Patent ID: 7284425

Claim:
A method for microwave signal based gauging of a distance to a surface with reflective properties at a filling level of a filling material in a tank having at least one interfering structure having a surface with reflective properties, comprising: transmitting at a first time first transmit signals towards the surfaces; receiving at essentially said first time first receive signals including a first surface echo; recording first propagation properties of the first transmit and receive signals associated with the first surface echo; transmitting at a second time second transmit signals towards the surfaces; receiving at essentially said second time second receive signals including a second surface echo; recording second propagation properties of the second transmit and receive signals associated with the second surface echo; wherein the first time and the second time are temporally separated by a first separation time; calculating a first difference between the first and second propagation properties; transmitting at a third time third transmit signals towards the surfaces; receiving at essentially said third time third receive signals including a third surface echo; recording third propagation properties of the third transmit and receive signals associated with the third surface echo; transmitting at a fourth time fourth transmit signals towards the surfaces; receiving at essentially said fourth time fourth receive signals including a fourth surface echo; recording fourth propagation properties of the fourth transmit and receive signals associated with the fourth surface echo; wherein the third time and the fourth time are temporally separated by a second separation time; calculating a second difference between the third and fourth propagation properties; comparing the first and second differences; selecting the greatest of said first and second differences as the difference associated with the surface of the filling material; and determining said distance to said surface of the filling material based on propagation properties of said transmit and receive signals.