Note: For. interested in. Radiation. A field pattern. H and a phase

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Lecture-3 Antenna parameters: (Continued ) 1.4.

power from an antenna. Mathematically it can be written as Fig.

surface is sufficiently far from antenna. 1.4.

the antenna as a function of space coordinates.

1 Lecture-3 Antenna parameters: (Continued ) Radiated Power With this information, now we are in a position to calculate the total radiated power from an antenna. Mathematically it can be written as Fig. 15: Calculation of radiated power Note: For antennas, mostly we are interested in its far-fieldd radiation. So, the integration in the above equation is over a closed surface with the antenna inside and the surface is sufficiently far from antenna Radiation Pattern Radiation pattern is a graphical representation of the radiation properties of the antenna as a function of space coordinates. A field pattern is a graph that describess the relativee far field vales, E or H, with direction at a fixed distance from the antenna. A field pattern includes an magnitude (amplitude) pattern E or H and a phase pattern E or H. A power pattern is a graph that describess the relative (average) radiated power density P ave of the far-field with direction at a fixed distance from the antenna.

2 A typical antenna radiation pattern is shown in Fig. 16 (a). The characteristics to note down from this pattern are: (i) (ii) (iii) (iv) Main (major) lobe Minor lobe (includes side lobes and back lobe) Half-power beamwidth (HPBW) Beamwidth between first nulls (BWFN) Note: A radiation pattern shows only the relative values but not the absolute values of the field or power quantity. Hence the values are usually normalized (i.e., divided) by the maximum value. [In Fig. 16, mark the maximum of the main lobe that is 1) The size of the minor lobes is much smaller than that of the major lobe. In order to clearly visualize the minor lobes, sometimes the scales of the radiation pattern are expressed in db, as shown in Fig. 16 (b). The calculation procedure of the beamwidths from the radiation pattern is shown in Fig. 17. Note: By the reciprocity theorem, the radiation pattern of an antenna in the transmitting mode is same as those for the antenna in the receiving mode.

3 Main lobe maximum direction 1.0 Half-power Beamwidth (HPBW) Main lobe 0.5 Beamwidth between first nulls (BWFN) Minor lobes (a) Main lobe 0 db - 3 db - 10 db (b) Fig. 16: Antenna radiation pattern

4 Fig. 17: Calculation of beamwidths from the radiation pattern. Isotropic Radiation Pattern: It is the pattern of a point source. o Characteristics Completely non-directional antenna Radiates and receives equally well inn all directionss Radiation pattern is spherical o Exists only as a mathematical concept o Used as a referencee Omnidirection nal Radiation Pattern: It is the patternn of a Hertzian dipole. [see Fig. 18] o Along the ends of the dipole there is no radiation (nulls) o Maximum radiation is along the broadside direction o Sometimes used a reference

5 z x y (a) y z sin x 0 HPBW 90 (b) (c) Fig. 18: Omnidirectional radiation pattern. Example: The step-by-step procedure of drawing the radiation pattern of a Hertzian dipole is as follows:

6 Step 1 Step 2 Step 3 Step 4

Step 5 1.4.5 Field Regions The space surrounding an antenna is usually divided into two regions: (i) near field field region. (See Fig.

This region is also called as the Fraunhofer region.

7 Step Field Regions The space surrounding an antenna is usually divided into two regions: (i) near field field region. (See Fig. 19) region and ( ii) far Far field is defined as that region of the field of an antenna where the angular field distribution is independent of the distance from the antenna. This region is commonly taken to exist at distances greater than 2D 2 / from the antenna, wheree D is the overall dimension of the antenna. This region is also called as the Fraunhofer region. In this region, the field components are essentially transverse and the angular distribution is independent of the radial distance where the measurements are made. The field immediately surrounding the antenna and the far field region is known as the near field region. This region is again divided into two sub regions as (a) reactive near field and (b) radiating near field, according to their characteristics. (See Fig. 19).

8 D 2D D Reactive region Radiating region Near field region Far field region Fig. 19: Near field and far field regions of an antenna.

Antenna & Propagation. Antenna Parameters

Antenna & Propagation. Antenna Parameters For updated version, please click on http://ocw.ump.edu.my Antenna & Propagation Antenna Parameters by Nor Hadzfizah Binti Mohd Radi Faculty of Electric & Electronics Engineering hadzfizah@ump.edu.my Chapter