Abstract: An antenna in a radar level gauge for determining the level of the surface of a medium stored in a tank. The antenna has a first and a second electrically conductive layer, and between the conductive layers a dielectric layer. The second of the conductive layers is provided with a number of holes in a predetermined pattern. Leading to the center of the dielectric layer is a transmission line. The microwaves from a radar unit in the radar level gauge are supplied to the dielectric layer in the antenna via the transmission line and transmitted out in a radial direction from a feed point in the dielectric layer that acts as a waveguide. Via said holes in the second conductive layer a microwave beam radiates out. Due to matching of the phase of the microwave and the placing of the individual holes in the pattern that the holes form, a predominant waveguide mode of the desired order is obtained.

Abstract: Radar antenna (1) for the transmission and reception of radar waves (4) for measuring the level of a surface of a liquid enclosed in a tank, wherein the radar antenna (1) is arranged above the surface (3a) of the liquid and substantially directed downwards towards said surface and said level determined by evaluation of the time lapsed between the transmission and reception of a signal included in said radar waves and wherein said radar antenna (1) has a front surface (1a) for transmission and reception of said radar waves, wherein said antenna (1) is a planar antenna having a sheet arranged on the surface (1a) of the antenna, wherein said sheet has a sheet surface (1b) between said antenna front surface (1a) and the surface (3a) of the liquid and said sheet surface (1b) being arranged in a predetermined angle &agr; being greater than 0° in relation to the horizontal plane H, whereby a fluid occurring on the surface (1b) of the sheet is drained off by means of gravity.