victor1985 wrote:Small size nuclear emp bombs could hit those icbms.
Yes they could. It might have been lost in translation, but I think you need to re-read my post again to understand why this is not a viable defence.
Or only emp no nuclear or a rocket whit a directed energy antenna on it....
Technically it could be possible. However there are a number of major issues.
Okay we'll start with range first. The recent revelation of the Mosow Radio Engineering Institute's super-high frequency (SHF) microwave cannon, suggests that the truck-sized weapon has a disabling range of 10km. Although it was stated that it would work against "warheads of high precision weapons", we don't know if that meant cruise missiles or GPS guided shells, neither of which has a lot of spare mass for EMP shielding. I'd be very surprised if US ICBM warheads didn't
have some shielding (just to protect them from the EMPs of nearby friendly nukes), so we have no idea if the BUK mounted EMP cannon could even affect it.
That caveat aside, its limited range is very problematic since an ICBM warhead will have a terminal velocity in the region of 7km/s. That leaves less than 1.5 seconds to fry the electronics, less if you consider the nuke is likely to be an air-burst... which is not a lot of time to acquire, pan and shoot if its a MARV. I'm specifically leaving out your proposal of an EMP missile akin to CHAMPS here since its limited volume would reduce the EMP strength/range still further and head-on closing speeds would render the intercept/fire period to a fraction of a second.
There is another significant problem with directed microwaves penetrating the plasma sheath of a ballistic warhead. Microwaves tend to be absorbed or reflected by the plasma of the re-entry shockwave, so much of the energy will be diffused leaving insufficient power to overwhelm its electronics. If your physics and math are up to it, take a look at http://www.dtic.mil/dtic/tr/fulltext/u2/865522.pdf
The final problem is that of economics. Assuming an effective EMP cannon capable of taking out a nuke was possible, you would be looking at a very large (probably immobile) installation to generate a powerful enough microwave beam. This would take a huge amount of electrical power so massive generators, capacitors, focussing dishes, cooling systems and so on. I wouldn't be surprised if building one cost at least as much as the ICBMs they were defending against, say $50 million a pop.
A worthy expenditure you might think, but in reality you are going to need to build hundreds - if not thousands - of them, since each microwave projector is going to only get a single shot off during the terminal approach of a MIRV volley and the weapons themselves will have a very limited range. The US submarine force alone has 1,152 MIRV warheads and when you add decoys to the attack, you're effectively swamping a weapon with limited reach, cycling and targeting window time.
So whilst the idea might sound feasible as a concept, directed EMP weapons are not the answer - at least not yet. The cheapest and most efficient method of destroying ballistic nukes is still a kinetic kill missile.