the altimetry satellite Jason-2 was launched from the Vandenberg site in California. Dedicated to the measure of ocean surface topography, one of the main instruments on-board is a radar altimeter, Poseidon-3, which essentially measures the altimetric range between the spacecraft and the surface.Poseidon-3 is a dual frequency radar altimeter operating in Ku and C bands, very similar to its predecessor Poseidon-2 on-board Jason-1. However some significant improvements have been implemented to improve its tracking capabilities over coastal and inland waters, that is, its capacity to maintain data acquisition over land or mixed land-sea terrain.The performance assessment is excellent: the range measurement accuracy is close to 1.5 cm for 1s averaging and the significant wave height (SWH) noise is less than 12 cm (for a 2m SWH at 1σ ).In terms of range, the short-term drift (along an orbit) is around 1 mm, and the long-term drift is negligible so far. The tracking success is close to 100% over oceans and 80% over land surfaces, the new acquisition and tracking modes inducing significantly higher data availability in comparison with Poseidon-2.We assess Poseidon-3 main improvements, with the presentation of the new modes of echo acquisition and tracking: the median tracking algorithm, DIODE/DORIS acquisition, and the coupling between DIODE and digital elevation model (DEM) information. The median tracking algorithm is shown to reinforce the robustness of the altimetry echoes outside the standard Brown conditions. DIODE acquisition mode increases data availability in land-to-water transitions, providing up to 5 km of extra measurements along track, which constitutes an asset for coastal and small water areas (lakes, rivers) observations. Both are now implemented as the default mode on Jason-2. DIODE/DEM mode remains experimental and requires further adjustments but shows promising features such as acquisition of water surfaces in rough terrain.

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International audienceThis paper presents a concept of a tunable cavity resonator composed of a resonating cavity and a dielectric perturber. This tunable resonator is designed and measured to prove the tuning mechanism obtained by varying the angle of rotation of the perturber. A rotation from 0 to 90 produces a tuning ratio of 1:1.25, i.e., a tuning range of 22.2% around 11.5 GHz while maintaining an unloaded Q factor between 1500 and 2300. After this first experimental validation, a third-order bandpass filter is then designed and measured using the same base principle. Using a single mechanical movement, all three resonators’ perturbers are synchronously rotated to create a third-order Chebyshev bandpass filter maintaining a 516±38-MHz bandwidth (for a return loss better than 10 dB) from 9.915 to 12.189 GHz. A 20.6% tuning range is then obtained at approximately 11 GHz with an estimated Q factor from 1400 to 2150. These performances have been obtained by using specifically shaped dielectric perturbers, which have been made by a ceramic additive manufacturing (AM) process (stereolithography). This technology has enabled the perturbers’ specific geometries and embedded supporting elements to be feasible. A sixth-order Chebyshev bandpass filter has also been theoretically proposed using full wave simulations

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