Re: Looking for a way to communicate with a cell phone confined inside a metal enclos

See post #3.

The open question is how good the coupling will be for a particular mobile phone or other GSM appliance. Like the device antenna itself, your coupler will be a compromise for different bands and different interface geometries. If you know the exact antenna geometry and matching circuit of the DUT, you could try to design a complementary coupler device with optimal Sxx parameters in an EM simulator.

I guess, this isn't a research project, so you'll probably start with a few cheap couplers available on the market and measure their performance.

The "DUT" can be any cell phone from the late 90's to the latest smartphones (likeliest option though). I just can't predict where the receiving antenna will be located inside the enclosure, and how good it will "couple" with the emitter.
Thus I am wondering what I should use in the simulator as the receiving antenna...

so the rx bands should be 600M-2700M for mobile 4G bands, and if including WiFi 5G, it should be noticed.
So you need design an antenna with wide band, such as spiral antenna or circular antenna, and it should work.