Antennas and Transmission Lines

Half Wavelength Dipole
‣ Two 1/4 λ elements
‣ Very easy to build over a wide frequency range
‣ Omnidirectional in the plane perpendicular to the elements
‣ 2.15 dBi gain
‣ 72 ohm input impedance nearly matches the 50 ohm coax
Can be used as feed for parabolic or corner reflectors.
It can be center fed as shown or fed at other points which will change the input impedance.
28
The dipole can be folded which will increase 4 times the impedance thus providing 288 ohm, very close to the characteristic impedance of
the flat twin line used in antenna receivers.
You can easily build a half wavelength dipole using a flat antenna TV cable by splitting a quarter wave section at the end in two halves and
fixing them horizontally with insulators.