This post subject is phased array antennas. They are many arranged radiators to behave like a single antenna.
Operation principle
The phased array antennas behave like a single antenna which can change the propagation direction of an electromagnetic wave without executing a mechanical movement, using the principle of wave interference.
Constructive and destructive interferences
When two or more waves meet each other at a point, occurs an interference. The interference will be totally constructive (on the right) if waves have the same phase and the resulting wave will have a higher amplitude than the individual ones that met each other. If the phase difference is 180º, interference is totally destructive (on the left) and waves cancel each other.
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What If the phase difference is between 0 and 180º (or π)? When closer to 0, more constructive will be and when closer to 180º, more destructive will be the interference.
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Phased array antennas
If all antennas transmit at same phase, the resulting electromagnetic wave will spread in the perpendicular direction to antennas’ alignment.
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The formula to calculate phase variation () between antennas.
Where is transmitted wave’s wavelength.
Types of phased array antennas
- Linear arrangement.
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- Planar arrangement.
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- Frequency sweep array: each radiator transmits in a different frequency to change propagation direction. It’s simpler because it doesn’t have phase shifters, but, for using many frequencies, it’s more subject to interference and has bandwidth limitations.
- PESA (Passive Electronically Steered Array): A single transceiver (transmitter and receiver) is used for all antennas.
- AESA (Active Electronically Steered Array): each radiator has a transceiver and a receiver.
- HBF (Hybrid Beam Forming): the combination of PESA and AESA, the array is divided into subarrays and each one of the subarrays has a transceiver for an antenna subarray.
Advantages and disadvantages
The advantages are:
- Allow a very fast beam’s direction change.
- The replacement of mechanical parts for electronics makes the system lighter.
- High directivity, which reduces interference.
- Allow many directions.
The disadvantages:
- Sweep is limited to 120º on both axes.
- Still expensive.
- High complexity.
Some applications
- 5G wireless communication systems.
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- Military radars that need to detect a large number of targets at high velocity use phased array antennas.
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- Space communication between satellites or between a satellite and a probe.