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.

iblamematthew

ok and can the antenna be sticking off the pcb? like pads on pcb and antenna no?

Thought for 1 min 23 sec

flux

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

U2 RXD - U4 RXD0

U2 STB - U4 IO6

JTAG1 Pin_4 - U4 IO39

LED1

U2 STB - U4 IO6

JTAG1 Pin_6 - U4 IO40

3V3

JTAG1 Pin_2 - U4 IO42

LED4 DI - U4 IO4

3V3

U1 DO(IO1) - U4 IO12

U2 CANH - R14 P1

J1 6 - U4 EN

U2 CANH - R14 P1

3V3

JTAG1 Pin_9 - GND GND

JTAG1 Pin_8 - U4 IO41

JTAG1 Pin_9 - GND GND

U2 CANL - R15 P2

JTAG1 Pin_9 - GND GND

U1 DI(IO0) - U4 IO11

J1 6 - U4 EN

JTAG1 Pin_6 - U4 IO40

C9 P1 - R14 P2

3V3

U2 CANL - R15 P2

JTAG1 Pin_9 - GND GND

IO0

U1 ~CS - U4 IO10

U1 CLK - U4 IO13

JTAG1 Pin_9 - GND GND

JTAG1 Pin_4 - U4 IO39

U2 TXD - U4 TXD0

JTAG1 Pin_9 - GND GND

U2 RXD - U4 RXD0

U2 CANH - R14 P1

LED4 DI - U4 IO4

JTAG1 Pin_9 - GND GND

3V3

IO0

JTAG1 Pin_9 - GND GND

U1 CLK - U4 IO13

JTAG1 Pin_9 - GND GND

U1 DI(IO0) - U4 IO11

3V3

LED1

3V3

U2 CANL - R15 P2

3V3

U1 ~CS - U4 IO10

JTAG1 Pin_9 - GND GND

C9 P1 - R14 P2

JTAG1 Pin_8 - U4 IO41

JTAG1 Pin_2 - U4 IO42

U2 TXD - U4 TXD0

3V3

U1 DO(IO1) - U4 IO12

Capacitance

22uF

JCANL

Capacitance

22uF

GND_TP

LED1

R14

Resistance

500 Ω

GND

JGND

R12

Resistance

10kΩ

R15

Resistance

500 Ω

C12

Capacitance

22uF

IO0_TP

Resistance

1kΩ

JCANH

C10

Capacitance

EN_TP

C11

Capacitance

J5V

R11

Resistance

10kΩ

Capacitance

0.1uF

Capacitance

LED4

Reviews

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natarius

Project Name

Description

R11:P2 Connected to nRESET Net for Persistent Pull-Up on Reset Line

Layout Rules

Dimension Unit

Enabled

Yes

Grid Spacing

10mm

Layer

Top

Rotation Unit

deg

Properties

Compliance

Role

ERC Review

System Architecture

Diagram

Domain

Part Type

DRC Review

Pricing & Availability

Distributor	Qty 1
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LCSC	$9.23–$9.44
Mouser	$11.76–$13.59
TME	$0.80
Verical	$2.55–$13.00

Controls

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