Yeah stealth aircraft are more vulnerable to lower frequency radars, it's how the F-117 was shot down over Serbia. However that does usually reduce the rage of your radar, which is the opposite of what you want with regards to early warning radars.

I think honestly to get a proper shot of detecting the radio signals of the drones and potentially jamming them at source, or even launching missiles at the source, you'd need some kind of electronic warfare aircraft. That is an asset that Ukraine does not have and will not be getting anytime soon. I can't see the US giving Ukraine some old EA-6Bs with updated EW capabilities or anything like that. Jamming the drones by placing jammers near or around potential targets is not going to cut it long term. You need some form of signals intelligence. Ukraine's military realise this, even in the article you posted.

We also need more access to electronic intelligence from our allies, including data from assets that collect signals intelligence, and expanded production lines for our anti-drone EW systems within Ukraine and abroad,” he wrote in The Economist.