A level gauge for detecting process variables related to a distance to an upper surface of a content in a tank, said level gauge comprising: a first circuitry arrangement comprising first transceiver circuitry for generating, transmitting and receiving first electromagnetic signals, and first processing circuitry connected to the first transceiver circuitry for determining a first process variable related to said distance, a second circuitry arrangement comprising second transceiver circuitry for generating, transmitting and receiving second electromagnetic signals, and second processing circuitry connected to the second transceiver circuitry for determining a second process variable related to said distance, said first and second circuitry arrangements being functionally independent, characterized by one transmission line probe with two or more conductors connected to said first and second circuitry arrangements, said transmission line probe being a wave guiding structure with a diameter much smaller than a wavelength of the first and second electromagnetic signals, said transmission line probe extending into the content in the tank and being adapted to guide said first and second electromagnetic signals towards and into the content and to guide reflected signals back to the first and second circuitry arrangements, said transmission line probe being adapted to allow propagation of first and second different transmission modes, and a feeding arrangement, connected to receive said first electromagnetic signal and couple said first electromagnetic signal into said transmission line probe in a first propagation mode, and connected to receive said second electromagnetic signal and couple said second electromagnetic signal into said transmission line probe in a second propagation mode, said second propagation mode being a different propagation mode than said first propagation mode. a first circuitry arrangement comprising first transceiver circuitry for generating, transmitting and receiving first electromagnetic signals, and first processing circuitry connected to the first transceiver circuitry for determining a first process variable related to said distance, a second circuitry arrangement comprising second transceiver circuitry for generating, transmitting and receiving second electromagnetic signals, and second processing circuitry connected to the second transceiver circuitry for determining a second process variable related to said distance, said first and second circuitry arrangements being functionally independent, characterized by one transmission line probe with two or more conductors connected to said first and second circuitry arrangements, said transmission line probe being a wave guiding structure with a diameter much smaller than a wavelength of the first and second electromagnetic signals, said transmission line probe extending into the content in the tank and being adapted to guide said first and second electromagnetic signals towards and into the content and to guide reflected signals back to the first and second circuitry arrangements, said transmission line probe being adapted to allow propagation of first and second different transmission modes, and a feeding arrangement, connected to receive said first electromagnetic signal and couple said first electromagnetic signal into said transmission line probe in a first propagation mode, and connected to receive said second electromagnetic signal and couple said second electromagnetic signal into said transmission line probe in a second propagation mode, said second propagation mode being a different propagation mode than said first propagation mode.