  The normal mode theory of the transmission lines is applied to the studies of
the Four-Rod RFQ. This resonator consists of four quadrupole electrodes and
stems. It can be simulated by the four-conductor shielded transmission line,
which is loaded by sets of coaxial transmission lines corresponding to the
support stems. The ideal case of the indefinite periodic Four-Rod RFQ is
considered. Formulas for resonance frequency, the voltage distribution along
the electrodes and the shunt impedance are obtained.
