well, in general, it could be anything, i used aluminium and copper. i even coated them by nicle and cobalt. often they made by copper, becouse the patches should be etched from the board and the boards mettal is often copper.
and, its not depend on the frequency, why you ask just for GSM? it should be just a mettal, better mettals (such as copper) is prefered.
rgds, marti
hi harmony,u means skin deph loss that degrade the effieciency of antenna as in conductor dielectric loss tanget but loss tangent describe the losses in dielectic not conductor that the espr is complex that have real and imaginary and loss tanget describe bu imaginary over real
regards