You'd end up jamming yourself. You can't really have radars or other strong electromagnetic warfare devices near each other operating on the same frequency since they tend to interfere and wash out each other's signals.

As a decoy makes sense though since you can send them far away on a drone or something.

That's just not how phased array systems work. The system we're talking about needs to have excruciatingly tight and correct timings regarding signal transmission and reception. These are beam forming systems, so a multidimensional array of antenna are using to steer the beam, using constructive and destructive interference to "point" the energy where you want it to go. That alone requires extremely tight timing. That's coupled with a phased array receiver system, so that you can detect very slight changes in the wavelength/ speed of the return signal to apply the doplar effect to detect things like motion. The github states that this system operates at 10.5 GHz, of which one RF cycle is about 95 ps, ~2.5cm. This puts the practical per-element beamforming granularity/error budget is very much in that sub-picosecond to picosecond-equivalent range. That would be practically impossible for anything but a coupled system.

Not completely impossible, I mean, probably US military systems exist in a decoupled system. But its technologically way, way way harder because timings need to be nano to pico second correct.