The monopulse method is an angle measuring method in radar technology. With a special monopulse antenna a plurality of receiving signals are formed of a transmitted test pulse of the pulse radar device, which can determine the position of the aircraft within the antenna diagram of the monopulse antenna. By the monopulse process is calculated by comparing the amplitude of the echo signal in the different channels, an angle which is referred to as the off-boresight angle (OBA ).
Monopulse antennas are antenna arrays whose individual antennas are connected together not only sum -forming. For different purposes, different sums and differences can be formed. Therefore can be done by amplitude comparison of the sum channel and the various differential channels to localize the reflecting object within the radar beam. ( " Delta azimuth " to them) formed by a phase coupling of the left to the right antenna groups a difference channel ( ΔAz ) is. The azimuth is then determined that this angle is at a maximum of the sum channel of the difference channel ( ΔAz ) must have a minimum.
An aircraft is exactly at the maximum of the sum channel, the difference channel has a signal. An aircraft is next to this maximum of the sum channel, then the difference channel has a signal with either a negative sign (here in the graph above the maximum ⇒ When radar more left of the angle) or positive sign ( ie below the maximum ⇒ more to the right of angle). The magnitude of this difference signal is a measure of the deviation from the maximum of the sum channel: the off-boresight angle. To determine the exact direction of the off-boresight angle to boresight angle ( direction of the antenna center axis ) is added.
In 2D radars a subdivision of the antenna array in a left and a right half will suffice. To 3D radars, the two antenna halves are again divided, an upper and a lower half in each. For the sum signal all four quarters are connected together in phase. (In this phase relation is also sent. ) The monopulse method of a 3D radar device requires at least three independent receiver channels:
- Sum channel
- Difference channel ( ΔAz )
- Difference channel ( ΔEl )
The difference channel ( ΔAz ) is formed from the difference of the left and the right sum of the upper and lower quarter. The second difference channel ( ΔEl ) is called "Delta Elevation ". Here, the difference of the sum of the upper and lower left and right quadrant is formed. Since the sum channel ( Σ ) and the difference between channels may be formed of one echo pulse, a pulse for the accurate calculation of the coordinates will suffice. Therefore, the entire system monopulse method is called and this antenna grouping is called monopulse antenna.
Is usually in a 3D radar or a fourth receiving channel, the
- Auxiliary Channel Ω
Utilized. It is not bound to the monopulse method. This channel has to compensate for side lobes almost always his own small antenna that is used with its intended broad antenna pattern for side lobe suppression and detection of active faults.