Magnetron with cathode decoupled from output

1. A magnetron comprising a cathode, an anode axially aligned with the cathode and including a plurality of radial vanes defining resonant cavities, an output coupler connected to a first set of the vanes, a second set of vanes not connected to the output coupler, and extensions formed on only the vanes of the second set, said extensions extending in the axial direction towards the output coupler in a direction parallel to the axis of the anode, the extensions not being connected to the output coupler, whereby a capacitance between the axial extensions and the cathode at least partly compensates for the capacitance between the output coupler and the cathode.

2. A magnetron as claimed in claim 1 , in which the axial extensions are at the tips of the anode vanes.

3. A magnetron as claimed in claim 1 , in which the magnetron has one or more strap rings connected to one set of the vanes.

4. A magnetron as claimed in claim 3 , in which there are a plurality of rings connected to the same set of vanes and distributed over the length of the anode.

5. A magnetron as claimed in claim 4 , in which the vanes of one set alternate with the vanes of the other set.

6. A magnetron as claimed in claim 5 , in which the output coupler is connected to a coaxial output line.

7. A magnetron as claimed in claim 6 , in which the frequency output lies within a range of from 8 to 12 GHz.