Antenna Selection for Wireless Projects: Type, Gain and Placement
Wi-Fi, Bluetooth, LoRa or a simple 433 MHz module — whichever wireless technology you use, range and link stability depend heavily on antenna choice and placement. Even the right chip and software can disappoint with a bad antenna. This article focuses less on defining what an antenna is and more on how to choose one for a project and where to put it. For general component decisions, our choosing components for an IoT device article is a good complement.
Antenna types: which one when?
| Type | Advantage | Best for |
|---|---|---|
| PCB trace antenna | No cost, no extra part | Cost-focused products with room to spare |
| Chip antenna (SMD) | Takes very little space | Compact wearables/small devices |
| External antenna (cable + connector) | Best range/performance | Long range, metal enclosure |
| Wire/monopole antenna | Cheap, good performance | Prototype, simple device |
External antennas usually connect through an RF connector (SMA/U.FL); U.FL is common on small devices, SMA on external antennas.
Gain and directivity
Antenna gain (dBi) shows how much the antenna concentrates energy in a particular direction; it is not a power amplifier. A high-gain antenna focuses energy in a specific direction, increasing range that way but narrowing the coverage angle:
- Omnidirectional (all directions): low-to-medium gain; for devices whose orientation is unknown (sensor networks).
- Directional: high gain; for fixed, point-to-point links.
Operating frequency is critical too: the antenna must be designed for your module's frequency (e.g. 2.4 GHz, 868/915 MHz).
50 Ω impedance matching
In the RF world almost everything is built around 50 Ω impedance: the module output, the transmission line and the antenna. If this match is broken, part of the signal reflects back, efficiency drops and range shortens. That's why the antenna feed line should be designed as a controlled-impedance trace, and tuned with a matching circuit if needed. Small-value RF inductors are among the parts frequently used in matching circuits; for the board side, the PCB stackup and impedance control article is a guide.
Golden rules of placement
Most of an antenna's performance is decided in the layout, not the schematic:
- Put it near the edge: the antenna is usually placed on one edge of the board, facing outward.
- Keep the ground plane clear: there should be no copper pour (ground) under the antenna region; breaking this rule is the most common range killer.
- Keep it away from metal and the battery: a metal case, battery and large components next to the antenna smother the signal.
- Account for the hand: if the user's hand will cover the antenna, performance can drop sharply.
Troubleshooting range problems
If you're getting shorter range than expected, follow this order before changing hardware:
- Review the placement: is the antenna at the edge, is there ground under it, is metal/battery nearby?
- Verify the frequency: do the antenna and module belong to the same band?
- Check the feed line: is the trace width appropriate for 50 Ω, are the solder joints solid?
- Do a comparative test: in the same environment, compare range against a different antenna (e.g. a simple wire antenna); this reveals whether the problem is the antenna or the environment.
Environmental factors (walls, metal shelves, interference from other devices) are often more decisive than the design; run the test in the real usage environment.
Common mistakes
- Pouring ground under the antenna: it renders the antenna useless; leave the clearance the manufacturer recommends.
- Wrong-frequency antenna: fitting a 2.4 GHz antenna to an 868 MHz module nearly zeroes the range.
- Ignoring impedance matching: a random trace width means reflection and loss.
- Placing the antenna in the middle of the case/next to metal: the surrounding material absorbs the signal.
Frequently asked questions
Is a PCB trace antenna or a chip antenna better?
A PCB trace antenna is free but takes space; a chip antenna is very small but typically needs slightly lower performance and careful matching. The decision depends on your space and cost constraints.
Is a higher-gain antenna always better?
No. High gain focuses energy in a particular direction; if you need to communicate in all directions, it can even be harmful by narrowing the coverage angle.
Can I design my own antenna?
It's possible, but RF design takes expertise. For most projects, copying the module manufacturer's recommended reference antenna design exactly is the safest route.
Conclusion
A good wireless design is the combination of the right antenna type, a frequency-appropriate choice, 50 Ω impedance matching and a clean layout. The most practical advice is to carefully apply the module manufacturer's reference design and layout notes. You can review current supplier offers for antennas and RF connectors with search and compare alternatives.