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radar:radarequation [2018/06/09 10:42] – [Hall Method] sidorettiradar:radarequation [2026/04/28 15:13] (current) – external edit 127.0.0.1
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   -$A_1$ is computed again using the new range $R_1$;   -$A_1$ is computed again using the new range $R_1$;
   -iterate until $R_i \approx R_{i+1}$.   -iterate until $R_i \approx R_{i+1}$.
-The convergence of the results to an acceptable value is usually fast, after 2 or 3 iterations the obtained values can be considered optimum.\\+The convergence of the results to an acceptable value is usually fast, after 2 or 3 iterations the obtained values can be considered valid.\\
 The noise captured by the antenna also depends on other phenomena in the atmosphere and on cosmic sources. In general, this noise is characterized by simply giving an antenna noise temperature $T_a$, from which the noise power can be computed as $kT_a$ (being $k$ the Boltzmann constant). This under the assumptions that the antenna is ideal, with no losses, and that the radiation pattern has no lobes pointing on the ground. Figure {{ref>fig-2.11}} shows how the antenna temperature changes with frequency and elevation angle. The noise captured by the antenna also depends on other phenomena in the atmosphere and on cosmic sources. In general, this noise is characterized by simply giving an antenna noise temperature $T_a$, from which the noise power can be computed as $kT_a$ (being $k$ the Boltzmann constant). This under the assumptions that the antenna is ideal, with no losses, and that the radiation pattern has no lobes pointing on the ground. Figure {{ref>fig-2.11}} shows how the antenna temperature changes with frequency and elevation angle.
  
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 \end{equation} \end{equation}
  
-$T_E$ is the noise produced by the device, comparing the equations (54) and (57) such noise can becomes: $\Delta P_{on} = GkT_EB$. This is the temperature referred to the input terminals of the device, if the noise power in input has a temperature $T_1$, the overall device noise temperature will be $T_1+T_E$. Hence the noise power:+$T_E$ characterizes the noise produced by the device, comparing the equations (54) and (57) such noise becomes: $\Delta P_{on} = GkT_EB$. This is the temperature referred to the input terminals of the device, if the noise power in input has a temperature $T_1$, the overall device noise temperature will be $T_1+T_E$. Hence the noise power:
  
 \begin{equation} \begin{equation}
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 ===Over The Horizon Backscattering (OTH-B)=== ===Over The Horizon Backscattering (OTH-B)===
  
-At low frequencies (HF band), signals directed to the sky with a certain angle are reflected by the ionosphere (where the refractive index changes) towards the ground The OTH-B radar can detect signals backscattered from the target back to the ionosphere and reflected again towards the receiver (see Figure {{ref>fig-2.31}}). The frequencies used for this kind of radar are strictly dependant on the meteorological conditions of the atmosphere. The OTH-B radar then needs a continuous monitoring of such conditions to adapt dynamically to changes.+At low frequencies (HF band), signals directed to the sky with a certain angle are reflected by the ionosphere (where the refractive index changes) towards the ground. The OTH-B radar can detect signals backscattered from the target back to the ionosphere and reflected again towards the receiver (see Figure {{ref>fig-2.31}}). The frequencies used for this kind of radar are strictly dependant on the meteorological conditions of the atmosphere. The OTH-B radar then needs a continuous monitoring of such conditions to adapt dynamically to changes.
  
 <figure fig-2.31> <figure fig-2.31>
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 One important characteristic of OTH-B radars is the poor resolution. Nowadays these radars are only used when precision is not needed, being less expensive than satellites. OTH-B radars built during the cold war, instead, were built because there was no better technology at the time, now for such military purposes, the use of satellites has made radars like the Duga obsolete. One important characteristic of OTH-B radars is the poor resolution. Nowadays these radars are only used when precision is not needed, being less expensive than satellites. OTH-B radars built during the cold war, instead, were built because there was no better technology at the time, now for such military purposes, the use of satellites has made radars like the Duga obsolete.
  
-Another way of exploiting the change of refractive index id the conduct effect (Figure {{ref>fig-2.35}}). In particular conditions, in fact, there is an inversion of the behavior of the refractive index, usually decreasing at higher altitudes, that instead starts increasing with the altitude. if the radar antenna is located inside this particular substrate of the atmosphere, the signals transmitted are also contained inside the substrate and can reach distances much greater than usual. In fact, the attenuation is directly proportional to the distance $R$, and not to $R^2$. The conduct effect can only be exploited when particular conditions arise, that depend on the aleatory behavior of the atmosphere. For this, the effect is not reliable.+Another way of exploiting the change of refractive index is the conduct effect (Figure {{ref>fig-2.35}}). In particular conditions, in fact, there is an inversion of the behavior of the refractive index, usually decreasing at higher altitudes, that instead starts increasing with the altitude. if the radar antenna is located inside this particular substrate of the atmosphere, the signals transmitted are also contained inside the substrate and can reach distances much greater than usual. In fact, the attenuation is directly proportional to the distance $R$, and not to $R^2$. The conduct effect can only be exploited when particular conditions arise, that depend on the aleatory behavior of the atmosphere. For this, the effect is not reliable.
  
 <figure fig-2.35> <figure fig-2.35>
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