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As of 2025-07-24

Implementation of Inverted-F Antenna

Notes on implementing an inverted-F antenna

This document describes important notes regarding the radio certification of the inverted-F pattern antenna (TWELITE-SMD-ANT-REVF).

The reference design is published at the following link.

monowireless/PCB_REF_DESIGN_KICAD: Reference Schematic/PCB design data for KiCAD

Requirements

The following conditions must be satisfied.

Wiring must be done according to the pattern and through-holes as per the design data.
- Do not modify areas marked as no-change (DO NOT WIRE) in the design data.
The specified printed circuit board must be used.
- Please specify a 1mm thickness to the PCB manufacturer.
- (If a thickness other than 1mm is required, please refer to the notes below.)
- Due to dielectric properties, glass epoxy (FR-4) must be specified. Other materials are not allowed.
- Layer structure must be double-sided or 4-layer.
- There are no specific requirements for solder mask color or silkscreen.
Confirm that manufacturing and assembly are performed as per the design.
- There should be no design deviations exceeding commonly accepted tolerances.
- The wireless module must be properly mounted.

Design and Performance

GND Area

The inverted-F antenna consists of an inverted-F shaped element and a GND pattern directly beneath the module. The area of the GND pattern significantly affects performance. The optimal size is between 20x20 mm and 40x40 mm.

Wiring

The inverted-F antenna is sensitive to external wiring. For example, wireless tags such as TWELITE CUE that place a coin cell holder on the GND surface without external wiring can achieve near-ideal performance.

If some wiring must be routed on the GND surface, keep it to a minimum. For example, having just one wire passing through generally has negligible impact.

Performance Evaluation

We offer a paid service to measure wireless performance (gain, etc.) on customer-designed boards. Especially for inverted-F pattern antennas, performance may fall below expectations depending on the parent board and wiring conditions. Measuring allows you to verify whether the design roughly meets expected values.

If your policy requires strict performance evaluation such as maximum gain, please conduct measurements at official sites (e.g., authorized testing facilities) that provide certified results.

Certification Status

Japan

Applicable Modules

TWE-L-WX
MW-R-WX

Requirements

Must satisfy the above requirements.

North America (FCC)

Please ensure compliance yourself regarding overseas certifications.

Applicable Modules

TWE-L-WX

Requirements

Must satisfy the above requirements.
Other requirements such as labeling should follow FCC rules.

Europe (EU)

Please ensure compliance yourself regarding overseas certifications.

Applicable Modules

TWE-L-WX

Requirements

Must satisfy the above requirements.
Other requirements such as labeling should follow CE rules.

Other Regions

No certification support.

About PCB Thickness

This design specifies an FR-4 1mm thick PCB. This thickness is the basis for radio certification approval, so using a different thickness will result in loss of certification.

However, for Japan domestic certification only, the following PCB thicknesses are also approved:

t=0.5mm (Not approved for overseas certifications obtained by us)
t=0.8mm (Not approved for overseas certifications obtained by us)
t=1.6mm (Not approved for overseas certifications obtained by us)

Since the antenna pattern is optimized for t=1mm, characteristics will slightly change. However, the change is usually very minor. Characteristic patterns on PCBs sized according to the ideal GND size show changes of about 1 to 3 dB.