Horn antenna is an antenna which is constructed by flaring (or opening) of a waveguide (a metallic material) in order to direct electromagnetic waves in one direction.
It is a directional antenna which is used to increase directivity It helps in improving impedance matching because the waveguide mostly has impedance of about 50Ω while the impedance of the free space is 377Ω. In order to match out the impedance so as to reduce power loss, a flaring is used to kind of concentrate the electromagnetic waves. It is used for long distance communication due to its directivity
The figure above shows a cross section diagram of horn antenna along the E-plane which can be used to analyze its parameters such as the flaring angle theta, the axial length L, the height of flaring or aperture H.
(L + δ)2 = L2 + (1/2h)2
L2 + 2Lδ +δ2 = L2 + (1/2h)2 ; expanding the bracket
As δ is very small compared to L, we neglect δ2 as it will be even smaller
L2 + 2Lδ = L2 + (1/2h)2
L2 - L2+ 2Lδ = + (1/2h)2
2Lδ = h2/4
L = h/8 δ
Tanθ = opp/adj = (1/2h)/L = h/2L or
Cosθ = adj/hyp = L/(L + δ)
Hence θ has it expression in terms of L and δ if cosine of the angle is used or in terms of h and L if tangent of the angle is used.
If the flare angle is small, there is uniform phase distribution as the beamwidth is small which also result in increase directivity.
If the flare angle is doubled, the directivity is reduced due to high beamwidth which then result in non-uniform phase distribution.
HPBW E – plane = 56°λ/A
where, A is area of aperture ( h x w(width) ) HPBW is Half Power BeamWidth and
FNBW is First Null BeamWidth
HPBW H – plane = 67°λ/A
FNBW E – plane = 115°λ/A
FNBW H – plane = 115°λ/A
It be categorized as
This type of antenna has its flaring in one direction. It is of two types
a) sectoral E-plane horn antenna
b) sectoral H-plane horn antenna
It has it flaring in the E (Electric field) direction i.e. the flaring is parallel to the E -plane.
It has it flaring in the H (Magnetic field) direction i.e. the flaring is parallel to the H -plane.
It has the flaring in both directions (i.e. both in the E-plane and H-plane direction)
It has cone like shape as its flaring and the waveguide is in a cylinder shape.
It consists of two conical antennas merged together.
In addition to the uses of horn antenna discussed above, here are some of its other applications