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20 DESIGN007 MAGAZINE I APRIL 2023 Designers who are new to RF face a variety of decisions regarding antennas. Should they design the antennas or use a commercially available antenna? Should they consider dual- band antennas, which seem to save board real estate? With the first part of this question, when you learn to design an RF PCB, it's only a matter of time until you must design an antenna. at is something you should take as a challenge in fur- thering your career. Considering a dual-band antenna would be the starting point of any PCB that requires an antenna. With a dual-band antenna, you are designing for the worst-case scenario, with space being a significant consideration. I believe it is better to design for the worst-case scenario instead of having to shi gears halfway through and finding out that another solution will not fit. What are some of the considerations designers should weigh when selecting RF materials? How much time do we have? Materials are an extensive part of RF, and this is where many designers make most of their mistakes, either by selecting the incorrect material for RF or designing a stackup that does not support such a design. Consider each material's engineering charac- teristics, such as coefficient of thermal expan- sion (CTE), dielectric constant (Dk), along with the weave of the substrate and the rough- ness of the copper foil. Above all, be consistent. Whatever material you use, make it consistent throughout your entire PCB. Mixing various materials causes significant problems in the RF world. Another point related to material is how the materials are used. When using the more densely stranded FR-4, even the direction of the weave in the stackup can cause an imbalance, resulting in losing control of the RF energy. e same holds true for copper foil. Again, keeping the smoothness consistent helps create a stable RF PCB. I have found that one major mistake that RF designers make is not keeping the symmetry of the PCB in the Z direction. We must deal with thermal expansion in RF designs, and using dif- ferent materials that expand at different rates will result in warping and most likely cracking vias and traces. What advice would you give to designers in the RF world now? First, be patient. If you expect to learn RF design in the next few months, I have some bad news for you: It's not going to happen. You're going to make mistakes. Some RF designers have studied this area for decades and still only scratched the surface. Is that a subconscious skin effect joke? It may be. With that said, study and don't stop studying. Understanding the basics of physics and Maxwell's equations in particular will help you grasp what is happening with RF. Pay atten- tion to the details. Assumptions cause huge problems in an RF PCB design. Even a success- ful RF design built upon assumptions will be much more expensive than it should be. Don't be afraid to ask the experts about what you've done. Various RF design experts throughout our industry are willing to evaluate what you've done. Get their input; this is how you learn. Thanks for speaking with us, John. ank you, Andy. DESIGN007 With a dual-band antenna, you are designing for the worst-case scenario, with space being a significant consideration.