|Karl Ferdinand Braun electromagnetism|
- 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.
- 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.
- 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.