Chauvin Arnoux ORITEL ANC 100/15 Notice De Fonctionnement page 14

The horn antenna
The horn antenna in the figure opposite is obtained by
progressive expansion of a traditional waveguide section, the
effect of which is to increase the equivalent area, and therefore
the radiating aperture gain.
It is indeed known that, for a rectangular waveguide of dimension
a and b, you have: a < λ and b ≤ a/2.
Its ab section is therefore such that: ab < λ
When in fact, bearing in mind the equation (2), the gain cannot
exceed 2 π.
The axial length l shall, moreover, be such that the phase of the electric and magnetic fields is constant
in the horn's output plane; this condition is obtained for:
l ≥ d
2 / 2λ
In practice, in order to reproduce distant field propagation conditions, two horns with identical dimensions,
one for emission and the other for reception, will have to be spaced out at a distance R such as:
R ≥ 2d
2
Although rather cumbersome, if you are looking for a high degree of gain, the horns are easy to adapt to
the excitation waveguide and have a high frequency band.
Expressing the gain of a couple of identical horns
If P is the power emitted and P
e
power P is given by the following equation:
r
λ
P G 2
e
P =
r
(4π) 2 R
You immediately get:
4π R
G =
λ
0
Or even: G
dB
Moreover, expression (4) very clearly shows the extent to which the ratio (P
Pr = (G λ
/ 2π)
0
3.3.2 Measuring the gain of a horn
Set up the assembly in the figure below, abiding by the following conditions:
CF 204
OSG 100 ISO 100 MOD 100
0
/ λ
0
the power received, G the gain and R the separation distance, the
r
2
0
2
Pr / Pe
1 (P
= - P ) + 10 log (4π R/k
rdB edB
2
1
2
2
R
ATM 100 OND 100
2 /2.
)
0
ATM 100
ANC 100/15
14
a
b
l
(4)
(5)
/P ) depends on 1/R
r e
(6)
R
d
ANC 100/15
c
d
2 .
IR 205
TGN 100 + DEN 100