Com-Power AD-100 Manual - Page 10

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Theory of Operation

This section describes the theory of operation of AD-100 Dipole Antenna.

3.1 Theory of Operation

The tuned dipoles are standard antennas used for calibrating Open Area Test Sites

(OATS), EMC measurement and as a reference antenna for calibrating other antennas.

These antennas are constructed according to ANSI standard C63.5 requirements.

For site attenuation measurement for the range of 30 MHz 1000 MHz, ANSI C63.5

recommends to using half wave tuned dipoles. Broadband antennas such as biconical

and log periodic antennas can also be used for site attenuation measurements. However,

use of dipole antennas are preferred because they are precise and reduce measurement

uncertainty. The broadband antennas are desirable for EMC testing because they do not

have be tuned to each frequency before making the measurement. To tune the dipole, the

wavelength of the frequency that is being measured must be calculated. The elements of

the dipole must be then adjusted to the half wavelength for that frequency before taking

measurements.

The wavelength for any frequency F the equation: Wavelength = C / Frequency in MHz

where C is the velocity of light, 3 x 10

Using this formula the wavelength of 30 MHz is 3 x 10

300/30 = 10 meter. Therefore, half wavelength is 10/2= 5 meters. This is the total dipole

length tip to tip. Since the balun has two sides, the elements of on both sides of the balun

head must be adjusted quarter wave length. That is 10/4 = 2.5 meters per side measured

from the center of the balun head.

It must be noted however, that these calculations are theoretical. The tuned dipole is

typically 4% smaller than this theoretical length. Table 3.1 lists the typical quarter

wavelength for adjusting the tuned dipole elements.

This chapter explains the following:

Overview

Theory of Operation

Functional Block Diagram

meters /sec.

m/sec divided by 30 x 10

3-1

Hz or

AD-100 Dipole Antenna