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Pulsed HPA for Ka band SAR instruments – feasibility study
Synthetic Aperture Radar (SAR) instruments have become essential for Earth Observation purposes since the first instrument in space back in 1978. The operational frequency has progressively evolved from L- to C-, S- and X-band and higher frequency bands are currently under study in Europe. In particular, Ka-band has already been used for Unmanned Aerial Vehicles (UAV) but not yet utilized for SAR from space, although the suitability of Ka-band of SAR imaging has been proven in various airborne demonstrators and instruments. A few years ago, an ESA internal study on the feasibility of a Ka-band SAR instrument and interferometer has pointed to the need of a Ka-band High Power Amplifier (HPA) with capabilities beyond what is currently available on the market. This need was also confirmed by an ESA activity with Industry on the feasibility of Ka-band SAR missions. The key issue relevant to the Ka-band SAR is the availability of a vacuum tube amplifier given the high output power required. Main characteristic and design driving requirements of the Ka-band HPA for SAR applications are: 1) Carrier frequency: 35.75 GHz, 2) Transmitted Peak Power: 3.5 kW (4 kW goal), 3) Operating bandwidth: 350 MHz minimum, 4) Duty cycle: 13%. The feasibility study has been focused on the definition of a possible solution, starting from the available vacuum tubes technologies and defining the required development plan to achieve a space qualification for the identified one. Starting from the driving requirements, a trade-off between the TWT and the EIK solutions was carried out, resulting in the choice of the klystron as a baseline technology. All critical aspects related to the application (namely, potential multipaction issues, extended lifetime requirements, both in terms of operative hours and switching cycles, and thermal control issues) have been investigated in order to achieve a design baseline that will be the starting point for the follow-up development. An updated technical requirement specification has been issued and a detailed development plan has been proposed to achieve the space qualification of the baseline HPA.
Dionisio Roberto, Galantini Paolo, Aloisio Marinella, Ludwig Michael
Paper for Seminar/Symposium/Conference
ESA Workshop 2014 - Advanced RF Sensors and Remote Sensing Instruments & Ka-band Earth Observation Radar Missions (04-07 November 2014, Noordwijk, The Netherlands)
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