Phased array Phased arrays Interference Commentary

Karl Ferdinand Braun electromagnetism

Phased array

• A radio antenna broadcasts in all directions.
• Karl Ferdinand Braun showed that three vertical antennas
• placed at the points of an equilateral triangle
• and operated so that the signal from two is delayed
• by a quarter of a cycle relative to the third
• have a combined directional broadcast perpendicular
• to the two that operate in phase and away from the third.

Phased arrays

• Radio transmitters use phased arrays
• to direct and strengthen broadcasts toward a target city,
• and to move the signal up to reflect from the sky at night
• and down to reflect from the ground during the day.
• Phased array radar systems scan
• more quickly than traditional rotating radar dishes
• and can serve multiple simultaneous uses.
• Radio-frequency identification systems
• use phased array antennas to extend their range.
• Optical phased arrays are used for holography.

Interference

• Rowers in a crew must pull with exactly the same stroke
• or risk skewing the sculling,
• but a photon slipping through more than one slit in a card
• interferes with itself.
• Phased arrays and holograms teach us
• interference is our friend.