Principles of Modern Radar - Volume 2 1891121537

562 CHAPTER 12 Electronic Protectionagainst sidelobe EW systems as these systems may already be stressed in detecting radarsidelobe emissions. We can estimate the minimum transmit power by rewriting the radarrange equation, Equation 12.5, asP t,min = SNR minL s (4π) 3 R 4 kTFG t G r λ 2 σ nτ(12.19)where P t,min is the minimum transmit power necessary to detect a target of a given RCS,σ , and range, R, and SNR min is the minimum SNR necessary for detection. The resultingvalue of P t,min can then be used in the expression for the jammer received power shown inEquation 12.17 to see if the signal received by the jammer exceeds its detection threshold.12.6.3 Emission ControlEmission control (EMCON) is a more dramatic way of reducing radar emissions thanpeak power reduction. It involves restricting radar transmissions to only the minimumamount of time necessary as well as to only the angular sectors necessary. This helpsprevent EW systems from detecting, identifying, and locating the radar [3,5,10]. It alsoreduces the radar vulnerability to ARMs that may be unable to accurately coast for longintervals without an angle measurement for guidance. A mobile radar might use EMCONcombined with rapid relocation to further defend against weapon attacks.Emission control using short, infrequent transmissions might be able to delay the detectionby EW systems or ARMs that employ scanning antennas or scanning narrowbandreceivers. Such systems may be sacrificing probability of intercept (POI) in favor of improvedsensitivity. Probability of intercept refers to the probability that the radar emissionis within both the antenna instantaneous field of view and receiver IBW of the EW system.Narrow beamwidth (higher spatial gain) and narrow IBW (less thermal noise) increasesensitivity but decrease POI, whereas wide beamwidth and wide IBW increase POI butdecrease sensitivity. Channelization of the EW receiver helps simultaneously preserveboth POI and sensitivity in the receiver but at the expense of higher cost, weight, size, andcomplexity.12.7 EXCITER-BASED EPThe radar exciter determines the characteristics and diversity of the radar waveformsthat are generated. Potential EP benefits are realized through long-duration waveforms,range-resolution waveforms, and waveform diversity and agility.12.7.1 Wide-Pulse WaveformWide-pulse, or long-pulse, waveforms provide an alternative to high peak transmit poweras a means of increasing the total energy of a target relative to noise jamming. TheJSR of a noise jammer is inversely proportional to the pulse width, as seen in Equation12.9. Some transmitters have a maximum pulse width capability, and therefore a widepulsewaveform must be compatible with the transmitter design. Range resolution isalso a possible concern. The range resolution, R, for a simple, unmodulated pulse isequal to cτ/2. Going from a 1-μs pulse to a 10-μs pulse, for example, would reducethe JSR by 10 dB but would also decrease the range resolution from 150 m to 1500 m,