RF PCB Design: The Devil’s in the Details

Estimated reading time: 2 minutes

Altium’s John Watson is a longtime designer and design instructor, not to mention a Design007 columnist. He’s been dealing with RF issues for years; his previous employer, Legrand, is one of the pioneers in smart lighting and data center solutions.

John discusses the differences between designing RF and “typical” PCBs, how to avoid the missteps and miscues that can bedevil new RF designers, and why the tiniest details can make or break an RF design.

How does designing PCBs for wireless communications differ from designing a traditional PCB?

The basis of any basic PCB is a balance of physics in a controlled situation. When RF is introduced to the party, it’s the equivalent to having a Bud Light on the hammock in the backyard vs. a full-blown kegger with all your neighbors and friends. When it comes to RF, everything becomes even more essential and critical to success—the physics change with high-frequency signals. 

The term radio frequency (RF) refers to the oscillation rate of an alternating electric current or voltage or a magnetic, electric, electromagnetic field, or mechanical system in the frequency range from around 20 kHz to around 300 GHz. That envelops many of today's electronic systems. Also, by definition, RF exists to transmit radiated information from one point to many points. Therefore, the emitted energy must be controlled in a specific area on the PCB level so as not to cause problems.

Is RF the black magic of the PCB world? It is commonly believed to be, but I would disagree with that. I believe it's a misunderstanding about the the physics and mathematics involved. Simulating how it all works together requires an in-depth study and understanding of various Maxwell equations. But many people don't want to take the time to learn Maxwell, because he’s not an easy read.

At RF speeds, there's no room for error. What sort of problems do designers face in the RF arena?

The problems designers will face specifically with RF are numerous, and they can’t be ignored. With a basic PCB, we have a much broader “window of operation and flexibility.” With RF, everything gets raised to a whole new level. I fully agree there is no room for errors, and understanding the details of the circuit is probably the first hurdle a designer must consider. Small items on a "basic" PCB become important issues quickly, and significantly impact the design.

But specifically to answer the question, one of the biggest problems is the massive amounts of energy flowing throughout the PCB that you must control. Having a lack of understanding or plan of how you intend to manage that energy is a failure at the offset.

To read this entire conversation, which appeared in the April 2023 issue of Design007 Magazine, click here.