Interrupting the signal isn't how multistatic radar works. You actually get two signals, the first is the transmission that traveled in a straight line to get

Interrupting the signal isn't how multistatic radar works. You actually get two signals, the first is the transmission that traveled in a straight line to get there, the second is the one that bounced off the plane and took a little longer to get there. By measuring the time delay you know how much longer two legs of the triangle are from the third. By doing this with multiple receivers you can solve a system of equations to figure out where the plane is. Solving the system of equations to make all the triangles work out is why it's called triangulation.