What makes antenna radiate

If the current can be made to swing back and forth in the dipole arms in time with the voltage source frequency for example on a swing, you push when the swing reaches the highest point and not before or after , you will get maximum radiation.

For example, a frequency transmission of MHz, the wavelength is 0. Electrically speaking, resonance occurs when any reactance component of an antenna disappears leaving only the real resistances radiation resistance and ohmic losses.

Rather like how pure resistance heaters convert electrical energy to useful heat energy, the radiation resistance can be imagined to be converting the electrical energy in the dipole to the EM waves we want. A point source of radiation known as an isotropic source would radiate uniformly in all directions as shown below. It follows the inverse square law, i. An isotropic antenna cannot exist in reality, so in practice all antennas exhibit some kind of directivity in their radiation patterns. For example, the pattern emitted by our dipole is shown below.

On the ends of the antenna, there is little or no radiation. Generally, these patterns also apply when the same antenna is receiving in a sense that the antenna would be more responsive to signals from one direction and not the other. All types of antennas have their own radiation pattern which targets them at specific applications.

Such topic will be discussed in future article. Circuit Design, Inc. Adiv Techno Services Inc. Saelig Company, Inc. Udea electronics Ltd. We come to the following remarkable conclusion:.

The radiation from an ideal twin lead transmission line with open circuit termination is negligible at distances much greater than the separation between the conductors.

Before proceeding, let us be clear about one thing: The situation at distances which are not large relative to separation between the conductors is quite different.

This is because the Hertzian dipole pairs do not appear to be quite so precisely collocated at field points close to the transmission line. Subsequently the cancellation of fields from Hertzian dipole pairs is less precise. The resulting sum fields are not negligible and depend on the separation between the conductors.

In the new scenario, the ends of the twin lead are bent into right angles. This new section has an overall length which is much less than one-half wavelength. To determine the current distribution on the modified section, we first note that the current must still be precisely zero at the ends of the conductors, but not necessarily at the point at which they are bent. Since the modified section is much shorter than one-half wavelength, the current distribution on this section must be very simple.

In fact, the current distribution must be that of the electrically-short dipole ESD , exhibiting magnitude which is maximum at the center and decreasing approximately linearly to zero at the ends. See Section 9. Finally, we note that the current should be continuous at the junction between the unmodified and modified sections.

Hence, when a voltage is applied across a metal, the electrons travel around a circuit - this flow of electrons is electric current measured in Amps. Let us get back to charge for a moment. Suppose that for some reason, there is a negatively charged particle sitting somewhere in space.

The universe has decided, for unknown reasons, that all charged particles will have an associated electric field with them. This is illustrated in Figure 1. Figure 1. A negative charge has an associated Electric Field with it, everywhere in space. So this negatively charged particle produces an electric field around it, everywhere in space. The Electric Field is a vector quantity - it has a magnitude how strong the field strength is and a direction which direction does the field point.

The field strength dies off becomes smaller in magnitude as you move away from the charge. Further, the magnitude of the E-field depends on how much charge exists. If the charge is positive, the E-field lines point away from the charge. Now, suppose someone came up and punched the charge with their fist, for the fun of it. The charge would accelerate and travel away at a constant velocity. How would the universe react in this situation? This means the electric fields around the charge will be disturbed, and this disturbance propagates away from the charge.

This is illustrated in Figure 2. Figure 2. The E-fields when the charge is accelerated. Once the charge is accelerated, the fields need to re-align themselves.

Remember, the fields want to surround the charge exactly as they did in Figure 1.