What Antenna Types Are Used in Embedded Wireless Designs?

Detailed Explanation

Antenna selection is one of the first physical design decisions in any RF product, and it affects board size, cost, range, enclosure design, and certification complexity simultaneously. For embedded wireless designs — where the radio is integrated or mounted on the PCB alongside an MCU and other circuitry — the choice typically comes down to four options.

For background on why frequency determines antenna size, and how ISM bands are regulated in Australia, see what are RF signals and how are they used in electronics?.

1. Chip Antenna

A chip antenna is a small surface-mount ceramic component — typically 2–4 mm long — that contains a wound or meandered conductor forming a resonant antenna structure. Chip antennas are the most commonly used antenna type in compact 2.4 GHz designs (BLE modules, Wi-Fi SoCs, Zigbee nodes).

Characteristics:

• Size: 1.5–4 mm at 2.4 GHz; physically larger at sub-GHz frequencies (which limits their use below ~900 MHz).
• Cost: AUD $0.30–$1.50 in production quantities.
• Performance: −2 to 0 dBi typical gain (slightly below an ideal isotropic radiator in most practical orientations).
• Keepout: requires a defined copper-free zone on all PCB layers — typically 5–15 mm depending on the antenna model. This area must be completely clear of ground copper, signal traces, vias, and mechanical components.

Best for: compact IoT nodes, wearables, indoor sensors, products where the BOM cost and board size are dominant constraints and range is adequate at 10–30 m indoors.

Key limitation: chip antennas are very sensitive to PCB layout — violating the keepout by even a few millimetres shifts the resonant frequency and reduces efficiency significantly. Always use the layout guidelines in the antenna's datasheet, and verify on the first prototype with a network analyser if range is critical.

2. PCB Trace Antenna (Inverted-F Antenna / IFA, PIFA)

A PCB trace antenna is a conductor pattern etched directly into the PCB copper — no additional component, and no BOM cost. The most common forms are the inverted-F antenna (IFA) and the planar inverted-F antenna (PIFA), which are widely used in ESP32, nRF52, and similar modules with integrated antennas.

Characteristics:

• Size: the antenna trace itself is compact (approximately 30–40 mm total length for a 2.4 GHz IFA), but the required ground plane clearance beside and around the trace occupies additional PCB area.
• Cost: zero component cost, but the keepout area increases board size.
• Performance: 0 to 2 dBi typical, comparable to a chip antenna and somewhat more consistent in the pattern.
• Keepout: similar to chip antennas — a defined copper-free area extends on all sides and through all layers.

Best for: modules where the antenna is integrated at design time (ESP32-WROOM, nRF52840 Dongle), products where minimising BOM cost is paramount, and where the PCB real estate for the keepout can be accommodated.

Key limitation: PCB trace antennas are optimised for specific stack-up parameters (dielectric thickness, εᵣ). Copying a PCB trace antenna pattern to a different board without re-simulating can result in significant detuning. Pre-certified modules solve this — the antenna is validated as part of the module's certification.

3. Quarter-Wave Whip (Monopole) Antenna

A quarter-wave monopole is a straight conductor of length λ/4 connected to the RF output and oriented perpendicular to the PCB ground plane. It is the simplest antenna that achieves good omnidirectional gain.

Characteristics:

• Performance: approximately 2 dBi omnidirectional gain in the horizontal plane — best directional performance of any of these types.
• Keepout: no copper keepout zone required in the way chip antennas need one; the monopole needs a solid ground plane beneath it and free space above.
• Cost: a short wire or formed metal rod soldered to a PCB pad or SMA connector jack.

Best for: sub-GHz applications where the antenna length is manageable (433/868/915 MHz LoRa, Sigfox, proprietary sub-GHz), outdoor applications where range is the priority, bench testing of radio circuit performance.

Key limitation: at 433 MHz, a quarter-wave wire is 173 mm — impractical inside a compact product. Helical antennas trade gain for compactness at sub-GHz frequencies: a helical wound tightly enough can achieve λ/4 electrical length in one-fifth the physical length, at a gain penalty of roughly 3 dB.

4. External Antenna via U.FL or SMA Connector

A U.FL (or IPEX MHF) connector is a miniature coaxial jack mounted on the PCB; an SMA connector is a larger screw-type coaxial jack for panel mounting or pigtail leads. Both allow the antenna to be physically separated from the PCB — mounted on the enclosure wall, extended outside the enclosure, or replaced.

Characteristics:

• Performance: the best achievable for a given protocol, limited only by the antenna and cable selected.
• Flexibility: supports PCB assembly and a separately shipped cable/antenna, useful for products in metallic enclosures (which block RF) or applications needing directional gain.
• Cost: the connector adds AUD $0.50–$2.00, the cable and antenna another AUD $2–$10 depending on the type.
• Reliability: U.FL connectors are rated for approximately 30 mate/unmate cycles — fragile for user-accessible connections. SMA is rated for 500+ cycles and is robust for field-replaceable antennas.

Best for: outdoor products (LoRa gateways, LPWAN end nodes in metal enclosures), products where radio performance is critical (long-range links with tight link budget), test jigs where the antenna is connected/disconnected regularly.

Key limitation: every connector mate/unmate cycle in production test is a reliability risk for U.FL. The coaxial cable between the connector and the antenna is a loss element — a 100 mm cable at 2.4 GHz may contribute 0.5–1 dB of insertion loss depending on cable type.

Choosing an Antenna Type

Use the following guide:

The RF PCB layout around the antenna — 50Ω trace, solid ground plane, keepout zone — is as important as the antenna itself. A correctly selected antenna on a poor PCB layout will perform worse than a simple wire antenna on a well-designed board. RF PCB layout is covered in how should you lay out the RF section of a PCB?.

The MCU and radio module you choose constrain your antenna options — pre-certified modules have a defined antenna type built in, while discrete radio ICs give you full antenna design flexibility. See how to choose a microcontroller for how ESP32, nRF52, and LoRa SiPs fit different design contexts.

For RF products combining custom antenna design with ACMA compliance requirements, Zeus Design's engineering team covers antenna selection, PCB layout validation, and pre-compliance testing — contact Zeus Design to discuss your wireless hardware design.

Design Considerations

• Controlled impedance between radio IC and antenna: regardless of which antenna type is chosen, the trace connecting the IC's RF pin to the antenna feed must maintain 50Ω characteristic impedance. See what is controlled impedance PCB design? for how trace geometry and stack-up set impedance.
• Ground plane size and shape affect monopole and chip antenna performance: for chip antennas, the required keepout defines a minimum clear area. For monopole antennas, the ground plane below the antenna acts as the antenna's counterpoise — a ground plane of at least 30×30 mm at 2.4 GHz is recommended, and the ground plane shape affects the antenna's radiation pattern. See how do you design PCB power and ground plane layouts? for ground plane design principles.
• EIRP and regulatory limits: adding an external antenna with gain increases EIRP above what the radio IC's certifiedpower output assumed. Check that transmitter output power (dBm) + antenna gain (dBi) − cable loss (dB) stays within the ACMA class licence EIRP limit for the band in use.
• Pre-certification on first prototypes: for 2.4 GHz designs with a custom antenna (not a pre-certified module), an informal pre-compliance scan on the first prototype identifies mismatches or layout problems before formal certification testing.

Common Mistakes

• Not implementing the chip antenna keepout: the most common cause of range disappointment on first boards. Placing copper — even a ground fill on the back of the board — within the chip antenna keepout reduces efficiency by 3–6 dB or more, which translates to 50–75% shorter range.
• Copying an IFA or PIFA pattern from a reference design to a different board thickness: PCB trace antennas are resonant at a frequency determined partly by the board's dielectric and copper geometry. A trace antenna copied to a board with different thickness or εᵣ will be off-resonance. Verify with a network analyser on the first prototype.
• Exceeding EIRP by connecting a high-gain antenna to a certified module: certified modules are certified at specific transmit power settings. Adding a 6 dBi external antenna to a module certified at +20 dBm produces 26 dBm EIRP — which may exceed the regulatory limit. Reduce transmit power if necessary to stay within EIRP limits.
• Using a U.FL connector in a user-accessible position: U.FL is not rated for repeated mate/unmate by users. For user-accessible RF ports, use an RP-SMA or SMA connector.
• Not accounting for enclosure effects: a metallic enclosure wall, battery, or motor assembly near the antenna all affect its tuning. Validate antenna performance with the product fully assembled in its final enclosure, not on the bare PCB.