The working frequencies for payload data downlinks of Earth Observation satellites are incrisingly shifiting toward bands different from the traditional S- and X-band, to avoid spectrum congestion and to increase the data rates. In this context ESA has embarked a few years ago on the technology preparation for the exploitation of the K band (approx. 26 GHz) for Earth Observation Missions. In particular, the SNOWBEAR project (Svalbard grouNd StatiOn for Wide Band Earth observation dAta Reception), supervised by the ESA Ground Station Engineering team (OPS-GS), is intended to de-risk the introduction of this new band for the forthcoming Metop Second Generation mission (EUMETSAT/ESA) and the future generation of Sentinels missions (Copernicus/ESA).
The SNOWBEAR project consists of two main phases: the deployment of a prototype ground station at Svalbard (completed in autumn 2018) and a two-years operational trial using the Earth Observation satellite NASA/NOAA JPSS-1. The SNOWBEAR consortium comprises industries from all over Europe, mainly Belgium France, Germany, Italy, and Norway.
This paper provides an overview of the SNOWBEAR ground station and presents the first preliminary results about some metrics used to analyse the quality of the signal received at the ground station.
The SNOWBEAR ground station operates in K-band (25.5 to 27 GHz, circular polarisation) for data reception and autotrack and in S-Band (2.2 to 2.3 GHz) for autockrack acquisition aid. The antennais composed by a 6.4 m parabolic reflector illuminated by a a ring-focus coaxial feeding system and is protected by a multilayer (MLR) radome. The drive system is provided with thee axes and can be operated either in the classical Elevation/Azimuth mode or in Elevation/Crosselevation (equivalent to X/Y). Ambient and cryogenic low noise amplifers are used, and downconverting is carried out at an intermediate frequency of 1.2 GHz and 70 MHz for data reception and autotrack, respectively.
The ground station is remotely controlled from the KSAT Tromso control Center (T-NOC). All parameters related to the ground station configiration and performance as well as the wheater conditions at the station are logged and accessed periodically to build the different metrics and operational statistics. These are then used to evaluate the quality of the communication link between the station and the satellite. This is determined both in terms of absolute performance (e.g., recevied power across the different satellite passes, at the different elevation angles), and in terms of residul performance with respect to the theoretical predictions. This allows for an indirect test of the current antenna, radome and athmospheric models, with the final aim of an overall better comprehension of the operating conditions for communication links at K-band frequencies in Polar installations, that will be translated into better design tools for future missions.

This paper presents the novel 6 meter K- and S-band monopulse tracking ground station antenna developed by Indra for the next generation of Earth Observation (EO) applications in the 25.5 to 27 GHz band. A brief review of the mechanical system with the 6 meter reflector, the innovative X/Y/Z positioner as well as the monopulse feed, which covers the design and development of a dual band coaxial horn, a TE21 resonant tracking coupler, OMTs and polarizers, are included. Characterization of the complete antenna in both bands is also summarized in the paper.

The K-band capability, working between 25.5 and 27 GHz, is used to receive the high data rates of future EO missions allocated in that band. Moreover, tracking capabilities have been added to the antenna at this band in order to correctly follow the trajectory of those satellites, typically located at Low and Medium Earth Orbits (LEO/MEO), while minimising the pointing losses. This is especially important at K-band, where the radiation beam-widths are very small for high diameter antennas. The selected tracking approach is the monopulse. Although this tracking strategy increases the complexity of the feed, as it requires additional ports, it has been selected due to its proven accuracy, which maximizes the received signal level, thus improving the carrier to noise ratio.

The K-band section includes a dual band coaxial horn, a circular waveguide, and a TE21 tracking coupler followed by a dedicated Ortho-mode Transducer (OMT) septum polarizer. The main challenge of the design is to achieve low axial ratio while maintaining high degree of isolation between the rectangular receiving ports. Furthermore, a maximum isolation between the fundamental TE11 modes and the tracking TE21 modes has to be assured in order to get appropriate null depth for the tracking signals

The S-band capability, working between 2.2-2.3 GHz in reception and 2.025-2.120 GHz in transmission, is included to provide TT&C functionality, for the reception of telemetry (TM) and the transmission of telecommands (TC) to the satellite. The S-band section consists of and OMT and a corrugated polarizer, connected to the dual band horn.

The mechanical subsystem of the ground station antenna, it comprises all the structural parts related with the antenna pointing mechanisms. Namely, the antenna structure, the positioner and the servo subsystem.
Firstly, the antenna structure consists of the hub, reflector panels, back-up structure, and the subreflector assembly and cladding.
Secondly, the innovative Positioner is based on a 2-axes tracking system (X and Y) with a third axis (Z) to place strategically the X-Y gimbal, minimizing the axes speed. Then, in an operational sequence, first the Z axis is positioned in a suitable position for the next satellite pass. The strategy here is to place the X axis perpendicular to the expected trajectory. This position minimizes the tracking axes speed during the pass. After that the Z axis is fixed with the stow pin. The new position angle in Z axis is taken into account for the correct X/Y interpretation. The satellite pass will be then tracked with both axes as with a typical X/Y mount. Additionally, it must be noted that the Y and X axes are aided by a counterweight, which reduces even more the torque of the cinematic chain.
Finally, the servo subsystem is devoted to manage the antenna pointing, including the control of the antenna motion, limiting the acceleration and velocity, ensuring the safety of the motion and the implementation of tracking strategies.

In conclusion, a new 6m K/S-band tracking ground station with an X/Y/Z positioner for the next generation of Earth Observation ground stations has been presented in the article

Under a GSTP contract with ESA, Kongsberg Spacetec and SINTEF DIGITAL are developing a high rate modulator and demodulator for the ground segment of Ka-band satellite missions. This Software Defined Radio will fully implement the standards DVB-S2, CCSDS SCCC as well as “conventional” or “heritage” modulation formats. Dual modulators and demodulators are implemented on PCIe boards. This enables dual-channel cross-polarized transmission and reception with arbitrary symbol rates ranging from 32 to 1200 Msymb/s.

The primary design goals for the modem are excellent performance, large degree of flexibility and high spectral efficiency. The receiver contains cross-polarization interference cancellers which enable cross polarized co-channel signals. A spectral efficiency of more than 8 bit/s/Hz and bit rates up to 14.4 Gbit/s over the air can therefore be achieved. Preliminary results show a typical performance within 0.3 dB from theoretical limits. High flexibility is achieved through use of Field Programmable Gate Arrays (FPGA) which enable flexible upgrades throughout the lifetime of the modem.

The modulator is designed as a combined modulator and test instrument. A number of impairments can be included in the modulated signal at 1200 or 2400 MHz center frequency. These impairments shall emulate degradations experienced in real satellite systems, such as I/Q phase and amplitude imbalance, dynamic doppler and amplitude variations, spectrum tilt and OMUX filter non-linear phase. Phase noise with arbitrary phase noise mask can be injected on the carrier. User controlled cross-coupling between the two co-channel signals is also provided. White Gaussian noise can be added digitally to the signal both in the modulator and the demodulator.

For the DVB-S2 and CCSDS SCCC standards the receiver takes advantage of the frame structure in the acquisition and tracking algorithms. The dual receiver is equipped with an LMS equalizer to handle inter-symbol interference. Two different cross-polarization interference cancellers are implemented. One is an extension of the LMS equalizer and is designed to handle cross coupling between synchronous co-channel signals. The other one is able cope with non-synchronized signals. The error correcting decoder implements both Turbo (SCCC) and LDPC decoders. Due to the high symbol rate and the fact the FPGAs are operating with a clock frequency of typically 250 MHz, a massive parallelization is necessary in the signal processing, both in the modulator and demodulator. This complicates the design and necessitates simplifications in the signal processing algorithms. One challenge is to do this without sacrificing performance.

The paper will present the details on the work performed in this project.

Currently, most of TT&C (Telemetry, Tracking and Control) and Earth Observation antenna systems still operate in S and or X bands. The World Radio communication Conference recently attributed new additional frequency spectrum allocations in Ka-band range 25.5-27 GHz for Remote sensing application.
Several Ka-band Ground stations have been recently delivered or are in process of being delivered to Customers such as EUMETSAT, NOAA or ISRO.
Our contribution presents the most relevant qualification results of the Ka-band Ground stations delivered by Zodiac Data Systems, the qualification methods used in the absence (or near absence) of Low Earth Orbit satellites and the limitations observed in the standard measurement methods (G/T, etc..) when applied to this novel frequency range.
In addition, these results are compared and highlighted with those obtained by ESA on the SNOWBEAR demonstration Antenna with similar characteristics.
Finally, this paper presents the first lessons learned on LEO satellite JPSS-1 operational tracking in S and Ka-bands (both ESA and Zodiac Data Systems).