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Feeding Systems of Phased Arrays
Figure 1: Tornado Nose Radar
Active Antenna
Active phased-array antennae are antennae at which the transmit power is produced by many rx/tx- moduls of low impact on the antenna directly. E.g.: the airborne Tornado-Nose-Radar, the air defense radar RRP-117 and the naval radar APAR.
Active antennae are usually phased array antennae at which instead of a central high-power oscillator/amplifier, every radiatig element got a small power amplifier in the antenna directly. This has the advantage that the necessary phase shifters must only process a small power.
This e.g. antenna shown in the beside picture consists of 428 active radiator elements.
Deeper explanation of active antennae you'll find in the
chapter „Transmitter”
Passive Antenna
Passive phased-array antennae are subdivided in:
The line feeding is the most applied manner of feeding the passive phased-array antenna. The line feeding needs a wave guide wiring or a strip line network for the power supplying. (E.g.: PAR-80).
A method more seldomly used represents the radiation feeding. At this the antenna area is illyminated with the transmit power by a feed horn. The power is received by small antennae elements, then modified in the phase and emitted again. (E.g.: FRK - Patriot).
Serial Feeding
Figure 2: serial feeding
At the series feed of the phased-array antennae the radiator elements are feeded with the transmit power after each other. The increased (adding) phase shifting by the longer feeding line at this must be taken into account at the adjusting of the phase shifters. A frequency change isn't possible straight away at a series feed so.
Should a frequency change be carried out anyway the computer also must calculate the phase shifting newly (or most in the practice: it use another phase shift table).
Figure 3: parallel feeding
Parallel feeding of a passive antenna
The transmit power is divided up in-phasely at every power-divider at the shunt feed of the phased-array antennae. Every radiating element has an equal long feeding line and is provided therefore in-phasely exactly.
This has the advantage that the computer can ignore the length of the feeding lines at the calculation of the phase shifting.
Transmission Type
Figure 4: transmission type radiation feeding
The place behind the antenna is obstructed by the feeding field. For this the horn radiator doesn't make any shadow in the radiating field in front of the antenna.
The „Patriot” SAM- complex has got a transmission type of phased-array antenna.
Reflection Type of Phased-Array Antenna
plane of the reflection Figure 5: reflection type radiation feeding
At the reflection type behind the antenna is sufficient place to mount modules (E.g.: phase shifter controls and power supplies). Against this the horn radiator disturbs now. Exactly in the best ray direction he forms not only a shadow but he would take the reflected energy again, too. This then produces a standing wave in the feeding system!
But the horn feed already should liking lightly be in the center someplace, if this is not the case different propagation times appear to the radiator elements again.
