NX40 Antenna Design
This page explains antenna design considerations for the NX40 Series BLE module.
NX40 variants can be organized by antenna type:
| Variant | Antenna Type | Main Design Focus |
|---|---|---|
| NX40i Series | Integrated chip antenna | Antenna placement, keep-out, and ground reference |
| NX40E Series | External antenna interface | RF trace, connector, and external antenna placement |
This page focuses only on antenna design. Power, SWD, GPIO, reset, and general PCB design are covered in NX40 Hardware Design.
Antenna Design Flow
Use this flow before PCB release.
| Step | Action |
|---|---|
| 1 | Confirm whether the design uses NX40i or NX40E |
| 2 | Place the module with the antenna requirement in mind |
| 3 | Reserve chip antenna keep-out or external RF path |
| 4 | Keep metal, battery, shield, and dense copper away from the antenna |
| 5 | Check ground reference around the RF path |
| 6 | Validate signal strength on prototype hardware |
| 7 | Re-test after enclosure assembly |
NX40i Chip Antenna Variant
The NX40i variant uses an integrated 2.4 GHz chip antenna.
For chip antenna designs, layout and mechanical placement strongly affect wireless performance.
| Area | Recommendation |
|---|---|
| Module placement | Place antenna side near the PCB edge where possible |
| Keep-out area | Keep antenna clearance free from copper, ground, and signal traces |
| Metal objects | Keep shield cans, batteries, screws, and metal enclosure parts away |
| Enclosure | Avoid metal directly over or around the antenna area |
| Ground reference | Follow the reference design for the required ground area |
| Validation | Test RSSI and range after final mechanical assembly |
Do not place ground pour, copper traces, components, battery, or metal parts inside the chip antenna keep-out area.
Chip Antenna Keep-out
The keep-out area is the most important layout requirement for the NX40i antenna.
| Item | Check |
|---|---|
| Copper | No copper under or inside the antenna keep-out area |
| Ground | No ground pour where the antenna requires clearance |
| Components | Avoid components near the antenna area |
| Battery | Do not place battery directly over the antenna |
| Shield | Keep shield structures away from the antenna |
| Enclosure | Validate with final plastic or mechanical housing |
Antenna performance should be checked on the final PCB and final enclosure, not only on an open development board.
NX40E External Antenna Variant
The NX40E variant should be used when the product needs external antenna placement or more control over antenna position.
| Area | Recommendation |
|---|---|
| RF trace | Use controlled impedance RF routing |
| Connector | Use the confirmed connector footprint from the NX40 reference design |
| Ground reference | Keep a continuous ground reference under RF path |
| Matching network | Follow the reference design and tune during RF validation if required |
| Cable routing | Route antenna cable away from noisy or high-current circuits |
| Mechanical strength | Avoid placing the connector where cable pull can damage the PCB |
Confirm the final external antenna connector type, matching network, and RF trace dimensions from the NX40 schematic and PCB stack-up before production.
RF Matching Network
The NX40i32 BOM includes RF matching components around the 2.4 GHz antenna path.
Do not treat matching values as universal for every PCB layout. Antenna matching can depend on:
| Factor | Impact |
|---|---|
| PCB stack-up | Changes impedance and antenna behavior |
| Ground plane shape | Affects antenna efficiency |
| Module placement | Changes RF environment |
| Enclosure material | Can detune the antenna |
| Battery position | May reduce antenna performance |
| Nearby metal | Can block or detune RF radiation |
Use the reference matching network as the starting point, then validate RF performance on the actual PCB and enclosure.
External Antenna Layout Checklist
| Check | Status |
|---|---|
| RF path uses controlled impedance | ☐ |
| RF trace is short and direct | ☐ |
| Ground reference is continuous | ☐ |
| Connector footprint is verified | ☐ |
| Matching network follows reference design | ☐ |
| Cable route avoids noisy circuits | ☐ |
| Antenna position is mechanically stable | ☐ |
| RF performance tested in final enclosure | ☐ |
Enclosure and Mechanical Effects
The antenna should be evaluated after mechanical assembly.
| Mechanical Factor | Possible Effect |
|---|---|
| Metal enclosure | Can block or detune antenna |
| Battery location | Can reduce range if too close |
| Shield can | Can affect antenna pattern |
| Screws or brackets | May create unexpected RF loss |
| Cable position | Can change external antenna behavior |
| Product orientation | RSSI may vary by orientation |
Antenna Validation
Validate the antenna using real hardware.
| Test | Purpose |
|---|---|
| BLE advertising scan | Confirms device is visible |
| RSSI comparison | Checks relative signal strength |
| Distance test | Verifies usable range |
| Orientation test | Checks signal stability |
| Enclosure test | Confirms final mechanical effect |
| Current check | Detects abnormal behavior during radio activity |
| Sample-to-sample check | Confirms consistency across multiple boards |
Common Antenna Issues
| Symptom | Possible Cause | Check |
|---|---|---|
| Weak BLE signal | Keep-out violation or poor placement | Check antenna clearance and enclosure |
| Device visible only nearby | Antenna detuning or blocked antenna | Check metal, battery, and orientation |
| Signal changes strongly by direction | Mechanical or antenna placement issue | Test multiple orientations |
| External antenna not working | Connector, RF trace, or cable issue | Inspect RF path and connector |
| Different boards behave differently | Assembly or matching variation | Compare soldering, antenna parts, and enclosure assembly |
What Not to Include Here
To keep this page focused:
| Topic | Go To |
|---|---|
| Power, SWD, reset, GPIO | NX40 Hardware Design |
| First board bring-up | NX40 Quick Start |
| BLE advertising / GATT behavior | NX40 BLE Application Guide |
| Sleep and current tuning | NX40 Low Power Guide |