What is a half wave dipole antenna?

What is a half wave dipole antenna?

Half-wave dipole antenna fed at the centre is the commonest type of dipole antenna and its length is almost half of the wavelength of the frequency for which it is meant. So the total length of a half-wave dipole antenna for the 40m amateur radio band will be almost 20 m. The space needed for the antenna increases as you go down along the amateur radio bands. I had the opportunity to use both 40m and 80m half-wave dipole antenna earlier. But I will have to struggle to get even a 20m half-wave dipole antenna up at my current location!

Maximum radiation from the half-wave dipole is perpendicular to the conductor with almost zero radiation along the axis of the conductor. This would also mean that it would act as an omnidirectional antenna if installed in a vertical position. But installing half-wave dipole in a vertical position would not be easy for a lower amateur band.

In my earlier days of ham radio, I used to simply tie the half-wave dipole across two tall coconut trees using plastic twisted flex threads! Threads would be tied to stones and flung up on top of palm leaves and pulled up in a pulley like fashion. Of course, those half-wave dipoles used to sag in the centre due to the weight of the connecting coaxial cable and it would be almost a V antenna!

A half-wave dipole antenna can also be used at odd multiples of its fundamental resonant frequency. Thus a 40 m or 7 MHz half-wave dipole can be used for 21 MHz, but not for 14 MHz. It will act as 3/2 wave dipole antenna at 21 MHz. The directional gain of a half-wave dipole antenna at the resonant frequency is about 2 dBi.