The first models of -21 had no radar, daytime/clear air only fighters. Someone's pulling your leg.
Edited to add in later years the soviets added one of the worst aerial radars ever flown (by the USSR anyway). Roughly the same performance as a modern marine radar. Think "Lowrance 3G level" performance. That outputs about 10 watts RF. (More like 20 watts DC in, and ancient microwave equipment was legendarily inefficient, so..)
Also the ground support vehicle runs the whole machine when the engine is off for ground maint, preflight, etc, and the max continuous is like 200 amps for the -21 ground support... so at 28 volts that's about 5 KW max for an entire aircraft.
Another way to look at it is tenth of a megawatt class TV stations were never surrounded by piles of dead birds. To shoot one outta the sky would take maybe 100 times the power.
So you're talking 10 megawatts out, minimum, given ancient RF gear that would require at least 100 megawatts power input... thats 100,000 horsepower or so. Also the waveguide feeding the antenna would arc over at those power levels, whoops.
There's a darwin award for a security guard at (I think) a TV studio who decided on christmas eve that work was too hard and instead spent the night sleep in front of one of their microwave transmitters. I believe they found him dead and cooked right through in the morning.
Did that actually happen? I know someone who worked at a shortwave (a.k.a. microwave) radio station when that almost happened. They had to shut down the transmitters occasionally to paint the radio towers, but someone had the bright idea that they could just power down long enough for the painters to climb on. Then, when they weren't grounded, they could power it back up during the painting. They actually did a test run with chickens before it dawned on anyone that they would be cooking anything up there!
During WWII, soldiers would stand in front of the radar to keep warm. This was before health and safety.