Exponaval 2016: Weibel Scientific Developed Combination of Simultaneously Transmitting Radar

Radar Technology – Waveforms
In essence, all radars must obey to the same physical laws of the Universe. The radar formula applies to all types of radars and the speed of light is definitely not easy to change. Radars are often purpose-built with focus on a specific application like ground surveillance, sea surface surveillance, air surveillance, target tracking for weapon control or ballistic testing, weather surveillance, etc. The major difference in these radars are the operating frequency band, the transmission power and the waveforms being used. Typically, both the optimisation and prioritization of these parameters are made for the specific radar to have the best performance for a certain application.

Most of the world’s radars uses the pulse principle, where a pulse is transmitted for a short time and the radar listens for echoes of that pulse caused by various targets, before a new pulse is transmitted. This goes on in a cyclic manner. This type of radar will provide range to targets and only one antenna is used for both transmitting and receiving. For ballistic testing, the Continuous Wave (CW) technique has been used for many years. It transmits constantly and therefore two antennas are required. One for transmitting and one for receiving the echoes. The CW radar sends out a frequency beam that hits a moving target and causes a return with a changed frequency. Subtracting the return frequency from the transmitted frequency gives the velocity of the target – also known as the Doppler effect. Besides to providing velocity of a target, the CW technique is unique in suppressing clutter which will have very low speed, typically close to zero, and thus easy to filter away.

In order to measure the range, the CW output must be changed in frequency, either in steps like Multi-Frequency CW or by modulating the frequency like Frequency Modulated Continuous Wave (FMCW) – the latter also being able to see zero Doppler targets moving radially to the radar itself.The FMCW technique is a type of pulse technique, where the modulation in frequency is somewhat similar to chirps made by some pulse radars. However, typically the FMCW technique uses longer duty cycles and lower output power and therefore FMCW is often used in LPI radars (Low Probability of Intercept) as the low transmitted output power is additionally divided over a large frequency bandwidth (the modulation of the frequency). FMCW radars are however more susceptible to clutter than the pure CW.

 

Publish date

11/30/2016

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