NX15 Antenna Design
This page explains the antenna design considerations for the NX15 Series BLE module.
NX15 has two antenna integration options:
| Variant | Antenna Type | Main Design Focus |
|---|---|---|
| NX15i Series | Integrated chip antenna | Antenna keep-out and host PCB ground area |
| NX15E Series | u.FL external antenna | 50 Ω RF trace and u.FL connector layout |
This page focuses only on antenna layout. Power, GPIO, SWD, reset, and general PCB design are covered in NX15 Hardware Design.
Antenna Design Flow
Use this flow before finalizing the PCB.
| Step | Action |
|---|---|
| 1 | Confirm whether the design uses NX15i or NX15E |
| 2 | Check module placement on the host PCB |
| 3 | Reserve antenna keep-out or RF trace area |
| 4 | Check ground plane requirement |
| 5 | Keep metal objects away from the antenna |
| 6 | Review enclosure and battery placement |
| 7 | Validate RF performance on real hardware |
NX15i Chip Antenna Variant
The NX15i variant uses an integrated chip antenna.
This option is useful when the design needs a compact module without an external RF connector. However, the antenna area must be protected from copper, ground, metal objects, and enclosure interference.
Placement Rules
| Rule | Recommendation |
|---|---|
| Module placement | Place the module at the top-left or top-right edge of the host PCB |
| Antenna clearance | Keep the antenna clearance area free from ground plane, copper traces, and metal shielding |
| Host PCB ground | Extend the host PCB ground plane below the module |
| Metal distance | Keep shields, batteries, and other metal objects away from the antenna |
| Enclosure | Avoid placing metal or dense material directly over the antenna area |
Do not place copper, ground pour, signal traces, or metal shielding inside the chip antenna keep-out area.
Chip Antenna Keep-out Area
The keep-out area is the most important layout requirement for the NX15i variant.
| Area | Requirement |
|---|---|
| Antenna area | Keep free from copper and ground |
| Nearby components | Avoid tall metal components near the antenna |
| Battery | Do not place battery directly over or beside the antenna area |
| Shield can | Keep shield structures away from the antenna |
| Host PCB edge | Place the antenna side toward the PCB edge |
For chip antenna modules, small mechanical changes can affect RF performance. Always validate the final PCB together with the actual enclosure and battery placement.
NX15E External Antenna Variant
The NX15E variant uses a u.FL / UMCC external antenna connector.
This option is useful when the antenna must be placed away from the PCB, outside an enclosure, or in a controlled RF location.
RF Trace Requirements
| Parameter | Requirement |
|---|---|
| RF impedance | 50 Ω controlled impedance |
| Connector | u.FL / UMCC, 50 Ω |
| Reference plane | Solid Layer 2 GND plane under the RF trace |
| Trace length | Keep short; avoid unnecessary length |
| Trace path | Avoid routing across gaps in the ground reference |
| Matching | Follow the reference design or RF validation result |
50 Ω Microstrip Guidance
For FR-4 PCB design, the datasheet gives a simple starting point for the RF microstrip.
| Parameter | Requirement |
|---|---|
| PCB material | FR-4, εr approximately 4.2 |
| Dielectric height | 0.2 mm to 0.4 mm |
| Trace width | W = H × 1.8 |
| Trace length | 7 mm to 25 mm |
| Layer 2 | Solid GND plane |
| Connector | u.FL / UMCC, 50 Ω impedance |
The RF trace must keep the same dielectric-to-ground-plane configuration along its entire length. Do not route the RF trace over an area without a solid Layer 2 GND plane.
Ground Via and Connector Area
For the u.FL connector area:
| Item | Recommendation |
|---|---|
| Ground vias | Place ground vias near the connector ground pads |
| RF return path | Keep return current path short and continuous |
| Connector footprint | Use the recommended u.FL / UMCC footprint |
| Mechanical stress | Avoid placing the connector where cable pull may damage the PCB |
| Cable routing | Route antenna cable away from noisy or high-current areas |
Enclosure and Mechanical Considerations
Antenna performance can change after the board is installed in the final product.
Check the following:
| Item | Why It Matters |
|---|---|
| Plastic enclosure | Usually better than metal around the antenna |
| Metal enclosure | Can block or detune the antenna |
| Battery location | Can reduce antenna efficiency if too close |
| Cable position | External antenna cable position affects repeatability |
| Product orientation | RSSI may change depending on orientation |
| Nearby ground / metal | Can reduce range or create unstable RF behavior |
Antenna Validation Checklist
Before release, validate the antenna in the final mechanical configuration.
| Test | Purpose |
|---|---|
| BLE advertising scan | Confirms device is visible |
| RSSI comparison | Checks relative signal strength |
| Distance test | Verifies expected operating range |
| Orientation test | Checks signal stability in different positions |
| Enclosure test | Confirms RF behavior after assembly |
| Battery placement test | Checks effect of battery position |
| Production sample check | Confirms repeatability across units |
Common Antenna Issues
| Symptom | Possible Cause | Check |
|---|---|---|
| Weak BLE signal | Antenna keep-out violated | Check copper, ground, metal, and battery placement |
| Device visible only at short range | Poor antenna placement | Check module position and enclosure |
| Signal changes strongly by orientation | Antenna blocked or detuned | Check mechanical layout |
| External antenna not working | u.FL connector or RF trace issue | Check connector soldering and 50 Ω trace |
| Inconsistent units | Assembly or cable variation | Check production process and antenna cable routing |
What Not to Include Here
To keep this page focused, the following topics should stay in other pages:
| Topic | Go To |
|---|---|
| Power, GPIO, SWD, reset | NX15 Hardware Design |
| First firmware bring-up | NX15 Quick Start |
| BLE advertising / GATT behavior | NX15 BLE Application Guide |
| Low-power firmware tuning | NX15 Low Power Guide |