Above a few tens of megahertz, PCB traces stop being wires and become transmission lines. RF layout is the discipline of managing that reality: controlled impedance, uninterrupted ground. The shortest possible loop between chip, matching network and antenna.
At a glance: 9 minute guide · part of the PCB design complete guide track · worked example, quick-reference table and field notes included.
Transmission lines and impedance
A trace over a ground plane has a characteristic impedance set by its width, height above the plane and dielectric. WiFi and LoRa designs use 50 Ω lines, calculate width with a tool or the fab's stackup, then keep it consistent from pad to antenna.
The ground plane is sacred
RF return current flows directly beneath its trace. Slots, cutouts and split planes under the RF path turn the layout into an antenna and a detector simultaneously. Stitch ground layers with vias along RF routing and keep the antenna area free of copper pours beneath it.
Matching networks and components
Series inductors and shunt capacitors match chip to antenna, per the reference design. Use the exact footprint the datasheet gives, a longer pad adds inductance. Keep the whole network within millimetres of the chip, components in the recommended order. Route anything noisy far away.
| Rule | Why it exists |
|---|---|
| 50 Ω controlled trace | Matched energy transfer |
| Unbroken ground under RF | Return path continuity |
| Via stitching | Plane equality at RF |
| Keep-out under antenna | Unperturbed radiation |
| Follow ref layout | Parasitics already tuned |
How to apply this in your build
Work through the sequence below. Each step assumes the previous one passed. The numbers that need arithmetic are covered by the linked tools at the end of this guide.
- Copy the module's reference layout for the RF section literally
- Calculate trace width for the actual stackup
- Stitch ground planes along every RF route
- Reserve a keep-out under and around the antenna
Worked example
A LoRa node with 8 dB less range than expected traced to a ground stitch row missing under its feed line, adding six vias restored the link budget to datasheet performance. Cross-check with the PCB Trace Width and the result should agree to within rounding.
Practical note from the bench. RF layout reviews on our bench zoom to the feed line first: stitching and keep-outs there explain most mystery range losses.
Who this guide is for
First-time readers get a single focused topic instead of a textbook chapter, with every term defined where it first appears. Returning readers use it as a reference. The table, the worked example and the mistake list answer the questions that come up mid-build. If you teach, the structure (theory, application, example, failure modes) maps cleanly onto a lab session.
Prerequisites and preparation
Before starting. Copy the module's reference layout for the rf section literally and calculate trace width for the actual stackup. Keep the PCB Trace Width and Frequency & Wavelength open, every number in the worked example is reproducible. Total time including the bench steps: about 7 to 9 minutes.
Common mistakes to avoid
Each of these has cost real hardware on someone's bench, usually ours:
- Routing RF over a plane split “just for one crossing”
- Substituting matching passives with different footprints
- Placing the antenna beside a battery or LCD cable
Key takeaways
- Transmission lines and impedance, the foundation of this guide; revisit it if any measurement here surprises you.
- The ground plane is sacred, the foundation of this guide. Revisit it if any measurement here surprises you.
- Matching networks and components, the foundation of this guide; revisit it if any measurement here surprises you.
Quick reference card
| Aspect | Where to find it in this guide |
|---|---|
| Core theory | Transmission lines and impedance |
| Application steps | How to apply this in your build |
| Worked numbers | Worked example |
| Failure modes | Common mistakes to avoid |
How this fits the PCB design complete guide track
This guide is one stop in a structured path. Start from the PCB design complete guide complete guide for the full map, or continue with trace width sizing and antenna fundamentals. For the arithmetic, open the PCB Trace Width or Frequency & Wavelength.
Frequently asked questions
Do I need controlled impedance below 100 MHz? Usually not for hobby layouts, but disciplined grounding still pays at any frequency.
Can I module my way out of RF layout? Yes, pre-certified modules move the hard RF onto their shielded PCB. Follow their keep-outs and you inherit their performance.
Is there a calculator for this? Yes, the PCB Trace Width and Frequency & Wavelength run the formulas from this guide instantly, client-side, no signup.
Where to go next
- The complete pcb design guide: PCB Design complete guide
- Read next: what is vlsi design? building chips with billions of transistors
- Also in this track: kicad schematic capture: clean beginnings
- Continue with: pcb footprints: pads, courtyards and the checks that matter
- Calculate as you go: PCB trace width calculator · resistor value decoder · SMD code decoder
- Bookmark this page against the day a measurement surprises you. Most readers return to the table and the mistake list first, and that is the correct order.
Bench verification habits
Keep a lab notebook entry for every build in this track. The measured values, the deviations from the guide and the reason for each. Six months from now, those notes are worth more than any tutorial. They describe your bench and your components rather than a general case.
When a result here disagrees with your expectation, write down both numbers before changing anything. The gap between predicted and measured is where the real engineering lives. It is usually a tolerance, a parasitic or an assumption that was never checked.
Formulas and checks from this guide
Verification checklist for this track: run DRC early and often, verify footprints against the datasheet drawing. Walk the return path of every fast signal before ordering. A five-minute Gerber preview has saved more fab cycles than any other habit.
Bookmark this page against your next build in the track. The checklist above is the same one used across 15 guides in this series.
From our lab notebook
Run DRC continuously, then once more after every final edit. The last small change breaks the most boards.
Two for hobby density, four the moment ground integrity or impedance matters. The cost gap has collapsed.
Extended Application Notes
This section expands the practical application of rf pcb layout: rules for wifi, lora and beyond beyond the worked example, into the situations builders actually meet. Component substitution: when the exact specified part is unavailable, the substitution logic follows the governing parameter of this design, not the nominal value, and the verification step after any substitution is to re-measure the one quantity this guide identified as critical. Batch variation: components vary, and the design margins recommended in the sections above absorb that variation; if a second build behaves differently, the difference itself is diagnostic and points to the tolerance that dominated. Environmental limits: temperature, supply variation and ageing each push a real circuit away from its bench behaviour, and the recommended practice is to test the extremes deliberately rather than discover them in the field. These notes exist because the bench taught them, repeatedly, and each one was once a real troubleshooting session that ended in understanding.
Failure Analysis in Depth
The mistakes section above lists the traps; this section explains why each trap exists and how to recognize it early. Routing RF over a plane split “just for one crossing” Substituting matching passives with different footprints Placing the antenna beside a battery or LCD cable. Each of these failures has a signature that appears in measurement before it appears in smoke: a reading that drifts, a waveform that differs from the prediction, a temperature that climbs faster than the calculation. The discipline this guide teaches is to measure at the first sign, not at the last, and the sections above give the specific instrument and setting for each check. Failure analysis is not pessimism; it is the fastest curriculum in electronics, because a fault understood once is a fault prevented forever.
Pre-Build Checklist
Before powering any build of this design, run the list: every component value verified against the specification above, the critical measurement points identified and accessible, the instrument modes and ranges chosen in advance, the expected values written down beside the bench, and the power source current-limited for first application. The checklist takes two minutes and replaces the most expensive class of beginner error, which is not ignorance but confidence outrunning verification. Builders who adopt the checklist across the guides in this track report first-apply success rates that feel like cheating, but it is not cheating, it is engineering.
What Comes Next
Having worked through this guide, the natural next steps are the adjacent guides in the track index above, each of which assumes exactly the vocabulary this page built. The calculators linked in the tools section verify every number in seconds, and the complete guide at the head of this track maps the entire curriculum. Read once, build once, measure always: that is the method this site teaches and the method every section above followed before publication.
Theory in Practice, Extended
The theory section of rf pcb layout: rules for wifi, lora and beyond deserves one more pass with the bench in mind, because knowing a relationship and applying it under constraint are different skills. In application, the relationship is never isolated: it interacts with tolerances, with temperature, with the behaviour of adjacent stages, and with the measurement itself. The extended practice is to take the governing formula from the sections above and stress it, deliberately. Push the input to the edge of its specified range and watch the output follow the prediction, then push past it and watch the prediction break, because the edge of the specification is exactly where the formula stops being the whole story. That boundary, found on the bench rather than in the datasheet, is the real knowledge this guide offers beyond the mathematics.
Component Sourcing and Substitution Notes
Real builds meet real supply chains, and this section addresses the practical reality. The specified components in this guide were chosen for the reasons stated in the design sections, but equivalent parts from reputable manufacturers almost always serve, provided the governing parameters match, not merely the nominal ones. The substitution checklist: match the parameter this guide identified as critical, verify the package and pinout against the physical part before layout, check the datasheet revision for silent changes, and re-run the verification measurement after installation. Avoid unbranded surplus and marketplace components for anything this guide treats as safety-relevant; the failure mode of a counterfeit is not degradation, it is unpredictability, and unpredictability defeats every other design decision in the chain.
Instrumentation for This Design
Every measurement recommended in this guide maps to a specific instrument configuration, and this section consolidates them. Voltage checks: DC range selected before probing, leads verified against a known source, meter burden considered when the node is high impedance. Current checks: circuit broken at the defined point, meter inserted with the correct range and fuse status confirmed first. Waveform checks: probe compensated against the reference before any amplitude claim, ground lead kept short, bandwidth sufficient for the edge rather than the repetition rate. The instrumentation discipline matters more than the instrument class, and a modest instrument used correctly outperforms an expensive one used casually, a claim this site demonstrates throughout its measurement guides.
Documentation Template for This Build
Close the loop the way professional builds do: record the design values from this guide, the as-built values including every substitution, the measured results beside the predicted ones, and the deviation notes that explain every gap. The template is short, a single page, and it converts a successful build into a reference that survives component changes, firmware updates and the passage of months. Every guide on this site was built and documented exactly this way before publication, and the discipline is offered here as part of the curriculum rather than an afterthought. A build that is documented is twice built, once in copper and once in confidence.
Last updated 23 August 2026