April 2015 | NTIA Technical Report TR-15-514
Robert J. Achatz; Paul M. McKenna; Roger A. Dalke; Frank H. Sanders; John E. Carroll
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 introduce unwanted emissions in the radar detection bandwidth and cause interference. Interference protection criteria (IPC) are needed to mitigate this effect. The primary IPC of concern are the interference to noise power ratio (INR) and the reliability of the radar link at a specified radar signal to noise power ratio (SNR). Reliability is determined by radio wave propagation path loss variability which increases with distance. Distance separation between base stations and radar for various spurious attenuations were calculated using reliability expressions for short radar to target ranges with constant SNR and for longer radar to target ranges with variable SNR. For a magnetron radar under clutter free conditions, 90 dB of spurious attenuation is needed to obtain 90% radar operational reliability at1.2 km when the INR is -6 dB and the SNR is constant. Reducing the INR to -9 and -12 dB increased the separation distance to 1.7 and 2.7 km, respectively. At longer base station to radar separation distances, variable SNR required less spurious attenuation than constant SNR. Consequently, constant SNR analysis can be considered worst case. Distance and frequency separation were calculated using frequency dependent rejection (FDR). These calculations showed that for constant SNR 92.8 MHz of frequency separation is required to meet the 90% reliability IPC at 1.2 km separation distance when the INR is -6 dB. Only 54.6 MHz frequency separation is needed when the separation distance is increased to 32.8 km.
Keywords: radar; interference; radio wave propagation; frequency dependent rejection; interference protection criteria (IPC); spurious emissions; broadband radio service; marine radar; radio spectrum engineering
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Robert J. Achatz
Institute for Telecommunication Sciences
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