Radar Transmitters

Radar technology is mainly put into use for detection of level in continuous level measurement applications. Radar level transmitters provide non contact type of level measurement in case of liquids in a metal tank. They make use of EM i.e. electromagnetic waves usually in the microwave X-band range which is near about 10 GHz. Hence, they can be also known as microwave level measurement devices. A radar level detector basically includes:  A transmitter with an inbuilt solid-state oscillator  A radar antenna  A receiver along with a signal processor and an operator interface The operation of all radar level detectors involves sending microwave beams emitted by a sensor to the surface of liquid in a tank. The electromagnetic waves after hitting the fluids surface returns back to the sensor which is mounted at the top of the tank or vessel. The time taken by the signal to return back i.e. time of flight (TOF) is then determined to measure the level of fluid in the tank. Pulse radar has been used widely for distance measurement since the very beginnings of radar technology. The basic form of pulse radar is a pure time of flight measurement. Short pulses, typically of millisecond or nanosecond duration, are transmitted and the transit time to and from the target are measured. The pulses of pulse radar are not discrete mono pulses with a single peak of electromagnetic energy, but are in fact a short wave packet. The number of waves and the length of the pulse depend upon the pulse duration and the carrier frequency used. These regularly repeating pulses have are relatively long time delay between them to allow the return echo to be received before the next pulse is transmitted. If we consider that the speed of light is approximately 300,000 kilometers per second. Then the time taken for a radar signal to travel one meter and back takes 6.7 nanoseconds or 6.7 x 10-9 seconds. How is it possible to measure this transit time and produce accurate vessel contents information? A special time transformation procedure is required to enable theses short time periods to be measured accurately. The requirement is for a ‘slow motion’. We mean milliseconds instead of nanoseconds. Pulse radar has a regular and periodically repeating signal with a high pulse repetition frequency (PRF). Using a method of sequential sampling, the extremely fast and regular transit times can be readily transformed into an expanded time signal. A common example of this principle is the use of a stroboscope to show down the fast periodic movements of rotating or reciprocating machinery. Pulse radar takes literally millions of ‘shots’ every second. The return echoes from the product surface are sampled and averaged which is particularly important in difficult applications where small amounts of energy are being received from low dielectric and agitated product surfaces. The averaging of the pulse technique reduces the noise curve to allow smaller echoes to be detected.