A radio detection and ranging, RADAR, level gauging apparatus comprising: an antenna configured to emit a RADAR signal to a level interface and receive the RADAR signal reflected from the level interface; and a controller configured to perform transmission control for the RADAR signal emitted by the antenna, reception control for the RADAR signal received by the antenna, and level measurement control using the received RADAR signal, wherein the antenna includes: a lens through which the RADAR signal is transmitted and received in a direction perpendicular to the level interface, wherein the lens includes a Luneburg lens of which a total length is minimizable because a distance between a focal point and a lens is short and through which the RADAR signal, which is transmitted and received in a wide direction, is focusable in the direction perpendicular to the level interface; an absorber configured to reduce a side lobe of the RADAR signal transmitted and received through the lens; a waveguide configured to guide the RADAR signal between the controller and the Luneburg lens; at least two lateral fixing rods configured to laterally fix the Luneburg lens; and an upper support configured to support the Luneburg lens in a direction from top to bottom, wherein the upper support comprises: a first upper support configured to support the Luneburg lens in an apex portion above the Luneburg lens; and a second upper support installed between the at least two lateral fixing rods and the first upper support and configured to partially support an upper spherical surface of the Luneburg lens. an antenna configured to emit a RADAR signal to a level interface and receive the RADAR signal reflected from the level interface; and a controller configured to perform transmission control for the RADAR signal emitted by the antenna, reception control for the RADAR signal received by the antenna, and level measurement control using the received RADAR signal, wherein the antenna includes: a lens through which the RADAR signal is transmitted and received in a direction perpendicular to the level interface, wherein the lens includes a Luneburg lens of which a total length is minimizable because a distance between a focal point and a lens is short and through which the RADAR signal, which is transmitted and received in a wide direction, is focusable in the direction perpendicular to the level interface; an absorber configured to reduce a side lobe of the RADAR signal transmitted and received through the lens; a waveguide configured to guide the RADAR signal between the controller and the Luneburg lens; at least two lateral fixing rods configured to laterally fix the Luneburg lens; and an upper support configured to support the Luneburg lens in a direction from top to bottom, wherein the upper support comprises: a first upper support configured to support the Luneburg lens in an apex portion above the Luneburg lens; and a second upper support installed between the at least two lateral fixing rods and the first upper support and configured to partially support an upper spherical surface of the Luneburg lens. a lens through which the RADAR signal is transmitted and received in a direction perpendicular to the level interface, wherein the lens includes a Luneburg lens of which a total length is minimizable because a distance between a focal point and a lens is short and through which the RADAR signal, which is transmitted and received in a wide direction, is focusable in the direction perpendicular to the level interface; an absorber configured to reduce a side lobe of the RADAR signal transmitted and received through the lens; a waveguide configured to guide the RADAR signal between the controller and the Luneburg lens; at least two lateral fixing rods configured to laterally fix the Luneburg lens; and an upper support configured to support the Luneburg lens in a direction from top to bottom, wherein the upper support comprises: a first upper support configured to support the Luneburg lens in an apex portion above the Luneburg lens; and a second upper support installed between the at least two lateral fixing rods and the first upper support and configured to partially support an upper spherical surface of the Luneburg lens. a first upper support configured to support the Luneburg lens in an apex portion above the Luneburg lens; and a second upper support installed between the at least two lateral fixing rods and the first upper support and configured to partially support an upper spherical surface of the Luneburg lens.