Space antenna handbook pdf

Space antenna handbook pdf half-wave dipole antenna receiving power from a radio wave. The action is shown slowed down in this animation. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole with a radiating structure supporting a line current so energized that the current has only one node at each end.

The most common form of dipole is two straight rods or wires oriented end to end on the same axis, with the feedline connected to the two adjacent ends, but dipoles may be fed anywhere along their length. This is the simplest type of antenna from a theoretical point of view. 4 wavelength long, so the whole antenna is a half-wavelength long. For a half-wave dipole the radiation is maximum, 2. More of a transmitter’s current is dissipated as heat due to the finite resistance of the conductors which is greater than the radiation resistance. However they can nevertheless be practical receiving antennas for longer wavelengths. 43Ω reactance, thus presenting a slightly inductive reactance.

This is because the effect of antenna length on reactance is much greater for thinner conductors. However these are rarely used. It is a desirable length because such an antenna has the highest gain for any dipole which isn’t a great deal longer. Three dimensional radiation pattern of a vertical half-wave dipole antenna. When mounted vertically this results in maximum radiation in horizontal directions, with relatively little power radiated up into the sky or down toward the Earth, making the vertical dipole a good antenna for terrestrial communication when the direction to the receiver is unknown or changing. 4 wave dipole the gain further increases to about 5. Such antenna designs, although based on the half-wave dipole, generally acquire their own names.

An important consequence is distortion of the antenna’s designed radiation pattern, and change in the impedance seen by the line. 4, thus closely matching that 300 Ω impedance. This is the most common household antenna for fixed FM broadcast band tuners, which usually include balanced 300 Ω antenna input terminals. Diagram of a short dipole antenna. Short dipoles are used in applications where a full half-wave dipole would be too long and cumbersome.