Radiation Pattern Of A Horn - Chauvin Arnoux ORITEL ANC 100/15 Manual De Instrucciones

3.4

Radiation pattern of a horn

Measuring the radiation pattern of a horn consists in determining:
- the amplitude of the main radiation lobe and its width at 3 dB,
- the amplitude of the secondary lobes.
In the case of a rectangular horn, therefore with linear polarisation, these readings will be performed in
the two planes E and H, at elevation angle and relative bearing.
3.4.1 A summary of the theory on which the experiment is based
An isotropic antenna is such that a source point emits into the whole of space.
A real antenna emits preferentially in certain directions, where its gain is maximum.
A radiation pattern is a representation of the field's strength or the power emitted in relation to the angle
of observation at a constant distance.
The radiation pattern of a horn is represented either in the E plane (parallel to the small side of the
waveguide), or in the H plane (parallel to the largest side of the waveguide).
The radiation pattern is made up of several lobes, with the major part of the power being concentrated in
the main lobe. Generally speaking, an antenna is designed in such a way as to minimise the power
radiated in the side lobes and rear lobe in order to increase directivity.
The width of the main lobe at 3 dB is the angle between two points at which the power emitted (and
therefore the gain) is equal to half the maximum value.
3.4.2 Measuring the radiation diagram of a horn
Set up the assembly below:
CF 204
OSG 100 ISO 100 MOD 100
Take the following precautions:
- Keep to the minimum distance between the two ANC 100/15 horns:
2 d 2
R ≥
λ
- The horns must radiate into free space, i.e. far from any metal obstacle, and in particular far from the
ground.
- The axes of the horns shall be perfectly aligned in the horizontal and vertical planes. Check this
alignment by moving the reception horn slightly until you obtain a peak level on the galvanometer of
the IR 205.
Proceed as follows:
- Place the ATM 100 attenuator located before the OND 100 wavemeter at zero.
- Adjust the output level on the IR 205 until you obtain a correct deviation by actuating the ATM 100
attenuator. Identify the A
- Rotate the receiving horn by an α
- Bring the ATM 100 attenuator located after the OND 100 wavemeter back to an A
you obtain the D
0
ATM 100 OND 100
attenuation read as well as the D
0
angle around an axis located in the horn's aperture plane.
1
identification read previously on the IR 205.
ATM 100
ANC 100/15
deviation on the IR 205.
0
16
R
d
TGN 100 + DEN 100
ANC 100/15
attenuation until
1
IR 205