The Society of Broadcast Engineers (SBE) July 19 filed comments with the FCC opposing a request from Wireless Strategies, Inc. (WSI) for a Declaratory Ruling to allow fixed point-to-point microwave links to use one or more distributed radiating elements in addition to a parabolic transmitting antenna.
The WSI request is related to links subject to Part 101 frequency coordination. Because Broadcast Auxiliary Service (BAS) at 950MHz and 18GHz, and TV BAS at 2.5GHz, 7GHz, 13GHz and 18GHz, are subject to Part 101 prior coordination notice, any FCC ruling on Part 101 could impact BAS, prompting the SBE to file comments, the filing said.
The society’s opposition to the WSI request is based on several technical and practical reasons, it said.
Among the reasons:
- A false assumption in the WSI request that there is always headroom between the actual side lobe amplitudes of a parabolic dish and the manufacturer’s radiation pattern envelope (RPE);
- Failure to recognize that manufacturers publish RPE rather than the actual pattern of side lobes to allow for manufacturing tolerances;
- The distributed radiating elements, which the SBE filing said were essential to a phased array, would be dynamically programmable, mounted at different heights and pointed directions other than that of the main parabolic dish. In such a situation, it would be “difficult, and perhaps impossible, to verify” direction, tilt and polarization of each element;
- Failure to address the fact that adding phased-array transmitting antennas requiring a power domain summation of total equivalent isotropic radiated power (EIRP) in a given direction is required to prevent EIRP from exceeding at any azimuth or elevation angle the EIRP based on the RPE of the main beam antenna;
- A suspicion on the part of SBE that the phased-array transmitting antennas envisioned by WSI would not “meet the minimum gain, minimum side lobe suppression or maximum half-power beam width (HPBW) that Category A and Category B antennas must achieve.”
Additionally, the SBE filing characterizes the WSI request for a Declaratory Ruling to be “an end-run attempt to create a new point-to-multipoint use,” which the society said would elevate the potential for interference to existing point-to-point microwave links to such a level as to make the change unwarranted.
For more information, visit www.sbe.org/documents/07-121.pdf.