Battletech Sensor warfare

I don't remember them in the main game, so without a mod, I think the Urban Warfare DLC is your only option.

There is a free mod that will help you out with having to buy DLC called Roguetech. The "downside" is that it is a super-comprehensive makeover to the game but it definitely includes your sought-after sensors, ECM, ECCM, and visual stealth components. It's also got all (or at least almost all) the other toys they've ever dreamed up for Battletech such as mechs (including a ton of variants), vehicles, weapons, melee components, and probably more stuff that I am forgetting. Frankly, I'm not sure I could ever go back to vanilla Battletech after playing Roguetech.

If this sounds interesting to you, the best place to check out is the Roguetech wiki (https://roguetech.gamepedia.com/Roguetech_Wiki). On the right side is an installation guide that should help you get started.