The Beagle Active Probe (BAP) is a suite of enhancement technology that, when attached to general electronic sensors, enables the equipped unit to detect and classify other battlefield units -with the exception of conventional infantry- whether they are camouflaged or even shut down.
The Inner Sphere Beagle Active Probe weighs 1.5 tons and takes up 2 critical spaces. It has a detection range of four hexes.
The BAP was not originally designed to be a "Radar Extender", it was designed to detect hidden enemy units within close range. Since battlemechs are generally really easy to spot, it had almost no use in the previous Mechwarrior games except as a radar extender. Ironically, now that we have combined arms that would make the BAP really useful (detecting BA) it doesn't function as originally intended.
ECM, additionally, is all supposed to blanket a large area, but previous MW games had it only affect the unit using it, cutting radar detection range down and extending the time needed for missile lock. Again, its original use was bastardized for MW play and so it had no effect on streak, targeting computers, NARC, Artemis IV FCS, etc. Now that there is a need for large area EW mechs the equipment isn't altered to fit the role needed, it is still using the old bastardized MW interpretations.