1905: Phased array - The book of science

Phased array
Phased arrays
Interference
Commentary

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.

During the Cold War, my father worked at the USAF general surveillance radar station on Mount Tamalpais, which featured a large domed rotating radar antenna. Modern computers and phased array radar stations eventually made such stations obsolete.

Sculling is when each rower has two oars; sweeping is when each rower has one oar.