Antenna Parameters

Topics: Electromagnetic radiation, Antenna, Polarization Pages: 5 (1396 words) Published: April 23, 2013
1.i)
• Antenna radiation pattern or antenna pattern is defined as “a mathematical function or a graphical representation of the radiation properties of the antenna as a function of space coordinates.” • The radiation pattern is determined in the far-field region and is represented as a function of the directional coordinates. • Radiation properties include power flux density, radiation intensity, field strength, directivity phase or polarization [pic]

ii)
■ The angular separation between the two half-power points is referred to as HPBW. ■ Half-power beamwidth (HPBW) is the angle between two vectors, originating at the pattern’s origin and passing through these points of the major lobe where the radiation intensity is half its maximum ■ To find the points where the pattern achieves its half-power (-3 dB points), relative to the maximum value of the pattern: o Field pattern at 0.707 value of its maximum. o Power pattern (in linear scale) at its 0.5 value of its maximum. o Power pattern (in dB) at -3 dB value of its maximum.

[pic][pic]

iii)
▪ First-null beamwidth (FNBW) is the angle between two vectors, originating at the pattern’s origin and tangent to the main beam at its base.

[pic]

2. Radiation lobes is a “portion of the radiation pattern bounded by regions of relatively weak radiation intensity.” Various lobes can be sub-classified in major or main, minor, side and back lobes [pic]

3.
▪ A major lobe (also called main beam) is defined as “the radiation lobe containing the direction of maximum radiation”. ▪ A minor lobe is any lobe except major lobe.
▪ A side lobe is “a radiation lobe in any direction other than intended lobe”. Usually a side lobe is adjacent to the main lobe and occupies the hemisphere in the direction of the main beam. ▪ A back lobe is “a radiation lobe whose axis makes an angle of approximately 180º with respect to the beam of the antenna”. ▪ Minor lobes usually represent radiation in undesired directions, and they should be minimized. ▪ Side lobes are normally the largest of minor lobes.

4.
i)Isotropic pattern is the pattern of an antenna having equal radiation in all directions. This is an ideal (not physically achievable) concept. However, it is used to define other antenna parameters. It is represented simply by a sphere whose center coincides with the location of the isotropic radiator. ii)Directional antenna is an antenna, which radiates (receives) much more efficiently in some directions than in others. Usually, this term is applied to antennas whose directivity is much higher than that of a half wavelength dipole. iii) Omnidirectional antenna is an antenna, which has a non-directional pattern in a given plane, and a directional pattern in any orthogonal plane (e.g. single-wire antennas).

5.Principal patterns are the 2-D patterns of linearly polarized antennas, measured in the E-plane (a plane parallel to the |Ē| vector and containing the direction of maximum radiation). The H-plane (a plane parallel to the vector, orthogonal to the E-plane, and containing the direction of maximum radiation).

6.
i)Reactive near-field region is defined as “that portion of the near-field region immediately surrounding the antenna wherein the reactive field predominates”. [pic]
ii) Radiating near-field region (Fresnel) is defined as “that region of the field of an antenna between the reactive near-field region and the far-field region wherein radiation fields predominate and wherein the angular field distribution is dependent upon the distance from the antenna”. [pic]

iii) Far-field region (Fraunhofer) is defined as “that region of the field of an antenna where the angular field distribution is essentially independent...