Linear antennas and to opening
Linear antennas
1) Expression of the magnetic field in the case of one thin antenna:
2) Width of lobe:
It is the included angle between the two directions to which the diagram of cancellation in field it is reduced to 0.707 of the maximum value.
3) short Antenna:
It is had that the current is almost constant along the
antenna, the H field it is reduced to 
, one obtains a
diagram of independent cancellation from j that is omnidirezionale for which the antenna it must be
put orthogonally to the direction in which it is wanted to be made
propagare the field. Width of lobe of 90° is had one.
4) Resistance of cancellation:
Draft of the hypothetical resistance in a position to
dissipating the irradiated power, it is worth 
,
for a short antenna h/l it is
much small and therefore the irradiated power is a lot little.
5) Expression of the current for one thin antenna:
6) Antenna to half wave:
The irradiated magnetic field to great 
distance is an antenna of length for it is 
which amplitude of lobe of 78° inferior corresponds a
diagram of cancellation in still omnidirezionale field but with one to
the case of the short antenna.
7) Antenna to entire wave:
The irradiated magnetic field to great 
distance is an antenna of length for it is 
which a diagram of cancellation in still omnidirezionale
field corresponds but with an amplitude of lobe of 47° therefore the
antenna it is more directive regarding that one to half wave but this
to discapito of a cost double inherent to the double dimensions
therefore of customary uses the antenna to half wave.
8) practical Realization of dipole antenna:
From a constructive point of view the antenna is much difficult one to break in two maintaining the property of mechanical resistance, therefore only average antenna is used and remaining is like if there were to pact to insert on the surface a metallic plan that therefore complys with the condition to the second contour which the electric field must be null in correspondence of the discontinuity surface.
Antennas to opening
9) Typology of antennas to opening:
- to) bugle antennas gradually in which the guide increases the own section to the aim to adapt the free space to the present dominant way in the guide
- b) reflector antennas in which the waveguide it still finishes on a bugle, dictate illuminator which finds itself in the fire of a metallic paraboloide towards which he irradiates in such a way obtaining a flat wave.
10) irradiated Electric field to great distance from an antenna to opening:
where Jms and Js are the superficial currents equivalents that we can introduce on the single mouth of the antenna in virtue of the equivalence theorem.
11) rectangular mouth Antenna:
It is the case of a bugle antenna or an antenna radar, in
which the long irradiation is wanted to be privileged one direction
that rather the long irradiation an other direction. The
produced field to great distance from the sun running magnetic is 
where JTms is the distribution of current cut to
the edges of the mouth of the antenna. In the case of constant
magnetic currents one finds that:
- to) in the horizontal plan the electric field it is polarized vertically and its diagram of cancellation is given from the product of a sinc for a cosine that is worth approximately 1 if to > >l.
- b) in the vertical plan the electric field to great distance lies on the vertical plan.
12) main Lobe of the cancellation diagram:
Draft of the angular region comprised between the first
two zeroes of the function cancellation diagram, for the horizontal plan
of a rectangular mouth antenna has 
while for
the vertical plan 
. It is observed therefore
that antenna in a plan can be increased to the direttività of one
increasing the frequency (…diminishing the wavelength) or
increasing the dimensions of the opening in the interested plan.
13) circular mouth Antenna:
A lot for the connections between fixed points is a used
antenna, the magnetic field to great due distance for semplicità to
the sun running magnetic equivalents è 
which
supposing a constantJ ms it
characterizes one width of the equal main lobe a 
.
14) elliptic mouth Antenna:
It is observed that when the mouth of an antenna comes extended (uniform contracts) nel relationship s:1 in a particular direction, the cancellation diagram is contracted (extends) the same direction second nel relationship 1:s.