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The Cassini mission crossed the source region of the Saturn kilometricradiation (SKR) on 17 October 2008. On this occasion, the Radio and Plasma WaveScience (RPWS) experiment detected both local and distant radio sources, whileplasma parameters were measured in situ by the magnetometer (MAG) and theCassini Plasma Spectrometer (CAPS). A goniopolarimetric inversion was appliedto RPWS 3-antenna electric measurements to determine the wave vector k and thecomplete state of polarization of detected waves. We identify broadbandextraordinary (X) as well as narrowband ordinary (O) mode SKR at lowfrequencies. Within the source region, SKR is emitted just above the X modecutoff frequency in a hot plasma, with a typical electron-to-wave energyconversion efficiency of 1% (2% peak). The knowledge of the k-vector is thenused to derive the locus of SKR sources in the kronian magnetosphere, thatshows X and O components emanating from the same regions. We also compute theassociated beaming angle at the source theta'=(k,-B) either from (i) in situmeasurements or a model of the magnetic field vector or from (ii) polarizationmeasurements. Obtained results, similar for both modes, suggestquasi-perpendicular emission for local sources, whereas the beaming pattern ofdistant sources appears as a hollow cone with a frequency-dependent constantaperture angle: theta'=75{\deg}+/-15{\deg} below 300kHz, decreasing at higherfrequencies to reach theta'(1000kHz)=50{\deg}+/-25{\deg}. Finally, weinvestigate quantitatively the SKR polarization state, observed to be stronglyelliptical at the source, and quasi-purely circular for sources located beyondapproximately 2 kronian radii. We show that conditions of weak mode couplingare achieved along the ray path, under which the magneto-ionic theorysatisfactorily describes the evolution of the observed polarization.

Emission and propagation of Saturn kilometric radiation: magneto-ionic modes, beaming pattern and polarization state