PCB Antenna Design for Small 2.4 GHz Devices

Illustration

A PCB antenna is a copper trace shaped to radiate, usually an inverted-F or meander at 2.4 GHz. It adds almost no parts, but it needs a copper-free keep-out, a suitable ground plane and a matching network. The enclosure, battery and hand all detune it, so tune it with a network analyzer inside the final housing.

Many 2.4 GHz devices, from BLE wearables to Wi-Fi speakers, radiate through an antenna drawn in copper on the main board or soldered onto its edge. On a small device that antenna shares space with a battery, a housing and the user's body, and each of them shifts its tuning. This guide covers antenna types, the trace versus chip choice, vendor layout rules, and how to measure the antenna in the product it ships in. For Wi-Fi products, 2.4 GHz vs 5 GHz Wi-Fi for IoT covers the band choice that comes first.

This is an engineering summary of public vendor notes. Every number belongs to the part or reference design named next to it. Confirm values with the datasheet for your exact chip and antenna.

What is a PCB antenna, and which type fits a small device?

A PCB antenna is a copper trace whose shape and length make it resonate at the radio frequency. At 2.4 GHz the free-space wavelength is about 122 mm, so a quarter-wave element is about 31 mm before the board material and bends shorten it. That is basic physics. The exact length on your board comes from the reference design and from tuning.

TI's antenna selection guide names PCB, chip and wire antennas as the three most common types for short range devices, and says size, cost and performance are the main factors in the choice (TI AN058, SWRA161B, revised October 2010, as of November 2026).

TI's guide also flags patents: antennas adapted from textbook forms are likely protected, so it advises keeping to textbook designs (TI AN058, as of November 2026).

If the antenna is part of a certified module, most of this article reduces to placement. Our PCB layout guide for small devices covers the module rules, such as putting the antenna at the board edge and cutting the base board around it.

Chip antenna vs PCB antenna: which should you choose?

TI lists the PCB antenna as very low cost, with good performance above 868 MHz and standard designs widely available. It lists the chip antenna as small, with a short time to market, medium performance and medium cost (TI AN058, as of November 2026). TI adds that chip antennas often need extra matching parts even when rated at 50 ohms. Their datasheet figures come from a test board, so they change on a board with a different ground plane.

Sources: TI AN043, TI AN058 and the Johanson 2450AT18D0100001E datasheet, Rev 5.0, all as of November 2026. The last two rows are engineering judgment based on these notes.

An external antenna on a connector is the fourth option. TI says it suits products where performance matters most and size and cost do not, and that a connector means conducted emission tests are also needed (TI AN058, as of November 2026). For a US product, check 47 CFR 15.203 first. It requires that an intentional radiator be designed so that no antenna other than the one furnished by the responsible party can be used. A permanently attached antenna or a unique coupling meets that, and a standard antenna jack or electrical connector is prohibited. The rule lists exemptions, such as intentional radiators that must be professionally installed (47 CFR 15.203, eCFR, as of November 2026).

What keep-out and ground plane does a BLE antenna need?

A BLE antenna follows the same physics as any 2.4 GHz antenna, and its own drawing sets the layout rules. For how BLE itself works, see what Bluetooth Low Energy is.

Keep-out

The radiating part of the antenna needs a zone with no copper under it. Johanson's recommended layout for its 2450AT18D0100001E chip antenna marks the clearance as no ground on all layers. A reference drawing for a circular board in the same datasheet adds that no other metallic parts, such as batteries and displays, should sit directly underneath the antenna. The datasheet also says ground vias are highly recommended for better antenna efficiency (Johanson datasheet, as of November 2026). Draw the keep-out on every copper layer.

Ground plane

The ground plane is half of most 2.4 GHz board antennas. When TI's AN043 dongle is plugged into a laptop, it sees a larger ground plane, and the measured bandwidth falls from about 250 MHz in free space to around 100 MHz. That is still enough to cover the 2.4 GHz band (TI AN043, SWRA117D, revised April 2008, as of November 2026). TI's selection guide adds that ground plane size and shape also change the radiation pattern (TI AN058, as of November 2026). A wearable board is often smaller than the reference board, so expect the tuning to move.

Neighbors

For the ESP32-C3, Espressif says to keep the RF antenna away from high-frequency parts such as crystals and DDR SDRAM, and to keep a complete ground plane on the layer next to the RF trace (Espressif ESP32-C3 hardware design guidelines, as of November 2026). For trackers with a satellite antenna, the GNSS rules differ, and our GNSS antenna placement guide covers them. When a cellular modem shares the device, read our guide to LTE and GNSS coexistence as well.

How does the matching network fit into antenna design?

The radio expects a 50 ohm load. TI calls antenna mismatch one of the largest factors that reduce the total RF link budget. Its guide treats a VSWR of 1.5 (14 dB return loss) as a good match, and says a VSWR above 2.0 (9.5 dB) means the matching network should be reviewed (TI AN058, as of November 2026). TI's AN043 design goal of better than -10 dB reflection means more than 90% of the available power reaches the antenna (TI AN043, as of November 2026).

Two matching networks often sit in series. Espressif says the ESP32-C3 needs a CLC matching circuit at the chip for chip tuning. For PCB antennas, it recommends an additional CLC circuit for antenna tuning, placed as close to the antenna as possible (Espressif guide, as of November 2026). Keep them apart in the schematic: the chip match comes from the reference design, and the antenna match is tuned on your board.

Reserve the footprint even when you expect not to need it. TI recommends adding a pi matching network so the antenna can always be matched, and filling it with a zero ohm resistor or DC block capacitor when the match is already good (TI AN058). Johanson recommends leaving slots for a pi network and says the matching values on your board will differ with layout, thickness and material (Johanson datasheet). Both as of November 2026.

What detunes the antenna, and how do you measure it in the housing?

A bare board on the bench is not the product. A device ships in plastic, next to a battery, against a wrist or in a hand. Each changes the tuning.

Enclosure

TI measured that plastic encapsulation of the AN043 dongle shifts the resonance to a lower frequency, and says this can be compensated by making the antenna slightly shorter (TI AN043). For a module's PCB antenna on the ESP32-C3, Espressif recommends at least 15 mm of clearance in all directions inside the housing, and asks designers to consider the housing's impact during end-product design (Espressif guide). Both as of November 2026. A wearable rarely has 15 mm to spare, so measure.

Battery, display and metal

Johanson's circular-board drawing rules out batteries and displays directly under its chip antenna. Vendor notes we read give no general keep-out distance for a battery beside the antenna. Treat battery position as a variable and measure it in your assembly.

Hand and body

TI's guide shows return loss for a handheld PCB antenna in free space, in plastic, and held in a hand. Plastic lowers the resonance, and the hand moves it further. TI concludes that you should characterize and tune the antenna where it will be used in normal operation, and that handheld devices should be held in a hand during the measurement (TI AN058, as of November 2026). Body-worn and handheld radios can also raise RF exposure questions; see our guide to SAR testing.

Measuring with a network analyzer

TI's method, from AN058 as of November 2026:

• Disconnect the antenna from the radio and solder a semi-rigid coax at the feed point, with the shield to ground close to the cable end.
• Calibrate the network analyzer over the band. To read impedance as well as return loss, move the reference plane to the feed point with electrical delay.
• Fix the cables in place. Ferrites help on boards whose ground plane is a fraction of a wavelength.
• Measure in free space for reference, then inside the final casing, and in a hand if the product is handheld.
• If the resonance is too low, shorten the antenna. If it is too high, lengthen it. Then set the match.

Expect some scatter. On the small AN043 dongle, TI found that moving the coax could change the resonance by 5 to 10 MHz and the reflection by 3 to 4 dB (TI AN043). Return loss is only the first check. Espressif says the final product should be tested for throughput and communication range (Espressif guide). Both as of November 2026.

What should you ask your hardware team?

Use this list at layout review and again when the first enclosure samples arrive.

• Which reference antenna are we copying, from which document and revision, and does our board thickness and material match it?
• Where is the keep-out drawn, and is it clear of copper on every layer, including ground pour?
• Is there a pi or CLC footprint between the radio match and the antenna, close to the antenna?
• What sits within the antenna clearance in the closed product: battery, display, screws, coated plastic, a metal frame?
• Has anyone measured S11 with the board inside the final housing, and with a hand or wrist where the user holds it?
• Are the tuned matching values in the BOM for the next build?
• Does the antenna plan fit the FCC route we chose, including the rule on antenna connectors?

Antenna, board and enclosure decisions sit inside one electronics and mechanical plan. For how that work is organized, see engineering.

If you want an antenna plan checked against your board size and housing, tell us about your device.

Sources. All pages accessed November 6, 2026. Vendor notes are revised, so confirm current values before you decide.

• Texas Instruments, Application Note AN043, Small Size 2.4 GHz PCB Antenna, SWRA117D (revised April 4, 2008) (link)
• Texas Instruments, Application Note AN058, Antenna Selection Guide, SWRA161B (revised October 5, 2010) (link)
• Espressif, ESP Hardware Design Guidelines, ESP32-C3 PCB Layout Design (link)
• Johanson Technology, 2.45 GHz RF Chip Antenna datasheet, P/N 2450AT18D0100001E, Revision 5.0 (2024) (link)
• 47 CFR 15.203, Antenna requirement, Electronic Code of Federal Regulations (link)