<P> Coherent microwave amplifiers operating above 1,000 watts microwave output, like travelling wave tubes and klystrons, require liquid coolant . The electron beam must contain 5 to 10 times more power than the microwave output, which can produce enough heat to generate plasma . This plasma flows from the collector toward the cathode . The same magnetic focusing that guides the electron beam forces the plasma into the path of the electron beam but flowing in the opposite direction . This introduces FM modulation which degrades Doppler performance . To prevent this, liquid coolant with minimum pressure and flow rate is required, and deionized water is normally used in most high power surface radar systems that utilize Doppler processing . </P> <P> Coolanol (silicate ester) was used in several military radars in the 1970s . However, it is hygroscopic, leading to hydrolysis and formation of highly flammable alcohol . The loss of a U.S. Navy aircraft in 1978 was attributed to a silicate ester fire . Coolanol is also expensive and toxic . The U.S. Navy has instituted a program named Pollution Prevention (P2) to eliminate or reduce the volume and toxicity of waste, air emissions, and effluent discharges . Because of this, Coolanol is used less often today . </P> <P> Radar (also: RADAR) is defined by article 1.100 of the International Telecommunication Union _́ s (ITU) ITU Radio Regulations (RR) as: </P> <P> A radiodetermination system based on the comparison of reference signals with radio signals reflected, or retransmitted, from the position to be determined . Each radiodetermination system shall be classified by the radiocommunication service in which it operates permanently or temporarily . Typical radar utilizations are primary radar and secondary radar, these might operate in the radiolocation service or the radiolocation - satellite service . </P>

Give an account of the relevance of radar