I would love to know the thinking behind this method.
Off the top of my head: They are adding Cesium ("screw the environment, I have to escape my pursuer") to the engine in order to leave a plasmonic plume. The plasma, which occurs because the electrons in Cesium are stripped off in the heat of the engine, absorbs microwaves (ie, radar) because of the expected cyclotron physics of a free-electron gas.
However as an electronic countermeasure, I do not see the point. The plasmonic plume will absorb the microwaves where the rest of the plane will continue to reflect it. To my thinking, the is exactly what you do not want to do: You've reduced the microwave signal where the plane is not present, and done nothing to the signal where the plane is present. So you've improved the signal-to-noise for the enemy, which are providing guidance for anti-aircraft missiles.
Considering how many years this program went on for, my thinking must be wrong. Maybe anti-aircraft missiles of the era did not intercept from oblique angles (which takes serious computation and sensors) but could only hit from behind (where the plume would attenuate a signal)?
For these kinds of radars, there won't really be any signal against the sky and, lets be honest here, nothing is going to be looking at the SR-71 from a top down aspect. In a tail chase situation though, a missile would have to fly straight at the exhaust which would give the aircraft some cover.
There's a bit of reading between the lines that needs to be done here though. The aircraft is already shaped to deflect radar waves from a tail or nose on aspect but the part that's very hard to 'stealth' is the insides of the engines, especially from the rear aspect. Turbine blades and all the other geometry inside tends to act like a radar disco-ball and leaves even many modern aircraft vulnerable. By making the exhaust radar absorbent you fix this issue.
Off the top of my head: They are adding Cesium ("screw the environment, I have to escape my pursuer") to the engine in order to leave a plasmonic plume. The plasma, which occurs because the electrons in Cesium are stripped off in the heat of the engine, absorbs microwaves (ie, radar) because of the expected cyclotron physics of a free-electron gas.
However as an electronic countermeasure, I do not see the point. The plasmonic plume will absorb the microwaves where the rest of the plane will continue to reflect it. To my thinking, the is exactly what you do not want to do: You've reduced the microwave signal where the plane is not present, and done nothing to the signal where the plane is present. So you've improved the signal-to-noise for the enemy, which are providing guidance for anti-aircraft missiles.
Considering how many years this program went on for, my thinking must be wrong. Maybe anti-aircraft missiles of the era did not intercept from oblique angles (which takes serious computation and sensors) but could only hit from behind (where the plume would attenuate a signal)?