– The bias is dependent upon the signal to interference mean power ratio. Therefore it is dependent upon both interference level and the number of “hits” in the estimate periodogram. – Maximum interference level for reflectivity is defined by the reflectivity bias. – A reflectivity bias (Rb) of 1 dB yields a power ratio of 1.2589. Power Ratio = 10(Rb/10) = 10(0.1) = 1.2589 Subtracting the unbiased power ratio from the power ratio at which a 1 dB bias occurs yields an interference to signal ratio of 0.2589. I/S = [10(Rb/10) – 10(Rb/10)] = [1.2589 – 1] = 0.2589 The interference power level can be computed from the following formula: This value translates to a 6.17 dB signal. IL (dB) = 10 log (4.14) = 6.17 dB For a signal-to-noise-ratio of 3 dB, I/N can be computed as follows: I/N = 6.17 dB + 3 dB = 9.17 dB Combining these factors into a function that describes I/N in relationship to Ns, I/N and Rb results in an equation that yields the maximum required I/N for a single “hit”: where: Ns: number of samples in the estimate; Smp: signal mean power; S/N: receiver ratio; I/S: interference-to-signal ratio, and I/S is expressed as: where: Rb: reflectivity bias; Nnf: normalized noise floor level. Combining the equations yields: An example calculation that is based upon the previous assumptions follows. 8.4.2.2.2 Example calculation Assumptions: Ns = 16; S/N = 3 dB; Rb = 1 dB; Nnf = 0 dB;
Antenna type (reflector, phased array, slotted array, etc.) metal parabolic Parabolic Parabolic Parabolic Solid parabolic Antenna polarization Vertical Horizontal Horizontal Horizontal Horizontal Antenna main beam gain dBi 39 44 50 40 40 Antenna elevation beamwidth degrees 4.8 0.95 < 0.55 < 1.0 1.65 Antenna azimuthal beamwidth degrees 0.65 0.95 < 0.55 < 1.0 1.65 Antenna horizontal scan rate degrees/s 0.65 0-36 (0-6 rpm) 21-24 30-48 30-48 Antenna horizontal scan type (continuous, random, 360⁰, sector, etc.) degrees 360 360 Continuous 360 Sector 360 360 Antenna vertical scan rate degrees/s N/A N/A 15 15 15 Antenna vertical scan type (continuous, random, 360⁰, sector, etc.) degrees N/A N/A Stepwise, 0.5-60 Stepwise, –2 to +60 –1 to +60 Antenna sidelobe (SL) levels (1st SLs and remote SLs) dB –26 –35 –27 –25 –25 Antenna height m 30 10 30 30 30 Receiver IF 3 dB bandwidth MHz 0.5 20 0.91 0.6 0.25 to 0.5 Receiver noise figure dB 7 4 2.3 3 3 . TABLE Characteristics Units Radar 6 Radar 7 Radar 8 Radar 9 Radar 10 Minimum discernable signal dBm –110 –97 –109 –109 to –112 –114 Tuning range MHz 5 600-5 650 5 600-5 650 5 250-5 725 5 600-5 650 5 600-5 650 Modulation Conventional With Doppler capability With Doppler capability With Doppler capability With Doppler capability (including noise calibration w/o emission) Tx power into antenna kW peak W avg. 250 150 250 150 2.25 250 250 Pulse width s 0.8-5 0.8-5 0.1 0.8-2, 5 and 10 0.5 to 3.3 Pulse rise/fall time s 0.2-2 0.2-2 0.005 Pulse repetition rate pps 250-1 200 50-1 200 100 000 50-1 200 and staggered 250-1 200
interleaved and staggered Output device Coaxial magnetron or Klystron Coaxial magnetron Coaxial magnetron Coaxial magnetron Coaxial magnetron Antenna pattern type (pencil, fan, etc.) Pencil Pencil Pencil Pencil Pencil Antenna type (reflector, phased slotted array, etc.) parabolic parabolic Solid parabolic Solid parabolic parabolic Antenna polarization Horizontal and/or vertical Horizontal or vertical Horizontal or vertical Horizontal Horizontal and vertical Antenna main beam gain dBi 40-50 40-50 35-45 44-48 45 Antenna elevation beamwidth degrees 0.5-2 0.5-2 2.4-12 0.65-1 0.9 Antenna azimuthal beamwidth degrees 0.5-2 0.5-2 1.5-12 0.65-1 0.9 Antenna horizontal scan rate degrees/s rpm 6-18 1-3 6-18 1-3 1.2 3-36 0.5-6 6-36 1-6 Antenna horizontal scan type (continuous, random, 360⁰, sector, etc.) degrees 360 360 360 360 360 Antenna vertical scan rate degrees/s 1-10 1-14 N/A TABLE Characteristics Units Radar 6 Radar 7 8 9 Radar 10 Antenna vertical scan type (continuous, random, 360⁰, sector, etc.) degrees –1 to +90 –5 to +90 N/A –2 to +90 –2 to +90 Antenna sidelobe (SL) levels (1st SLs and remote SLs) dB –25 to –35 –25 to –35 –20 –25 to –45 –25 to –45 Antenna height m 6-30 6-30 10 6-30 7-30 Receiver IF 3 dB bandwidth MHz 0.7 to 4 0.1 to 3.0 10 0.1 to 1.25 0.3 to 2 Receiver noise figure dB 3.5-8 1.5-8 3 3 3 Minimum discernable signal dBm 113 to 120 113 to 120 113 to 118 30 to 54 (at 1 km) 107 to 115 TABLE Characteristics Radar 11 Radar 12 Radar 13