Additional short stub in simple balun

See "Ideal balun model" in https://www.microwaves101.com/encyclopedias/baluns

This article says "Also note that in the simple balun design, ".a shorted stub is required to match the circuit (quarterwave at 10 GHz).

However, I think TL3 rather degrade frequency characteritics as balun.

Is this description truely reasonable ?

Does article want to say this short stub is for adjusting balance in actual design ?

I think, the explanation is misleading. You get a perfect balun by using an ideal (hypothetic) coupled line with infinite common mode impedance.

My main objection to the balun model is exactly about this unrealistic high common mode (even) line impedance. Also electrical length of differential and common mode part usually don't match.

If the circuit is intended to model a real balun, we should know about the used technology and feasible transmission line parameters.