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The MoD is unable to release full technical details of the Trimingham radar due to ITAR which restricts the divulgence of certain data. Therefore, it is necessary to make some assumptions on the Pd performance of the TPS-77 radar based on publically available data from the Lockheed Martin TPS-77 Factsheet. In particular, information on the TPS-77 antenna parameters is not directly available.


From the Lockheed Martin TPS-77 Factsheet, the detection capabilities of the radar are quoted as detecting a target with a Radar Cross Section (RCS) of 1m2 at 180NM (333km) with a Pd of 80%. The transmitted power is quoted at 19.9kW. Using this information, it is possible to estimate the parameters required to calculate the turbine Pd.

39. Assuming the operating frequency of the radar to be 1,250MHz, the free space path loss (amount of energy absorbed by the atmosphere without any terrain or shielding) to a target at 333km is calculated to be -144.8dB.


The amount of energy reflected back towards the radar is proportional to the RCS. For any particular radar frequency, the amount of reflected energy can be calculated from the RCS, known as RCS gain. A 1m2 RCS target at 1,250MHz has an effective RCS gain of 23.4dB.

41. 42.

The radar sensitivity can be assumed to be 2 x Path loss + RCS Gain = (2 x -144.8) +23.4 = 266.2dB

If the receiver sensitivity of the TPS-77 radar is assumed to be similar to current generation radars, a figure of -125dBm is typical. Using these figures, this would indicate an antenna gain of circa 34dBi to achieve the quoted Pd. These figures are not dissimilar to an equivalent state of the art L-Band radar such as a Raytheon ASR- 23SS. The calculation is shown at Diagram 7.

Preliminary Environmental Information May 2014

East Anglia THREE Offshore Windfarm

Appendix 0 Example Page 10

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