www.radartutorial.eu Radar Basics

Overview of Radar Transmitter

The radar transmitter produces the short duration high-power rf pulses of energy that are radiated into space by the antenna. The radar transmitter is required to have the following technical and operating characteristics:

The radar transmitter is designed around the selected output device and most of the transmitter chapter is devoted to describing output devices therefore:

Figure: keyed-oscillator type transmitter of russian P-37 (“Bar Lock”)

permanent magnet permanent magnet Magnetron Control-block for the power supply Waveguide-section high-voltage transformer modulator thyratron charging diode pulse-forming network pulse transformer high-voltage condensator high-power resistors

Figure: keyed-oscillator type transmitter of russian P-37 (“Bar Lock”)

Pictured is a keyed oscillator transmitter of the historically russian radar set P-37 (NATO-Designator: „Bar Lock”).
The picture shows the typical transmitter system that uses a magnetron oscillator and a waveguide transmission line. The magnetron at the middle of the figure is connected to the waveguide by a coaxial connector. High-power magnetrons, however, are usually coupled directly to the waveguide. Beside the magnetron with its magnetes you can see the modulator with its thyratron. The impulse-transformer and the pulse-forming network with the charging diode and the high-voltage transformer are in the lower bay of this rack.

Solid-state transmit/receive modules appear attractive for constructing phased array radar systems. However, microwave tube technology continues to offer substantial advantages in power output over solid-state technology. Transmitter technologies are summarized in the following table.

Technology Maximum Frequency Peak/ Average   
Power
Typical Gain Typical Bandwidth
POT Magnetron 95 GHz 1 MW / 500 W )¹ - Fixed…10%
Impatt diode 140 GHz 30 W / 10 W )¹ - Fixed…5%
Extended interaction oscillator (EIO) 220 GHz 1 kW / 10 W )² - 0.2% (elec.)
4% (mech.)
PAT Helix traveling wave tube (TWT) 95 GHz 4 kW / 200 W )¹ 40…60dB Octave/ multioctave
Ring-loop TWT 18 GHz 8 kW / 400 W )¹ 40…60dB 5…15%
Coupled-cavity TWT 95 GHz 100 kW / 25 kW )¹ 40…60dB 5…15%
Extended interaction Klystron (EIK) 280 GHz 1 kW / 10 W )² 40…50dB 0.5…1%
Klystron 35 GHz 50 kW / 5 kW )¹ 30…60dB 0.1…2% (inst.)
1…10% (mech.)
Crossed-Field amplifier (CFA) 18 GHz 500 kW / 1 kW )¹ 10…20dB 5…15%
Solid state Silicon BJT 5 GHz 300 W / 30 W )³ 5…10dB 10…25%
GaAs FET 30 GHz 15 W / 5 W )¹ 5…10 dB 5…20%
)¹ demonstrated at X-Band
)² demonstrated at 95 GHz
)³ demonstrated at 1 GHz

Table 1: Pulse Radar Transmitter Technology
Source: Tracy V. Wallace, Georgia Tech Research Institute, Atlanta, Georgia.