Land-based antennas

1.8m parabolic dish and rotator

The Dartcom 1.8m antenna is a prime focus aluminium parabolic dish with an F/D ratio of 0.42 and a gain of 27.5dBi. This enables a G/T of better than 6.0dBK at 5° to be achieved. An integrated feed, LNA and downconverter is mounted at the focal point of the antenna in a hermetically sealed unit.

The 1.8m antenna system allows continuous tracking of satellites with no cone of silence (loss of data) and a bit error rate of better than 1:10⁶ from 1° elevation. Azimuth and elevation control of the rotator is achieved via an RS232–RS422 link to the host computer.

The reflector is finished in light grey paint to PML specification RS20. The antenna is fixed to the rotator using interface steelwork galvanised to BS729 specification. The rotator is precision engineered using aluminium castings and machined steel for strength. The antenna and rotator are mounted on a durable galvanised steel pedestal.

1.5m and 1.2m parabolic dish and rotator

The Dartcom 1.5m antenna is a prime focus aluminium parabolic dish with an F/D ratio of 0.36 and a gain of 26.0dBi. This enables a G/T of better than 4.5dBK at 5° to be achieved. The 1.5m antenna system allows continuous tracking of satellites with no cone of silence (loss of data) and a bit error rate of better than 1:10⁶ from 2° elevation.

The Dartcom 1.2m antenna is a prime focus aluminium parabolic dish with an F/D ratio of 0.38 and a gain of 24.6dBi. This enables a G/T of better than 3.0dBK at 5° to be achieved. The 1.2m antenna system allows continuous tracking of satellites with no cone of silence (loss of data) and a bit error rate of better than 1:10⁶ from 3.5° elevation.

With both options an integrated feed, LNA and downconverter is mounted at the focal point of the antenna in a hermetically sealed unit. Azimuth and elevation control of the rotator is achieved via an RS232–RS422 link to the host PC.

The reflector is finished in light grey paint to PML specification RS20. The antenna is fixed to the rotator using a counter-weighted aluminium frame assembly. The rotator is a compact unit with a separate housing for the power supply and control electronics.

The antenna assembly is mounted on a steel pedestal (galvanised with the 1.2m antenna option). The 1.5m antenna is mounted inside a two-part (plus base) glass-fibre radome with bottom or side inspection hatches.

Left: Dartcom 1.8m parabolic dish antenna and rotator; Centre: Dartcom 1.5m parabolic dish antenna and rotator inside glass-fibre radome; Right: Dartcom 1.2m parabolic dish antenna and rotator

Feed:
Beamwidth	3dB at 80°, 10dB at 150°
Gain	+4.5dBi
Polarisation	Right-hand circular
Filter/LNA:
Insertion loss	0.4dB (maximum)
Filter bandwidth	200MHz (maximum)
Noise figure	0.8dB (maximum)
Gain	+35dB (minimum)
LNA bandwidth	100MHz (minimum)
Bandpass filter:
Insertion loss	1.5dB (maximum)
Bandwidth	1690MHz to 1710MHz
Downconverter:
RF-IF gain	40dB (nominal)
Input range	1690MHz to 1710MHz
IF output	125MHz to 145MHz

1.3m active-stabilised marine antenna

The Dartcom 1.3m active-stabilised marine antenna is capable of tracking NOAA, Feng Yun, SeaStar, Metop and NPOESS polar-orbiting satellites on-board moving vessels.

The antenna uses a state-of-the-art X-Y pedestal to compensate for the pitch, roll and yaw of the vessel. It provides continuous axis movement, eliminating cable wrap problems without the need for slip-rings or rotary joints. Together with the pedestal's very high speed and accuracy, this also ensures that there is no "cone of silence", even during overhead passes.

The antenna control unit is located below decks in a 19" rack with the receiving equipment and rack-mount computer. It provides fully-automatic control of the X-Y pedestal using an advanced stabilisation algorithm. Full diagnostics and maintenance tools are available via a graphical user interface on a TFT colour display.

When not ingesting polar-orbiter data, options are available which allow the reception of LRIT data from geostationary satellites (such as MSG direct broadcast, GOES and MTSAT) or Ku-band satellite TV transmissions (in conjunction with a suitable receiver).

Features:

• 1.3m parabolic dish antenna.
• 1.7GHz L-band RHC feed, pre-LNA filter and LNA unit.
• High-speed, high-accuracy, high-reliability X-Y pedestal compensating for pitch, roll and yaw, with continuous axis movement to eliminate cable wrap problems.
• Weather-tight glass fibre radome and base, with access hatch.
• Fully-automatic antenna control unit with full diagnostics and maintenance tools provided via a TFT colour display and GUI.
• Below-decks equipment mounted in a 19" rack.
• Bit error rate of better than 1:10⁶ from 3.5° elevation for HRPT, AHRPT and LRD, 5° for SeaWiFS and 7.5° for CHRPT.
• System G/T of 3.4dB/K at 5° elevation.
• Designed to meet MIL-STD specifications.
• ISO9001/CE certified.

Left: Dartcom 1.3m active-stabilised marine antenna; Right: Equipment rack installed on Oden

Dartcom 1.3m active-stabilised marine antenna installed on the Swedish Polar Institute icebreaker Oden