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Basic Radiowave and Antenna Parameters

 Basic Radiowave and Antenna Parameters

Terms and definitions commonly encountered in the study of antennas and

radio wave communication can be found in Institute of Electrical and Electron-

ics Engineers (IEEE) [19, 20] and European Telecommunications Standards

Institute (ETSI) [21] standards, as well as in FCC rules [3] and ITU-R reports

and recommendations [22]. Here, we will present some of the parameters and

definitions that are especially relevant and specific to the problems in this

textbook.

Antenna factor (AF) in a receiving antenna is the ratio of electric field

strength to the voltage across the terminating impedance connected to the

antenna. By common usage in the telecommunications industry [23], the

antenna factor is sometimes stated under conditions where the field incident on

the antenna is not uniform along the antenna. Antenna factor is therefore, by

common usage, a parameter that is measurement site dependent.

Antenna illumination efficiency, sometimes called the aperture illumination

efficiency, is the ratio of the directivity D of an antenna to its reference directivity

Dref , given by

D

A

ref

area = 4

2

Ï€

λ (1.40)

written in terms of the wavelength and aperture area Aarea.

Antenna pattern lobes are defined as follows:

• Back lobe is the radiation lobe whose axis makes an angle of 180° with

respect to the axis of the main lobe. The back lobe is not defined for

omnidirectional vertical collinear array antennas.

• Front-to-side-lobe ratio is the ratio of the maximum directivity of an

antenna to the peak radiation in a specified side-lobe direction.

• Major lobe, or the main lobe, is the antenna pattern radiation lobe con-

taining the direction of maximum radiation.

• Side lobes are antenna pattern radiation lobes in any direction other

than that of the main or major antenna pattern lobe.

Aperture distribution is the field over the antenna aperture described by

amplitude, phase, and polarization distributions. For collinear arrays of dipole

antennas, the aperture distribution is given approximately by the dipole

excitations.

Beamwidth is the angular width of the main lobe of an antenna far-field

radiation pattern as measured between the amplitude points on the main patternlobe that are 3 dB below the peak of the main lobe. The beamwidth in a plane

varies with the inverse of the effective antenna dimension in that same plane.

Beamwidth and directivity are also inversely related. See Section 2.5 for further

discussion of collinear antenna vertical beamwidth and directivity.

Bandwidth is commonly defined by the frequency band of a rectangular

power spectral density (PSD) that integrates to the actual signal power having

the same peak PSD.

• 3-dB bandwidth: For simple filters, the bandwidth equals the frequency

separation between the 3-dB down points of the filter response.

• 99% power bandwidth: This is the bandwidth containing 99% of the

total signal power.

• Fractional bandwidth: This is the bandwidth divided by the arithmetic

average of the upper and lower bandwidth defining points.

• UWB bandwidth: See UWB.

Collinear array antenna is a linear arrangement of radiating elements that

are usually polarized in the direction of the antenna axis and exhibit a nominally

omnidirectional pattern in the plane perpendicular to the antenna axis.

Directive gain (see also gain) is also a far-field quantity and is defined as the

ratio of radiation density in a particular angular direction to the radiation den-

sity of the same power Prad radiated isotropically. Directive gain can be found

from the far-field radially directed Poynting vector in ratio to the average

Poynting vector over the radian sphere.


It is easy to show that the directive gain of the infinitesimal current ele-

ment considered earlier can be found using (1.41) to be D = 1.5 sin2

( ) by not-

ing that the functional form of the product of E and H is simply sin2

( ) in the

far field and by carrying out the simple integration in the denominator of

(1.41). From duality, the directive gain of the infinitesimal loop is the same as

that of the infinitesimal dipole.

Directivity D is the directive 





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