Monopulse method

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The monopulse method is an angle measurement method in radar technology . With a monopulse antenna , several received signals are generated from a transmitted measuring pulse of the pulse radar device , which signals determine the position of the detected object within the antenna diagram of the monopulse antenna. By the monopulse method is by comparing the amplitude of the echo signal is calculated, an angle in the different channels, of as English off boresight angle is referred to (OBA).

Monopulse antennas are groups of antennas, the individual antennas of which are not only connected to form a sum. Different sums and differences can be formed for different purposes. Therefore, by comparing the amplitudes of the sum channel and the different difference channels, the reflecting object can be localized within the radar beam. A differential channel (ΔAz) (read: “Delta Azimuth”) is formed by coupling the left and right antenna groups in phase opposition. The azimuth is now determined by the fact that the difference channel (ΔAz) must have a minimum at this angle at a maximum of the sum channel.

If a detected object is exactly in the maximum of the sum channel, then the difference channel has no signal. If a detected object is located next to this maximum of the sum channel, then the difference channel also has a signal with either a negative sign (i.e. here in the graphic above the maximum ⇒ more to the left of the angle for radar) or a positive sign (i.e. below the maximum ⇒ more to the right from the angle). The size of this difference signal is the measure of the deviation from the maximum of the sum channel: the off-boresight angle. To determine the exact direction, this off-boresight angle is added to the boresight angle (direction of the antenna center axis).

Illumination zones of the difference and sum channels

In the case of 2D radars, it is sufficient to divide the antenna group into a left and a right half. In the case of 3D radars , the two halves of the antenna are in turn divided into an upper and a lower half. For the sum signal, all four quarters are connected in phase. (Transmission is also carried out in this phase reference.) The monopulse method of a 3D radar device requires at least three independent reception channels:

  • Sum channel
  • Difference channel (ΔAz)
  • Difference channel (ΔEl)

The difference channel (ΔAz) is formed from the difference between the left and right sums of the upper and lower quarters. The second difference channel (ΔEl) is called "Delta Elevation". The difference between the upper and lower sum of the left and right quarters is formed here. Since the sum channel (Σ) and the difference channels can be formed from just one echo pulse, one pulse is sufficient to calculate the coordinates precisely. That is why the entire system is called the monopulse method and this grouping of antennas is called a monopulse antenna.

Usually a fourth reception channel is used in 3D radars, the

  • Auxiliary Channel Ω

utilized. This is not tied to the monopulse procedure. This channel for compensating for sidelobes practically always has its own small antenna, which, with its intentionally wide antenna pattern, serves to suppress sidelobes and detect active interference.

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