Frequently Asked Questions On Antenna Theory With Answers -20.


This page contains basic questions and short notes on some of the keywords on antenna theory:


96) What is Antenna matching?

When the antenna is receiving with a load resistance matched to the antenna radiation resistance, maximum power is transferred to the load and the power is also re-radiated from the dipole. This is called antenna matching.


97) What is a Short Dipole?

A short dipole is one in which the field is oscillating because of the oscillating voltage and current. It is called so, because the length of the dipole is short and the current is almost constant throughtout the entire length of the dipole.


98) How are fields created from short dipole / oscillating dipole?

The dipole has two equal charges of opposite sign oscillating up and down in a harmonic motion. The charges will move towards each other and electric filed lines were created. When the charges meet at the midpoint, the field lines cut each other and new field are created.This process is spontaneous and so more filed are created around the antenna. This is how radiations are obtained from a short dipole.


99) What are Antenna Field Zones?

The regions containing the radiations that are present around the antenna are called field zones. The fields around an antenna ay be divided into two principal regions.
  • Near field zone (Fresnel zone).
  • Far field zone (Fraunhofer zone).


100) What is self impedance and mutual impedance?

Self impedance of an antenna is defined as its input impedance with all other antennas are completely removed i.e away from it.

The presence of near by antenna no.2 induces a current in the antenna no.1 indicates that presence of antenna no.2 changes the impedance of the antenna no.1. This effect is called mutual coupling and
results in mutual impedance.


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