Contents
What is reactive near field?
The reactive near field is the region where the fields are reactive i.e the E and H fields are out of phase by 90 degrees to each other. For propagating or radiating fields, the fields must be orthogonal to each other but in phase.
What is a antenna conductor?
The conductor, or element, is aligned with the electrical field of the desired signal, normally meaning it is perpendicular to the line from the antenna to the source (or receiver in the case of a broadcast antenna). The radio signal’s electrical component induces a voltage in the conductor.
Why are reactive near field not suitable for testing an antenna?
The radiative near field (sometimes called the Fresnel region) does not contain reactive field components from the source antenna, since it is far enough from the antenna that back-coupling of the fields becomes out of phase with the antenna signal, and thus cannot efficiently return inductive or capacitive energy from …
What is the boundary for a reactive near field?
Phase difference theory states that for a temporal phase difference of ≤ 37.30 the field can be considered as reactive near field and for a temporal phase difference of ≥ 82.7 0 the field region can be considered as far-field region. In between these end-points, lies the reactive near field region.
How does the near field of an antenna work?
Consider a well-designed dipole antenna; you can place an array of “other elements” around it and turn the dipole into a Yagi-Uda antenna: – The Yagi-Uda antenna uses “other elements” constructively to produce an EM emission directed towards a particular direction. These extra elements are in the near-field of the dipole-section of the antenna.
Can a bit of metal near an antenna cause signal loss?
Bits of metal near antenna may or may not have induced current, but needn’t cause signal loss. They can just as well cause beam steering, or (if, for example, the metal is a dish) can cause significant antenna gain (not power gain, ‘antenna gain’ means focusing, or direction limiting to form a beam).
Which is true about the reactive portion of the antenna?
The reactive portion is dictated by the capacitance and inductance of the antenna and exists predominately in the near field . The real portion is dictated by something called radiation resistance, caused by the propagation delay, and exists at large distance from the antenna in the far field .
How is the inductance of an antenna determined?
The circulation of this magnetic field results in inductance of the antenna. The antenna is therefore a reactive device having both capacitance from the charge distribution and inductance from the current distribution. Figure 3. (a) Electric field E and (b) magnetic field H and TEM field from dipole charge and current