Property generates them of the antennas

1) Parameters of cancellation:

The field to great distance is the product of one constant for a spherical wave for a vectorial factor that is function of r₀ (…payer who combines the origin with the point of P observation place at a distance r) has that is , the third factor depends on the distribution spaces them of the currents impresse in the antenna that therefore they can vectorially be described from the diagram of cancellation in field , the cancellation modalities instead is expressed scalarmente from the diagram of cancellation in power that coincides with the density of irradiated power to unit of solid angle in fact the power total irradiated from an antenna is . For an antenna in transmission they come moreover defined the following parameters:

to)                   the function of gain draft that is of the diagram of cancellation in power standardized to the medium angular density of power irradiated in adaptation conditions, the maximum is the antenna gain.

b)                  the function of direttività draft that is of the diagram of cancellation in power standardized to the medium angular density of irradiated power, it can also be expressed in function of the reaction in fact the diagram of cancellation in power is where and_¥ comes calculated by means of a source electrical worker of having test moment M oriented second and_¥ and therefore the reaction is_{the TA}= ME_¥ from which it is gained and_¥ . Dividend for obtains the expression of the direttività whose maximum is said direttività of the antenna.

 

2) Antennas in reception:

An antenna in reception picks up the electromagnetic field incident and makes available a power W _Rto the income of the transmission line, considering that this is lacking in dissipations and that a single guided way is active, is had that the received power W_R is the flow of the carrier of Poynting through the S section_g of the guide

in which the fields can be decomposed in the product of one constant tied to the amplitude of the field for a vectorial function of coordinates x , V trasverse to the axis of guide e replacing has . With analogous considerations the power transmitted present on the line is gained .

Applying to the reciprocity theorem choosing a surface S_T that encloses sources of the emitter it only has the not null integral pu² to be considered on the line where H the @ H_and e and @ and_rthe therefore has from which is gained through which the expression of the power is obtained ricevuta

The relationship between the received power and the density of power P incident characterizes the area equivalent of the antenna , replacing obtains .

For the calculation of the reaction integral a surface is chosen S sluice_To that it is leaned to the external mouth To_g of the antenna, has replacing e , obtains therefore the expression of the received power is , replacing this relation in the expression of the equivalent air, is obtained

, if the polarization is adapted and_T and and is parallels and therefore outside from the integral can be carried while the virtually transmitted power is estimated like flow of the carrier of Poynting replacing where describes the distribution on the external mouth of the antenna of the virtually transmitted field and becoming simpler is obtained which applying the inequality of Schwarz gives To_and=h_toTo_g being h_to the rendering of norm opening has 0,5 £ h_to £ 0,8.

 

3) Tie between equivalent area and direttività:

The equivalent area is where P is the carrier of Poynting produced on the ricetrasmittente antenna To from a source of test (…oriented according to the field and product gives To), it is worth while for the reciprocity of means is had where_{the TA} can be gained inverting the relation that expresses the direttività , replacing obtain .

 

4) Transmission between antennas:

One supposes of having an antenna 1 with a diagram of cancellation in power P₁ , and oriented so as to to maximize the direttività in the direction of antenna receiving 2, on the mouth of which it creates a superficial density of power which a received power corresponds and therefore the coefficient of equal transmission to the relationship between the received power and the transmitted power is had that using the relations e it can be placed in 3 various shapes which they evidence as T₁₂ grows with the geometric dimensions of the antennas and with frequency while naturally it decreases with the distance.