April 2015 | NTIA Technical Report TR-15-515
Robert J. Achatz; Mark A. McFarland; Roger A. Dalke; Geoffrey A. Sanders; Paul M. McKenna; Frank H. Sanders; Robert T. Johnk
Abstract: Spectrum reallocations may place broadband radio services (BRS) near spectrum used by 2900–3100 MHz band marine radars. Signals from the BRS base stations can potentially cause the radar front-end to overload and cause interference. This report provides a method that can be used to estimate front-end filter attenuation required at various radar to base station separation distances. The attenuation is the difference between the interfering power at the radar low-noise front-end (LNFE) and the allowable interference power. The BRS signal was emulated with 10 MHz bandwidth Gaussian noise. The allowable interference power IPC is determined from probability of detection measurements with a custom test fixture. Two front-ends were tested. One was an off-the shelf magnetron radar front-end assembly consisting of a circulator, limiter, and low-noise front-end. The other, referred to as the reference front-end, was constructed of discrete components. The reference front-end was tested without the frequency selectivity of the circulator and limiter. Results showed that the allowable interference power is -11.5 and -9 dBm for the reference front-end and magnetron front-end assembly, respectively. Additional front-end filtering is not required for either front-end at distances as close as 400 meters. Distances less than 400 meters were not analyzed due to near-field effects. Gain compression and noise enhancement metrics, which are simpler to measure than performance degradation, were also evaluated to determine if they could reliably predict allowable interference power. Only the noise enhancement metric could reliably predict the performance degradation. This result is important since many front-end overload studies are based on the gain compression point metrics.
Keywords: radar; interference; radio wave propagation; front-end overload; interference protection criteria (IPC); broadband radio service; marine radar; radio spectrum engineering; front-end filter; gain compression; noise enhancement
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Robert J. Achatz
Institute for Telecommunication Sciences
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