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The fundamental resonance of a thin linear conductor occurs at a frequency whose free-space wavelength is twice the wire's length; i.e. where the conductor is 1 / 2 wavelength long. Dipole antennas are frequently used at around that frequency and thus termed half-wave dipole antennas. This important case is dealt with in the next section.
When considering an antenna's directional pattern, gain with respect to a dipole does not imply a comparison of that antenna's gain in each direction to a dipole's gain in that direction. Rather, it is a comparison between the antenna's gain in each direction to the peak gain of the dipole (1.64). In any direction, therefore, such numbers are 2 ...
G: the antenna gain; is the magnetic constant; is the electric constant; For antennas which are not defined by a physical area, such as monopoles and dipoles consisting of thin rod conductors, the effective length (units: meter) is used to measure the ratio between voltage and electric field.
The difference between EIRP and ERP is that ERP compares the actual antenna to a half-wave dipole antenna, while EIRP compares it to a theoretical isotropic antenna. Since a half-wave dipole antenna has a gain of 1.64 (or 2.15 dB) compared to an isotropic radiator, if ERP and EIRP are expressed in watts their relation is = If they are expressed ...
The driven element of the antenna is usually a half-wave dipole, its length half a wavelength of the radio waves used. The parasitic elements are of two types. A "reflector" is slightly longer (around 5%) than a half-wavelength. It serves to reflect the radio waves in the opposite direction.
Hence, the monopole antenna has a radiation pattern identical to the top half of the pattern of a similar dipole antenna, and a radiation resistance a bit less than half of a dipole. Since all of the equivalent dipole's radiation is concentrated in a half-space, the antenna has twice the gain (+3 dB) of a similar dipole, neglecting power lost ...
An antenna array consisting of two such antennas, one above the other and driven in phase has a gain of up to 17 dBi. Being log-periodic, the antenna's main characteristics ( radiation pattern , gain, driving point impedance ) are almost constant over its entire frequency range, with the match to a 300 Ω feed line achieving a standing wave ...
Note that at zero spacing we obtain the self-impedance of a half-wave dipole, 73 + j43 Ω. When a passive radiator is placed close (less than a quarter wavelength distance) to the driven dipole, it interacts with the near field, in which the phase-to-distance relation is not governed by propagation delay, as would be the case in the far field ...