TABLE D.1 Parameters of Two Federal Aviation Administration Air Route Surveillance Radars

Name

Frequency (MHz)

Peak Power (kW)

Antenna Gain (dBi)

Azimuth Beamwidth (degrees)

Scan Rate (rpm)

Pulse Width (μsec)

Pulse Repetition Frequency (PRF) (Hz)

ARSR-3

1250-1350

5000

34

1.25

5

2

310-365

ARSR-4

1215-1400

60

35

1.4

5

9/60

216/72

SOURCE: J.R. Piepmeier and F.A. Pellerano, “Mitigation of Terrestrial Radar Interference in L-Band Spaceborne Microwave Radiometers,” in Proceedings of the 2006 International Geoscience and Remote Sensing Symposium (IGARSS), Denver, Colorado, 2006, pp. 2292-2296, DOI 10.1109/IGARSS.2006.593.

radiated power in a 1 MHz bandwidth is specified by the FCC. It is therefore possible to radiate larger out-of-band total powers in bandwidths larger than 1 MHz. These regulations specify for the ARSR-4 radar, for example, that the allowed OOB emission is Pt_OOB = 10 log(6 · 104W) − (43 + 10 log(6 · 104W)) = −43 dBW (peak) in a 1 MHz bandwidth.

The Friis formula specifies the power received by an EESS radiometer from a transmitting source:

where LFDR is the frequency dependent rejection (FDR) factor, Pt is the transmit power of the radar, is the gain of the radar transmitting antenna in the direction of the radiometer, is the gain of the radiometer antenna in the direction of the radar, λ is the wavelength of the radar frequency, and R is the range between the radar and the radiometer. Using this equation to test the permissible spurious and OOB power levels according to §27.53, set LFDR = 1.0, since it is assumed that the OOB emissions occur within the radiometer bandwidth.

Assume that 20 dBi ( ~ −15 dB from maximum gain due to elevation differences in the line-of-sight [LOS] to the space-based radiometer), of the Aquarius (or similar) radiometer is ~25 dB, λ = 0.21 m, and R ≈ 1 × 106 m LOS from a low Earth orbit (LEO) of altitude ~700 km. These values result in: PRFI_OOB ~ (−43 dBW) + (20 dBi) + (25 dBi) + (−155.5 dB) = −153.5 dBW for an ARSR-4 radar system. This is a peak power level whose impact would be reduced when integrated over a longer integration period; the most conservative (i.e., shortest) relevant ratio of the radar pulse width to the radiometer integration time is ~(6 × 10−5)/(1 × 10−3) = 6 × 10−2 ≈ 12.2 dB. However, the OOB received



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