Seems like this would be defeatable by radar that sends out pings with an unpredictable characteristic that the decoy won't be able to mimic with a stronger return signal.
Radar already does something similar to what you are suggesting, there are spread spectrum techniques that are much more jam/spoof-proof than just a constant ping or even a linear frequency sweep. You pseudo-randomly hop frequencies to avoid having someone broadcast a really strong signal at one frequency and to have someone be able to track your pattern of hopping. The pattern is generated similar to crypto, you start with a seed (the plaintext) and encrypt it with a key to get the pattern that you hop with.