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Antenna Connectors and Remote Antennas

The FCC regulations impose limitations and restrictions on antennas and connectors that may be used in a 2.4-GHz or 5-GHz WLAN system. Although the FCC wrote these regulations, a few other countries have also adopted them. Because of increased popularity of WLAN in the United States, and the desire to build units as a single model, many vendors just follow the same rules for connectors for all the products shipped worldwide.

The Code of Federal Regulations, Part 15.203, states that an intentional radiator (transmitter) must be designed so the user cannot use an antenna that was not provided for the transmitter. The rationale behind this is to prevent the use of improper antennas, which can cause improper action of the transmitter, and to prevent the use of antennas that exceed the maximum permitted gain.

To comply, the regulations suggest that the antenna be permanently attached, or that a unique connector be used. The regulations state that a standard antenna connector is prohibited. The FCC has unofficially stated that their interpretation of a unique connector implies that the connector cannot be readily available to the general public. This antenna and connector requirement does not apply to certain carrier current devices or to devices operated under the provisions of Parts 15.211, 15.213, 15.217, 15.219, or 15.221.

One area of confusion regarding the regulations is this statement: "This requirement does not apply to intentional radiators that must be professionally installed or to other intentional radiators, which, in accordance with §15.31(d), must be measured at the installation site."

However, the regulations go on to state, "The installer shall be responsible for ensuring that the proper antenna is employed so that the limits in this part are not exceeded."

The statement was intended to provide those who install more complicated wireless systems, such as long-range broadband fixed wireless systems or wireless perimeter security systems, with the flexibility they need. The meaning of professionally installed is a subjective one, and the definition is not provided in the regulations. Using a definition straight out of a dictionary, a professional is anyone who receives any compensation for services or work, and there are no ties to licensing or certification. However, if an installer claims that he is a professional installer, and exercises this exemption, he becomes the responsible party. As the responsible party, noncompliance with FCC regulations makes the installer subject to fines and even imprisonment.

This exemption afforded professional installers is intended to allow them the design flexibility to shape antenna coverage patterns that allow for maximum power density and, of course, do so in a manner that will not violate any part of the regulations. Professional installers must consider two factors as part of their customer installations. First, applying maximum power to a specific antenna or area is far from the accepted normal practice. A considerable amount of radio interference comes from existing radio systems already installed and operating. Frequency planning mitigates this to a large extent, but the experienced professional installer will typically use the minimum power necessary to provide suitable link margins and performance. Second, the professional installer tends to use antennas that shape the RF beams no wider than absolutely necessary to provide suitable link margins. This in turn helps provide suitable reliability and performance, with minimum interference offered or received from adjacent radios systems.

In legal terms, this statement requires the installer to test the system, once installed, to verify it complies with all regulations, including transmitted emissions that are generated outside of the legal band, noise generated by the receiver, and overall EIRP ratings. In most cases, these types of measurements are well beyond the scope of most WLAN installers.

In mid-2004, the FCC made some changes to Part 15.204 regarding the use of antennas that were not certified by the manufacturer of the transmitter. Basically it states that any antenna may use the transmitter, as long as it is of a similar type (omni-directional, patch, Yagi, dish, and so on) and that it is of equal or lesser gain. It also cites the manufacturer of the WLAN gear with the responsibility of providing users a list of antennas that have been certified.