A planar antenna comprising a process separation device for a fill level radar for measuring a fill level, with the planar antenna comprising: a planar radiator element for radiating an electromagnetic transmission signal to an exterior region of the antenna; a dielectric, plate-shaped process separation device for separating the exterior region of the antenna, underneath of the process separation device, from an interior region of the antenna, above the process separation device; a metal wall as ground surface for the planar radiation element, wherein the metal wall is arranged at a distance from the planar radiation element; and high-frequency connection in form of a coaxial input, which comprises an inner conductor and an external conductor and which forms a feedthrough trough the metal wall, wherein the metal wall serves as the external conductor for connecting with a microwave module; characterized in that: - a circumferential rim in the interior region of the antenna is provided between the process separation device and the metal wall, to support to the process separation device against pressure; - a planar radiation element within the said circumferential rim is plated on the metal wall facing backside of the plate-shaped process separation device; - within the circumferential rim between the metal wall and the process separation device respectively between the metal wall and the planar radiation element is a gas or vacuum; and - a melted-in glass seal is provided in the high-frequency connection at the area of the coaxial feedthrough between the inner conductor and the external conductor, that represents a safe zone separation in a potentially explosive area. a planar radiator element for radiating an electromagnetic transmission signal to an exterior region of the antenna; a dielectric, plate-shaped process separation device for separating the exterior region of the antenna, underneath of the process separation device, from an interior region of the antenna, above the process separation device; a metal wall as ground surface for the planar radiation element, wherein the metal wall is arranged at a distance from the planar radiation element; and high-frequency connection in form of a coaxial input, which comprises an inner conductor and an external conductor and which forms a feedthrough trough the metal wall, wherein the metal wall serves as the external conductor for connecting with a microwave module; - a circumferential rim in the interior region of the antenna is provided between the process separation device and the metal wall, to support to the process separation device against pressure; - a planar radiation element within the said circumferential rim is plated on the metal wall facing backside of the plate-shaped process separation device; - within the circumferential rim between the metal wall and the process separation device respectively between the metal wall and the planar radiation element is a gas or vacuum; and - a melted-in glass seal is provided in the high-frequency connection at the area of the coaxial feedthrough between the inner conductor and the external conductor, that represents a safe zone separation in a potentially explosive area.