Principles of Modern Radar - Volume 2 1891121537

548 CHAPTER 12 Electronic ProtectionTABLE 12-2Noise Jammer Example ParametersRadar Parameter Value Jammer Parameter ValueTransmit power (P t ) 5000 W ESJ transmit power (P j ) 100 WTransmit antenna gain (G t ) 30 dBi ESJ transmit antenna gain at radar 3 dBiReceive antenna gain (G r ) 30 dBi receive polarization (G j,tx )Transmit antenna gain to –5 dBi ESJ receive antenna gain at radar 3 dBisidelobe jammer (G tj )transmit polarization (G j,rx )Receive antenna gain to –5 dBi ESJ noise bandwidth (B j ) 100 MHzsidelobe jammer (G rj )ESJ duty factor (d j ) 1.0Frequency ( f c ) 6 GHz SOJ transmit power (P j ) 500 WRadar wavelength (λ) 0.05 m SOJ transmit antenna gain at radar 17 dBiPulse width (τ)2 μs receive polarization (G j,tx )Waveform bandwidth (B) 10 MHz SOJ noise bandwidth (B j ) 100 MHzNumber of pulses (n) 16 SOJ duty factor (d j ) 1.0System noise figure (F) 5dBtoward the target, receive antenna gain toward the jammer, waveform pulse width, andnumber of pulses coherently integrated. The equation also indicates that the target returnincreases faster with decreasing range (R −4 ) than the jammer return (R −2j ).For an SSJ, and generally also for an ESJ, the target and jammer are both at the samerange and angle, making the JSRJSR SSJ = P j G j d j 4π R 2B j P t G t σ nτ(12.10)Note that the JSR is directly proportional to range squared for the SSJ (and typically theESJ). Thus as the target gets closer, the JSR decreases, and eventually the signal willbecome stronger than the jammer.12.3.4 Noise Jammer Computation ExampleTo illustrate the application of the noise jammer formulas, consider a ground-based radarthat is trying to detect an incoming, airborne target whose RCS is 10 m 2 . An ESJ accompaniesthe target at the same range and angle, and an SOJ is located 100 km from the radarand is in the radar sidelobe; both jammers use barrage noise. The assumed parameters forthe radar and jammers are summarized in Table 12-2. The ESJ ERP is 23 dBW, and theSOJ ERP is 44 dBW; otherwise, both jammers have the same noise bandwidth and dutyfactor.Using the assumed values in Table 12-2, Figure 12-6 plots the target signal, thermalnoise, and jammer noise as a function of the target range. The plot uses a logarithmic scalefor range and plots the various parameters in units of power (dBW). The received targetsignal (S) varies as R −4 , increasing with decreasing range. The ESJ flies at the same rangeas the target, and therefore its noise level increases with decreasing range, but its powerlevel varies as R −2 because it experiences the R 2 spreading loss only in one direction.The SOJ is at a constant 100-km range, and therefore its noise level is independent of thetarget range.If we assume that the radar requires 15-dB SNR for detection, then in the absenceof any jamming, the detection range would be approximately 50 km: this is the point at