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{| class=wikitable style="width:100%;" align=center
|+ style="background:DarkSlateBlue; color:white; text-align:center;"|''Artículo de Friis''
Línea 118 ⟶ 116:
 
<br />
 
 
'''Comparación de la ecuación 3.1 con la ecuación de friis '''<br />
Línea 173 ⟶ 170:
'''A.Small Dipole with No Heat Loss'''<br />
For a small uniform current element the available output power is equal to the induced voltage squared divided by four times the radiation resistance. Thus<br />
 
 
<math>P_r=\frac{E^2a^2}{4R_{rad}}</math><br />
 
 
where<br />
Línea 192 ⟶ 187:
 
The area of a rectangle with one-half wavelength and one-quarter wavelength sides is <math>0.125\lambda ^2 </math> and it is, therefore, a good approximation for the effective areas of small dipoles and half-wavelength dipoles.
 
 
<math>A_{0.5}=0.1305\lambda^2</math><br />
Línea 204 ⟶ 198:
The hypothetical isotropic antenna has the same radiation intensity in all directions. It has two thirds of the gain’ or effective area of the small dipole. Therefore<br />
<math>A_{isotr.}=\frac{\lambda ^2}{4\pi}.</math> .<br />
 
 
'''(Ítem C Arrays ) '''<br />
 
 
[[File:Dimensiones en Lambda.png||centro|miniaturadeimagen|300x300px|Dimensiones en Lambda]]
Línea 214 ⟶ 206:
 
[[File:Orden de los dipolos.png||centro|miniaturadeimagen|300x300px|Orden de los dipolos]]
 
 
<math>A_{pinetree}=n*0.5\lambda * 0.5\lambda</math><br />
 
 
'''C. Broadside Arrays (Pine- Tree Antennas)'''<br />
Línea 223 ⟶ 213:
<math>A_{pire-tree} \approx n\times 0.5\lambda \times 0.5\lambda</math><br />
where n is the total number of half-wave dipoles in the front curtain. Formula (7) is a good approximation for large antennas. For example, an antenna of 6 rows of 17 dipoles each gave a calculated effective area only 3 per cent below the value obtained by (7). It should be pointed out that the heat loss in the connecting transmission lines will reduce the effective areas in actual antennas.<br />
 
 
[[File:N=102_dipolos_Ares(pineetree)_=_n_∗_0,_5λ_∗_0,_5λ.png||centro|miniaturadeimagen|300x300px| n=102 dipolos Ares(pineetree) = n ∗ 0, 5λ ∗ 0, 5λ]]
Línea 229 ⟶ 218:
<math>Apt=102*0.5\lambda *0.5\lambda =\frac{51\lambda^2}{2}</math><br />
<math>A_{circulo}=\pi r^2----A_{pinetree}= 25.5\lambda ^2</math><br />
 
 
[[File:Radios.png||centro|miniaturadeimagen|300x300px|Radio]]
 
 
<math>\pi r^2 = 25.5\lambda</math><br />
Línea 246 ⟶ 233:
The effective area of the parabolic type of antenna with a proper feed has been found experimentally to be approximately two thirds of the projected area of the reflector.<br />
.<br />
 
 
'''(Ítem E)'''<br />
Línea 256 ⟶ 242:
'''DERIVATION OF TRANSMISSION FORMULA (1)'''<br />
Having defined the effective area of an antenna, it is a simple matter to derive (1). As shown in Fig. 1, consider a radio circuit made up of an isotropic transmitting<br />
 
 
[[File:Explicacion figura.png|centro|miniaturadeimagen|300x300px|]]
 
 
antenna and a receiving antenna with effective area Ar. The power flow per unit area at the distance d from the transmitter is<br />
Línea 268 ⟶ 252:
<math>\frac{P_r}{P_t}=\frac{A_r}{4\pi d^2 A_{isotr}}</math><br />
Introducing the effective area (6) for the isotropic antenna, we have (1).<br />
 
 
'''LIMITATIONS OF TRANSMISSION FORMULA (1)'''<br />
Línea 277 ⟶ 260:
he advantage of (1) over other formulations is that, fortunately, it has no numerical coefficients. It is so simple that it may be memorized easily. Almost 7 years of intensive use has proved its utility in transmission calculations involving wavelengths up to several meters, and it may become useful also at longer wavelengths. It is suggested that radio engineers hereafter give the radiation from a transmitting antenna in terms of the power flow per unit area which is equal to <math>P_t A_t / \lambda^2 d^2 </math>, instead of giving the field strength in volts per meter. It is also suggested that an antenna be characterized by its effective area, instead of by its power gain or radiation resistance. The ratio of the effective area to the actual area of the aperture of an antenna is also of importance in antenna design, since it gives an indication of how efficiently the antenna is utilizing the physical space it occupies. *The directional pattern, which has not been discussed in this note,is, of course, always an important characteristic of an antenna.
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[[File:RADIOELACES.cmap.cmap.pdf|centro|miniaturadeimagen|700x700px900x500px|Último párrafo (Héctor Javier Vega Lozano)]]