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EIRP Density: A Regulatory Tool?

By | October 1, 2009

      The challenge: Attending to the ever-growing demand for smaller antennas while maintaining the integrity of the 2-degree satellite separation standard. The solution: The use of uplink effective isotropic radiated power EIRP density as a regulatory tool.

      The U.S. Federal Communications Commission (FCC) has lately used EIRP density (a calculation of antenna uplink EIRP spread over a fixed bandwidth) to speed up the licensing of smaller antennas as well as to regulate the emissions from new services such as Earth stations on vessels and vehicle-mounted Earth stations. 

      The 2-Degree Standard

      Since 1983, the United States has operated on a 2-degree standard of separation between domestic satellites along the geostationary arc. This standard was a reduction from the 1970’s standard of 3 degrees and 4 degrees for C- and Ku-band, respectively. The reduction to 2 degrees came as a response to a growing demand for more satellites in orbit, but this decision has placed a greater burden on ground antennas that now must operate under improved sidelobe performance. Smaller antennas have larger sidelobes, which have greater potential for causing harmful interference to adjacent satellites.

      The FCC published directives whereby the sidelobes of antenna gain plots had to fall below a certain limit or “envelope.” If antenna sidelobes exceeded the prescribed envelope, the antenna was said to be “non 2-degree compliant.” This meant that such antenna could only be licensed if the FCC examined the application under a case-by-case review process, and the applicant could implement measures for mitigating adjacent satellite interference.

      The FCC typically required a license applicant to secure affidavits from adjacent satellite operators in which the operators acknowledged the potential interference from the applicant antenna. The problem with this approach was that these affidavits often were difficult to obtain because the applicant had a business relationship with the operator of the satellite with which it intended to communicate but not with adjacent satellite operators.

      The EIRP Density Tool

      To address the challenge of limiting adjacent satellite interference while licensing smaller antennas (especially stabilized antennas), the FCC turned to EIRP density to solve this riddle. In the 2005 Earth Stations on Vessels (ESV) order, the FCC required that applicant antennas comply with EIRP density envelopes specifically developed for ESV applications. It is interesting to note that this FCC posture is different from the stance taken by some European regulators, which set a minimum antenna diameter standard for ESV licenses.

      The FCC’s use of EIRP density allowed ESV applicants to use an antenna of any diameter, however small, so long as the antenna sidelobes fell below the prescribed EIRP density envelope. Because EIRP density is the combination of the power density supplied to the antenna and the antenna gain, an applicant could comply with the regulations by just reducing the input power density into the antenna.

      In February, the FCC issued an order allowing non-2-degree compliant antennas to apply for routine treatment (the process of expeditious handling of applications rather than a case-by-case review). The caveat again was that applicants’ antennas fall below an EIRP density envelope developed specifically for this purpose. This meant that affidavits from adjacent satellite operators no longer were required as long as applicants reduced their input density to below the set limit.

      Most recently, the FCC issued an order in August allowing vehicle-mounted Earth stations to operate in the Ku-band on a primary basis. Because of the need to use small antennas to fit in space-constrained vehicles, vehicle-mounted units are prone to increased risk of causing adjacent satellite interference. However, the FCC again decided to use EIRP density, rather than a minimum antenna diameter, as a factor in the license application.

      With today’s pressure to reduce costs, the use of smaller diameter antennas has become more widespread just as the number of satellite applications that cater to space-restricted customers have become available. Yet, the satellite community wants to keep adjacent satellite interference under control. By using EIRP density as a gate keeper of sorts, both goals are attainable.

      Raul Magallanes runs a Houston-based law firm focusing on telecommunications law. He may be reached at +1 (281) 317-1397 or by email at raul@

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