Changing Your Antenna After FCC Certification?

We are often asked if it is possible to change the antenna that is used with a product after the product has FCC certification. The answer is yes, but with some strings attached.

CFR 47 Part 2.1043 defines three types of permissive changes:

A Class I permissive change includes those modifications in the equipment which do not degrade the characteristics reported by the manufacturer and accepted by the Commission when certification is granted. No filing is required for a Class I permissive change.

A Class II permissive change includes those modifications which degrade the performance characteristics as reported to the Commission at the time of the initial certification. Such degraded performance must still meet the minimum requirements of the applicable rules. When a Class II permissive change is made by the grantee, the grantee shall provide complete information and the results of tests of the characteristics affected by such change. The modified equipment shall not be marketed under the existing grant of certification prior to an acknowledgment that the change is acceptable.

 A Class III permissive change includes modifications to the software of a software defined radio transmitter that change the frequency range, modulation type or maximum output power (either radiated or conducted) outside the parameters previously approved, or that change the circumstances under which the transmitter operates in accordance with Commission rules.

Changes to the antenna will fall under either a Class 1 or Class 2 permissive change.  The Class 1 is preferred because no testing or filing is required. Part 15.204 describes using different antennas and the FCC issued KDB Publication 178919 D01 to provide more specific details on permissive changes, including speaking specifically to antenna changes.

The summary of these documents is that a Class 1 permissive change is allowed if the new antenna is equivalent to the antenna with which the product was tested. They define an equivalent antenna as well.

Equivalent antennas must be of the same type (e.g., yagi, dish, etc.), must be of equal or less gain than an antenna previously authorized under the same grant of certification (FCC ID), and must have similar in-band and out-of-band characteristics (consult specification sheet for cutoff frequencies).

This gives three conditions that must be met:

  1. Same type
  2. Equal or lesser gain
  3. Similar in-band and out-of-band characteristics

Some of these are fairly obvious and some not so much, so here is a closer look at each.

Same Type

Many customers tend to miss this one. In this requirement, the type refers to the radiation patterns produced by the antenna (§15.204 (c) (1)). This is also related to the physical construction and connection of the antennas. A monopole antenna can only be replaced by another monopole antenna.  A dipole antenna can only be replaced by a dipole antenna. A Yagi antenna can only be replaced by a Yagi antenna.

This rule has some subtle complexities that tend to get glossed over. Monopole and dipole antennas produce similar radiation patterns on paper, but the reality is not that simple. Monopole antennas require a ground plane to complete the antenna structure. The size, shape, and orientation of the plane to the monopole element all have a critical impact on the overall performance. There would need to be data showing that the monopole on the same size plane with the appropriate orientation as in the end product has the same radiated performance as the dipole.

The connection method also comes into play here.  An antenna with a connector that is screwed onto a connector on the product cannot necessarily be replaced by an antenna that is mounted directly on the product’s circuit board. Not only must equivalency be shown in the performance of the two antennas, but this also changes the product’s PCB, which may now not be electrically equivalent. The new antenna should connect to the product in the same way as the old antenna or the product should be re-tested.

Equal or Lesser Gain

This is the one that is easiest to understand. Higher peak gain means that the antenna can interfere with other things and it is reasonable that testing is required. Antennas with the same or lesser gain are less likely to cause problems with other things out in the world. This is typically derived from the gain values listed on the antenna data sheets.

There may be questions with monopole antennas. These are half of the antenna with the other half being a counterpoise either on the products PCB or enclosure. Since this is half the antenna’s structure, it is critical to the antenna’s performance. Not all manufacturers use the same counterpoise dimensions when specifying the gain and those dimensions are likely different from the end product dimensions. If there is a lot of variability in these dimensions, then testing may be required.

Similar in-band and out-of-band characteristics

This one has the least definition around it. The basic meaning is that the new antenna must have similar bandwidth and VSWR to the original antenna. These are specified in the antenna data sheets. The issue here is that if the new antenna is a better radiator at restricted frequencies or harmonics, then it could fail the requirements. So the new antenna should have a similar frequency response as the old antenna.

The FCC has done a good job of outlining when a company can replace the antenna without testing and filing. This has helped companies choose antennas that improve product cost or better fit the form of the product. We also get asked about other countries, specifically Canada and Europe.

Industry Canada (IC)

Devices certified under RSP-100 generally follow the same rules as the FCC. RSP-100 outlines the same Permissive Change classes for Class 1 and Class 2. Although IC has not outlined the antenna change policy as clearly as the FCC, they have the same language in their permissive change rules, so companies generally follow the same guidelines.

Europe

Europe has a different view of placing radio equipment on the market from the FCC and IC. ETSI does not have a certification program.  Instead, the manufacturer of the end product declares that the product conforms to the ETSI regulations. If the antenna is changed then the manufacturer must still declare that the product conforms to the regulations. This means that the new antenna produces the same or lesser radiated emissions across all in-band and out-of-band frequencies when placed in the end product.

ETSI prefers that every product gets tested as it will be placed on the market. All of the regulations and Technical Guidance notes make this clear. This means testing each antenna option to ensure it meets the appropriate radiated requirements.

Ultimately, the company placing the product on the market is responsible for ensuring that it conforms to the rules, so they must have sufficient data to support their Declaration of Conformity.

Conclusion

There are many reasons why there is an advantage to being able to change the antenna after an FCC certification has been completed. Cost, supplier performance, aesthetic look, and feel. All of these reasons are valid.  However, the manufacturer is responsible for ensuring that the end product as it will be placed on the market complies with the appropriate rules and regulations. If in doubt, it is always best to consult an accredited test lab to see if the cost and time for testing is warranted.

References

353028 D01 – Basic Equipment Authorization Guidance for Antennas Used with Part 15 Intentional Radiators

178919 D01 Permissive Change Policy

Industry Canada RSP-100 – 7. Modification of Certified Products

Radio Equipment Directive (RED) – 2014/53/EU

EU Radio Equipment Directive (RED) Page

Guide to the Radio Equipment Directive 2014/53/EU

Harmonised Standards for the RED and EMC Directives

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