Why The Zeppelin, or Zepp, antenna is a half-wavelength radiator fed at one end rather than at the center, traditionally matched with a quarter-wavelength section of open-wire line. It got its name from the trailing wire antennas dangled from Zeppelin airships, where feeding from one end was the only practical arrangement. Because the feed point is at a voltage maximum (high impedance), it needs a matching section or tuner rather than a direct 50 ohm connection.
Watch out The choices about horizontal or vertical arrays that steer their pattern by changing phasing lines describe phased arrays, a completely different technique covered elsewhere in this group.
Zepp = Zeppelin's trailing wire: half wave, fed at the END.