The loss of the 1390-1400 MHz band segment under OBRA 93 and the proposed reallocation of the 1385-1390 MHz band segment from military to civilian users will result in an 8 percent reduction of the frequencies available for the Navy’s shipborne radars and the MK 23 TAS. The reallocation approach that could be taken is to retune the radars and the MK 23 TAS within the remaining 1215-1385 MHz frequency range.The reaccommodation approach that could be taken by Navy is to retune within the 1215-1390 MHz frequency band. The overall economic impact of restricting the tuning range of these radars cannot be measured simply by the initial spectrum loss. Reducing the available bandwidth will reduce the anti-jamming/interference margin of the radar and make it more susceptible to interference from new and existing systems within the remaining portion of the band. The high-power requirements of shipboard radars, combined with the physics of over-water radio propagation, result in an interference range extending several hundred kilometers. The resulting increase in radar-to-radar interference would reduce the number of ships that could operate in close proximity within Naval task force formations.
Reallocation of the 1385-1390 MHz band segment will further reduce the number of available unique channels for the MK 23 TAS, and reallocation of the 1390-1400 MHz band segment will reduce the number of available unique channels for TAS from 28 to 25 in blue water operations, and to as few as two channels in operations within 200 nautical miles (nmi) of the United States. The reduction of available channels when operating within 200 nmi off shore is because of radiation restrictions already imposed on MK 23 TAS to prevent interference to FAA air traffic control radars. The impact of reallocating additional spectrum in the 1350-1390 MHz band is particularly severe if two or more of the ships are operating within 200 nmi of each other. Electromagnetic (EM) energy from one MK 23 TAS [the EM interference (EMI) source] couples into the receiver of another MK 23 TAS (the EMI victim) and the interference can be of such severity as to render the MK 23 TAS incapable of detecting targets and performing its mission.
The reallocation of the 1385-1400 MHz portion of the band will require software modifications for the frequency hopping algorithms and hardware modifications to design and install filters. Engineering studies will also be necessary to analyze the specific impact and provide guidance on measures to avoid electromagnetic interference.