It will bit of a long read, takes long time to write also.
@Tps43 if you could stop flirting in the members section and visit this thread please to help me where i miss and point out where i am wrong.
There is a requirement for a strike mission to include an Electronic Attack aircrafts('s) to ensure mission success and survivability of all aircrafts taking part in that mission.
In a general scenario, if the attack is going to be carried out by 4-6 PAF's strike aircrafts, atleast 1-2 EA aircraft could support them. The enemy Radar detects them and then attempts to starts tracking them as they enter the enemy air space. The receivers of the EA aircarft pick up the radiations from the Radar and starts sampling them to bring up a counter measure. So assuming that S-400 radar is tracking PAF's aircraft, where as the mission is not taking out the S-400 missile battery or S-400 Radar, but taking out any other strategic target. And its not just S-400 radar but other IAF ground based radars as well as IAF Mig-29's or SU30 MKI on CAP. This is where PAF's EA aircraft will provide cover to PAF's strike aircraft (this scenario was seen on 27th Feb through Falcon DA-20 which you mentioned before). In this assumption PAF's EA aircraft is not Falcon DA-20 but either JF-17 or F-16, armed with ECM/ECCM pods. So PAF's EA aircraft starts sending out effective radiated power on IAF's radar, whichever is conceived to be the biggest threat (strong signal level, enough to send a missile towards PAF aircrafts). So two ways to go around that:
1. Stand Off: stay away and direct jammer towards that Radar.
2. Go in: keep flying towards the radar (if it comes in the way or along the way of the target) and barrage with Electromagnetic energy.
The IAF Radar (or any Radar for that matter) will not have the same power and signal strength in all of its coverage area or coverage radius. The power will be reduced in certain areas, such as on edges of the coverage radius. So as PAF's aircrafts fly towards it, it has more chances of detection, targeting and locking on to PAF's aircraft. Other factors are RCS of PAF aircraft, weather conditions, altitude at which PAF aircraft are flying etc. I have not come to S-400 missiles as yet, as that would be a DEAD (basically destroy IAF's radar and if possible batteries) mission, and this current scenario is part of a SEAD mission (suppress IAF radar's and jamming ability).
So if PAF EA aircraft cannot fully jam the Radar, it could still provide enough cover to strike aircraft to weaken the signal from Radar in the area where PAF aircraft are flying so the IAF Radar cannot lock on to PAF aircraft. IAF Radar would know that something is happening in that area and the radar is being jammed, so IAF may vector in Migs or SU30MKI's to investigate, but the threat of a SAM lock would have dried down mostly. It also depends on the amount of time that PAF aircraft stay in IAF airspace, strike and leave. PAF EA aircraft will be the first to go in and last one to leave IAF airspace and land in PAF airbase.
When jamming comes to mind, its like a fight between jammer and radar, like if u see Star war movies or cartoons, pointing swords and rays coming of swords and the one with more power wins. Its in a way like that but not entirely because jamming has many types. PAF EA aircraft has to do the following things in a high threat environment when IAF radar or IAF aircraft are trying to Jam or target or lock on to PAF strike fighters:
1. Deny IAF jamming attempts
2. Deceive IAF jamming by counter jamming (or ECCM)
3. Degrade IAF jamming, detecting, tracking, targeting attempts.
PAF EA can do 1 or all 3 of the above. Its a cat and mouse game. IAF Radar sends in Freq A (as example), PAF EA aircraft's DRFM memorizes (stores) that and re-transmits back, then IAF Radar jumps to Freq B, PAF EA aircraft memorizes and sends back, so on and so forth. A constant endeavor from both sides. Then IAF Radar tries to lock on PAF's strike aircraft, their RWR and other related sensors light up, so PAF EA aircraft starts creating false/misleading targets OR denies/delays/confuses locking onto PAF's strike aircraft by re-transmitting same frequency. IAF S-400 Radar will pick up whether these decoys has "skin returns" or not, and it will pick up those false targets as decoys. Therefore PAF EA aircraft will use DRFM's coherent jamming technique by creating slight variations in transmitted frequency to create doppler errors for IAF's S-400 Radar. IAF Radar will increase power, proving its location which will be picked up and marked by PAF EA aircraft and relayed back (if data transfers are enabled). Since the IAF's S-400 Radar will have more power available to it (logically), therefore PAF EA aircraft will start jamming its side lobes, instead of main lobe of radar beam tracking PAF's aicrfats, as it will reduce radar coverage area to lock on to PAF aicrafts. This will force S-400 Radar to enable its function of "side lobe jamming canceler" or side lobe blanker to counter PAF EA aircrfat's side lobe jamming. This could reduce some power from the main lobe of IAF Radar so PAF EA aircraft will shift to noise jamming or deception jamming to prevent a lock-on again. This is all going to happen with-in seconds.
Now if PAF EA aircraft was employing MALD's (just google it.. for those who dont know) or UAV's as decoys, or even as jamming support, the S-400 Radar will pick up multiple targets. A capability which I am not sure if PAF has or not currently.
Moving on, IAF's Migs and SU30's: One of the main aims of PAF EA aircraft is to deny a lock on by IAF's S-400 Radar and once IAF's Migs and SU30MKIs reach the scenario, it will continue to do so in air combat now. It will start jamming IAF Migs and SU30MKI's radar to prevent a lock on. In an ideal world, IAF aicrafts should not catch up with PAF's strike package of strike aicrafts and EA aicrafts. But if it does then the main threat are AAM's whose seeker once activated is very very difficult to jam or break lock. AAM has a vision or radar coverage area of its own. BVR AAM"s have narrow but long coverage areas, IR or short range AAM's have wide but short coverage areas. Either towed decoy would help or breaking 90 degrees to get out of field of vision of BVR AAM could possible save PAF's aircrafts.
Just a bird's eye view why an EA aircraft is necessary to escort a strike package entering enemy's airspace and making it back in one piece.
@Khafee . any corrections ?
F-16's DRFM is priceless, whether Block 52+ or UAE-AF's Block 60.