What is a radar transmitter?

Answer 1

A radar transmitter is the portion of the radar system that generates the high power microwave signal that is transmitted. This is the electromagnetic wave that the radar sends out to see if it will be reflected off anything in the field of the antenna. The transmitter generates the pulse (in a pulsed system) when the control system tells it to, and this high energy pulse leaves the transmitter and goes down the waveguide to the antenna. From there it goes out into the medium being "looked through" by the radar. After a time (during which the receiver is listening for returns), the transmitter is again told to create the next pulse. Some radars use a continuously broadcast signal, but most use the pulse. The above statements are correct but not quite complete as it describes pulsed transmitters only. A Transmitter in Essence is either one of two thing a High-Power Amplifier or a High-Power Signal Source. Transmitter can also be either Pulse Modulated (AM) or Continues Wave (CW) and some timed both. Both of these types can be either phase coherent on non-phase coherent. The first practical transmitter was invented by the British and this transmitter made Radar practical, as until then the effect of signal reflection was known but the power transmitted was so low the practical range was so limited it was of little or no use. For this reason the British are regarded as the innovators of Radar (and the inventor by some). The first practical high power transmitter was a magnetron and it was a RF resonate cavity machined from solid cast metal. The advantages of this transmitter is that it is high power and Pulsed, and allows a low transmit duty radio. However the disadvantage is that it is non-phase coherent and fairly narrow from one pulse to the next; however Magnetrons are still used today in almost all Marine Radars. The next radar transmitter to emerge was a Klystron and a Klystron was a high power amplifier rather then high power signal source like the magnetron. Klystrons where phase coherent but where lower power and narrow band. However since the transmitter was now phase coherent, Fourier integration in the signal processing could be used to provide a higher signal to noise ratio in the detection stage to compensate for the reduction in power. The Klystron design differed from the magnetron by not being a circular resonate cavity like the magnetron but was effetely strained out into a liner length and this fixed length made the Klystron Phase Coherent as the path length was known and the amount of tuning received was equal in every pulse, but the coupling to the path length in the design made it narrow band. The Klystron design was modified to provide a standing wave transmitter know as the Travelling Wave Tube (TWT), The Travelling Wave Tube (or Twit as in known), is a wider band version of the Klystron that still maintained the phase coherency. Today the trend is not to have one single large transmitter but to have thousands of small cooperating ones that transmit individually at a low power but when constructively combined provide a high power source as either Pulses of CW. This technology provides a transmitter and a combined receiver in thousands of modules known as TR Modules and there advantage is no single point of failure and element phase control to electronically steer a radar beam.