A birdcage resonator for magnetic resonance applications has two ferrules
disposed in spaced-apart parallel ferrule planes. A line connecting the
ferrule centers defines the antenna axis of the birdcage resonator, which
orthogonally intersects the ferrule planes. The birdcage resonator has a
number of antenna rods regularly distributed around the antenna axis,
extending from ferrule to ferrule. The birdcage resonator has two
coupling rings in addition to the ferrules that surround the antenna axis
in respective coupling ring planes orthogonal to the antenna axis, and
that are spaced from but coupling with the ferrules. The coupling rings
are tuned to cause the ferrules to be resonant at frequencies other than
without the coupling rings. The ferrules couple with one another in
common eigenmodes, namely a common mode with a common mode frequency, and
a push-pull mode with a push-pull frequency differing from the common
mode frequency. The coupling rings are tuned such that the frequency of
one of the eigenmodes does not correspond with any resonance frequency of
the antenna rods. A feed device feeds electrical energy into the ferrules
at the frequency of the eigenmode that corresponds with no resonance
frequency of the antenna rods.