def METHOD_NAME(self):
    filename, _ = QtWidgets.QFileDialog.getOpenFileName(
        filter="Touchstone Files (*.s1p *.s2p);;All files (*.*)"
    )
    if filename != "":
        self.app.resetReference()
        t = Touchstone(filename)
        t.load()
        self.app.setReference(t.s11, t.s21, filename)