higher quality circuit board material and processing to get good, repeatable designs. This paper demonstrates the danger of using FR-4 for some RF & Microwave designs.