Patent Number: 
Section: claims

1. An X-ray tube comprising:an electron beam generation unit emitting an electron beam;a limiting electrode unit limiting the electron beam emitted from the electron beam generation unit; anda target unit comprising a target material emitting an X-ray when the limited electron beam collides with the target material,wherein the limiting electrode unit comprises an electron beam limiting electrode allowing a portion of the emitted electron beam to pass therethrough and to be delivered to the target unit,wherein the portion of the emitted electron beam has a size corresponding to a size of a focal spot of the X-ray. 2. The X-ray tube of claim 1, wherein the limiting electrode unit further comprises a penetration type electron beam limiting electrode having a limiting opening having a predetermined diameter. 3. The X-ray tube of claim 2, wherein the penetration type electron beam limiting electrode delivers, to the target unit, a portion of the electron beam having passed the limiting opening among the emitted electron beams. 4. The X-ray tube of claim 2, wherein the penetration type electron beam limiting electrode is configured to have an equal electric potential as the target unit. 5. The X-ray tube of claim 1, wherein the limiting electrode unit comprises at least one slit type electron beam limiting electrode having a slit having a predetermined width. 6. The X-ray tube of claim 5, wherein the at least one slit type electron beam limiting electrode comprises:at least one spacer having a thickness corresponding to the predetermined width; anda plurality of metal electrodes spaced by the at least one spacer. 7. The X-ray tube of claim 5, wherein the at least one slit type electron beam limiting electrode is disposed such that slits are aligned with each other at a predetermined angle. 8. The X-ray tube of claim 5, wherein the slit has an incident surface into which the emitted electron beam is incident and an emitting surface through which the portion of the electron beam is delivered to the target unit, and a width of the incident surface is greater than a width of the emitting surface. 9. The X-ray tube of claim 1, wherein the electron beam limiting electrode is made of at least one of tungsten, molybdenum or gold. 10. The X-ray tube of claim 1, further comprising a filter disposed between the target unit and an object to which the X-ray is delivered, the filter being configured to remove a low energy X-ray. 11. The X-ray tube of claim 10, wherein the filter is integrally provided with the target unit. 12. The X-ray tube of claim 1, wherein the electron beam generation unit comprises a cathode emitting the electron beam, and the target unit comprises an anode. 13. The X-ray tube of claim 12, wherein the electron beam generation unit further comprises a focusing unit focusing the electron beam emitted from the cathode in a micrometer-scale.