Wireless and antenna integration

1.Wireless protocol selection

Picking the wrong protocol leads to range, battery life, or interoperability problems that surface at first user trial.

1.1Protocol comparison

1.2Selection criteria

2.Module selection: pre-cert vs. custom

The biggest decision in wireless design. Pre-certified modules are faster and cheaper for low volume; custom designs are better for premium products at scale.

2.1Pre-certified module

• Pre-tested and certified by the module manufacturer (RED, FCC Part 15C, IC).
• Modular certification transferYour product inherits the certification when used per the module manufacturer's design guide.
• Limited customisationFixed antenna interface, sometimes fixed antenna.
• Higher per-unit costModule typically $3–15 in volume.
• Faster time-to-market4–8 weeks lead time + standard EMC testing only.

2.2Custom RF design

• Full control of antenna, layout, performance.
• Lower per-unit cost at scaleOften 30–50 % cheaper than a pre-cert module.
• Full certification requiredRED + FCC Part 15C lab testing from scratch.
• Longer time-to-market12–20 weeks + $10–30k in test fees.
• Higher engineering investmentRequires RF engineer or external consultant.

2.3Module ecosystem (popular pre-cert modules)

2.4Selection criteria for modules

• Certifications already obtainedLook for RED, FCC Part 15C, IC certified.
• Module integration design guideModular cert transfer requires following the design guide.
• Antenna interfaceInternal antenna (most modules) vs. external coaxial connection.
• Pin compatibilitySame footprint across module variants to enable upgrade path.
• Supplier stabilityModule suppliers go through EoL cycles; check NRND status.

3.Antenna topology

The antenna is the most-overlooked piece of RF design. Wrong antenna = poor range, no certification, no compliance.

3.1Antenna types

3.2Antenna placement rules

• Antenna outside the caseUse coax-to-PCB connection. Best performance.
• PCB trace antenna with clearance zone10–20 mm keep-out around the antenna; no copper, no components.
• Ceramic chip antenna on board edge5 mm keep-out; ground plane shape matters.
• Avoid placing antenna nearBattery, metal screws, conductive plastic, LCD, ICs.

3.3Antenna tuning

• Tune at the antenna feed pointSeries + parallel components to match 50 Ω.
• Match for return lossS₁₁ < -10 dB (≥90 % power transferred) at operating frequency.
• Verify with Smith chartLook at impedance across band.
• Re-tune for production varianceBuild 5–10 units of each material/finish and check.

3.4Cable / coax considerations

• U.FL connectorsCommon for small RF connections; 50 Ω. Limited mating cycles (~30).
• MHF / IPEXSimilar to U.FL but different keying.
• SMA connectorsHigher quality, more mating cycles, used for external antennas.
• Coax cable typeRG-178 (0.3 mm OD), RG-316 (1.5 mm OD), MMCX. Choose by loss vs. flexibility.

4.RF design rules

Schematic + PCB layout discipline that separates good RF design from EMC-failure RF design.

4.1Schematic rules

• Matching network footprint reserved2–3 components (series L + shunt C, or pi-network).
• 50 Ω impedance trace to the antenna feed.
• Ground reference plane continuous under the antenna feed and matching network.
• ESD protection at the antenna feedBidirectional TVS, typically clamping at 6–8 V.

4.2PCB layout for RF

• Antenna trace impedance 50 ΩCalculated for the layer stack-up.
• Antenna feed length minimalFrom module to antenna match, then to antenna. Total typically <20 mm.
• Ground plane shapeCeramic chip antennas often need a specific ground plane size (typically PCB length × 1/4 wavelength minimum).
• No copper near the antennaCuts in ground plane act as antenna parasitic.
• Capacitor placementDecoupling caps at the RF amplifier should be ground-referenced and very close.

4.3Common RF mistakes

• Antenna trace too longBecomes a parasitic emitter; affects radiation pattern.
• Antenna too close to batteryBattery absorbs RF; range halves.
• Antenna in a metallic enclosureFaraday cage; needs an antenna outside or window.
• Two antennas too closeCoupling; isolation < 20 dB causes interference.
• No ground plane under antenna feedAsymmetric ground, radiation pattern shifts.

5.Regulatory paths

Each wireless technology has a defined certification path. Choose the path before sample order.

5.1RED (Radio Equipment Directive, EU)

• Applies to all radio transmitters above 9 kHz, with intentional emission.
• Notified Body assessmentOptional for most consumer products (self-declaration if harmonized standards are used).
• Required tests (per harmonized standards):

- EN 300 328 (2.4 GHz general) - EN 301 893 (5 GHz Wi-Fi) - EN 301 489 (EMC for radio) - EN 62311 (RF exposure) - EN 62479 (RF exposure for low-power devices) - EN 50360 / EN 62209 (SAR for body-worn)

5.2FCC Part 15 (US)

• Part 15BUnintentional radiators (DCs, MCUs, digital logic).
• Part 15CIntentional radiators (Wi-Fi, BLE, transmitters > 9 kHz).
• 15.247License-exempt low-power transmitters in ISM bands (2.4 GHz, 5 GHz).
• FCC ID requiredUnique identifier per device model.
• Modular cert transferWhen using pre-cert modules per manufacturer's design guide.

5.3IC (Industry Canada / ISED)

• Mirror of FCC for Canadian market.
• IC IDRequired, similar to FCC ID.
• Many modules pre-cert for both FCC and IC.

5.4Test scope per certification type

5.5Wireless module pre-cert advantage

A pre-certified module saves typically 8–12 weeks of compliance time and $10–20k in lab fees vs. custom RF design. The trade-off is the per-unit cost premium ($3–10 vs. $1–3 in custom).

For volumes under 100k units/year, pre-cert modules are almost always cheaper net. Above that volume, custom designs amortise.

6.Wireless certification timeline

For a typical new device with one wireless protocol (BLE or Wi-Fi).

6.1Pre-certified module path

6.2Custom RF design path