Antenna pattern measurement
This section explains the Antenna Pattern Measurements in detail. The antenna pattern is also termed as radiation pattern of an antenna. The radiation pattern is nothing but the plot of the intensity of radiation taken at different points that are at equal distance from the antenna.
Antenna Pattern Measurements:
- The antenna pattern is also termed as radiation pattern of an antenna.
- The radiation pattern is nothing but the plot of the intensity of radiation taken at different points that are at equal distance from the antenna. It is also defined as plot of power density with respect to the direction.
- The radiation pattern of an antenna is a 3-D figure. Hence, it needs intensity of radiation measurement over all spatial angles.
- Let us assume a 3-coordinate Cartesian system in which the antenna, whose pattern is to be measured, is placed at the origin as shown in figure 5.1
- The plane XY is horizontal plane. For horizontal plane antenna, the two patterns exhibited are,
(a) The ‘θ’ component of E-field (horizontal) is measured as a function of (j) in XY plane (0 = 90°). This is indicated as E Φ (θ = 90°, (j>) and called as E-plane pattern.
(b)The Φ component of E-field is measured as a function of c in XZ plane (Φ = 0°). This is represented as E Φ = (θ, Φ = 0°) and called as H-plane pattern.These E-plane and H-plane patterns are mutually perpendicular to the major lobe.
- The plane XZ is called vertical plane and the two patterns to be measured in this plane are,
(a) The ' θ ' component of it-field is measured as a function of Φ in XY plane (θ = 90°). This is represented by Eθ (θ=90°, Φ) and called as H-plane pattern.
(b) The θ component of E-field is measured as a function of θ in XZ plane ((j) = 0°). This is represented as Eθ(θ, (j) = 90°) and called as E-plane pattern.
- For circularly or elliptically polarized antennas, these four patterns should be measured.
- The two types of techniques for measuring antenna pattern in any one of the plane are,
- The primary antenna is fixed, and the secondary antenna is equipped for free rotation around the primary antenna in circular fashion.
- The field strength and direction of secondary antenna with respect to primary is noted at different points on the circular path of secondary antenna. Then, the required antenna pattern plot is made.
- In this procedure, the primary antenna is rotated along vertical axis with respect to secondary antenna.
- The field strength at primary receiving antenna with respect to transmitting secondary antenna is recorded at different point on the vertical rotation path of primary antenna. Then, with recorded values, plot is made.