Flexible Thinking: The Key to a Successful Flex Circuit Design Transfer
Happy’s Tech Talk #29: Bend-to-Install Semi-flex FR-4
RF PCB Design Tips and Tricks
May 8, 2025 | Cherie Litson, EPTAC MIT CID/CID+Estimated reading time: 1 minute
There are many great books, videos, and information online about designing PCBs for RF circuits. A few of my favorite RF sources are Hans Rosenberg, Stephen Chavez, and Rick Hartley, but there are many more. These PCB design engineers have a very good perspective on what it takes to take an RF design from schematic concept to PCB layout.
Here’s a quick summary of the common suggestions that I’ve learned from them and others over time:
- A schematic shows the “ideal” functionality of the RF circuit. When creating a schematic in the PCB layout, the “real” physics of the copper strips, dielectric material, and adjacent circuits and metal features create parasitic influences: resistance, inductance, and capacitance.
- It is the responsibility of the layout engineer to minimize the differences between the “ideal” and “real.”
- Electronic devices and systems operate at frequencies ranging from a few megahertz to several gigahertz. Finding the best method to control the parasitic influences requires only a few basic guidelines.
- Identify and understand the current loops in the circuit
- The shorter the loop, the lower the impedance and resistance ratios
- Use an uninterrupted ground plane as close as possible to the referenced signal
- Give each ground connection its own via as close as possible to the pad
To do this in a PCB, remember it is a 3D environment. Uninterrupted ground plane layers close to their signal, impedance calculations, material selection, copper thicknesses, trace thicknesses, shielding, and spacing become the tools to control the parasitic influences of the “real” circuit.
Methods for applying each of these tools in your PCB design are available for all designers. Then download a tool such as Saturn’s free PCB Toolkit and see how switching to different parameters in the “differential pairs/XTALK” tab will change the values of your target impedances. This will get you in the ballpark of creating a good RF design.
To continue reading this article, which originally appeared in the April 2025 issue of Design007 Magazine, click here.
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