EngNote - J/S Ratio

"EngNotes" are my engineering notes.  This is my way of creating a digital version of an engineering notebook.  This particular entry is on Jam to Signal Ratio.

The Jam to Signal Ratio (J/S) is a useful quantity when evaluating an EW scenario.  Below is a simplistic derivation of how to calculate the Jam to Signal Ratio.

Note that the isotropic antenna effective area is present twice in the jammer's equation and only once in the target's equation.  This is due to the fact that the jammer must "convert" the received power density into power before re-transmitting.


$ \begin{matrix}
P_{target.rx} & = & P_{radar}Gain_{radar.tx}(\frac{1}{4\pi Range^{2}})\sigma _{rcs}(\frac{1}{4\pi Range^{2}})(\frac{\lambda ^{2}}{4\pi})Gain_{radar.rx} \\
P_{jam.rx} & = & P_{radar}Gain_{radar.tx}(\frac{1}{4\pi Range^{2}})(\frac{\lambda ^{2}}{4\pi})Gain_{sys}(\frac{1}{4\pi Range^{2}})(\frac{\lambda ^{2}}{4\pi})Gain_{radar.rx} \\
\frac{Jam}{Signal} & = & \frac{P_{jam.rx}}{P_{target.rx}} \\
 & = & (\frac{\lambda ^{2}}{4\pi})Gain_{sys}(\frac{1}{\sigma _{rcs}}) \\
\end{matrix} $
Where:

$ (\frac{\lambda ^{2}}{4\pi}) = IsotropicAntenna_{EffectiveArea} $