The phrase "same wavelength" means that two or more people understand each other very well and think in a similar way. It suggests that they are on the same page and often have similar thoughts or ideas. Full definition
Very dangerous if they're all on same wavelength. (justarsenal.com)
watching replays, often times it seems welbeck not on same wavelength as ppl passing to him (ozil, caz, giroud). (justarsenal.com)
It is constant interaction with such likeminded individuals, who are on same wavelength as you, which develops you so much intellectually. (safalniveshak.com)