Re-design of the ESA Deep Space Antennas feed system to support future moon missions
TT&C and High Data Rate Communication services for Moon missions will be extensively required soon. Such services are foreseen to be covered mainly in X- and K-band respectively, according to the following allocation as recommended by the ITU.
Earth to Lunar Orbit (Uplink)
|Lunar Orbit to Earth (Downlink)|
7190 – 7235 MHz
8400 – 8500 MHz
|K-band||22550 – 23150 MHz||K-band||
22500 – 27000 MHz
Prior to this project, ESA developed a new X/K-band coaxial feed system, that was deployed in DSA2 (Cebreros, Spain) and recently in DSA3 (Malargüe, Argentina). Such feed system covers the frequency bands as defined in the previous table for the K-band for Uplink.
Objective & Scope
The first objective of the present activity was to trade-off different alternatives of feed systems architecture in order to implement a simultaneous X- and K-band Uplink and Downlink in all three ESA’s DSAs (Cebreros, Malargüe and New Norcia). Whichever solution was selected, the global performance of the existing subsystems within each DSA had to remind unaffected.
Among all the possible architectures, the selected solutions consisted of the following:
- For DSA1:
a. Replace a specific dichroic mirror with a new version able to reflect the S-Band and the X-Band and able to transmit K-band.
b. Develop a new feed able to operate in both S- and X-Band (both TX and RX) and install it in place of the existing S-band feed.
c. Develop a new feed able to operate in K-Band (both TX and RX) and install it in place of the existing X-band feed.
- For DSA2 and DSA3
a. Replace a specific mirror with a new dichroic mirror able to reflect the X-band (both TX and RX) and transmit the K-band (both TX and RX
b. Install a second solid mirror to extend the Beam Wave Guide.
c. Develop a new feed able to operate in K-band, both TX and RX.
TTI was focused on the tasks 1.b, 1.c and 2.c while the partners oversaw the rest.
1. Four bands S/S/X/X Feed.
The complete system was successfully designed and fully simulated. However, its manufacturing was not carried out since during the project, ESA determined that the S-band would not be finally installed in future DSAs developments.
2. K/K Feed with Tracking capability
The feed manages two kinds of signals: the sum signal (Σ) containing the information sent and received from the tracked vessel; and the delta signal (Δ) which allows the automatic self-steering of the DSA to track the ship.
Regarding the Σ the return loss of both polarizations is better than 25 dB for all the bands with an isolation between ports of 30 dB in the downlink band an 25 dB in the uplink without the duplexing stage. After the diplexer, the isolation is increased up to 50 dB in the uplink band and to 90 dB in the downlink band. The axial ratio is better than 0.55 dB, with a high efficiency and a calculated maximum power handling capability of 2 kW.
The tracking radiation pattern exhibits a null depth better than 43 dB for all RX frequencies with a null staticity of 50 mdeg