Post Mixer Spectra of Periodic FM Altimeters with Area Target Returns

A periodic FM altimeter is postulated and its illuminated area target modeled as an array of elemental scatterers. A computational form is then developed expressing the desired post mixer spectrum as a sum of spectral components corresponding to the individual scatterer returns. Application of the model is made to the case of a triangular linear sweep FM altimeter and samples of the calculated post mixer spectrum presented, illustrating the effects of antenna beam geometry, target surface properties, and modulation parameters.