Planar antenna achieving a wide frequency range and a radio apparatus used therewith

摘要

A planar antenna includes a ground plate and a conductive plate arranged in parallel to the ground plate. The conductive plate has a ground terminal at a first position thereof and has a feed terminal at a second position thereof. The planar antenna further includes a frequency change switch which is used to charge the antenna resonance frequency by electrically connecting the conductive plate to the ground plate at a third position which is different from the first and second positions.