A level gauge for determining a filling level of a product in a tank, said level gauge comprising: a transceiver for transmitting an electromagnetic transmit signal and receiving an electromagnetic echo signal, processing circuitry connected to said transceiver and adapted to determine said filling level based on a relationship between said transmit signal and said echo signal, and a two-channel directional antenna (6; 6'; 6"; 60) connected to the transceiver and arranged to emit said transmit signal into the tank and to receive said echo signal from the tank, said antenna comprising: an antenna aperture defined by an opening of a geometrically delimited interior space of said antenna and adapted to emit electromagnetic energy in a direction of radiation, a partition wall (22; 58) dividing the antenna into a first partition for emitting the electromagnetic transmit signal, and a second partition for receiving the electromagnetic echo signal, and an electromagnetic coupling arrangement comprising a first waveguide feeder arranged to couple said transmit signal from the transceiver into said first antenna partition, and a second waveguide feeder arranged to couple said echo signal from said second antenna partition to the transceiver, characterized in that said partition wall includes a protruding lip portion extending a distance outside said opening, and an electromagnetic de-coupling structure is arranged at least partly on said protruding lip portion in order to reduce coupling between said first and second partitions also a distance outside said opening to reduce any leakage of electromagnetic energy from said transmit signal into said echo signal. a transceiver for transmitting an electromagnetic transmit signal and receiving an electromagnetic echo signal, processing circuitry connected to said transceiver and adapted to determine said filling level based on a relationship between said transmit signal and said echo signal, and a two-channel directional antenna (6; 6'; 6"; 60) connected to the transceiver and arranged to emit said transmit signal into the tank and to receive said echo signal from the tank, said antenna comprising: an antenna aperture defined by an opening of a geometrically delimited interior space of said antenna and adapted to emit electromagnetic energy in a direction of radiation, a partition wall (22; 58) dividing the antenna into a first partition for emitting the electromagnetic transmit signal, and a second partition for receiving the electromagnetic echo signal, and an electromagnetic coupling arrangement comprising a first waveguide feeder arranged to couple said transmit signal from the transceiver into said first antenna partition, and a second waveguide feeder arranged to couple said echo signal from said second antenna partition to the transceiver, characterized in that said partition wall includes a protruding lip portion extending a distance outside said opening, and an electromagnetic de-coupling structure is arranged at least partly on said protruding lip portion in order to reduce coupling between said first and second partitions also a distance outside said opening to reduce any leakage of electromagnetic energy from said transmit signal into said echo signal. an antenna aperture defined by an opening of a geometrically delimited interior space of said antenna and adapted to emit electromagnetic energy in a direction of radiation, a partition wall (22; 58) dividing the antenna into a first partition for emitting the electromagnetic transmit signal, and a second partition for receiving the electromagnetic echo signal, and an electromagnetic coupling arrangement comprising a first waveguide feeder arranged to couple said transmit signal from the transceiver into said first antenna partition, and a second waveguide feeder arranged to couple said echo signal from said second antenna partition to the transceiver, characterized in that said partition wall includes a protruding lip portion extending a distance outside said opening, and an electromagnetic de-coupling structure is arranged at least partly on said protruding lip portion in order to reduce coupling between said first and second partitions also a distance outside said opening to reduce any leakage of electromagnetic energy from said transmit signal into said echo signal.