Overview
This article summarizes FCC performance metrics for satellite earth station antennas, specifically the antenna pattern or antenna radiation pattern. Antenna radiation patterns are a primary factor determining minimum satellite spacing and therefore affect how effectively spectrum resources can be used.
What is an antenna radiation pattern
A frequency spectrum plot shows power versus frequency over a range, which is one-dimensional. An antenna radiation pattern shows radiated power versus direction over a spatial range. Strictly speaking, the antenna pattern is a three-dimensional shape, but two orthogonal planar cuts are commonly used for analysis, covering co-polarization and cross-polarization metrics.
Co-polarization
Section 25.209(a) addresses co-polarization gain limits for earth station antennas operating in the Fixed-Satellite Service (FSS) and transmitting to geostationary-satellite orbit (GSO) satellites, including earth stations providing feeder links for non-FSS space services. The limits in (a) are general standard limits; non-standard or special provisions are described elsewhere.
Fixed-Satellite Service (FSS)
Fixed-Satellite Service (FSS). A radiocommunication service between earth stations at given positions, when one or more satellites are used; the given position may be a specified fixed point or any fixed point within specified areas; in some cases this service includes satellite-to-satellite links, which may also be operated in the inter-satellite service; the Fixed-Satellite Service may also include feeder links of other space radiocommunication services.
Co-polarization refers to transmit and receive antennas having the same polarization plane and direction. Cross-polarization refers to orthogonal polarization. For satellite earth stations, the two orthogonal planes are the plane tangent to the GSO arc and the plane perpendicular to the GSO arc, hereafter referred to as the GSO tangent plane and the GSO perpendicular plane.
Co-polarization limit cases
Co-polarization limits depend on frequency band and plane orientation and are categorized into six cases:
(1) Tangent plane, for earth stations not operating in the conventional Ku band, 24.75–25.25 GHz, or 27.5–30 GHz: see table below.
Here θ denotes the angle between the antenna main-lobe axis and the direction to the specified orbital location. For θ in the ±7–180° range, up to 10% of sidelobes may exceed the envelope by up to 3 dB. In the region of main reflector spillover, exceedance up to 6 dB is permitted.
(2) Tangent plane, conventional Ku band: limits as shown below. The same allowances for main-lobe and sidelobe exceedance apply.
(3) Tangent plane, 24.75–25.25 GHz or 27.5–30 GHz: limits as shown below. The same allowances for main-lobe and sidelobe exceedance apply.
(4) Perpendicular plane, for earth stations not operating in the conventional Ku band, 24.75–25.25 GHz, or 27.5–30 GHz: see table below.
For θ in the ±3–180° range, up to 10% of sidelobes may exceed the envelope, but by no more than 6 dB. In the region of main reflector spillover, exceedance up to 6 dB is permitted.
(5) Perpendicular plane, conventional Ku band: limits as shown below. The same allowances for main-lobe and sidelobe exceedance apply.
(6) Perpendicular plane, 24.75–25.25 GHz or 27.5–30 GHz: limits as shown below. The same allowances for main-lobe and sidelobe exceedance apply.
Cross-polarization
Example co-polarized and cross-polarized patterns are illustrated below; the solid line indicates co-polarization and the dashed line indicates cross-polarization.
Cross-polarization limit requirements are:
(1) Tangent plane, earth stations not operating in 24.75–25.25 GHz or 27.5–30 GHz: 19 – 25 log θ dBi for 1.8° < θ ≤ 7°.
(2) Perpendicular plane, earth stations not operating in 24.75–25.25 GHz or 27.5–30 GHz: 19 – 25 log θ dBi for 3° < θ ≤ 7°.
(3) Either plane, earth stations operating in 24.75–25.25 GHz or 27.5–30 GHz: 19 – 25 log θ dBi for 2° < θ ≤ 7°.
Interference protection rights for certain earth stations
(1) Under sections 25.115(b)(1) and 25.115(b)(3) regarding receive-only earth stations that are licensed or registered to operate with or to receive from GSO FSS space stations: if the receive-band gain pattern of a receive-only earth station meets the levels specified in sections (a) and (b) of this rule, that earth station is not entitled to interference protection from authorized operations of other stations.
(2) 17/24 GHz BSS telemetry earth stations are not entitled to protection from harmful interference caused by authorized space station operations if the receive antenna gain pattern meets the levels in sections (a) and (b). Receive-only earth stations in the 17/24 GHz BSS are protected from harmful interference by other space stations only within the scope specified in section 25.224.
Earth stations without skew angle adjustment
Earth stations using asymmetric antennas that lack skew angle adjustment capability must meet the gain values specified in section (a)(1) on the plane orthogonal to the antenna's principal plane, or on the plane corresponding to the maximum skew angle that the earth station may experience at any location. The skew angle is illustrated below.
Special earth stations that do not meet the above requirements
GSO FSS earth station antennas that do not meet the applicable standards in sections (a) and (b) will be approved only if the applicant demonstrates that the antenna will not cause unacceptable interference. The demonstration must show that the earth station's transmissions comply with the off-axis EIRP density envelopes in section 25.218 for FSS earth stations transmitting in specified frequency bands, or the applicant must demonstrate that the earth station operation has been coordinated in accordance with section 25.220.
NGSO earth station antenna limits
For gateway earth stations communicating with NGSO FSS satellites in the 10.7–11.7 GHz, 12.75–13.15 GHz, 13.2125–13.25 GHz, 13.8–14.0 GHz, and/or 14.4–14.5 GHz bands, any transmitting antenna gain must be below the defined limits shown below.
The definition of θ is the same as in section (a)(1). For θ in the ±7–180° range, up to 10% of sidelobes may exceed the specified limits by up to 3 dB.
