The Office of Telecommunications (OT) undertook a detailed program to measure and analyze spectrum utilization in the 2.7. to 2.9 GHz band in the Los Angeles and San Francisco areas in support of an Office of Telecommunications Policy (OTP) Spectrum Resource Assessment task. The measurement program consisted of on-site visits to compare predicted and actual PPI interference patterns, and utilization of the Radio Spectrum Measurement System (RSMS) van to validate the component models used in predicting radar-to-radar interference.
From the measured data and a supporting literature search, it was concluded that ducting and man-made clutter (building attenuation) should be included in the propagation loss predictions in order to improve the prediction accuracy of radar-to-radar interference and radar frequency assignments. Even though potential multipath wave interference conditions can be identified, to account for this analytically would require and extremely complex antenna and terrain model. Due to modeling inaccuracies, the difference between the predicted and actual radar-to-radar Interference-to-noise Ratio (INR) levels may be as large as 22 dB (2σ standard deviation region). However, INR errors of approximately 25 dB can still result in relatively accurate predictions of interference patterns on the victim PPI display for conditions where mainbeam-to-backlobe antenna coupling predominates. In summary, it was concluded that the analytical radar-to-radar interference techniques used in this investigation can be used to predict interference patterns on the victim radar PPI display with sufficient accuracy to allow assessment of radar band congestion, frequency assignment flexibility, and potential of the band to absorb new users.