Minimum bearing
Some older tracking radars use the minimum bearing to determine heading. In English this type of target tracking is called "conical scan". The first radar that worked with this method, which was Wuerzburg D .
The antenna pattern in this radar is generated by a rapid rotation of the radiator in the antenna . The antenna diagram thus rotates around the linear geometric axis of the antenna. A funnel-shaped signal minimum is now formed in the optical direction of the antenna. The target is on the side of the antenna diagram, which at this point has a fairly good slope, i.e. H. a relatively large change in signal level takes place even with the smallest changes in angle.
Compared to simple direction finding , this method has the advantage that when the aircraft leaves the central antenna direction, the direction can be identified and tracking of the antenna is made easier.
If the target is exactly on the central axis, a relatively constant but very small echo is always received. But if the target moves even a little away from this axis, then the levels change during one antenna beam rotation. If the target is e.g. B. too far to the left, then the echo signal will show a maximum if the rotary motor of the antenna feed points to the left and if it points to the right, then a minimum is received. So if the target moves slightly to the left from the minimum, a computer or an analog follow-up system evaluates this information and generates control signals for the servomechanism of the antenna, which now also moves a little to the left until the echo signal receives a constant level again becomes. In this way, the direction to the target is always automatically and very precisely determined in terms of lateral and elevation angles.
The comparatively easy manipulation is a disadvantage. If the target knows or can determine the operating parameters such as the speed of rotation, the intelligent target unit with a jammer can actively and synchronously send out an interference pulse when the received radar signal is weakest. The determined position is thus reflected in the radar receiver.
Web links
Individual evidence
- ↑ a b Wodek Gawronski, Emily M. Craparo: Antenna Scanning Techniques for Estimation of Spacecraft Position . Ed .: Jet Propulsion Laboratory [JPL], California Institute of Technology. tape 44 , no. 6 . IEEE Antenna's and Propagation Magazine, 2002, pp. 38-45 , doi : 10.1109 / MAP.2002.1167263 ( faculty.nps.edu [PDF]).