Filament considerations for high stability radar

A summary of filament voltage control techniques for MTI (moving target indicator) systems is presented. It is shown that the selection of the type of filament voltage control to be used depends on a number of factors that influence the stability of the transmitter, including tube type gain, RF frequency, and the PRF (pulse forming network) with its associated stagger and burst patterns. Typically, higher frequency and higher gain tubes are more susceptible to the voltage variations on the filament. For radar transmitters with MTI improvement factors of less than 35 dB, the use of AC on the filament is generally acceptable. From 40 to 45 dB, the use of some type of filament voltage control circuitry offers a 3 to 6 dB benefit in MTI improvement factor. As the requirement for MTI improvement factor is further increased, the improvements resulting from the use of DC or synchronized AC are even more pronounced