ESP32 module placement: why your WiFi range is 3 meter
I review boards from customers every week. Same mistake, 7 of 10
Contents
Every week customers send me ESP32 board for review before production. 7 of 10 have the same problem. They say "WiFi range very bad, maybe ESP32 is bad". ESP32 is fine. Layout is bad.
1. Antenna at board edge, nothing under it
The PCB antenna on the module (the zigzag part) must be at the edge of your board, or better, hanging out past the edge. Under the antenna: no copper on any layer. No ground pour, no traces, no vias. Many people put ground fill on the whole bottom layer and forget the antenna area. Then the antenna is detuned and you lose many dB.
Espressif hardware design guidelines have the keepout drawing for each module. Read it. Minimum: antenna at edge, nothing under it. I like 15 mm clear around the antenna if the board can allow.
2. No metal near antenna
- Battery next to antenna: bad
- Metal screw next to antenna: bad
- Metal enclosure: very bad. It is a Faraday cage. Use plastic, or use the module with external antenna connector (for example ESP32-WROOM-32UE) and put antenna outside the box
- Big electrolytic capacitor or inductor next to antenna: also bad
3. Good ground around the module
Module GND pads connected to a solid ground plane, many vias (stitching) around module, but not under the antenna part. Short return path.
4. Power can give the peak current
WiFi TX peak is a few hundred mA for short time. If your LDO is 150 mA or 250 mA, or your trace is thin and long, voltage drop during TX, then brownout reset, or TX power is weak. Use LDO 500 mA or more. 10 µF + 0.1 µF close to module 3V3 pin. If on battery, also bigger bulk cap.
5. How to check
Put your laptop and your board at the same place. Laptop shows -45 dBm, your ESP32 shows WiFi.RSSI() -80 dBm: layout problem. Good layout should be within maybe 5 to 10 dB of a phone or laptop at same place.
Cost
A respin for prototype here: 5 boards, assembly, around 200 RMB (about 28 USD) plus one week. Not expensive, but one week is one week. Do it right first time. If not sure, post your layout here, I can look. Free for small boards, I don't bite.
Written by
Leo Chen 陈立
Hardware engineer in Shenzhen. ESP32, PCB, small batch manufacturing. Huaqiangbei is my supermarket. Can help with BOM and sourcing.
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