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Radar ionizing radiation

Unread postPosted: 15 Apr 2019, 22:51
by tank-top
Just a theoretical question about the ability of radar. I know if you throw tinfoil in a microwave bad things happen. What are the physics behind this a greater ranges or effective ranges for an aircraft? How much energy and can you focus it enough to be practical at say 10 miles or 25 miles or 50 miles. I’m pretty sure if possible we aren’t there yet but is feasible and probable in the future?

Re: Radar ionizing radiation

Unread postPosted: 16 Apr 2019, 02:37
by eloise
tank-top wrote:Just a theoretical question about the ability of radar. I know if you throw tinfoil in a microwave bad things happen. What are the physics behind this a greater ranges or effective ranges for an aircraft? How much energy and can you focus it enough to be practical at say 10 miles or 25 miles or 50 miles. I’m pretty sure if possible we aren’t there yet but is feasible and probable in the future?

Current radar can look far further than 50 miles
The physic of radar:
https://basicsaboutaerodynamicsandavion ... ermeasure/
https://basicsaboutaerodynamicsandavion ... s-part-ii/
https://www.youtube.com/watch?v=Qwh-1jRGuDc
http://www.radartutorial.eu/01.basics/R ... le.en.html

Re: Radar ionizing radiation

Unread postPosted: 16 Apr 2019, 11:42
by Dragon029
He's talking about destructive effects of high power microwave radiation - radars can be used to cause damage (like how metal combined with flammable material inside of a microwave can start a fire), but the range at which this can happen is quite short.

This is because the inverse square law states that the amount of power delivered onto a target equals some constant (a function of antenna gain, output power, wavelength, etc) divided by distance squared.

You can also look up free space path loss and related equations.

For example; the power received by an "antenna" (anything conductive) = (transmitter power * transmitter antenna gain * receiver antenna gain * wavelength^2) / (16 * pi^2 * distance between antennas^2)

So let's say you have a radar that can operate at 20kW and it has a 35 decibel gain (ballpark figure for that of a fighter radar), the receiving element has a gain of 3 decibels (I'm being generous and assuming we're dealing with something akin to a typical wifi dipole antenna), the distance between the 2 targets is 10km and the wavelength being used is 0.1m (around 3GHz).

In an idea world then, the receiving antenna would receive about 0.04 milliwatts, not even enough to power a small LED.

To get proper destructive effects you need to get a lot closer, or boost your transmitter pulse power several orders of magnitude, or increase your transmitter antenna gain by making it orders of magnitude larger.