Dipoles and Monopoles Antenna

The vertical dipole—or its electromagnetic equivalent, the monopole—could beconsidered one of the best antennas for LMR applications. It is omnidirectional (in azimuth) and, if it is a half-wavelength long, has a gain of 1.64 (or G = 2.15 dBi) in the horizontal plane. Although this is a simple antenna, it can be difficult to mount on a mast or vehicle. It is half a dipole placed in halfspace, with a perfectly conducting, infinite surface at the boundary.



A monopole over an infinite ground plane is theoretically the same (identical gain,
pattern, etc., in the half-space above the ground plane) as the dipole in free space. In practice, a ground plane cannot be infinite, but a ground plane with a radius approximately the same as the length of the active element, is an effective, practical solution. The flat surface of a vehicle’s trunk or roof can act as an adequate ground plane. Below shows to you typical monopole antennas for base-station and mobile applications.