Here is one technique. It's called RGPO or Range Gate Pull Off
The ECM system receives the target emitter, then duplicates and amplifies the signal. It's a synthesizer at its basic element. It then creates an offset. In the example above, the target signal is a Bravo Scan. Aka Horizontal scanning radar. When the target radar receives the signal, it sees the target as being on a different azimuth (bearing from origin). The ECM system "walks" this offset out to a predefined limit, resets, and repeats the process. The goal of RGPO is to pull an incoming missile off its course.
In the case of missile homing radar, that horizontal window is going to be VERY narrow. RGPO is designed to open up that window. Get the missile to fly off course so you can evade (if in an aircraft) or get a hard kill with CIWS (if on a ship).