wavelength of monopole antenna

why do we always take quarter wavelength to be the monopole antenna ?
any reference to study !

thanks

A λ/4 antenna with a groundplane has an impedance which is mostly resistive rarther than reactive, is around 50-75ohms which is easy to match to transmitters and has a radiation pattern that is reasonably suited to typical uses of radio equipment such a a two way radio in a car where you want the tranmitted energy to go out perpendicular to the antenna rarther than up into the sky and uselessly out into space.

monopole is a quarter wave because the other quarter wave is below the ground plane from image theory. it's like a dipole.

check out the ebooks section and type in antenna. look for balanis or stultzman.

First of all not always the monopole is a quarter-wave. Could be λ/8 (the peak current located at a position well above the top, to give lower-angle of radiation and additional gain). Or if is a bent monopole could have different electrical length.

The impedance of a quarter-wave monopole (Marconi Antenna) with perfect ground, is 36.6 ohms.