CAN Transceiver Connections Explained
Thought for 1 min 43 sec
Short answer: Yes—any copper or parts on any layer under the ESP32 module’s antenna will degrade RF. That includes bottom-layer CAN traces and the CAN transceiver placed under the antenna projection.
What the docs require (ESP32-S3 HW Design Guidelines / module datasheet):
- Keep at least 15 mm clearance around the antenna area.
- No copper, no traces, no vias, no components in that area on any layer.
- Prefer a board cutout under the antenna if possible.
Your PCB right now:
- U4 is at the origin with the antenna end defined in the footprint; I see 57cfc4e2-133e-4f3e-bc11-a59269bbb67b/d9f9a055-e850-4ab5-ac5e-f936252b3a99 routed on the Bottom in the 9.7–13.4 mm X region near U4, which falls under the module’s footprint area and is very likely within the antenna projection.
- U2 is placed at about 9.05 mm, -3.94 mm, i.e., underneath/adjacent to the module; that also risks being under the antenna zone.
Recommendations (pick one or combine):
- Move U2 and reroute CAN so no copper exists under the antenna projection of U4.
- Add an all-layer keepout matching the antenna projection plus a 15 mm margin; forbid polygons, traces, and vias inside it.
- If space is truly constrained, add a board cutout under the antenna region; even then, keep parts away from the 15 mm zone.
- If you must violate this for an early proto, expect reduced range/detuning; verify with RSSI/range testing.
If you want, I can mark the antenna projection zone in the layout for you and list any nets crossing it so you can reroute around it.
ok and can the antenna be sticking off the pcb? like pads on pcb and antenna no?
Thought for 1 min 23 sec
Yes—this is actually the preferred placement. For the ESP32-S3 module U4, Espressif recommends putting the antenna portion outside the main PCB outline (overhanging the board edge). That minimizes detuning from the baseboard.
Key rules to follow
- Overhang OK (recommended): Keep the castellated pads fully on the PCB, and let only the antenna end project past the edge.
- All-layer keepout: No copper, traces, vias, or components under the antenna area on any layer. If the antenna cannot overhang, maintain at least 15 mm clearance around the antenna region on all layers.
- Enclosure clearance: Keep metal (shields, screws, battery cans, cables) out of that antenna zone. Test range in the final enclosure.
- Assembly/mechanical: Ensure the module is well supported during reflow (panel rails or nearby board material) so the overhanging antenna isn’t stressed. Do not route board-edge fiducials or breakaways through the antenna keepout.
If you want, I can mark the antenna keepout in your layout around U4 and flag any traces/vias that cross it so you can reroute.
Confirm overhang distance
Ask about board cutout
Enclosure constraint
Keepout setup
Check current placement
