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High- and Low- Beam

high beam
low beam
high-beam
receiver
low-beam
receiver
power
divider
transmitter

Figure 2: Radar antenna with high- and low- beam pattern

high-beam receiver low-beam receiver power divider transmitter high-beam circulator low-beam circulator Feedhorn for „low-beam”- Chanel Feedhorn for „high-beam”- Chanel
high beam
low beam

Figure 2: Radar antenna with high- and low- beam pattern

The Figure shows the power supply by two horn radiators. In practice, the horn radiator for the lower pattern (i.e. the upper one of the two) is supplied with more power than the one for the upper pattern. The transmitters power is split by a power splitter. Both horn radiators feed separate receiving channels to avoid interference.

Antenna of the ATC-Radar STAR-2000
(click to enlarge: 300·361px = 17 kByte)

Figure 1: STAR-2000 with High- and Low-Beam- Feeding of the Antenna

It is also possible to feed only the radiator of the low-beam with the transmitter. This allows a greater range to be achieved at lower altitudes. Nevertheless, both channels are used for reception. This is possible because the diagram limits only show a level of -3 dB. With lower power components, however, both diagrams overlap almost completely. In the block diagram, the power divider and one of the duplexers will then be omitted. Since the high-beam radiator also receives some of the transmitter's energy directly from the low-beam radiator, the input of the receiver, which has no duplexer, must be protected with a limiter.