That's what is technically known as a "non-denial denial", I think.
What's it all about? Well, radar is the heart of air defence, so the first step in defeating an integrated air defence is to disrupt its supply of information. This means targeting the radars - which is of course a chicken and egg problem. The answer is to use the various techniques of electronic warfare to jam or deceive the system temporarily so that (if desired) aircraft or missiles can destroy key radars and headquarters. The phrase "soft kill" is used to describe jamming a radar, in order to then move on to a "hard kill" - i.e. blow it to pieces. In order to co-ordinate the "first night of the war" - the very complicated process of defeating the air defence system, requiring electronic warfare, fighter operations against enemy fighters, precision attack on radars, HQs, SAM sites etc and the tanker and AWACS support needed by everything else - it's first necessary to locate and identify the other side's radars.
The Iranians apparently suspect that the drones' main purpose is to explore their air defence, inducing alerts and the activation of more radars so that satellites, the EC135 Rivet Joint electronic-warfare planes and (perhaps) sensors on the drones themselves can pick up the transmissions. This hoped-for electronic aggression display would likely be of more intelligence value than whatever the drones collect themselves. There are, of course, countermeasures. One is to shoot down the drones (incidentally running the risk of exposing the locations of the SAMs used). Another is to produce a deceptive response of some sort. The simplest countergame strategy is simply to turn off all the radars and give nothing away. That is exactly what the Iranians did.
As always, of course, there's a cost. You lose the use of those radars, at least until you decide to switch them back on (light them off, as they say). There's a cost to the drone activity, too. As the article makes clear, monitoring the drone sightings told the Iranians where the US intelligence and reconnaissance effort was focused. They say they proceeded to concentrate defences in those areas - although, of course, this could be disinformation. Once you know where they're looking, you can show them what you want them to see. Note this paragraph:
" But it did not work. "The United States must have forgotten that they trained half our guys," the Iranian official said. After a briefing by their air force three weeks ago, Iran's national security officials ordered their forces not to turn on the radar or come into contact with the drones in any way.The nameless "sources" quoted go on to some considerable extent about using the drones to check for radioactive particles in the air, but I suspect the ELINT reconnaissance is more important (monitoring for particles doesn't require the risky step of illegal overflights; they drift on the wind).
"Our decision was: Don't engage," the Iranian official said. Leaving the radar off deprives U.S. forces of vital information about the country's air defense system, but it also makes it harder for Iran to tell if an attack is underway."
Very interestingly, the Iranians apparently consulted with Russia about the "UFOs". I can't be the only reader who thinks this is transparent nonsense. They signed an agreement with Russia to find out more about the drones - this is the only realistic interpretation. What form such cooperation takes remains open. Did the Russians help to identify the sightings? I wonder what capability Russia has in the field of electronic intelligence in the Middle East. If they still have southward-facing long range radars or were monitoring the radio links that control the drones, they might well have been able to give a full account of the activity. They may have given advice on countermeasures in return for full reports of the activity. I'm sure Russia would love to know more about the UAVs.
In fact, that makes me think - surely electronic countermeasures against the signals that control UAVs are about to be slap bang on top of the agenda?