[ars]

It's related, but not the same. SDR happen after you received your signal, where you can, in software, pick different ways of decoding the signal.

This, however lets you dynamically choose the antenna length, and each frequency has a perfect length that works best for it.

So the two are complimentary, but at different parts of the process.

[linguistbreaker]

Right so it's like SDA - a software defined antenna